- Email: [email protected]
Mixed valence CoCuMnOx spinel nanoparticles by sacrificial template method with enhanced ORR performance
Applied Surface Science 487 (2019) 1145–1151
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Full length article
Mixed valence CoCuMnOx spinel nanoparticles by sacrificial template method with enhanced ORR performance
T
⁎
Kai Huanga, Junchen Liua, Lu Wanga, Gang Changb, Ruyue Wanga, Ming Leia, , ⁎ ⁎ Yonggang Wanga, , Yunbin Heb, a
State Key Laboratory of Information Photonics and Optical Communications, School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, China b Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Ministry-of-Education Key Laboratory for the Green Preparation and Application of Functional Materials, Hubei Key Laboratory of Polymer Materials, School of Materials Science and Engineering, Hubei University, Wuhan 430062, China
A R T I C LE I N FO
A B S T R A C T
Keywords: CoCuMnOx nanoparticles Sacrificial template method Mixed valence Oxygen reduction reaction
Spinel-type mixed transition metal oxides CoCuMoOx nanoparticles were synthesized through a modified sacrificial template method, by utilizing mashed carbon microspheres as templates. Compared with the direct calcination of mixture precursor, we obtained well-crystallized CoCuMnOx sample with high purity and sizes of 5–20 nm. Mixed valence states of transition metal elements are revealed by X-ray photoelectron spectroscopy, which is a desirable feature for oxygen reduction reaction (ORR) catalyst. Moreover, we further investigated the electrochemical performance of CoCuMoOx for the ORR by cyclic voltammetry, rotating disk electrode and chronoamperometry test in alkaline medium. It is revealed that CoCuMoOx exhibits both outstanding catalytic activity and super stability, which are important properties for an excellent catalyst. As a result, the CoCuMoOx holds high potential as a suitable candidate for ORR catalysts of alkaline fuel cell because of its low-cost and high-efficiency.
1. Introduction Regenerative fuel cells, metal-air batteries, and Li-ion batteries that used in portable mobile devices are being developed very fast due to the growing energy crisis and environment protection concerns [1–13]. Among the various catalysts, spinel oxides with the formula of AB2O4, where metal A occupies the centers of tetrahedrally coordinated positions and metal B occupies the centers of octahedrally coordinated positions in general, have exhibited great importance in applications of environmental-friendly energy storage and conversion technologies, such as lithium ion batteries, electrochemical capacitors, fuel cells, and metal-air batteries [14–22]. It has been proved that the electrochemical properties of spinel oxides strongly depend on their precise structures and compositions. Particularly, for the crucial but sluggish oxygen reduction reaction (ORR) in fuel cells and metal-air batteries, singlephase ternary and quaternary metal spinel oxides (usually including Co, Mn, Cu, Zn, Fe, Ni, etc.) rather than binary metal oxides have been regarded as a promising family of mixed transition-metal oxides (MTMOs) for high-performance non-precious ORR catalysts [23–35]. With respect to the aforementioned distribution of metal cations in crystal structure, the presence and multiple distribution of metal
⁎
cations in various valences will be obtained in quaternary metal spineltype. The synergetic effects between their complex chemical compositions, the donor-acceptor chemisorption sites for the reversible adsorption of oxygen formed by metal cations with multiple valences, and the high electrical conductivity due to their relatively low activation energy for charge transfer between different cations, have been demonstrated to be of great benefits for ORR [36–38]. To make full use of such quaternary metal spinel oxides as efficient ORR catalysts, a facile and high-yield preparation method should be involved for spinel nanocrystals. Although the direct calcination of mixtures of transition-metal nitrates, chlorides or carbonates can produce spinel-type MTMOs in a large scale [39,40], products with micrometer-size and irregular shape always show an inferior catalytic performance due to lack of active sites. To address this issue, continuous efforts such as microwave-assisted combustion method, solvothermal templating method and modified wet co-precipitation method have been dedicated [41–48]. Generally, taking advantage of sacrificial templates (for example, colloidal carbon spheres) in the synthesis process can form various binary and mixed-phase multiple complex metal oxides with a porous hollow microsphere structure [42,49]. Due to the different adsorption and diffusion behaviors of
Corresponding authors. E-mail addresses: [email protected] (M. Lei), [email protected] (Y. Wang), [email protected] (Y. He).
https://doi.org/10.1016/j.apsusc.2019.05.183 Received 22 January 2019; Received in revised form 1 May 2019; Accepted 16 May 2019 Available online 17 May 2019 0169-4332/ © 2019 Elsevier B.V. All rights reserved.
Applied Surface Science 487 (2019) 1145–1151
K. Huang, et al.
XSP). The specific surface areas were measured at 500 °C using a Quantachrome Autosorb-iQ instrument and determined via the Brunauer-Emmett-Teller (BET) method.
more than three kinds of metal ions by carbonaceous particles with rich surface functional groups [50–53], it still remains a challenge to obtain a single crystal-phase multiple MTMOs by template-based synthesis for further understanding of structure-activity relationship in ORR. Herein, we developed a modified template-assisted calcination method for the synthesis of single-phase quaternary CoCuMnOx spinel nanocrystals as high ORR catalysts with sizes ranging from 5 to 20 nm, by sufficient grinding the dry gel of carbon microspheres with fully absorbed cobalt, copper and manganese nitrates before thermal annealing. Compared with the powder CoCuMnOx catalyst (P-CoCuMnOx, CuO as a minor impurity) without the addition of carbon microspheres, this newly developed nano-sized CoCuMnOx catalyst (N-CoCuMnOx) exhibited a more comparable activity and enhanced stability in comparison to commercial Pt/C catalyst in alkaline ORR electrochemical process. Moreover, this modified template-assisted calcination method can be further adopted to synthesize other single-phase multiple functional compounds.
