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Hierarchical polypyrrole based composites for high performance asymmetric supercapacitors
Accepted Manuscript Hierarchical polypyrrole based composites for high performance asymmetric supercapacitors Gao-Feng Chen, Zhao-Qing Liu, Jia-Ming Lin, Nan Li, Yu-Zhi Su PII:
S0378-7753(15)00348-1
DOI:
10.1016/j.jpowsour.2015.02.103
Reference:
POWER 20731
To appear in:
Journal of Power Sources
Received Date: 18 January 2015 Revised Date:
16 February 2015
Accepted Date: 18 February 2015
Please cite this article as: G.-F. Chen, Z.-Q. Liu, J.-M. Lin, N. Li, Y.-Z. Su, Hierarchical polypyrrole based composites for high performance asymmetric supercapacitors, Journal of Power Sources (2015), doi: 10.1016/j.jpowsour.2015.02.103. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Hierarchical polypyrrole based composites for high performance asymmetric supercapacitors Gao-Feng Chen, Zhao-Qing Liu*, Jia-Ming Lin, Nan Li, Yu-Zhi Su*
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School of Chemistry and Chemical Engineering/Guangzhou Key Laboratory for Environmentally Functional Materials and Technology, Guangzhou University, Guangzhou 510006, China
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An advanced asymmetric supercapacitor with high energy density, exploiting hierarchical polypyrrole (PPy) based composites as both the anode [three dimensional (3D) chuzzle-like
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Ni@PPy@MnO2] and (3D cochleate-like Ni@MnO2@PPy) cathode, has been developed. The ultrathin PPy and flower-like MnO2 orderly coating on the high-conductivity 3D-Ni enhances charge storage while the unique 3D chuzzle-like and 3D cochleate-like structures provide storage chambers and fast ion transport pathways for benefiting the transport of electrolyte ions. The 3D
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cochleate-like Ni@MnO2@PPy possesses excellent pseudocapacitance with a relatively negative voltage window while preserved EDLC and free transmission channels conducive to hold the high
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power, providing an ideal cathode for the asymmetric supercapacitor. It is the first report of assembling hierarchical PPy based composites as both the anode and cathode for asymmetric
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supercapacitor, which exhibits wide operation voltage of 1.3~1.5 V with maximum energy and power densities of 59.8 Wh kg-1 and 7500 W kg-1. —————————————————————————————————— Keywords:
Hierarchical
polypyrrole;
Three
dimensional;
Chuzzle-like;
Asymmetric supercapacitor
*
Corresponding author. Tel.: +86 20 39366908; Fax: +86 20 39366908.
E-mail addresses: [email protected] (Z.-Q. Liu); [email protected] (Y.-Z. Su) 1
Cochleate-like;
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1. Introduction The practical applications of supercapacitors are still limited by an unsatisfactory energy density compared with other rechargeable batteries and fuel cell. [1-3] To meet the future energy demands,
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it is urgent to design and develop advanced supercapacitors with high energy density and power density. [4] According to the equation E = 1/2CV2, the energy density is determined by the
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capacitance (C) and the work voltage. [5] Recently, a great deal of burgeoning efforts have been made on increasing both C and V to achieve larger E. [6-9] Particularly, construction of
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asymmetric supercapacitors is an effective way to achieve a wide work voltage window (V) and consequently high energy density (E) in aqueous electrolytes. Thus far, various electrode materials such as transition metal oxides/hydroxides and carbon materials serving as both positive and negative electrodes have been extensively investigated for asymmetric supercapacitors. For
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example, NiO//activated carbon (AC), [10] MoO3//AC, [11] CoO@polypyrrole//AC, [12] CoO@C//AC, [13] MnO2//grapheme [14] and graphene-Ni(OH)2//grapheme [15] fabricated for
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asymmetric supercapacitors, achieving a high work voltage ranging from 1.2 to 2 V and large energy density region, respectively. Unfortunately, the low capacitive performance of carbon
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materials suppresses the enhancement of energy density in these asymmetric supercapacitors. In addition, carbon-based materials must be mingled with binders to evaluate their electrochemical performances, further limiting their actual applications. Therefore, some researchers have turned their attentions to other negative materials with facile, scalable, and binder-free preparation technology, low cost, environmentally benign nature, and high capacitance. For instance, the asymmetric supercapacitors based on pseudocapacitance materials, such as Co(OH)2//VN, [16]
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ACCEPTED MANUSCRIPT PANI//MoO3 [17] and VN-MWCNT//MnO2-MWCNT, [18] can effectively enhance the capacitance and thus obviously improve the energy density. To our best knowledge, there are only a few of pseudocapacitance materials (such as RuO2, [19]
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Fe2O3, [20] MoO3, [21] V2O5 [22] and VN [23]) that are considered to serve as the cathode materials in asymmetric supercapacitors. Polypyrrole (PPy) based composites as cathodes using in
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asymmetric supercapacitors almost have not been reported so far. It may be mainly because that the potential of PPy based composites has not enough negative and the electrochemical studies are
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usually performed within a potential range of -0.5 to +0.4 V versus SCE, [24] or within the more positive potential. [25] Nevertheless, PPy has been well-known as a kind of promising electrode material for supercapacitors because of its high special capacitance, good conductivity and outstanding mechanical properties. Hence, developing PPy based composites as new negative
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materials with more negative working potential window, high special capacitance (Csp), and low electrical resistance for high power density might be significant for achieving a higher Csp and
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energy density of an asymmetric supercapacitor with a retained high power density. Recently, surface coating on 3D Ni metal framework was known as a promising way to
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fabricate advanced electrode materials. [26-27] In our previous work, we demonstrated novel 3D-Ni@MnO2, [28] 3D-Ni@Ni(OH)2 [29] and 3D-Ni@PPy [30] composites for supercapacitors with high Csp and remarkable cycling stability. In this work, the composites of 3D chuzzle-like Ni@PPy@MnO2 and 3D cochleate-like Ni@MnO2@PPy based on 3D Ni metal framework were prepared by simply changing the order of electrodeposition. As expected, both the two composites exhibit excellent electrochemical performance within different stable voltage window in a neutral
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ACCEPTED MANUSCRIPT aqueous electrolyte. Furthermore, an asymmetric supercapacitor is firstly assembled by serving Ni@PPy@MnO2 as anode and Ni@MnO2@PPy as cathode. Notably, Ni@MnO2@PPy cathode has a more negative voltage window (-0.7 to +0.1 V) in the 0.5 M Na2SO4 electrolyte.
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Consequently, Ni@PPy@MnO2//Ni@MnO2@PPy has a large work voltage of 1.3~1.5 V and achieves an energy density as high as 59.8 Wh kg-1 at a large power density of 1500 W kg-1, and
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thus this pattern for choice of Ni@MnO2@PPy as cathode could also provide a promising route for novel asymmetric supercapacitor with high energy and power densities.
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2. Experimental 2.1 Fabrication of hierarchical PPy based composites
Electrodeposition was conducted on a piece of nickel foam with a geometric area of 1.5 × 1 cm2. The 3D-Ni current collectors were fabricated according to the previously reported method, [28-30]
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and the Ni@PPy@MnO2 anode was prepared by a simple three-step electrochemical deposition process. The electropolymerization of PPy was directly carried out on the surfaces of 3D-Ni metal
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framework in acetonitrile solution containing of 0.01 M pyrrole + 0.1 M anhydride LiClO4 by potentiostat electrolysis with positive potential of +1 V in a three-electrode cell with a platinum
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plate as the counter electrode and saturated calomel electrode (SCE) as the reference electrode. Then, MnO2 was also deposited on Ni@PPy surface by using electrochemical deposition method. The electrolytic bath was composed of 0.01 M Mn(NO3)2, 0.01 M NaNO3 and 10% dimethylsulfoxide (water solution volume ratio). The potentiostat electrolysis was worked at a potential of +1 V in a three-electrode cell with a carbon rod as the counter electrode and saturated calomel electrode (SCE) as the reference electrode. The Ni@MnO2@PPy cathode was prepared by
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ACCEPTED MANUSCRIPT simply changing the order of electrodeposition as the above method. The loading mass of PPy and
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MnO2 are calculated using Faraday's Law of electrolysis:
For PPy, where Q is the electropolymerization charge, Mpy is the molecular mass of pyrrole, F is the Faraday constant of 96500 C mol-1, and y is a stoichiometric factor evaluating the anion
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insertion degree, which is inserted for charge compensation on the electropolymerization process.
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[31] The model of overall electropolymerization process should be as follow:
where n is the degree of polymerization, y is the above mentioned degree of anion insertion. PPy
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with anodic α,α-coupling of pyrrole rings can be formed, and then, the polymeric radial cation containing three or four monomer units as a segment of the conjugated backbone can be yielded by further being oxidized. [32] For MnO2, Q is is total charge of the electrodeposition process, MMnO
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2
is the molecular mass of MnO2, F is the Faraday constant, Z is the number of electrons of the Mn
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ion transferred from Mn2+ to MnO2 (Mn2+ + 2H2O = MnO2 + 4H+ + 2e-). [33] The loading mass of both PPy and MnO2 can be tunable through changing the electrodeposition time. The mass ratio of active material [PPy (0.35 mg) : MnO2 (1.00 mg)] for the optimized Ni@PPy@MnO2 anode is about 1 : 3. Meanwhile, for the optimized the Ni@MnO2@PPy cathode, the mass ratio between MnO2 (0.40 mg) and PPy (0.60 mg) is about 2 : 3. 2.2. Physicochemical characterizations
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ACCEPTED MANUSCRIPT The morphology of the as-prepared samples was analyzed by using field emission scanning electron microscopy (FE-SEM, JEOL JSM-7001F). The structure of the samples were analyzed by powder X-ray diffraction (XRD, Bruker , D8 ADVANCE) with Kα radiation (λ = 1.5418 Å).
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Optical properties of the as-prepared samples were tested by Fourier transform infrared spectrum (FT-IR, Nicolet 5700 spectrometer) and Raman spectrometer (Renishawin Via). The chemical state
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and compositions of the samples were analyzed using X-ray Photoelectron Spectroscopy (XPS, ESCALab250).
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2.3. Assembly of asymmetric supercapacitor and electrochemical characterizations The fabricating process of asymmetric supercapacitor is illustrated in Figure 1. An aqueous 1.5 × 1.5 cm2 asymmetric supercapacitor device (Ni@PPy@MnO2//Ni@MnO2@PPy) was assembled through integrating Ni@PPy@MnO2 as an anode and Ni@MnO2@PPy as a cathode. A piece of
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NKK TF48 (1.5 × 1.5 cm2) was as the separator in a two electrode system. The electrochemical properties of the as-prepared samples were investigated with cyclic voltammetry (CV),
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galvanostatic charge-discharge (GCD) measurements by employing a CHI 760D electrochemical workstation (Chenhua, Shanghai). All the electrochemical measurements were performed in 0.5 M
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Na2SO4 electrolyte.