2.3. Electrochemical measurements Electrochemical characterizations were performed on a CHI660A electrochemical workstation with a three-electrode system consisting of a glassy carbon electrode of 5 mm in diameter as the working electrode, a Pt foil as the counter electrode, and an Hg/HgO electrode as the reference electrode. All potential values were calibrated with respect to reversible hydrogen electrode (RHE) by E (RHE) = E (Hg/ HgO) + 0.92 V. For electrode preparation, P-CoCuMnOx, N-CoCuMnOx or commercial Pt/C (20 wt% Pt on Vulcan XC-72, Johnson Matthey) were dispersed by sonication for 30 min in ice-bath to form homogeneous ink (Note: 20 wt% of XC-72R Carbon was employed for PCoCuMnOx and N-CoCuMnOx catalysts ink to make a good electrochemical contact). The mixture is of 800 μl of ultrapure water, 200 μl of isopropanol, and 20 μl of Nafion solution (5.0 wt%). Then 20 μl of the catalysts ink was loaded onto the glassy carbon electrode and dried under ambient temperature with a catalyst loading of 0.5 mg/cm2. Cyclic voltammograms (CV) measurements were performed from 0.05 to 1.05 V with a scan rate of 50 mV/s in N2- and O2-saturated 0.1 M KOH solution, respectively. Rotating disk electrode (RDE) measurements were conducted at different rotating speeds from 400 to 2000 rpm at a scan rate of 5 mV/s, and chronoamperometry was carried out on a constant potential of 0.65 V in O2-saturated 0.1 M KOH solution. All ORR polarization curves were calibrated with LSV data tested in N2 to subtract the corresponding capacitance current. The electron transfer number in ORR can be calculated according to KoutechyLevich equation as follows:
2. Experimental 2.1. Materials and synthesis All starting materials were of analytical pure grade, purchased from commercial sources and used without further purification. Carbon spheres template (with an average diameter of ~500 nm, as shown in Fig. S1) in this work was prepared by means of hydrothermal carbonization of glucose at 160 °C according to a previous work [54]. CoCuMnOx nanoparticles (N-CoCuMnOx) were synthesized by a sacrificial template method followed by thermal annealing in air. In a typical process, 10 mmol of Cu(NO3)2·3H2O, Co(NO3)2·6H2O, Mn(NO3)2·4H2O and 0.15 g of carbon spheres were dissolved in 20 ml of anhydrous alcohol with the aids of ultrasonic dispersion and stirring, then heated in air at 60 °C for 48 h to yield a fluffy mixture powder. After annealing at 500 °C in air for 6 h, washing by DI water and anhydrous alcohol for several times and drying at 60 °C overnight, the powder was reground, pressed into pellets, and calcined for another 6 h to obtain the final NCoCuMnOx sample. For comparison, sub-micron CoCuMnOx powder sample (P-CoCuMnOx) was also collected using a similar synthetic process as described above without the addition of carbon spheres.
imeasured−1 = ik −1 + id−1 = ik −1 + Bω−1/2 B = 0.2nFCD 2/3υ−1/6 where imeasured and ik are the measured and kinetic-limiting current densities, ω is the rotation speed (rpm), n is the transferred electron number, F is the Faraday constant (96,485 C mol−1), C is the concentration of O2 in 0.1 M KOH solution (1.2 × 10−6 mol cm−3), D is the diffusion coefficient of O2 (1.9 × 10−5 cm2 s−1), υ is the kinematic viscosity (0.01 cm2 s−1). In addition, accelerated durability test (ADT) was carried out in the voltage range of 0.6–1.0 V (vs. RHE) for 1000 cyclic voltammetry cycles with a scan rate of 100 mV/s. Electrochemical Impedance Spectra (EIS) were further acquired in the constant voltage mode with the frequency ranging from 100 kHz to 1 Hz using a frequency response analyzer controlled by a potentiostat (Autolab PGSTAT-204) at open circuit potential.
2.2. Morphology and structural characterizations Morphology and microstructure of the samples were characterized by transmission electron microscopy (TEM) (JEOL, JEM-2011), highresolution TEM (HRTEM), and aberration-corrected scanning transmission electron microscopy (STEM) (JEOL, JEM-ARM200F) equipped with a CEOS probe aberration corrector. Phase structures of the samples were examined by X-ray diffraction (XRD) (RIGAKU, D/MX-IIIA) with Cu Kα radiation (λ = 1.54 Å) and Co Kα radiation (λ = 1.79 Å) which was chosen for the refinement analysis (carried out by the Rietveld method with the FULLPROF package) [55]. X-ray photoelectron spectroscopy (XPS) measurements were carried out on an ESCALAB 250Xi spectrometer (Thermo Scientific) with an internal standard (C 1 s peak at 284.4 eV) and a standard deviation of 0.2 eV. The concentration of every element was determined by inductive coupled plasma atomic emission spectrometry (ICP-AES) (Thermo Electron, IRIS Intrepid II
3. Results and discussion Carbon spheres as sacrificial templates have been widely used to fabricate hollow metal oxide microspheres, due to the rich surface functional groups which are available for metal ion adsorption [54]. It is even controllable for the formation of multiple-shell hollow structures with a specific number of shells by processing the metal ion loading for a wide range of metal oxide materials. However, to the best Fig. 1. Schematic illustration for the possible formation mechanism of quaternary spinel-type transition metal oxide N-CoCuMnOx.
1146
Applied Surface Science 487 (2019) 1145–1151
K. Huang, et al.
As previously mentioned, the surface valences distribution of cations in spinel transition metal oxides is highly relevant to their electrocatalytic performances, especially for ORR process. To illustrate this, Fig. 6 shows the XPS analysis results of N-CoCuMnOx, and all elements of Co, Cu, Mn and O have been identified (Fig. 6A). Moreover, the existence of mixed-valences for all transition metal atoms has been also confirmed, where two typical peaks in Co 2p 3/2 spectrum located at 779.8 eV and 781.3 eV correspond to Co2+ and Co3+ (Fig. 6B) [56], two peaks in Cu 2p 3/2 spectrum centered at 931.1 eV and 933.9 eV with another two shake-up satellite peaks (941.3 and 943.8 eV) can be attributed to Cu+ and Cu2+ (Fig. 6C) [57–59], and a dominant characteristic peak of Mn3+ at 641.9 eV (Mn4+ at 643.4 eV) exists in the high-resolution spectrum of Mn 2p 3/2 (Fig. 6D) [60], respectively. Considering the site preference of bivalent, trivalent and tetravalent cations driven by energy difference within the spinel structure as well as the MneCo active sits for ORR electro-catalysis, a possible general formula of N-CoCuMnOx can be expressed as (Cu+Cu2+) [Co2+Co3+Mn3+Mn4+]O4, where the cations within the square brackets are in octahedral sites and the outside cations occupy the tetrahedral sites [53]. Fig. 7 shows the oxygen reduction electro-catalytic performance of N-CoCuMnOx, P-CoCuMnOx and commercial Pt/C catalysts in 0.1 M KOH solution. In addition to the enhanced current density, cyclic voltammograms in Fig. 7A also suggest that no significant oxidation or reduction peak appears for N2-saturated electrolyte while additional metal cations reduction peak (Mn4+ → Mn3+) and oxidation peak (Mn3+ → Mn4+) can be observed for N-CoCuMnOx in O2-saturated electrolyte. This result indicates that the N-CoCuMnOx sample has been endowed with a superior ORR activity and surface-rich mixed-valence metal cations due to the significantly reduced size. As shown in Fig. 7B, the ORR polarization curve of N-CoCuMnOx obviously shifts towards higher potential and lies closer to that of Pt/C catalyst. The onset potential of N-CoCuMnOx is about 0.92 V vs. RHE, which is just 30 mV lower than that of Pt/C catalyst but 70 mV higher than that of P-CoCuMnOx. This advantage of N-CoCuMnOx has been further confirmed by Tafel analysis with a smaller Tafel slope of 67.3 mV dec−1 in comparison with P-CoCuMnOx (82.6 mV dec−1), as shown in Fig. 7C. By varying the rotating speed from 400 to 2000 rpm (Fig. 7D and E), the average numbers of electrons transferred per oxygen molecule involved in the N-CoCuMnOx, P-CoCuMnOx, and Pt/C catalysts for ORR are 3.84, 3.71, and 3.92, respectively, which suggests a dominant direct 4-electron reduction process for the N-CoCuMnOx catalyst (Fig. S4). In addition, a comparison between this study and the most recent relevant results is given in Table S1, which suggests that the N-CoCuMnOx catalyst exhibits a comparable ORR activity with other relevant catalysts, in terms of onset potential, half-wave potential, and Tafel slope. As for the durability, the chronoamperometric responses of different catalysts were further investigated (Fig. 7F). In contrast to the dramatic decrease in the current density of Pt/C catalyst, both N-CoCuMnOx and P-CoCuMnOx samples exhibit a relatively tardy loss. The relative current density of N-CoCuMnOx stays above 90% during the stability test, demonstrating a better stability of N-CoCuMnOx than both P-CoCuMnOx and Pt/C catalysts. Similar results have also been identified by accelerated durability tests. As shown in Fig. S5, reproducible ORR polarization curve of N-CoCuMnOx catalyst can be achieved after 1000 CV cycles. Therefore, this mixed metal spinel oxide N-CoCuMnOx can be regarded as an alternative candidate for non-precious ORR catalysts in alkaline electrolyte. As demonstrated by EIS analysis in Fig. S6, the enhanced ORR performance of N-CoCuMnOx can be attributed to the higher conductivity (smaller charge transfer resistance) corresponding to the facile charge transfer process between multiple valences metal cations and the increased specific surface area relative to P-CoCuMnOx (34.7 vs. 24.4 m2 g−1).