3. Results and Discussion 3.1 Chuzzle-like Ni@PPy@MnO2 anode and cochleate-like Ni@MnO2@PPy cathode The typical low and high magnification scanning electron microscopy (SEM) images of as-prepared samples are clearly illustrated in Figure 2a-d. Figure 2a shows the 3D full-gapped morphology that ultrathin PPy is uniformly coated on the surface of 3D Ni framework. The coat of
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ACCEPTED MANUSCRIPT MnO2 grown on the Ni@PPy is also presented in the Figure 2b. The high-magnification SEM image (Figure 2b, inset) reveals with the formation of 3D chuzzle-like Ni@PPy@MnO2 (average diameter about 7-8 µm), which is different with flower-like Ni@MnO2 (Figure 2c), in which
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MnO2 tends to grow on the length of nanosheets that may lead to an unstable structure after elongated electrochemical process. For Ni@PPy@MnO2, three kinds of efficacy may be achieved
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from PPy: 1) on the surface of 3D Ni framework, PPy provides more reaction sites to grow MnO2, which can restrict the excessive growth of MnO2 nanosheets to protect the structural stability of
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MnO2. 2) PPy not only enhances the conductivity of the composites, but also increases the electrical connection between MnO2 and 3D-Ni current collector. 3) According to our previous work, [28] the capacitance contribution from 3D Ni framework can be negligible in electrochemical processes, thus Ni@PPy endowed with appreciable capacitance will enhance the
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whole capacitance of Ni@PPy@MnO2. The 3D cochleate-like Ni@MnO2@PPy was synthesized via direct electropolymerization of PPy on flower-like Ni@MnO2. Typical SEM images of the
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Ni@MnO2@PPy are illustrated in Figure 2d. It is clearly observed that the Ni@MnO2@PPy exhibits a cochleate-like shape and the corresponding high magnification image (inset in Figure 2d)
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exhibits that the external surface of cochleate-like shape is relatively rough and decorated by PPy with spiral distribution. And the 3D Ni@MnO2@PPy shows cochleate-like structures with uniform diameter of 2-3 µm.
Figure S1 shows XRD patterns of the Ni@PPy@MnO2 and Ni@MnO2@PPy powder collected by scraped off the as-prepared composites from nickel foam. All of the diffraction peaks can be indexed to 3D-Ni and there is no peak pertaining to PPy and MnO2, implying that the deposited
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ACCEPTED MANUSCRIPT PPy and MnO2 are amorphous in nature. It is generally known that amorphous materials contain enormous structure distortion, which provide more active sites and surface molecules in more active states for Faradaic redox reaction, revealing the intrinsically high performance of
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amorphous PPy and MnO2. The Fourier transform infrared spectroscopy (FT-IR) and Raman spectrum provide additional evidence for the presence of PPy and MnO2. Figure 2e displays the
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FT-IR spectrum of Ni@PPy@MnO2 and Ni@MnO2@PPy composite. In details, the absorption peaks at 1625 cm-1 is attributed to the vibration of C=C and C-C on the pyrrole ring, while the
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peaks at 1541 cm-1 and 1458 cm-1 are assigned to the pyrrole ring vibration. [34] The absorption peaks at 1159 cm-1 and 1125 cm-1 are induced by absorption of C-N stretching vibrations and C-C stretching vibrations between two pyrrole rings of the PPy, while other peaks at 1073 cm-1 and 645 cm-1 are due to N-H in-plane deformation vibration and absorption of C-H on pyrrole, respectively.
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[25] Moreover, the peak at 512 cm-1 is indicative of vibrations Mn-O. [35] The result of FT-IR spectrum indicates the presence of PPy and MnO2. It is obvious that relative peaks strength of PPy
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and MnO2 are affected by the hierarchical structure. The peaks strength of PPy in Ni@PPy@MnO2 are weaker than that of Ni@MnO2@PPy and the peaks strength of MnO2 in Ni@PPy@MnO2 are
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stronger than that of Ni@MnO2@PPy. A similar effect also appears in Raman spectrum. Figure 2f exhibits that there are almost no correlation peaks of PPy for Ni@PPy@MnO2 and the bands from 502 cm-1 to 626 cm-1 are attributed to the Mn-O stretching vibration. [36] In addition, for Ni@MnO2@PPy composite, characteristic peaks at about 675 cm-1, 935 cm-1, 1068 cm-1 and 1085 cm-1 confirm the presence of PPy, [37] while the bands at 502 cm-1, 626 cm-1 for MnO2. [36] The chemical composition and valence states of the Ni@PPy@MnO2 and Ni@MnO2@PPy
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ACCEPTED MANUSCRIPT were further investigated by X-ray Photoelectron Spectroscopy (XPS). The XPS survey spectrum (Figure S2 a) demonstrates the presence of Ni, Mn, O, N, and C in both composites. Figure S2 b shows the Ni 2p XPS of the both composites that demonstrates the formation of 3D-Ni (Ni0) metal
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and a small number of Ni2+ ascribing to the partially surface oxidation of 3D-Ni metal exposing to the air. [38] The high-resolution spectra for Mn 2p, O 1s and N 1s are shown in Figure 2h-g. In
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Figure 2h, the Mn 2p spectrum exhibits multiple splitting. Two main peaks located at 643.8 and 653.9 eV can be assigned to Mn 2p3/2 and Mn 2p1/2 of Mn4+ in MnO2, respectively. [39]
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Meanwhile, the two weaker peaks for Mn3+ and Mn5+ species were also detected in the spectrum, implying that element Mn has the main chemical state of Mn4+. [40] In the O 1s region (Figure 2i), the broad multi-peak can be divided into two peaks at 529.7 eV and 531.3 eV, corresponding to the Mn-O-Mn bond and Mn-OH bond respectively. [39] Figure 2g shows the N 1s XPS pattern, in
of PPy. [41-42]
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which two peaks centered at 399.9 eV and 398.4 eV are attributed to the –NH- bond and =N- bond
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Electrochemical characterization of the chuzzle-like Ni@PPy@MnO2 anode and cochleate-like Ni@MnO2@PPy cathode were investigated by using CV and GCD test with a three-electrode cell
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in a 0.5 M Na2SO4 electrolyte. Figure 3a shows the CV curves of chuzzle-like Ni@PPy@MnO2 anode at scan rates of 5, 10, 20, 50, 100 mV s-1. The CV curves with nearly box shape indicates good capacitive behavior in the voltage window of 0 to +0.8 V versus SCE and the enhancement in current with increasing scan rate indicated good capacitance retention. The GCD plots of chuzzle-like Ni@PPy@MnO2 anode at different applied current densities are present in Figure 3b, which exhibits the triangular symmetry and linear slopes, further confirming the excellent
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ACCEPTED MANUSCRIPT capacitive performance of Chuzzle-like Ni@PPy@MnO2 anode. The specific capacitance (Csp) is calculated by the discharge curves. As shown in Figure 3c, large Csp of 306, 318, 324, 343 and 350 F g-1 can be achieved by increasing current densities from 2 to 10 A g-1, which demonstrates a
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superior rate capability with a small decay of 13% in Csp. Compared to Ni@PPy@MnO2 anode, the Ni@MnO2 electrode (Figure S3) only shows smaller Csp of 162, 171, 186, 199.5 and 225 F g-1
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ferior rate capability (28% decay in Csp) with current densities from 2 to 10 A g-1. The possible reasons can be mainly attributed to the high conductivity of PPy interlayer providing the abundant
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electrical connection between MnO2 and 3D-Ni current collector and enhance the capacitance of Ni@PPy@MnO2. It is also suggested that the 3D-Ni@PPy network could improve the electronic conductivity of the composite, which is beneficial for the charge-discharge reactions. It is well known that the pseudocapacitive effect is limited only to a region near the surface. In this case, the
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major capacitance of hierarchical Ni@PPy@MnO2 can be attributed to the MnO2, which has been demonstrated in the voltage window (0 to +0.8 V versus SCE), consistent with the typical voltage
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window of MnO2. The mechanism of charge storage of MnO2 in a neutral Na2SO4 aqueous solution may proceed via the following reaction (Na+ cations are involved in the charging of MnO2
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in the positive potential range):
MnO2Na = MnO2 + Na+ +e-
(1)
According to the above reaction equation, the homogeneously dispersed 3D chuzzle-like Ni@PPy@MnO2 can increase the specific surface area and form porous structures that act as ion reservoirs to improve the diffusion rate of Na+ ions and facilitate the charge-discharge reactions. The cycle stability of the Ni@PPy@MnO2 electrode is evaluated for 5000 continuous cycles in 0.5
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ACCEPTED MANUSCRIPT M Na2SO4 at a scan rate of 100 mV s-1 (Figure 3d). The Csp can be maintained as high as ≈91.3 of the initial value, which is more stable than the value for Ni@MnO2 electrode in Figure S3 (retaining 70.1% of initial Csp after 5000 cycles). The improved stability of the Ni@PPy@MnO2
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electrode might be due to the proper growth of MnO2 nanosheets on Ni@PPy surface protecting the structural stability of MnO2 during the rapid migration of electrolyte ion on electrode material
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surface.
Figure 4a presents the CV curves of the cochleate-like Ni@MnO2@PPy cathode at different
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scan rates in a potential window between -0.7 V and +0.1 V (versus SCE), which exhibits its redox peak-incorporated rectangular shape and almost unchangeable shape with the increasing scan rates, implying that the 3D cochleate-like structure is beneficial for the rapid redox reaction and easy access of ions to the interfaces between electrode and electrolyte, resulting in superior capacitive
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and high-rate performance. In this case, CV measurement is also served as the appropriate tool to identify Faradic and non-Faradic reaction of energy storage mechanism. In all CV curves, two
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broad redox humps during the anodic (-0.4 V to -0.2 V) and cathodic (-0.7 V to -0.5 V) scans and the wide current-potential response can be observed, indicating both electrical double layered (EDLC)
and
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capacitance
pseducapacitance
of
cochleate-like
Ni@MnO2@PPy.
The
pseducapacitance is mainly attributed to the functional groups of spiral-decorated PPy, where the cathodic wave and the anodic wave are owing to the insertion and expulsion of Na+ ions in the electrolyte. [43] We propose that the apparently presentation of redox reaction for Ni@MnO2@PPy can be ascribed to the unique 3D cochleate-like structure, being conducive to the exposure of PPy in the electrolyte and full utilization of functional groups. To verify this
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ACCEPTED MANUSCRIPT hypothesis, Ni@PPy is also investigated for comparsion by using CV test. Figure S4 shows the CV curves of Ni@PPy collected in potential window of -0.3 to +0.5, -0.4 to +0.4 and -0.5 to +0.3 at the scan rate of 20 mV s-1. It is worthily noting that the Ni@PPy only exhibits the EDLC nature
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and when the working potential decreases to -0.5 V, obvious polarization current is observed, indicated the unstable characteristic in the relatively negative potential range, further
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demonstrating the advantage structure of 3D cochleate-like Ni@MnO2@PPy in the presentation of pseducapacitance. Additionally, basing on the different order of MnO2 and PPy in hierarchical
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Ni@PPy@MnO2 and Ni@MnO2@PPy, the major capacitance contributor for Ni@MnO2@PPy should be different with that of Ni@PPy@MnO2. In Ni@MnO2@PPy cathode, the major capacitance can be ascribed to the PPy, which has also been demonstrated in the voltage window (-0.7 to +0.1 V versus SCE) of Ni@MnO2@PPy, closing to the typical voltage window of PPy.
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Fig. 4b shows the GCD curves, where almost linear and typical triangular symmetrical curves can be observed, displaying perfect reversibility of the redox reactions for cochleate-like
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Ni@MnO2@PPy in 0.5 M Na2SO4 aqueous electrolyte. A high Csp of 473.8 F g-1 can also be calculated at a current density of 2 A g-1 (Fig. 4c). Moreover, the Ni@MnO2@PPy exhibits
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excellent rate capability, and the retention rate is 63.1% with increasing the discharging current density from 2 to 10 A g-1. Due to the high conductive 3D-Ni collector, cochleate-like structure and combined electroactivities of PPy and MnO2, Ni@MnO2@PPy exhibits higher capacitance, better rate capability and a relatively negative charge storage potential window. The long-term cycle stability was tested by CV scans at a scan rate of 100 mV s-1 for 5000 cycles and the results are shown in Fig. 4d. The Csp of the Ni@MnO2@PPy only has a slight fluctuation and remains above
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ACCEPTED MANUSCRIPT 100% of the initial Csp in the whole process, which is more stable than Ni@PPy maintaining 79.1% of the initial Csp after 5000 cycles (Figure S5 d). 3.2 Asymmetric supercapacitor based on chuzzle-like Ni@PPy@MnO2 and cochleate-like
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Ni@MnO2@PPy
Considering the remarkable Csp and rate capability of the EDLC and pseudocapacitance
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properties for chuzzle-like Ni@PPy@MnO2 and cochleate-like Ni@MnO2@PPy, an asymmetric supercapacitor was fabricated using the two materials as anode and cathode, respectively. Figure
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5a exhibits that Ni@PPy@MnO2 electrode was measured at a scan rate of 50 mV s-1 with a voltage window of 0 V to 0.8 V (versus SCE), while Ni@MnO2@PPy was measured within a voltage window of -0.7 to +0.1 V (versus SCE). Thus, the operation window of asymmetric supercapacitor can be extended up to 1.5 V by tuning the mass ratio of the two electrodes. Since the charges
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stored in the two capacitor electrodes should be equal in magnitude with opposite signs. The charge balance will follow the relationship Q+ = Q-, where the charge stored by each electrode
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usually depends on the C, the potential range for the charge-discharge process (∆V), and the mass of the electrode (m) following the equation: Q = C × ∆V × m. For the asymmetric capacitor
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developed here, the Csp of the Ni@PPy@MnO2 and Ni@MnO2@PPy electrodes are 350 F g-1 and 473.8 F g-1, respectively, at a discharge current of 2 A g-1. As a result, designing an asymmetric capacitor, the optimal mass ratio of the two electrodes (m(Ni@PPy@MnO2)/m(Ni@MnO2@PPy)) can be deduced to be 1.35. In a controlled experiment, a Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor with a mass ratio of 1.35 performs at different voltage windows in 0.5 M Na2SO4 aqueous electrolyte at a scan rate of 50 mV s-1 (Figure 5b). When voltage windows is
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ACCEPTED MANUSCRIPT worked at 1.2, 1.3, and 1.4 V, a nearly box CV curve implies an ideal capacitive behaviour response from the asymmetric supercapacitor. By increasing the voltage windows to 1.5 V, relatively obvious polarization current appear in the CV curve, indicating excessive positive
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potential on the Ni@PPy@MnO2 electrode. Figure 5c shows the variation of Csp with increasing voltage window for the asymmetric supercapacitor. Remarkably, the Csp increased significantly
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from 135.2 to 168.9 F g-1 with an increasing the operation potential from 1.2 to 1.5 V at a scan rate of 50 mV s-1. For evaluating the optimal voltage window, cyclic stability of the cell was also be
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investigated by CV test at a scan rate of 100 mV s-1 for 1000 cycles with different operating potential (Figure 5d). It can be observed that the Csp retention at voltage window of 1.3, 1.4 and 1.5 V after 1000 cycles was about 100.9%, 84.8%, and 49.8%, respectively. The Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor was subjected to detailed
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measurements for obtaining more information on the capacitive performance of the optimized asymmetric supercapacitor. Figure 6a presents the CV curves of the asymmetric capacitor at
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different scan rates of 5, 10, 20, 50, and 100 mV s-1 with the 1.3 V operating potential in a two-electrode system. The cell shows a near rectangular shape CV curve with any signs of
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distortion by increasing potential scan rate, indicating an ideal capacitive behavior under 1.3 V operating potential. The Csp of the Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor at different scan rates calculated from CV curves is shown in Figure 6c. The Csp gradually decreased from 184.6 to 136.2 F g-1 with increasing scan rate. A better rate capability with small decay of 26.2% in Csp can be achieved, exhibiting excellent capacitance retention and indicating the almost unlimited diffusion of Na+ ions in both anode and cathode even at high scan rates. GCD
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ACCEPTED MANUSCRIPT curves of the optimized Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor were measured at current densities of 2, 4, 6, 8 and 10 A g-1 with the 1.3 V operating potential. As shown in Fig. 6b, all the curves are highly linear and symmetrical at current densities from 2 to 10
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A g-1, implying that the Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor has good Coulombic efficiency related to superior charge-discharge reversibility. Figure 6d presents the Csp
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of asymmetric supercapacitor at different discharge current densities. The Csp decreased from 165.0 to 132.3 F g-1 with the discharge current density increasing from 2 to 10 A g-1, revealing the
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excellent capacitance retention again.
On the basis of above results, the energy density and power density of the asymmetric supercapacitor were calculated from the discharges curves and plotted on a Ragone diagram in Figure 7a. The maximum energy density were 38.7, 46.7, and 59.8 Wh kg-1 at the power density of
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1300, 1400, and 1500 W kg-1 under discharge current 2 A g-1 at voltage window of 1.3, 1.4 and 1.5 V, respectively. The values gradually decreased to 31.1, 33.0, and 29.2 Wh kg-1 at the power
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density of 6500, 7000, and 7500 W kg-1 under discharge current 10 A g-1. The obtained maximum energy density is considerably comparable to those of recently reported symmetric and asymmetric
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supercapacitors, such as RuO2//RuO2 (18.8 Wh kg-1), [44] Fe3O4-GNS//Fe3O4-GNS (11.0 Wh kg-1), [45] CoO@PPy//AC (43.5 Wh kg-1), [12] PANI//MoO3 (38.9 Wh kg-1), [17] MnO2@NCs//AC (52.1 Wh kg-1), [46] MnO2//CNT (47.4 Wh kg-1), [47] CNT/MnO2//CNT/InO3 (25.5 Wh kg-1), [48] RGO-RuO2//RGO-PANI (26.3 Wh kg-1) [49] and Fe2O3-FGS//MnO2-FGS (50.7 Wh kg-1) [50]. Most importantly, the power density of Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor are higher than those related to similar maximum energy density, indicating the
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ACCEPTED MANUSCRIPT allowed significant improvement both power and energy characteristics of the asymmetric supercapacitor. Additionally, we further evaluate the long-term cycling stability of the Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor by CV test at a scan rate of 100
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mV s-1 for 3000 cycles with 1.3 V operating potential. Figure 7b shows the capacitance retention ratio of the asymmetric supercapacitors scan at 1.3 V as a function of the cycle number. The device
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exhibits electrochemical stability with about 83.5% retention of the initial Csp after 3000 cycles. It is worthily noting that the Csp start decreasing is the initial 1000 cycles (retained 100.1% of its
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initial capacitance). The capacitance decrease may be due to the positive polarization (excessive positive potential on the Ni@PPy@MnO2 electrode) or the electrode matching problems, because individual Ni@MnO2@PPy electrode showed good capacitance retention in corresponding voltage windows in the same electrolyte. Furthermore, three supercapacitors in series have been assembled
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and after charging for only 20 s to 4 V, the device can power a red round light-emitting diode (LED) indicator (1.9-2.2 V, 20 mA) light brightly for 8 min (Figure 7 c-d).
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The high energy density, excellent rate capability and long-term cycling capability of the Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor can be attributed to the
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advantageous morphology and structure of both 3D chuzzle-like Ni@PPy@MnO2 anode and 3D cochleate-like Ni@MnO2@PPy cathode, as shown in Figure 8. The main reasons towards capacitance enhancement might be mainly summarized in the following factors: (i) 3D chuzzle-like Ni@PPy@MnO2 and 3D cochleate-like Ni@MnO2@PPy formed by the 3D-Ni serving as a high conductive framework, display high conductivity, unique 3D structure with large accessible specific activity area and more active sites for enhancement of EDLC and
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electrolyte accessibility. (iii) Conductive ultrathin-PPy also plays an important role for benefits of hierarchical PPy based composites, which not only enhances the conductivity of the composites
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and protect the nanoplate structure of MnO2, but also endows with appreciable capacitance for the composites. (iv) 3D hierarchical PPy based composites directly decorated on the Ni foam avoiding
collector and hierarchical composites.
4. Conclusions
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the use of polymer binder, which may offer effective electron transport pathways between current
In summary, Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor was fabricated by
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using 3D chuzzle-like Ni@PPy@MnO2 as the anode and 3D cochleate-like Ni@MnO2@PPy as the cathode. Particularly, the 3D cochleate-like Ni@MnO2@PPy was the first time to develop for
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the asymmetric supercapacitor cathode. Benefiting from the high capacitance of EDLC and pseudocapacitance of both electrodes, the device exhibits excellent performance in the voltage
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potential of 1.3~1.5 V and achieves a high Csp of 191.3 F g-1, a large energy of 59.8 Wh kg-1 and a power density 7500 W kg-1 for the whole cell. It is believed that the hierarchical PPy based composites electrodes will provide a new choice for the developing asymmetric supercapacitors.
Acknowledgments The authors acknowledge the financial support of this work by Natural Science Foundations of China (Grant No. 21306030), the Natural Science Foundations of Guangdong Province (Grant No.
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Appendix A. Supplementary data Supplementary
data
related
to
this
article
can
be
found
at
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http://dx.doi.org/00.0000/j.jpowsour.2015.00.00.
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University (Grant No. 201302).
References
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[1] G. Wang, L. Zhang, J. Zhang, Chem. Soc. Rev. 41 (2012) 797-828.
[2] Z. Tang, C. H. Tang, H. Gong, Adv. Funct. Mater. 22 (2012) 1272-1278. [3] S. Giri, D. Ghosh, C. K. Das, Adv. Funct. Mater. 24 (2013) 1312-1324. [4] S. W. Lee, N. Yabuuchi, B. M. Gallant, S. Chen, B. S. Kim, P. T. Hammond, Y. S. Horn, Nat.
TE D
Nanotechnol. 5 (2010) 531-537.
[5] L. L. Zhang, X. S. Zhao, Chem. Soc. Rev. 28 (2009) 2520-2531.
EP
[6] Q. Lu, M. W. Lattanzi, Y. Chen, X. Kou, W. Li, X. Fan, K. M. Unruh, J. G. Chen, J. Q. Xiao, Angew. Chem. Int. Ed. 50 (2011) 6847-6850.
AC C
[7] W. Chen, R. B. Rakhi, L. Hu, X. Xie, Y. Cui, H. N. Alshareef, Nano Lett. 11 (2011) 5165-5172 .
[8] Q. Gao, L. Demarconnay, E. Raymundo-Piñero, F. Béguin, Energy Environ. Sci. 5 (2012) 9611-9617. [9] Q. Qu, Y. Zhu, X. Gao, Y. Wu, Adv. Energy Mater. 2 (2012) 950-955. [10] B. Wang, J. S. Chen, Z. Y. Wang, S. Madhavi, X. W. Lou, Adv. Energy Mater. 2 (2012)
18
ACCEPTED MANUSCRIPT 1188-1192. [11] W. Tang, L. Liu, S. Tian, L. Li, Y. Yue, Y. Wu, K. Zhu, Chem. Commun. 47 (2011) 10058-10060.
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[12] C. Zhou, Y. Zhang, Y. Li, J. Liu, Nano Lett. 13 (2013) 2078-2085.
[13] H. Wang, C. Qing, J. Guo, A. A. Aref, D. Sun, B. Wang, Y. Tang, J. Mater. Chem. A 2 (2014)
SC
11776-11783.
[14] H. Gao, F. Xiao, C.B. Ching, H. Duan, ACS Appl. Mater. Interfaces, 4 (2012) 2801-2810.
Mater. 22 (2012) 2632-2641.
M AN U
[15] J. Yan, Z. Fan, W. Sun, G. Ning, T. Wei, Q. Zhang, R. Zhang, L. Zhi, F. Wei, Adv. Funct.