Fig. 2. XRD patterns of the sample prepared with (a) and without (b) carbon microspheres as templates.
of our knowledge, it has been rarely attempted to prepare metal oxides nanoparticles by taking the adsorption capacity of carbonaceous spheres. As illustrated in Fig. 1, we further developed a modified carbon spheres template method for the synthesis of quaternary spinel metal oxides, where a significant amount of metal ions such as Co2+, Cu2+ and Mn2+ can be adsorbed within the interior of the carbonaceous spheres, mixed and confined very well after further grinding in the mashed carbonaceous particles, and then yield transition metal oxide CoCuMnOx nanoparticles (N-CoCuMnOx) by annealing in air atmosphere. And this facile and effective strategy successfully bridges the mismatch in size between the final nano-sized products and micron carbon spheres template. To investigate the structure and morphology features, Fig. 2 shows the XRD patterns of N-CoCuMnOx and P-CoCuMnOx prepared with and without carbon spheres as templates, respectively. It is obvious that all main diffraction peaks at 2θ = 18.7°, 30.8°, 36.4°, 38.1°, 44.2°, 54.9°, 58.6° and 64.3° can well be indexed to CoCuMnOx (JCPDF#: 47-0324), while two additional diffraction peaks at 2θ = 35.6° and 38.7° corresponding to CuO crystal phase (JCPDF#:48-1548) are identified for PCoCuMnOx sample. This suggests that higher-purity of crystal phase can be obtained for N-CoCuMnOx sample (further proved by the Rietveld refinement result as shown in Fig. S2), due to the homogeneous mixing of various metal ions with the aids of carbon spheres templates. Moreover, the transmission electron microscopy (TEM) images in Fig. 3 demonstrate that the randomly distributed and well crystallized N-CoCuMnOx particles exhibit small sizes of 5–20 nm (P-CoCuMnOx is in submicron size and agglomerated, as shown in Fig. S3) and a clear lattice fringe (d spacing of 0.25 nm) matching very well with (311) facets. The corresponding energy dispersive spectrometry (EDS) mapping of N-CoCuMnOx sample was further obtained and displayed in Fig. 4, where the uniform distributions of Co, Cu, Mn and O elements are in good accordance with the morphology features of selected nanoparticles. This result indicates a homogeneous distribution of different elements in N-CoCuMnOx nanoparticles. To further visualize the atomic-scale microstructure, aberration-corrected STEM image of a typical N-CoCuMnOx nanoparticle recorded along the [101] is shown in Fig. 5A. Based on the enlarged distribution of transition metal atoms in Fig. 5B and corresponding model in Fig. 5C, we can infer that 24 transition metal atoms as well as at most 32 oxygen atoms with octahedral and tetrahedral arrangements exist in a unit cell. Considering the result of elemental mass analysis by ICP, where the atom ratio in the NCoCuMnOx can be determined as Co: Cu: Mn: O = 1:0.98:1.01:3.86, the as-synthesized N-CoCuMnOx sample can be regarded as a pure phase of CoCuMnO4 with a certain amount of oxygen vacancies. 1147
Applied Surface Science 487 (2019) 1145–1151
K. Huang, et al.
Fig. 3. TEM (A, B) and HRTEM (C, D) images of N-CoCuMnOx nanoparticles.
Fig. 4. EDX mapping of N-CoCuMnOx (A) Co, (B) Cu, (C) Mn and (D) O. 1148
Applied Surface Science 487 (2019) 1145–1151
K. Huang, et al.
Fig. 5. (A) HRTEM image recorded along the [1 0 1] direction. (B) The position of the transition metal atoms in the HRTEM image where the transition metal atoms are shown in the pink spheres and the oxygen atoms are shown in the blue spheres. (C) Polyhedral view of the CoCuMnOx crystal structure projected along the [1 0 1] with the tetrahedra shown in pink and the octahedra shown in blue. The pink and blue spheres denote the tetrahedral and octahedral sites, respectively.
Fig. 6. (A) Full scan XPS spectrum of N-CoCuMnOx and high-resolution XPS spectra of (B) Co 2p 3/2, (C) Cu 2p 3/2, and (D) Mn 2p 3/2.
4. Conclusion
octahedral and tetrahedral sites. Moreover, we identified the enhanced ORR electro-catalytic performance of N-CoCuMnOx compared with PCoCuMnOx and commercial Pt/C catalysts in terms of activity and stability, suggesting N-CoCuMnOx as a rational candidate for low-cost and high-efficiency ORR catalysts.
In summary, we modified the conventional carbonaceous template method by an additional grinding process, and thus enabled the synthesis of highly phase-pure quaternary spinel oxide N-CoCuMnOx with a nano-size about 5–20 nm. Revealed by the measurements of XRD, TEM, STEM, EDX and XPS, all the transition-metal atoms are of mixed valences and distribute with a preferred location between
1149
Applied Surface Science 487 (2019) 1145–1151
K. Huang, et al.
Fig. 7. Cyclic voltammetry curves in N2-saturated (black line) and O2-saturated (red line) 0.1 M KOH (A), ORR activity (B), and Tafel slope (C) of N-CoCuMnOx, PCoCuMnOX and commercial Pt/C as ORR catalysts. LSV curves (D), Koutechy-Levich (K-L) plots at different electrodes (E) of N-CoCuMnOx, and the chronoamperometric response (F) of the CoCuMnOX catalysts and commercial Pt/C catalyst.
Acknowledgments
density, Nano Energy 51 (2018) 513–523. [5] X.T. Wang, Y. Cui, T. Li, M. Lei, J.B. Li, Z.M. Wei, Recent advances in the functional 2D photonic and optoelectronic devices, Adv. Opt. Mater. 7 (2019) 1801274. [6] Y. Wang, Y. Song, Y. Xia, Electrochemical capacitors: mechanism, materials, systems, characterization and applications, Chem. Soc. Rev. 45 (2016) 5925–5950. [7] S. Lin, X.P. Bai, H.Y. Wang, H.L. Wang, J.N. Song, K. Huang, C. Wang, N. Wang, B. Li, M. Lei, H. Wu, Roll-to-roll production of transparent silver nanofiber network electrode for flexible electrochromic Smart windows, Adv. Mater. 29 (2017) 1703238. [8] Q. Wang, X. Li, L.Y. Wu, P.F. Lu, Z.F. Di, Electronic and Interface properties in graphene oxide/hydrogen-passivated Ge heterostructure, Phys. Status Solidi RRL 13 (2019) 1800461. [9] K. Bi, D.Q. Yang, J. Chen, Q.M. Wang, H.Y. Wu, C.W. Lan, Y.P. Yang, Experimental demonstration of ultra-large-scale terahertz all-dielectric metamaterials, Photonics Res 7 (2019) 457–463. [10] J. Wei, F.W. Guo, X. Wang, K. Xu, M. Lei, Y.Q. Liang, Y.C. Zhao, D.S. Xu, SnO2-inpolymer matrix for high-efficiency perovskite solar cells with improved reproducibility and stability, Adv. Mater. 30 (2018) 1805153. [11] K. Bi, X.Y. Wang, Y.N. Hao, M. Lei, G.Y. Dong, J. Zhou, Wideband slot-coupled dielectric resonator-based filter, J. Alloys Compd. 785 (2019) 1264–1269. [12] W.W. Zhong, S.J. Shen, S.S. Feng, Z.P. Lin, Z.P. Wang, B.Z. Wang, Facile fabrication of alveolate Cu2-xSe microsheets as a new visible-light photocatalyst for discoloration of rhodamine B, Crystengcomm 20 (2018) 7851–7856. [13] Q. Zhao, Z. Yan, C. Chen, J. Chen, Spinels: controlled preparation, oxygen
This work was financially supported by National Natural Science Foundation of China (Grant nos. 61874014, 61874013, 51572032, 51572073, 51672074, 61674019, 61574020), and Open Fund of State Key Laboratory of Information Photonics and Optical Communications (Beijing University of Posts and Telecommunications, China). References [1] L.Y. Wu, P.F. Lu, R.G. Quhe, Q. Wang, C.H. Yang, P.F. Guan, K.S. Yang, Stanene nanomeshes as anode materials for Na-ion batteries, J. Mater. Chem. A 6 (2018) 7933–7941. [2] H.J. Yang, L. Geng, Y.T. Zhang, G. Chang, Z.L. Zhang, X. Liu, M. Lei, Y.B. He, Graphene-templated synthesis of palladium nanoplates as novel electrocatalyst for direct methanol fuel cell, Appl. Surf. Sci. 466 (2019) 385–392. [3] W.W. Zhong, W.G. Tu, S.S. Feng, A.J. Xu, Photocatalytic H-2 evolution on CdS nanoparticles by loading FeSe nanorods as co-catalyst under visible light irradiation, J. Alloys Compd. 772 (2019) 669–674. [4] K. Bi, M.H. Bi, Y.N. Hao, W. Luo, Z.M. Cai, X.H. Wang, Y.H. Huang, Ultrafine coreshell BaTiO3@SiO2 structures for nanocomposite capacitors with high energy
1150
Applied Surface Science 487 (2019) 1145–1151
K. Huang, et al.
[14] [15] [16]
[17]
[18]
[19]
[20]
[21]
[22]
[23] [24]
[25]
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37] H.N. Cong, K.El. Abbassi, P. Chartier, Electrocatalysis of oxygen reduction on polypyrrole/mixed valence spinel oxide nanoparticles, J. Electrochem. Soc. 149 (2002) A525–A530. [38] L. Hu, L. Wu, M. Liao, X. Hu, X. Fang, Electrical transport properties of large, individual NiCo2O4 nanoplates, Adv. Funct. Mater. 22 (2012) 998–1004. [39] C. Fu, G. Li, D. Luo, X. Huang, J. Zheng, L. Li, One-step calcination-free synthesis of multicomponent spinel assembled microspheres for high-performance anodes of Liion batteries: a case study of MnCo2O4, ACS Appl. Mater. Interfaces 6 (2014) 2439–2449. [40] S. Jiang, Y. Sun, H. Dai, P. Ni, W. Lu, Y. Wang, Z. Li, A facile enhancement in battery-type of capacitive performance of spinel NiCo2O4nanostructure via directly tuning thermal decomposition temperature, Electrochim. Acta 191 (2016) 364–374. [41] A.M.M. Durka, S.A. Antony, A novel synthesis, structural, morphological, and optomagnetic characterizations