[16] R. Wang, X. Yan, J. Lang, Z. Zheng, P. Zhang, J. Mater. Chem. A 2 (2014) 12724-12732. [17] H. Peng, G. Ma, J. Mu, K. Sun and Z. Lei, J. Mater. Chem. A 2 (2014) 10384-10388.
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[18] Y. Su, I. Zhitomirsky, J. Power Sources 267 (2014) 235-242. [19] H. Wang, Y. Liang, T. Mirfakhrai, Z. Chen, H.S. Casalongue, H. Dai, Nano Res. 4 (2011)
EP
729-736.
[20] S. Sun, J. Lang, R. Wang, L. Kong, X. Li, X. Yan, J. Mater. Chem. A 2 (2014) 14550-14556.
AC C
[21] J. Cheng, M. Jin, F. Yao, T. H. Kim, V. T. Le, H. Yue, F. Gunes, B. Li, A. Ghosh, S. Xie, Y. H. Lee, Adv. Funct. Mater. 23 (2013) 5074-5083. [22] A. Q. Pan, H. B. Wu, L. Yu, T. Zhu, X. W. Lou, ACS Appl. Mater. Interfaces 4 (2012) 3874-3879. [23] X. Lu, M. Yu, T. Zhai, G. Wang, S. Xie, T. Liu, C. Liang, Y. Tong, Y. Li, Nano Lett. 13 (2013) 2628-2633.
19
ACCEPTED MANUSCRIPT [24] K. Shi, I. Zhitomirsky, J. Power Sources 240 (2013) 42-49. [25] M. Yu, Y. Zeng, C. Zhang, X. Lu, C. Zeng, C. Yao, Y. Yang, Y. Tong, Nanoscale 5 (2013) 10806-10810.
RI PT
[26] D. Chao, X. Xia, C. Zhu, J. Wang, J. Liu, J. Lin, Z. Shen, H. J. Fan, Nanoscale, 6 (2014) 5691-5697.
SC
[27] Z. Su, C. Yang, B. Xie, Z. Lin, Z. Zhang, J. Liu, B. Li, F. Kang, C.P. Wong, Energy Environ. Sci. 7 (2014) 2652-2659.
M AN U
[28] K. Xiao, J.W. Li, G. F. Chen, Z. Q. Liu, N. Li, Y. Z. Su, Electrochim. Acta 149 (2014) 341-348.
[29] Y. Z. Su, K. Xiao, N. Li, Z. Q. Liu, S. Z. Qiao, J. Mater. Chem. A 2 (2014) 13845-13853. [30] G. F. Chen, Y. Z. Su, P. Y. Kuang, Z. Q. Liu, D. Y. Chen, X. Wu, N. Li, S. Z. Qiao, Chem.
TE D
Eur. J. DOI: 10.1002/chem.201405976.
[31] Y. Hou, L. Chen, P. Liu, J. Kang, T. Fujita, M. Chen, J. Mater. Chem. A 2 (2014)
EP
10910-10916.
[32] M. Schirmeisen, F. Beck, J. Appl. Electrochem. 19 (1989) 401-409.
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[33] B. Anothumakkool, S. Kurungot, Chem. Commun. 50 (2014) 7188-7190. [34] P. Mavinakuli, S.Y. Wei, Q. Wang, A. B. Karki, S. Dhage, Z. Wang, D. P. Young, Z. H. Guo, J. Phys. Chem. C 114 (2010) 3874-3882. [35] B. Wang, X. He, H. Li, Q. Liu, J. Wang, L. Yu, H. Yan, Z. Li, P. Wang, J. Mater. Chem. A 2 (2014) 12968-12973. [36] M. Polverejan, J.C. Viliegas, S. L. Suib, J. Am. Chem. Soc. 126 (2004) 7774-7775.
20
ACCEPTED MANUSCRIPT [37] J. Zhang, Y. Yu, L. Liu, Y. Wu, Nanoscale 5 (2013) 3052-3057. [38] Z. Zhao, H. Wu, H. He, X. Xu, Y. Jin, Adv. Funct. Mater. 24 (2014) 4698-4705. [39] M. Toupin, T. Brousse, D. Belanger, Chem. Mater. 16 (2004) 3184-3190.
RI PT
[40] Y. Zhao, P. Jiang, S.S. Xie, J. Power Sources 239 (2013) 393-398. [41] W. Yao, H. Zhou, Y. Lu, J. Power Sources 241 (2014) 359-366.
SC
[42] P. Li, Y. Yang, E. Shi, Q. Shen, Y. Shang, S. Wu, A.Y. Cao, D. H. Wu, ACS Appl. Mater. Interfaces 6 (2014) 5228-5234.
M AN U
[43] A. Lin, C. Li, H. Bai, G. Shi, J Phys Chem C 114 (2010) 22783-22789.
[44] H. Xia, Y. S. Meng, G. Yuan, C. Cui, Li Lu, Electrochem. Solid-State Lett. 15 (2012) A60-A63.
[45] K. Karthikeyan, D. Kalpana, S. Amaresha, Y. S. Lee, RSC Adv. 2 (2012) 12322-12328.
12519-12525.
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[46] M. Yang, Y. Zhong, X. Zhou, J. Ren, L. Su, J. Wei, Z. Zhou, J. Mater. Chem. A 2 (2014)
EP
[47] H. Jiang, C. Li, T. Sun and J. Ma, Nanoscale 4 (2012) 807-812. [48] P. C. Chen, G. Shen, Y. Shi, H. Chen, X. Zhou, ACS Nano 4 (2010), 4403-4411.
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[49] J. Zhang, J. Jiang, H. Li, X. S. Zhao, Energy Environ. Sci. 4 (2011) 4009-4015. [50] H. Xia, C. Hong, B. Li, B. Zhao, Z. Lin, M. Zheng, S. V. Savilov, S. M. Aldoshin, Adv. Funct. Mater. 25 (2015) 627-635.
Figure Captions Figure 1. Fabrication process of Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor
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Ni@MnO2, and 3D cochleate-like Ni@MnO2@PPy; (e-f) FT-IR and Raman spectra of Ni@PPy@MnO2 and Ni@MnO2@PPy; (h-g) Mn2p, O1s, and N1s spectra of Ni@PPy@MnO2 and Ni@MnO2@PPy.
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Figure 3. (a) CV curves of Ni@PPy@MnO2 collected at different scan rates; (b) Galvanostatic
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charge-discharge curves of Ni@PPy@MnO2 under different constant current densities; (c) specific capacitance at different current densities; (d) the cycling stability for Ni@PPy@MnO2 from the 1st to the 5000th cycles at scan rates of 100 mV s-1.
Figure 4. (a) CV curves of Ni@MnO2@PPy collected at different scan rates; (b) Galvanostatic
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charge-discharge curves of Ni@MnO2@PPy under different constant current densities; (c) specific capacitance at different current densities; (d) the cycling stability for Ni@MnO2@PPy from the 1st
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to the 5000th cycles at scan rates of 100 mV s-1.
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Figure 5. (a) CV curves of Ni@PPy@MnO2 and Ni@MnO2@PPy electrodes measured in different voltage windows by using a three-electrode system in a 0.5 M Na2SO4 aqueous solution; (b) CV curves of the optimized asymmetric supercapacitor measured in different potential windows with a scan rate of 50 mV s-1 in a 0.5 M Na2SO4 aqueous solution; (c) the specific capacitance of the asymmetric supercapacitor with the increase of voltage window at a scan rate of 50 mV s-1. (d) the cycling stability of asymmetric supercapacitor measured in different potential windows from the 1st to the 1000th cycles at scan rates of 100 mV s-1.
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1.3 V)
7.
(a)
Ragone
plot
related
to
energy
and
power
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Figure
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different scan rates and discharge current densities, respectively. (in a working potential window of
densities
of
the
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Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor in comparison to the asymmetric supercapacitor recently reported in the literature; [12, 17, 46, 47, 48, 49] (d) the cycling stability of the Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor in a potential window of 1.3 V from the 1st to the 3000th cycles at scan rates of 100 mV s-1. (c) a picture showing that three
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supercapacitors in series after charging for 20 s to 4 V can lighten up LED indicators; (d) images of the red LED at different lightening time.
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Figure 8. Schematic of the advantageous structures of 3D hierarchical PPy based composites.
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GRAPHICAL ABSTRACT
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ACCEPTED MANUSCRIPT HIGHLIGHTS 1. The polypyrrole based electrodes were prepared via a facile electrodeposited method. 2. The sample possesses excellent performance and provides an ideal cathode for supercapacitor.
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3. The as-prepared asymmetric supercapacitor exhibits superior energy and power densities.
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Supporting Information Hierarchical polypyrrole based composites for high
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performance asymmetric supercapacitors Gao-Feng Chen, Zhao-Qing Liu*, Jia-Ming Lin, Nan Li, Yu-Zhi Su* Calculation formulas:
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The discharge capacitance (C), specific capacitance (Csp), energy density (E), and power density (P) reported in this work were calculated from the galvanostatic charge discharge (GCD) curves or cyclic voltammetry (CV) curves using the equations as given in the literature: [1-2]
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The specific capacitance (Csp) was calculated from the slope of the discharge curve from the following:
(S1)
where Csp (F g-1), I (A), dt (s), and dV are the specific capacitance, the discharge current, the
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discharge time, and the potential window, respectively. The m (g) at this equation is the mass of the single electrode active materials for three electrode cell, and the total mass of two active electrode materials for two electrode cell.
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The specific capacitance (Csp) was also calculated from the area under the CV curves by the
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following equation:
(S2)
where m is the mass of the electroactive materials in the electrodes (g), v is the potential scan rate (mV s-1), Va is the anodic potential (V), Vc is the cathodic potential (V), I is the response current (A) and V is the potential (V).
*Corresponding author. Tel.: +86 20 39366908; Fax: +86 20 39366908. E-mail addresses: [email protected] (Z.-Q. Liu); [email protected] (Y.-Z. Su) 1
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(S3)
(S4)
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where ∆V is the potential at the end of charge (V) and ∆t is the discharge time (s).
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Figure S1. XRD of Ni@PPy@MnO2 and Ni@MnO2@PPy.
Figure S2. (a) XPS survey spectrum; (b) Ni2p of Ni@PPy@MnO2 and Ni@MnO2@PPy.
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Figure S3. (a) CV curves of Ni@MnO2 collected at different scan rates; (b) Galvanostatic
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charge-discharge curves of Ni@MnO2 under different constant current densities; (c) specific capacitance at different current densities; (d) the cycling stability for Ni@MnO2 from the 1st to
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the 5000th cycles at scan rates of 100 mV s-1.
Figure S4. CV curves of the optimized Ni@PPy measured in different potential windows with a 3
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scan rate of 20 mV s-1 in a 0.5 M Na2SO4 aqueous solution.
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Figure S5. CV curves of Ni@PPy collected at different scan rates; (b) Galvanostatic charge-discharge curves of Ni@PPy under different constant current densities; (c) specific capacitance at different current densities; (d) the cycling stability for Ni@PPy from the 1st to the
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5000th cycles at scan rates of 100 mV s-1. (in a working potential window from -0.3 to +0.5)
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Figure S6. CV curves of Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor measured at different scan rates; (b) Galvanostatic charge-discharge curves of asymmetric supercapacitor under different constant current densities; (c-d) specific capacitance collected at
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of 1.4 V)
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different scan rates and discharge current densities, respectively. (in a working potential window
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Figure S7. CV curves of Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor measured at different scan rates; (b) Galvanostatic charge-discharge curves of asymmetric
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supercapacitor under different constant current densities; (c-d) specific capacitance collected at
1.5 V) .
References
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different scan rates and discharge current densities, respectively (in a working potential window of
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[S1] A. Pendashteh, M.S. Rahmanifar, R.B. Kanerc, M.F. Mousavi, Chem. Commun. 50 (2014) 1972-1975.
[S2] H. Wang, H.S. Casalongue, Y. Liang, H. Dai, J. Am. Chem. Soc. 132 (2010) 7472-7477.
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S0378-7753(15)00348-1
DOI:
10.1016/j.jpowsour.2015.02.103
Reference:
POWER 20731
To appear in:
Journal of Power Sources
Received Date: 18 January 2015 Revised Date:
16 February 2015
Accepted Date: 18 February 2015
Please cite this article as: G.-F. Chen, Z.-Q. Liu, J.-M. Lin, N. Li, Y.-Z. Su, Hierarchical polypyrrole based composites for high performance asymmetric supercapacitors, Journal of Power Sources (2015), doi: 10.1016/j.jpowsour.2015.02.103. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Hierarchical polypyrrole based composites for high performance asymmetric supercapacitors Gao-Feng Chen, Zhao-Qing Liu*, Jia-Ming Lin, Nan Li, Yu-Zhi Su*
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School of Chemistry and Chemical Engineering/Guangzhou Key Laboratory for Environmentally Functional Materials and Technology, Guangzhou University, Guangzhou 510006, China
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An advanced asymmetric supercapacitor with high energy density, exploiting hierarchical polypyrrole (PPy) based composites as both the anode [three dimensional (3D) chuzzle-like
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Ni@PPy@MnO2] and (3D cochleate-like Ni@MnO2@PPy) cathode, has been developed. The ultrathin PPy and flower-like MnO2 orderly coating on the high-conductivity 3D-Ni enhances charge storage while the unique 3D chuzzle-like and 3D cochleate-like structures provide storage chambers and fast ion transport pathways for benefiting the transport of electrolyte ions. The 3D
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cochleate-like Ni@MnO2@PPy possesses excellent pseudocapacitance with a relatively negative voltage window while preserved EDLC and free transmission channels conducive to hold the high
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power, providing an ideal cathode for the asymmetric supercapacitor. It is the first report of assembling hierarchical PPy based composites as both the anode and cathode for asymmetric
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supercapacitor, which exhibits wide operation voltage of 1.3~1.5 V with maximum energy and power densities of 59.8 Wh kg-1 and 7500 W kg-1. —————————————————————————————————— Keywords:
Hierarchical
polypyrrole;
Three
dimensional;
Chuzzle-like;
Asymmetric supercapacitor
*
Corresponding author. Tel.: +86 20 39366908; Fax: +86 20 39366908.
E-mail addresses: [email protected] (Z.-Q. Liu); [email protected] (Y.-Z. Su) 1
Cochleate-like;
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1. Introduction The practical applications of supercapacitors are still limited by an unsatisfactory energy density compared with other rechargeable batteries and fuel cell. [1-3] To meet the future energy demands,
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it is urgent to design and develop advanced supercapacitors with high energy density and power density. [4] According to the equation E = 1/2CV2, the energy density is determined by the
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capacitance (C) and the work voltage. [5] Recently, a great deal of burgeoning efforts have been made on increasing both C and V to achieve larger E. [6-9] Particularly, construction of
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asymmetric supercapacitors is an effective way to achieve a wide work voltage window (V) and consequently high energy density (E) in aqueous electrolytes. Thus far, various electrode materials such as transition metal oxides/hydroxides and carbon materials serving as both positive and negative electrodes have been extensively investigated for asymmetric supercapacitors. For
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example, NiO//activated carbon (AC), [10] MoO3//AC, [11] CoO@polypyrrole//AC, [12] CoO@C//AC, [13] MnO2//grapheme [14] and graphene-Ni(OH)2//grapheme [15] fabricated for
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asymmetric supercapacitors, achieving a high work voltage ranging from 1.2 to 2 V and large energy density region, respectively. Unfortunately, the low capacitive performance of carbon
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materials suppresses the enhancement of energy density in these asymmetric supercapacitors. In addition, carbon-based materials must be mingled with binders to evaluate their electrochemical performances, further limiting their actual applications. Therefore, some researchers have turned their attentions to other negative materials with facile, scalable, and binder-free preparation technology, low cost, environmentally benign nature, and high capacitance. For instance, the asymmetric supercapacitors based on pseudocapacitance materials, such as Co(OH)2//VN, [16]
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Fe2O3, [20] MoO3, [21] V2O5 [22] and VN [23]) that are considered to serve as the cathode materials in asymmetric supercapacitors. Polypyrrole (PPy) based composites as cathodes using in
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asymmetric supercapacitors almost have not been reported so far. It may be mainly because that the potential of PPy based composites has not enough negative and the electrochemical studies are
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usually performed within a potential range of -0.5 to +0.4 V versus SCE, [24] or within the more positive potential. [25] Nevertheless, PPy has been well-known as a kind of promising electrode material for supercapacitors because of its high special capacitance, good conductivity and outstanding mechanical properties. Hence, developing PPy based composites as new negative
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materials with more negative working potential window, high special capacitance (Csp), and low electrical resistance for high power density might be significant for achieving a higher Csp and
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energy density of an asymmetric supercapacitor with a retained high power density. Recently, surface coating on 3D Ni metal framework was known as a promising way to
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fabricate advanced electrode materials. [26-27] In our previous work, we demonstrated novel 3D-Ni@MnO2, [28] 3D-Ni@Ni(OH)2 [29] and 3D-Ni@PPy [30] composites for supercapacitors with high Csp and remarkable cycling stability. In this work, the composites of 3D chuzzle-like Ni@PPy@MnO2 and 3D cochleate-like Ni@MnO2@PPy based on 3D Ni metal framework were prepared by simply changing the order of electrodeposition. As expected, both the two composites exhibit excellent electrochemical performance within different stable voltage window in a neutral
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Consequently, Ni@PPy@MnO2//Ni@MnO2@PPy has a large work voltage of 1.3~1.5 V and achieves an energy density as high as 59.8 Wh kg-1 at a large power density of 1500 W kg-1, and
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thus this pattern for choice of Ni@MnO2@PPy as cathode could also provide a promising route for novel asymmetric supercapacitor with high energy and power densities.
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2. Experimental 2.1 Fabrication of hierarchical PPy based composites
Electrodeposition was conducted on a piece of nickel foam with a geometric area of 1.5 × 1 cm2. The 3D-Ni current collectors were fabricated according to the previously reported method, [28-30]
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and the Ni@PPy@MnO2 anode was prepared by a simple three-step electrochemical deposition process. The electropolymerization of PPy was directly carried out on the surfaces of 3D-Ni metal
EP
framework in acetonitrile solution containing of 0.01 M pyrrole + 0.1 M anhydride LiClO4 by potentiostat electrolysis with positive potential of +1 V in a three-electrode cell with a platinum
AC C
plate as the counter electrode and saturated calomel electrode (SCE) as the reference electrode. Then, MnO2 was also deposited on Ni@PPy surface by using electrochemical deposition method. The electrolytic bath was composed of 0.01 M Mn(NO3)2, 0.01 M NaNO3 and 10% dimethylsulfoxide (water solution volume ratio). The potentiostat electrolysis was worked at a potential of +1 V in a three-electrode cell with a carbon rod as the counter electrode and saturated calomel electrode (SCE) as the reference electrode. The Ni@MnO2@PPy cathode was prepared by
4
ACCEPTED MANUSCRIPT simply changing the order of electrodeposition as the above method. The loading mass of PPy and
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MnO2 are calculated using Faraday's Law of electrolysis:
For PPy, where Q is the electropolymerization charge, Mpy is the molecular mass of pyrrole, F is the Faraday constant of 96500 C mol-1, and y is a stoichiometric factor evaluating the anion
SC
insertion degree, which is inserted for charge compensation on the electropolymerization process.
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[31] The model of overall electropolymerization process should be as follow:
where n is the degree of polymerization, y is the above mentioned degree of anion insertion. PPy
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with anodic α,α-coupling of pyrrole rings can be formed, and then, the polymeric radial cation containing three or four monomer units as a segment of the conjugated backbone can be yielded by further being oxidized. [32] For MnO2, Q is is total charge of the electrodeposition process, MMnO
EP
2
is the molecular mass of MnO2, F is the Faraday constant, Z is the number of electrons of the Mn
AC C
ion transferred from Mn2+ to MnO2 (Mn2+ + 2H2O = MnO2 + 4H+ + 2e-). [33] The loading mass of both PPy and MnO2 can be tunable through changing the electrodeposition time. The mass ratio of active material [PPy (0.35 mg) : MnO2 (1.00 mg)] for the optimized Ni@PPy@MnO2 anode is about 1 : 3. Meanwhile, for the optimized the Ni@MnO2@PPy cathode, the mass ratio between MnO2 (0.40 mg) and PPy (0.60 mg) is about 2 : 3. 2.2. Physicochemical characterizations
5
ACCEPTED MANUSCRIPT The morphology of the as-prepared samples was analyzed by using field emission scanning electron microscopy (FE-SEM, JEOL JSM-7001F). The structure of the samples were analyzed by powder X-ray diffraction (XRD, Bruker , D8 ADVANCE) with Kα radiation (λ = 1.5418 Å).
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Optical properties of the as-prepared samples were tested by Fourier transform infrared spectrum (FT-IR, Nicolet 5700 spectrometer) and Raman spectrometer (Renishawin Via). The chemical state
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and compositions of the samples were analyzed using X-ray Photoelectron Spectroscopy (XPS, ESCALab250).
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2.3. Assembly of asymmetric supercapacitor and electrochemical characterizations The fabricating process of asymmetric supercapacitor is illustrated in Figure 1. An aqueous 1.5 × 1.5 cm2 asymmetric supercapacitor device (Ni@PPy@MnO2//Ni@MnO2@PPy) was assembled through integrating Ni@PPy@MnO2 as an anode and Ni@MnO2@PPy as a cathode. A piece of
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NKK TF48 (1.5 × 1.5 cm2) was as the separator in a two electrode system. The electrochemical properties of the as-prepared samples were investigated with cyclic voltammetry (CV),
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galvanostatic charge-discharge (GCD) measurements by employing a CHI 760D electrochemical workstation (Chenhua, Shanghai). All the electrochemical measurements were performed in 0.5 M
AC C
Na2SO4 electrolyte.
3. Results and Discussion 3.1 Chuzzle-like Ni@PPy@MnO2 anode and cochleate-like Ni@MnO2@PPy cathode The typical low and high magnification scanning electron microscopy (SEM) images of as-prepared samples are clearly illustrated in Figure 2a-d. Figure 2a shows the 3D full-gapped morphology that ultrathin PPy is uniformly coated on the surface of 3D Ni framework. The coat of
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ACCEPTED MANUSCRIPT MnO2 grown on the Ni@PPy is also presented in the Figure 2b. The high-magnification SEM image (Figure 2b, inset) reveals with the formation of 3D chuzzle-like Ni@PPy@MnO2 (average diameter about 7-8 µm), which is different with flower-like Ni@MnO2 (Figure 2c), in which
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MnO2 tends to grow on the length of nanosheets that may lead to an unstable structure after elongated electrochemical process. For Ni@PPy@MnO2, three kinds of efficacy may be achieved
SC
from PPy: 1) on the surface of 3D Ni framework, PPy provides more reaction sites to grow MnO2, which can restrict the excessive growth of MnO2 nanosheets to protect the structural stability of
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MnO2. 2) PPy not only enhances the conductivity of the composites, but also increases the electrical connection between MnO2 and 3D-Ni current collector. 3) According to our previous work, [28] the capacitance contribution from 3D Ni framework can be negligible in electrochemical processes, thus Ni@PPy endowed with appreciable capacitance will enhance the
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whole capacitance of Ni@PPy@MnO2. The 3D cochleate-like Ni@MnO2@PPy was synthesized via direct electropolymerization of PPy on flower-like Ni@MnO2. Typical SEM images of the
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Ni@MnO2@PPy are illustrated in Figure 2d. It is clearly observed that the Ni@MnO2@PPy exhibits a cochleate-like shape and the corresponding high magnification image (inset in Figure 2d)
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exhibits that the external surface of cochleate-like shape is relatively rough and decorated by PPy with spiral distribution. And the 3D Ni@MnO2@PPy shows cochleate-like structures with uniform diameter of 2-3 µm.