of magnetically separable spinel CoXMn1-X Fe2O4 (0 ≤ X ≤ 1) nano-catalysts, J. Supercond. Nov. Magn. 27 (2014) 2841–2857. [42] L. Zhang, Y. Wang, H. Jiu, W. Zheng, J. Chang, Controllable synthesis of spinel nano-CoMn2O4 via a solvothermal carbon templating method and its application in lithium ion batteries, Electrochim. Acta 182 (2015) 550–558. [43] M.H. Habibi, M. Mardani, Synthesis and characterization of Bi-component ZnSnO3/ Zn2SnO4 (perovskite/spinel) nano-composites for photocatalytic degradation of intracron blue: structural, opto-electronic and morphology study, J. Mol. Liq. 238 (2017) 397–401. [44] J. Wan, X. Chen, Z. Wang, X. Yang, Y. Qian, A soft-template-assisted hydrothermal approach to single-crystal Fe3O4 nanorods, J. Cryst. Growth 276 (2005) 571–576. [45] Y. Song, R.M. Garcia, R.M. Dorin, H. Wang, Y. Qiu, E.N. Coker, W.A. Steen, J.E. Miller, J.A. Shelnut, Synthesis of platinum nanowire networks using a soft template, Nano Lett. 7 (2007) 3650–3655. [46] B. Liu, H. Shioyama, H. Jiang, X. Zhang, Q. Xu, Metal-Organic Framework (MOF) as a template for syntheses of nanoporous carbons as electrode materials for supercapacitor, Carbon 48 (2010) 456–463. [47] Y. Sun, B.T. Mayers, Y. Xia, Template-engaged replacement reaction: a one-step approach to the large-scale synthesis of metal nanostructures with hollow interiors, Nano Lett. 2 (2002) 481–485. [48] Z. Wang, X. Li, Y. Yang, Y. Cui, H. Pan, Z. Wang, B. Chen, G. Qian, Highly dispersed β-NiS nanoparticles in porous carbon matrices by a template metal-organic framework method for lithium-ion cathode, J. Mater. Chem. A 2 (2014) 7912–7916. [49] J.J. Miao, L.P. Jiang, C. Liu, J.M. Zhu, J.J. Zhu, General sacrificial template method for the synthesis of cadmium chalcogenide hollow structures, Inorg. Chem. 46 (2007) 5673–5677. [50] M. Yang, G. Zhang, C. Wu, Z. Chang, X. Sun, X. Duan, Preparation of multi-metal oxide hollow sphere using layered double hydroxide precursors, Chin. J. Chem. 30 (2012) 2183–2188. [51] S. Tang, S. Vongehr, X. Meng, Controllable incorporation of Ag and Ag-Au nanoparticles in carbon spheres for tunable optical and catalytic properties, J. Mater. Chem. 20 (2010) 5436–5445. [52] S.J. Kim, C.W. Na, I.S. Hwang, J.H. Lee, One-pot hydrothermal synthesis of CuOZnO composite hollow spheres for selective H2S detection, Sensors Actuators B Chem. 168 (2012) 83–89. [53] C. Wei, Z. Feng, G.G. Scherer, J. Barber, Y. Shao Horn, Z.J. Xu, Cations in octahedral sites: a descriptor for oxygen electrocatalysis on transition metal spinels, Adv. Mater. 29 (2017) 1606800. [54] M. Sevilla, A.B. Fuertes, The production of carbon materials by hydrothermal carbonization of cellulose, Carbon 47 (2009) 2281–2289. [55] D.L. Bish, S.A. Howard, Quantitative phase analysis using the Rietveld method, J. Appl. Crystallogr. 21 (1988) 86–91. [56] M.C. Biesinger, B.P. Payne, A.P. Grosvenor, L.W.M. Lau, A.R. Gerson, R.S.C. Smart, Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Cr, Mn, Fe, Co and Ni, Appl. Surf. Sci. 257 (2011) 2717–2730. [57] S. Ramamurthy, R.D. Davidson, N.S. McIntyre, J.T. Francis, A. McBride, A.M. Brennenstuhl, A. Roberts, Mechanisms for pitting corrosion in alloy N04400 as revealed by imaging XPS, ToF-SIMS and low-voltage SEM, Surf. Interface Anal. 33 (2002) 29–34. [58] R.S. Vishwanath, S. Kandaiah, Metal ion-containing C3N3S3 coordination polymers chemisorbed to a copper surface as acid stable hydrogen evolution electrocatalysts, J. Mater. Chem. A 5 (2017) 2052–2065. [59] L.H. Zhang, C. Zheng, F. Li, D.G. Evans, X. Duan, Copper-containing mixed metal oxides derived from layered precursors: control of their compositions and catalytic properties, J. Mater. Sci. 43 (2008) 237–243. [60] Y. Zhou, S. Sun, S. Xi, Y. Duan, T. Sritharan, Y. Du, Z.J. Xu, Superexchange effects on oxygen reduction activity of edge sharing [CoxMn1-xO6] Octahedra in spinel oxide, Adv. Mater. 30 (2018) 1705407.