Figure S1 shows XRD patterns of the Ni@PPy@MnO2 and Ni@MnO2@PPy powder collected by scraped off the as-prepared composites from nickel foam. All of the diffraction peaks can be indexed to 3D-Ni and there is no peak pertaining to PPy and MnO2, implying that the deposited
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ACCEPTED MANUSCRIPT PPy and MnO2 are amorphous in nature. It is generally known that amorphous materials contain enormous structure distortion, which provide more active sites and surface molecules in more active states for Faradaic redox reaction, revealing the intrinsically high performance of
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amorphous PPy and MnO2. The Fourier transform infrared spectroscopy (FT-IR) and Raman spectrum provide additional evidence for the presence of PPy and MnO2. Figure 2e displays the
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FT-IR spectrum of Ni@PPy@MnO2 and Ni@MnO2@PPy composite. In details, the absorption peaks at 1625 cm-1 is attributed to the vibration of C=C and C-C on the pyrrole ring, while the
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peaks at 1541 cm-1 and 1458 cm-1 are assigned to the pyrrole ring vibration. [34] The absorption peaks at 1159 cm-1 and 1125 cm-1 are induced by absorption of C-N stretching vibrations and C-C stretching vibrations between two pyrrole rings of the PPy, while other peaks at 1073 cm-1 and 645 cm-1 are due to N-H in-plane deformation vibration and absorption of C-H on pyrrole, respectively.
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[25] Moreover, the peak at 512 cm-1 is indicative of vibrations Mn-O. [35] The result of FT-IR spectrum indicates the presence of PPy and MnO2. It is obvious that relative peaks strength of PPy
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and MnO2 are affected by the hierarchical structure. The peaks strength of PPy in Ni@PPy@MnO2 are weaker than that of Ni@MnO2@PPy and the peaks strength of MnO2 in Ni@PPy@MnO2 are
AC C
stronger than that of Ni@MnO2@PPy. A similar effect also appears in Raman spectrum. Figure 2f exhibits that there are almost no correlation peaks of PPy for Ni@PPy@MnO2 and the bands from 502 cm-1 to 626 cm-1 are attributed to the Mn-O stretching vibration. [36] In addition, for Ni@MnO2@PPy composite, characteristic peaks at about 675 cm-1, 935 cm-1, 1068 cm-1 and 1085 cm-1 confirm the presence of PPy, [37] while the bands at 502 cm-1, 626 cm-1 for MnO2. [36] The chemical composition and valence states of the Ni@PPy@MnO2 and Ni@MnO2@PPy
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ACCEPTED MANUSCRIPT were further investigated by X-ray Photoelectron Spectroscopy (XPS). The XPS survey spectrum (Figure S2 a) demonstrates the presence of Ni, Mn, O, N, and C in both composites. Figure S2 b shows the Ni 2p XPS of the both composites that demonstrates the formation of 3D-Ni (Ni0) metal
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and a small number of Ni2+ ascribing to the partially surface oxidation of 3D-Ni metal exposing to the air. [38] The high-resolution spectra for Mn 2p, O 1s and N 1s are shown in Figure 2h-g. In
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Figure 2h, the Mn 2p spectrum exhibits multiple splitting. Two main peaks located at 643.8 and 653.9 eV can be assigned to Mn 2p3/2 and Mn 2p1/2 of Mn4+ in MnO2, respectively. [39]
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Meanwhile, the two weaker peaks for Mn3+ and Mn5+ species were also detected in the spectrum, implying that element Mn has the main chemical state of Mn4+. [40] In the O 1s region (Figure 2i), the broad multi-peak can be divided into two peaks at 529.7 eV and 531.3 eV, corresponding to the Mn-O-Mn bond and Mn-OH bond respectively. [39] Figure 2g shows the N 1s XPS pattern, in
of PPy. [41-42]
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which two peaks centered at 399.9 eV and 398.4 eV are attributed to the –NH- bond and =N- bond
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Electrochemical characterization of the chuzzle-like Ni@PPy@MnO2 anode and cochleate-like Ni@MnO2@PPy cathode were investigated by using CV and GCD test with a three-electrode cell
AC C
in a 0.5 M Na2SO4 electrolyte. Figure 3a shows the CV curves of chuzzle-like Ni@PPy@MnO2 anode at scan rates of 5, 10, 20, 50, 100 mV s-1. The CV curves with nearly box shape indicates good capacitive behavior in the voltage window of 0 to +0.8 V versus SCE and the enhancement in current with increasing scan rate indicated good capacitance retention. The GCD plots of chuzzle-like Ni@PPy@MnO2 anode at different applied current densities are present in Figure 3b, which exhibits the triangular symmetry and linear slopes, further confirming the excellent
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ACCEPTED MANUSCRIPT capacitive performance of Chuzzle-like Ni@PPy@MnO2 anode. The specific capacitance (Csp) is calculated by the discharge curves. As shown in Figure 3c, large Csp of 306, 318, 324, 343 and 350 F g-1 can be achieved by increasing current densities from 2 to 10 A g-1, which demonstrates a
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superior rate capability with a small decay of 13% in Csp. Compared to Ni@PPy@MnO2 anode, the Ni@MnO2 electrode (Figure S3) only shows smaller Csp of 162, 171, 186, 199.5 and 225 F g-1
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ferior rate capability (28% decay in Csp) with current densities from 2 to 10 A g-1. The possible reasons can be mainly attributed to the high conductivity of PPy interlayer providing the abundant
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electrical connection between MnO2 and 3D-Ni current collector and enhance the capacitance of Ni@PPy@MnO2. It is also suggested that the 3D-Ni@PPy network could improve the electronic conductivity of the composite, which is beneficial for the charge-discharge reactions. It is well known that the pseudocapacitive effect is limited only to a region near the surface. In this case, the
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major capacitance of hierarchical Ni@PPy@MnO2 can be attributed to the MnO2, which has been demonstrated in the voltage window (0 to +0.8 V versus SCE), consistent with the typical voltage
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window of MnO2. The mechanism of charge storage of MnO2 in a neutral Na2SO4 aqueous solution may proceed via the following reaction (Na+ cations are involved in the charging of MnO2
AC C
in the positive potential range):
MnO2Na = MnO2 + Na+ +e-
(1)
According to the above reaction equation, the homogeneously dispersed 3D chuzzle-like Ni@PPy@MnO2 can increase the specific surface area and form porous structures that act as ion reservoirs to improve the diffusion rate of Na+ ions and facilitate the charge-discharge reactions. The cycle stability of the Ni@PPy@MnO2 electrode is evaluated for 5000 continuous cycles in 0.5
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ACCEPTED MANUSCRIPT M Na2SO4 at a scan rate of 100 mV s-1 (Figure 3d). The Csp can be maintained as high as ≈91.3 of the initial value, which is more stable than the value for Ni@MnO2 electrode in Figure S3 (retaining 70.1% of initial Csp after 5000 cycles). The improved stability of the Ni@PPy@MnO2
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electrode might be due to the proper growth of MnO2 nanosheets on Ni@PPy surface protecting the structural stability of MnO2 during the rapid migration of electrolyte ion on electrode material
SC
surface.
Figure 4a presents the CV curves of the cochleate-like Ni@MnO2@PPy cathode at different
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scan rates in a potential window between -0.7 V and +0.1 V (versus SCE), which exhibits its redox peak-incorporated rectangular shape and almost unchangeable shape with the increasing scan rates, implying that the 3D cochleate-like structure is beneficial for the rapid redox reaction and easy access of ions to the interfaces between electrode and electrolyte, resulting in superior capacitive
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and high-rate performance. In this case, CV measurement is also served as the appropriate tool to identify Faradic and non-Faradic reaction of energy storage mechanism. In all CV curves, two
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broad redox humps during the anodic (-0.4 V to -0.2 V) and cathodic (-0.7 V to -0.5 V) scans and the wide current-potential response can be observed, indicating both electrical double layered (EDLC)
and
AC C
capacitance
pseducapacitance
of
cochleate-like
Ni@MnO2@PPy.
The
pseducapacitance is mainly attributed to the functional groups of spiral-decorated PPy, where the cathodic wave and the anodic wave are owing to the insertion and expulsion of Na+ ions in the electrolyte. [43] We propose that the apparently presentation of redox reaction for Ni@MnO2@PPy can be ascribed to the unique 3D cochleate-like structure, being conducive to the exposure of PPy in the electrolyte and full utilization of functional groups. To verify this
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ACCEPTED MANUSCRIPT hypothesis, Ni@PPy is also investigated for comparsion by using CV test. Figure S4 shows the CV curves of Ni@PPy collected in potential window of -0.3 to +0.5, -0.4 to +0.4 and -0.5 to +0.3 at the scan rate of 20 mV s-1. It is worthily noting that the Ni@PPy only exhibits the EDLC nature
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and when the working potential decreases to -0.5 V, obvious polarization current is observed, indicated the unstable characteristic in the relatively negative potential range, further
SC
demonstrating the advantage structure of 3D cochleate-like Ni@MnO2@PPy in the presentation of pseducapacitance. Additionally, basing on the different order of MnO2 and PPy in hierarchical
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Ni@PPy@MnO2 and Ni@MnO2@PPy, the major capacitance contributor for Ni@MnO2@PPy should be different with that of Ni@PPy@MnO2. In Ni@MnO2@PPy cathode, the major capacitance can be ascribed to the PPy, which has also been demonstrated in the voltage window (-0.7 to +0.1 V versus SCE) of Ni@MnO2@PPy, closing to the typical voltage window of PPy.