reduction/evolution reaction application, and beyond, Chem. Rev. 117 (2017) 10121–10211. V. Augustyn, P. Simon, B. Dunn, Pseudocapacitive oxide materials for high-rate electrochemical energy storage, Energy Environ. Sci. 7 (2014) 1597–1614. L. Croguennec, M.R. Palacin, Recent achievements on inorganic electrode materials for lithium-ion batteries, J. Am. Chem. Soc. 137 (2015) 3140–3156. H. Wang, R.P. Liu, Z.M. Cui, X.J. Lv, Y.T. Li, X. Li, S. Xin, R. Zhang, M. Lei, Z.Q. Lin, Hollow porous spinel ZnMnCoO4 microspheres with a high oxygen reduction activity, Joule 2 (2018) 337–348. P. Stelmachowski, A.H.M. Videla, K. Ciura, S. Specchia, Oxygen evolution catalysis in alkaline conditions over hard templated nickel-cobalt based spinel oxides, Int. J. Hydrog. Energy 42 (2017) 27910–27918. A.H.M. Videla, P. Stelmachowski, G. Ercolino, S. Specchia, Benchmark comparison of Co3O4 spinel-structured oxides with different morphologies for oxygen evolution reaction under alkaline conditions, J. Appl. Electrochem. 47 (2017) 295–304. R.A.M. Esfahani, L.M.R. Gavidia, G. García, E. Pastor, S. Specchia, Highly active platinum supported on Mo-doped titanium nanotubes suboxide (Pt/TNTS-Mo) electrocatalyst for oxygen reduction reaction in PEMFC, Renew. Energy 120 (2018) 209–219. R.A.M. Esfahani, S.K. Vankova, A.H.A. Monteverde Videla, S. Specchia, Innovative carbon-free low content Pt catalyst supported on Mo-doped titanium suboxide (Ti3O5-Mo) for stable and durable oxygen reduction reaction, Appl. Catal. B Environ. 201 (2017) 419–429. C. Wei, R.R. Rao, J. Peng, B. Huang, I.E. Stephens, M. Risch, Y. Shao-Horn, Recommended practices and benchmark activity for hydrogen and oxygen electrocatalysis in water splitting and fuel cells, Adv. Mater. 31 (2019) 1806296. X. He, S.Z. Luan, L. Wang, R.Y. Wang, P. Du, Y.Y. Xu, H.J. Yang, Y.G. Wang, K. Huang, M. Lei, Facile loading mesoporous Co3O4 on nitrogen doped carbon matrix as an enhanced oxygen electrode catalyst, Mater. Lett. 244 (2019) 78–82. Y. Eunjoo, Z. Hao, Li-air rechargeable battery based on metal-free graphene nanosheet catalysts, ACS Nano 5 (2011) 3020–3026. X. Bo, Y. Zhang, M. Li, A. Nsabimana, L. Guo, NiCo2O4 spinel/ordered mesoporous carbons as noble-metal free electrocatalysts for oxygen reduction reaction and the influence of structure of catalyst support on the electrochemical activity of NiCo2O4, J. Power Sources 288 (2015) 1–8. F.M. Courtel, H. Duncan, Y. Abu-Lebdeh, I.J. Davidson, High capacity anode materials for Li-ion batteries based on spinel metal oxides AMn2O4 (A = Co, Ni, and Zn), J. Mater. Chem. 21 (2011) 10206–10218. H. Zhang, X. Tian, C. Wang, H. Luo, J. Hu, Y. Shen, A. Xie, Facile synthesis of RGO/ NiO composites and their excellent electromagnetic wave absorption properties, Appl. Surf. Sci. 314 (2014) 228–232. P. Lavela, J.L. Tirado, C. Vidal-Abarca, Sol-gel preparation of cobalt manganese mixed oxides for their use as electrode materials in lithium cells, Electrochim. Acta 52 (2007) 7986–7995. Y. Xu, W. Bian, J. Wu, J.H. Tian, R. Yang, Preparation and electrocatalytic activity of 3D hierarchical porous spinel CoFe2O4 hollow nanospheres as efficient catalyst for oxygen reduction reaction and oxygen evolution reaction, Electrochim. Acta 151 (2015) 276–283. L. Wang, X. Zhao, Y. Lu, M. Xu, D. Zhang, R.S. Ruoff, K.J. Stevenson, J.B. Goodenough, CoMn2O4 spinel nanoparticles grown on graphene as bifunctional catalyst for lithium-air batteries, J. Electrochem. Soc. 158 (2011) A1379–A1382. A. Serov, N.I. Andersen, A.J. Roy, I. Matanovic, K. Artyushkova, P. Atanassov, CuCo2O4 ORR/OER Bi-functional catalyst: influence of synthetic approach on performance, J. Electrochem. Soc. 162 (2015) F449–F454. Y. Liang, H. Wang, J. Zhou, Y. Li, J. Wang, T. Regier, H. Dai, Covalent hybrid of spinel manganese-cobalt oxide and graphene as advanced oxygen reduction electrocatalysts, J. Am. Chem. Soc. 134 (2012) 3517–3523. Y. Sharma, N. Sharma, G.V.S. Rao, B.V.R. Chowdari, Lithium recycling behaviour of nano-phase-CuCo2O4 as anode for lithium-ion batteries, J. Power Sources 173 (2007) 495–501. L. Osmieri, A.H.M. Videla, M. Armandi, S. Specchia, Influence of different transition metals on the properties of Me–N–C (Me = Fe, Co, Cu, Zn) catalysts synthesized using SBA-15 as tubular nano-silica reactor for oxygen reduction reaction, Int. J. Hydrog. Energy 41 (2016) 22570–22588. L. Osmieri, R. Escudero-Cid, M. Armandi, P. Ocón, A.H.M. Videla, S. Specchia, Effects of using two transition metals in the synthesis of non-noble electrocatalysts for oxygen reduction reaction in direct methanol fuel cell, Electrochim. Acta 266 (2018) 220–232. P. Stelmachowski, A.H.M. Videla, T. Jakubek, A. Kotarba, S. Specchia, The effect of Fe, Co, and Ni structural promotion of Cryptomelane (KMn8O16) on the catalytic activity in oxygen evolution reaction, Electrocatalysis 9 (2018) 762–769. Y. Liang, H. Wang, J. Zhou, Y. Li, J. Wang, T. Regier, H. Dai, Covalent hybrid of spinel manganese-cobalt oxide and graphene as advanced oxygen reduction electrocatalysts, J. Am. Chem. Soc. 134 (2012) 3517–3523.