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Fig. 4b shows the GCD curves, where almost linear and typical triangular symmetrical curves can be observed, displaying perfect reversibility of the redox reactions for cochleate-like
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Ni@MnO2@PPy in 0.5 M Na2SO4 aqueous electrolyte. A high Csp of 473.8 F g-1 can also be calculated at a current density of 2 A g-1 (Fig. 4c). Moreover, the Ni@MnO2@PPy exhibits
AC C
excellent rate capability, and the retention rate is 63.1% with increasing the discharging current density from 2 to 10 A g-1. Due to the high conductive 3D-Ni collector, cochleate-like structure and combined electroactivities of PPy and MnO2, Ni@MnO2@PPy exhibits higher capacitance, better rate capability and a relatively negative charge storage potential window. The long-term cycle stability was tested by CV scans at a scan rate of 100 mV s-1 for 5000 cycles and the results are shown in Fig. 4d. The Csp of the Ni@MnO2@PPy only has a slight fluctuation and remains above
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ACCEPTED MANUSCRIPT 100% of the initial Csp in the whole process, which is more stable than Ni@PPy maintaining 79.1% of the initial Csp after 5000 cycles (Figure S5 d). 3.2 Asymmetric supercapacitor based on chuzzle-like Ni@PPy@MnO2 and cochleate-like
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Ni@MnO2@PPy
Considering the remarkable Csp and rate capability of the EDLC and pseudocapacitance
SC
properties for chuzzle-like Ni@PPy@MnO2 and cochleate-like Ni@MnO2@PPy, an asymmetric supercapacitor was fabricated using the two materials as anode and cathode, respectively. Figure
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5a exhibits that Ni@PPy@MnO2 electrode was measured at a scan rate of 50 mV s-1 with a voltage window of 0 V to 0.8 V (versus SCE), while Ni@MnO2@PPy was measured within a voltage window of -0.7 to +0.1 V (versus SCE). Thus, the operation window of asymmetric supercapacitor can be extended up to 1.5 V by tuning the mass ratio of the two electrodes. Since the charges
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stored in the two capacitor electrodes should be equal in magnitude with opposite signs. The charge balance will follow the relationship Q+ = Q-, where the charge stored by each electrode
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usually depends on the C, the potential range for the charge-discharge process (∆V), and the mass of the electrode (m) following the equation: Q = C × ∆V × m. For the asymmetric capacitor
AC C
developed here, the Csp of the Ni@PPy@MnO2 and Ni@MnO2@PPy electrodes are 350 F g-1 and 473.8 F g-1, respectively, at a discharge current of 2 A g-1. As a result, designing an asymmetric capacitor, the optimal mass ratio of the two electrodes (m(Ni@PPy@MnO2)/m(Ni@MnO2@PPy)) can be deduced to be 1.35. In a controlled experiment, a Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor with a mass ratio of 1.35 performs at different voltage windows in 0.5 M Na2SO4 aqueous electrolyte at a scan rate of 50 mV s-1 (Figure 5b). When voltage windows is
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ACCEPTED MANUSCRIPT worked at 1.2, 1.3, and 1.4 V, a nearly box CV curve implies an ideal capacitive behaviour response from the asymmetric supercapacitor. By increasing the voltage windows to 1.5 V, relatively obvious polarization current appear in the CV curve, indicating excessive positive
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potential on the Ni@PPy@MnO2 electrode. Figure 5c shows the variation of Csp with increasing voltage window for the asymmetric supercapacitor. Remarkably, the Csp increased significantly
SC
from 135.2 to 168.9 F g-1 with an increasing the operation potential from 1.2 to 1.5 V at a scan rate of 50 mV s-1. For evaluating the optimal voltage window, cyclic stability of the cell was also be
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investigated by CV test at a scan rate of 100 mV s-1 for 1000 cycles with different operating potential (Figure 5d). It can be observed that the Csp retention at voltage window of 1.3, 1.4 and 1.5 V after 1000 cycles was about 100.9%, 84.8%, and 49.8%, respectively. The Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor was subjected to detailed
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measurements for obtaining more information on the capacitive performance of the optimized asymmetric supercapacitor. Figure 6a presents the CV curves of the asymmetric capacitor at
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different scan rates of 5, 10, 20, 50, and 100 mV s-1 with the 1.3 V operating potential in a two-electrode system. The cell shows a near rectangular shape CV curve with any signs of
AC C
distortion by increasing potential scan rate, indicating an ideal capacitive behavior under 1.3 V operating potential. The Csp of the Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor at different scan rates calculated from CV curves is shown in Figure 6c. The Csp gradually decreased from 184.6 to 136.2 F g-1 with increasing scan rate. A better rate capability with small decay of 26.2% in Csp can be achieved, exhibiting excellent capacitance retention and indicating the almost unlimited diffusion of Na+ ions in both anode and cathode even at high scan rates. GCD
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ACCEPTED MANUSCRIPT curves of the optimized Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor were measured at current densities of 2, 4, 6, 8 and 10 A g-1 with the 1.3 V operating potential. As shown in Fig. 6b, all the curves are highly linear and symmetrical at current densities from 2 to 10
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A g-1, implying that the Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor has good Coulombic efficiency related to superior charge-discharge reversibility. Figure 6d presents the Csp
SC
of asymmetric supercapacitor at different discharge current densities. The Csp decreased from 165.0 to 132.3 F g-1 with the discharge current density increasing from 2 to 10 A g-1, revealing the
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excellent capacitance retention again.
On the basis of above results, the energy density and power density of the asymmetric supercapacitor were calculated from the discharges curves and plotted on a Ragone diagram in Figure 7a. The maximum energy density were 38.7, 46.7, and 59.8 Wh kg-1 at the power density of
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1300, 1400, and 1500 W kg-1 under discharge current 2 A g-1 at voltage window of 1.3, 1.4 and 1.5 V, respectively. The values gradually decreased to 31.1, 33.0, and 29.2 Wh kg-1 at the power
EP
density of 6500, 7000, and 7500 W kg-1 under discharge current 10 A g-1. The obtained maximum energy density is considerably comparable to those of recently reported symmetric and asymmetric
AC C
supercapacitors, such as RuO2//RuO2 (18.8 Wh kg-1), [44] Fe3O4-GNS//Fe3O4-GNS (11.0 Wh kg-1), [45] CoO@PPy//AC (43.5 Wh kg-1), [12] PANI//MoO3 (38.9 Wh kg-1), [17] MnO2@NCs//AC (52.1 Wh kg-1), [46] MnO2//CNT (47.4 Wh kg-1), [47] CNT/MnO2//CNT/InO3 (25.5 Wh kg-1), [48] RGO-RuO2//RGO-PANI (26.3 Wh kg-1) [49] and Fe2O3-FGS//MnO2-FGS (50.7 Wh kg-1) [50]. Most importantly, the power density of Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor are higher than those related to similar maximum energy density, indicating the
15
ACCEPTED MANUSCRIPT allowed significant improvement both power and energy characteristics of the asymmetric supercapacitor. Additionally, we further evaluate the long-term cycling stability of the Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor by CV test at a scan rate of 100
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mV s-1 for 3000 cycles with 1.3 V operating potential. Figure 7b shows the capacitance retention ratio of the asymmetric supercapacitors scan at 1.3 V as a function of the cycle number. The device
SC
exhibits electrochemical stability with about 83.5% retention of the initial Csp after 3000 cycles. It is worthily noting that the Csp start decreasing is the initial 1000 cycles (retained 100.1% of its
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initial capacitance). The capacitance decrease may be due to the positive polarization (excessive positive potential on the Ni@PPy@MnO2 electrode) or the electrode matching problems, because individual Ni@MnO2@PPy electrode showed good capacitance retention in corresponding voltage windows in the same electrolyte. Furthermore, three supercapacitors in series have been assembled
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and after charging for only 20 s to 4 V, the device can power a red round light-emitting diode (LED) indicator (1.9-2.2 V, 20 mA) light brightly for 8 min (Figure 7 c-d).
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The high energy density, excellent rate capability and long-term cycling capability of the Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor can be attributed to the
AC C
advantageous morphology and structure of both 3D chuzzle-like Ni@PPy@MnO2 anode and 3D cochleate-like Ni@MnO2@PPy cathode, as shown in Figure 8. The main reasons towards capacitance enhancement might be mainly summarized in the following factors: (i) 3D chuzzle-like Ni@PPy@MnO2 and 3D cochleate-like Ni@MnO2@PPy formed by the 3D-Ni serving as a high conductive framework, display high conductivity, unique 3D structure with large accessible specific activity area and more active sites for enhancement of EDLC and
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ACCEPTED MANUSCRIPT pseudocapacitance (completely exposed pseudocapacitance of PPy for 3D cochleate-like Ni@MnO2@PPy cathode); (ii) The full-gapped structure between each 3D units may provide a storage chamber and fast transmission channels for electrolyte ions to transfer and finally enhance
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electrolyte accessibility. (iii) Conductive ultrathin-PPy also plays an important role for benefits of hierarchical PPy based composites, which not only enhances the conductivity of the composites
SC
and protect the nanoplate structure of MnO2, but also endows with appreciable capacitance for the composites. (iv) 3D hierarchical PPy based composites directly decorated on the Ni foam avoiding
collector and hierarchical composites.
4. Conclusions
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the use of polymer binder, which may offer effective electron transport pathways between current
In summary, Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor was fabricated by
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using 3D chuzzle-like Ni@PPy@MnO2 as the anode and 3D cochleate-like Ni@MnO2@PPy as the cathode. Particularly, the 3D cochleate-like Ni@MnO2@PPy was the first time to develop for
EP
the asymmetric supercapacitor cathode. Benefiting from the high capacitance of EDLC and pseudocapacitance of both electrodes, the device exhibits excellent performance in the voltage
AC C
potential of 1.3~1.5 V and achieves a high Csp of 191.3 F g-1, a large energy of 59.8 Wh kg-1 and a power density 7500 W kg-1 for the whole cell. It is believed that the hierarchical PPy based composites electrodes will provide a new choice for the developing asymmetric supercapacitors.
Acknowledgments The authors acknowledge the financial support of this work by Natural Science Foundations of China (Grant No. 21306030), the Natural Science Foundations of Guangdong Province (Grant No.
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ACCEPTED MANUSCRIPT s2012010009719 and s2013040015229), Scientific Research Project of Guangzhou Municipal Colleges and Universities (Grant No. 2012A064), and the Fresh Talent Program of Guangzhou
Appendix A. Supplementary data Supplementary
data
related
to
this
article
can
be
found
at
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http://dx.doi.org/00.0000/j.jpowsour.2015.00.00.
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University (Grant No. 201302).
References
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[1] G. Wang, L. Zhang, J. Zhang, Chem. Soc. Rev. 41 (2012) 797-828.
[2] Z. Tang, C. H. Tang, H. Gong, Adv. Funct. Mater. 22 (2012) 1272-1278. [3] S. Giri, D. Ghosh, C. K. Das, Adv. Funct. Mater. 24 (2013) 1312-1324. [4] S. W. Lee, N. Yabuuchi, B. M. Gallant, S. Chen, B. S. Kim, P. T. Hammond, Y. S. Horn, Nat.
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Nanotechnol. 5 (2010) 531-537.
[5] L. L. Zhang, X. S. Zhao, Chem. Soc. Rev. 28 (2009) 2520-2531.
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[6] Q. Lu, M. W. Lattanzi, Y. Chen, X. Kou, W. Li, X. Fan, K. M. Unruh, J. G. Chen, J. Q. Xiao, Angew. Chem. Int. Ed. 50 (2011) 6847-6850.
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[7] W. Chen, R. B. Rakhi, L. Hu, X. Xie, Y. Cui, H. N. Alshareef, Nano Lett. 11 (2011) 5165-5172 .
[8] Q. Gao, L. Demarconnay, E. Raymundo-Piñero, F. Béguin, Energy Environ. Sci. 5 (2012) 9611-9617. [9] Q. Qu, Y. Zhu, X. Gao, Y. Wu, Adv. Energy Mater. 2 (2012) 950-955. [10] B. Wang, J. S. Chen, Z. Y. Wang, S. Madhavi, X. W. Lou, Adv. Energy Mater. 2 (2012)
18
ACCEPTED MANUSCRIPT 1188-1192. [11] W. Tang, L. Liu, S. Tian, L. Li, Y. Yue, Y. Wu, K. Zhu, Chem. Commun. 47 (2011) 10058-10060.
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[12] C. Zhou, Y. Zhang, Y. Li, J. Liu, Nano Lett. 13 (2013) 2078-2085.
[13] H. Wang, C. Qing, J. Guo, A. A. Aref, D. Sun, B. Wang, Y. Tang, J. Mater. Chem. A 2 (2014)
SC
11776-11783.
[14] H. Gao, F. Xiao, C.B. Ching, H. Duan, ACS Appl. Mater. Interfaces, 4 (2012) 2801-2810.
Mater. 22 (2012) 2632-2641.
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[15] J. Yan, Z. Fan, W. Sun, G. Ning, T. Wei, Q. Zhang, R. Zhang, L. Zhi, F. Wei, Adv. Funct.
[16] R. Wang, X. Yan, J. Lang, Z. Zheng, P. Zhang, J. Mater. Chem. A 2 (2014) 12724-12732. [17] H. Peng, G. Ma, J. Mu, K. Sun and Z. Lei, J. Mater. Chem. A 2 (2014) 10384-10388.
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[18] Y. Su, I. Zhitomirsky, J. Power Sources 267 (2014) 235-242. [19] H. Wang, Y. Liang, T. Mirfakhrai, Z. Chen, H.S. Casalongue, H. Dai, Nano Res. 4 (2011)
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729-736.
[20] S. Sun, J. Lang, R. Wang, L. Kong, X. Li, X. Yan, J. Mater. Chem. A 2 (2014) 14550-14556.
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[21] J. Cheng, M. Jin, F. Yao, T. H. Kim, V. T. Le, H. Yue, F. Gunes, B. Li, A. Ghosh, S. Xie, Y. H. Lee, Adv. Funct. Mater. 23 (2013) 5074-5083. [22] A. Q. Pan, H. B. Wu, L. Yu, T. Zhu, X. W. Lou, ACS Appl. Mater. Interfaces 4 (2012) 3874-3879. [23] X. Lu, M. Yu, T. Zhai, G. Wang, S. Xie, T. Liu, C. Liang, Y. Tong, Y. Li, Nano Lett. 13 (2013) 2628-2633.
19
ACCEPTED MANUSCRIPT [24] K. Shi, I. Zhitomirsky, J. Power Sources 240 (2013) 42-49. [25] M. Yu, Y. Zeng, C. Zhang, X. Lu, C. Zeng, C. Yao, Y. Yang, Y. Tong, Nanoscale 5 (2013) 10806-10810.
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[26] D. Chao, X. Xia, C. Zhu, J. Wang, J. Liu, J. Lin, Z. Shen, H. J. Fan, Nanoscale, 6 (2014) 5691-5697.
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[27] Z. Su, C. Yang, B. Xie, Z. Lin, Z. Zhang, J. Liu, B. Li, F. Kang, C.P. Wong, Energy Environ. Sci. 7 (2014) 2652-2659.
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[28] K. Xiao, J.W. Li, G. F. Chen, Z. Q. Liu, N. Li, Y. Z. Su, Electrochim. Acta 149 (2014) 341-348.
[29] Y. Z. Su, K. Xiao, N. Li, Z. Q. Liu, S. Z. Qiao, J. Mater. Chem. A 2 (2014) 13845-13853. [30] G. F. Chen, Y. Z. Su, P. Y. Kuang, Z. Q. Liu, D. Y. Chen, X. Wu, N. Li, S. Z. Qiao, Chem.
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Eur. J. DOI: 10.1002/chem.201405976.
[31] Y. Hou, L. Chen, P. Liu, J. Kang, T. Fujita, M. Chen, J. Mater. Chem. A 2 (2014)
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10910-10916.
[32] M. Schirmeisen, F. Beck, J. Appl. Electrochem. 19 (1989) 401-409.
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[33] B. Anothumakkool, S. Kurungot, Chem. Commun. 50 (2014) 7188-7190. [34] P. Mavinakuli, S.Y. Wei, Q. Wang, A. B. Karki, S. Dhage, Z. Wang, D. P. Young, Z. H. Guo, J. Phys. Chem. C 114 (2010) 3874-3882. [35] B. Wang, X. He, H. Li, Q. Liu, J. Wang, L. Yu, H. Yan, Z. Li, P. Wang, J. Mater. Chem. A 2 (2014) 12968-12973. [36] M. Polverejan, J.C. Viliegas, S. L. Suib, J. Am. Chem. Soc. 126 (2004) 7774-7775.
20
ACCEPTED MANUSCRIPT [37] J. Zhang, Y. Yu, L. Liu, Y. Wu, Nanoscale 5 (2013) 3052-3057. [38] Z. Zhao, H. Wu, H. He, X. Xu, Y. Jin, Adv. Funct. Mater. 24 (2014) 4698-4705. [39] M. Toupin, T. Brousse, D. Belanger, Chem. Mater. 16 (2004) 3184-3190.
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[40] Y. Zhao, P. Jiang, S.S. Xie, J. Power Sources 239 (2013) 393-398. [41] W. Yao, H. Zhou, Y. Lu, J. Power Sources 241 (2014) 359-366.
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[42] P. Li, Y. Yang, E. Shi, Q. Shen, Y. Shang, S. Wu, A.Y. Cao, D. H. Wu, ACS Appl. Mater. Interfaces 6 (2014) 5228-5234.
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[43] A. Lin, C. Li, H. Bai, G. Shi, J Phys Chem C 114 (2010) 22783-22789.
[44] H. Xia, Y. S. Meng, G. Yuan, C. Cui, Li Lu, Electrochem. Solid-State Lett. 15 (2012) A60-A63.
[45] K. Karthikeyan, D. Kalpana, S. Amaresha, Y. S. Lee, RSC Adv. 2 (2012) 12322-12328.
12519-12525.
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[46] M. Yang, Y. Zhong, X. Zhou, J. Ren, L. Su, J. Wei, Z. Zhou, J. Mater. Chem. A 2 (2014)
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[47] H. Jiang, C. Li, T. Sun and J. Ma, Nanoscale 4 (2012) 807-812. [48] P. C. Chen, G. Shen, Y. Shi, H. Chen, X. Zhou, ACS Nano 4 (2010), 4403-4411.
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[49] J. Zhang, J. Jiang, H. Li, X. S. Zhao, Energy Environ. Sci. 4 (2011) 4009-4015. [50] H. Xia, C. Hong, B. Li, B. Zhao, Z. Lin, M. Zheng, S. V. Savilov, S. M. Aldoshin, Adv. Funct. Mater. 25 (2015) 627-635.
Figure Captions Figure 1. Fabrication process of Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor
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Ni@MnO2, and 3D cochleate-like Ni@MnO2@PPy; (e-f) FT-IR and Raman spectra of Ni@PPy@MnO2 and Ni@MnO2@PPy; (h-g) Mn2p, O1s, and N1s spectra of Ni@PPy@MnO2 and Ni@MnO2@PPy.
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Figure 3. (a) CV curves of Ni@PPy@MnO2 collected at different scan rates; (b) Galvanostatic
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charge-discharge curves of Ni@PPy@MnO2 under different constant current densities; (c) specific capacitance at different current densities; (d) the cycling stability for Ni@PPy@MnO2 from the 1st to the 5000th cycles at scan rates of 100 mV s-1.
Figure 4. (a) CV curves of Ni@MnO2@PPy collected at different scan rates; (b) Galvanostatic
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charge-discharge curves of Ni@MnO2@PPy under different constant current densities; (c) specific capacitance at different current densities; (d) the cycling stability for Ni@MnO2@PPy from the 1st
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Figure 5. (a) CV curves of Ni@PPy@MnO2 and Ni@MnO2@PPy electrodes measured in different voltage windows by using a three-electrode system in a 0.5 M Na2SO4 aqueous solution; (b) CV curves of the optimized asymmetric supercapacitor measured in different potential windows with a scan rate of 50 mV s-1 in a 0.5 M Na2SO4 aqueous solution; (c) the specific capacitance of the asymmetric supercapacitor with the increase of voltage window at a scan rate of 50 mV s-1. (d) the cycling stability of asymmetric supercapacitor measured in different potential windows from the 1st to the 1000th cycles at scan rates of 100 mV s-1.
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ACCEPTED MANUSCRIPT Figure 6. (a) CV curves of Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor measured at different scan rates; (b) Galvanostatic charge-discharge curves of asymmetric supercapacitor under different constant current densities; (c-d) specific capacitance collected at
1.3 V)
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(a)
Ragone
plot
related
to
energy
and
power
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Figure
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different scan rates and discharge current densities, respectively. (in a working potential window of
densities
of
the
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Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor in comparison to the asymmetric supercapacitor recently reported in the literature; [12, 17, 46, 47, 48, 49] (d) the cycling stability of the Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor in a potential window of 1.3 V from the 1st to the 3000th cycles at scan rates of 100 mV s-1. (c) a picture showing that three
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Figure 8. Schematic of the advantageous structures of 3D hierarchical PPy based composites.
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GRAPHICAL ABSTRACT
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ACCEPTED MANUSCRIPT HIGHLIGHTS 1. The polypyrrole based electrodes were prepared via a facile electrodeposited method. 2. The sample possesses excellent performance and provides an ideal cathode for supercapacitor.
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3. The as-prepared asymmetric supercapacitor exhibits superior energy and power densities.
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Supporting Information Hierarchical polypyrrole based composites for high
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performance asymmetric supercapacitors Gao-Feng Chen, Zhao-Qing Liu*, Jia-Ming Lin, Nan Li, Yu-Zhi Su* Calculation formulas:
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The discharge capacitance (C), specific capacitance (Csp), energy density (E), and power density (P) reported in this work were calculated from the galvanostatic charge discharge (GCD) curves or cyclic voltammetry (CV) curves using the equations as given in the literature: [1-2]
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The specific capacitance (Csp) was calculated from the slope of the discharge curve from the following:
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where Csp (F g-1), I (A), dt (s), and dV are the specific capacitance, the discharge current, the
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discharge time, and the potential window, respectively. The m (g) at this equation is the mass of the single electrode active materials for three electrode cell, and the total mass of two active electrode materials for two electrode cell.
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The specific capacitance (Csp) was also calculated from the area under the CV curves by the
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following equation:
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where m is the mass of the electroactive materials in the electrodes (g), v is the potential scan rate (mV s-1), Va is the anodic potential (V), Vc is the cathodic potential (V), I is the response current (A) and V is the potential (V).
*Corresponding author. Tel.: +86 20 39366908; Fax: +86 20 39366908. E-mail addresses: [email protected] (Z.-Q. Liu); [email protected] (Y.-Z. Su) 1
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(S3)
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where ∆V is the potential at the end of charge (V) and ∆t is the discharge time (s).
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Figure S1. XRD of Ni@PPy@MnO2 and Ni@MnO2@PPy.
Figure S2. (a) XPS survey spectrum; (b) Ni2p of Ni@PPy@MnO2 and Ni@MnO2@PPy.
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Figure S3. (a) CV curves of Ni@MnO2 collected at different scan rates; (b) Galvanostatic
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Figure S4. CV curves of the optimized Ni@PPy measured in different potential windows with a 3
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scan rate of 20 mV s-1 in a 0.5 M Na2SO4 aqueous solution.
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Figure S5. CV curves of Ni@PPy collected at different scan rates; (b) Galvanostatic charge-discharge curves of Ni@PPy under different constant current densities; (c) specific capacitance at different current densities; (d) the cycling stability for Ni@PPy from the 1st to the
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Figure S6. CV curves of Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor measured at different scan rates; (b) Galvanostatic charge-discharge curves of asymmetric supercapacitor under different constant current densities; (c-d) specific capacitance collected at
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of 1.4 V)
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Figure S7. CV curves of Ni@PPy@MnO2//Ni@MnO2@PPy asymmetric supercapacitor measured at different scan rates; (b) Galvanostatic charge-discharge curves of asymmetric
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References
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different scan rates and discharge current densities, respectively (in a working potential window of
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[S1] A. Pendashteh, M.S. Rahmanifar, R.B. Kanerc, M.F. Mousavi, Chem. Commun. 50 (2014) 1972-1975.
[S2] H. Wang, H.S. Casalongue, Y. Liang, H. Dai, J. Am. Chem. Soc. 132 (2010) 7472-7477.
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