1151
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Full length article
Mixed valence CoCuMnOx spinel nanoparticles by sacrificial template method with enhanced ORR performance
T
⁎
Kai Huanga, Junchen Liua, Lu Wanga, Gang Changb, Ruyue Wanga, Ming Leia, , ⁎ ⁎ Yonggang Wanga, , Yunbin Heb, a
State Key Laboratory of Information Photonics and Optical Communications, School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, China b Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Ministry-of-Education Key Laboratory for the Green Preparation and Application of Functional Materials, Hubei Key Laboratory of Polymer Materials, School of Materials Science and Engineering, Hubei University, Wuhan 430062, China
A R T I C LE I N FO
A B S T R A C T
Keywords: CoCuMnOx nanoparticles Sacrificial template method Mixed valence Oxygen reduction reaction
Spinel-type mixed transition metal oxides CoCuMoOx nanoparticles were synthesized through a modified sacrificial template method, by utilizing mashed carbon microspheres as templates. Compared with the direct calcination of mixture precursor, we obtained well-crystallized CoCuMnOx sample with high purity and sizes of 5–20 nm. Mixed valence states of transition metal elements are revealed by X-ray photoelectron spectroscopy, which is a desirable feature for oxygen reduction reaction (ORR) catalyst. Moreover, we further investigated the electrochemical performance of CoCuMoOx for the ORR by cyclic voltammetry, rotating disk electrode and chronoamperometry test in alkaline medium. It is revealed that CoCuMoOx exhibits both outstanding catalytic activity and super stability, which are important properties for an excellent catalyst. As a result, the CoCuMoOx holds high potential as a suitable candidate for ORR catalysts of alkaline fuel cell because of its low-cost and high-efficiency.
1. Introduction Regenerative fuel cells, metal-air batteries, and Li-ion batteries that used in portable mobile devices are being developed very fast due to the growing energy crisis and environment protection concerns [1–13]. Among the various catalysts, spinel oxides with the formula of AB2O4, where metal A occupies the centers of tetrahedrally coordinated positions and metal B occupies the centers of octahedrally coordinated positions in general, have exhibited great importance in applications of environmental-friendly energy storage and conversion technologies, such as lithium ion batteries, electrochemical capacitors, fuel cells, and metal-air batteries [14–22]. It has been proved that the electrochemical properties of spinel oxides strongly depend on their precise structures and compositions. Particularly, for the crucial but sluggish oxygen reduction reaction (ORR) in fuel cells and metal-air batteries, singlephase ternary and quaternary metal spinel oxides (usually including Co, Mn, Cu, Zn, Fe, Ni, etc.) rather than binary metal oxides have been regarded as a promising family of mixed transition-metal oxides (MTMOs) for high-performance non-precious ORR catalysts [23–35]. With respect to the aforementioned distribution of metal cations in crystal structure, the presence and multiple distribution of metal
⁎
cations in various valences will be obtained in quaternary metal spineltype. The synergetic effects between their complex chemical compositions, the donor-acceptor chemisorption sites for the reversible adsorption of oxygen formed by metal cations with multiple valences, and the high electrical conductivity due to their relatively low activation energy for charge transfer between different cations, have been demonstrated to be of great benefits for ORR [36–38]. To make full use of such quaternary metal spinel oxides as efficient ORR catalysts, a facile and high-yield preparation method should be involved for spinel nanocrystals. Although the direct calcination of mixtures of transition-metal nitrates, chlorides or carbonates can produce spinel-type MTMOs in a large scale [39,40], products with micrometer-size and irregular shape always show an inferior catalytic performance due to lack of active sites. To address this issue, continuous efforts such as microwave-assisted combustion method, solvothermal templating method and modified wet co-precipitation method have been dedicated [41–48]. Generally, taking advantage of sacrificial templates (for example, colloidal carbon spheres) in the synthesis process can form various binary and mixed-phase multiple complex metal oxides with a porous hollow microsphere structure [42,49]. Due to the different adsorption and diffusion behaviors of
Corresponding authors. E-mail addresses: [email protected] (M. Lei), [email protected] (Y. Wang), [email protected] (Y. He).
https://doi.org/10.1016/j.apsusc.2019.05.183 Received 22 January 2019; Received in revised form 1 May 2019; Accepted 16 May 2019 Available online 17 May 2019 0169-4332/ © 2019 Elsevier B.V. All rights reserved.
Applied Surface Science 487 (2019) 1145–1151
K. Huang, et al.
XSP). The specific surface areas were measured at 500 °C using a Quantachrome Autosorb-iQ instrument and determined via the Brunauer-Emmett-Teller (BET) method.
more than three kinds of metal ions by carbonaceous particles with rich surface functional groups [50–53], it still remains a challenge to obtain a single crystal-phase multiple MTMOs by template-based synthesis for further understanding of structure-activity relationship in ORR. Herein, we developed a modified template-assisted calcination method for the synthesis of single-phase quaternary CoCuMnOx spinel nanocrystals as high ORR catalysts with sizes ranging from 5 to 20 nm, by sufficient grinding the dry gel of carbon microspheres with fully absorbed cobalt, copper and manganese nitrates before thermal annealing. Compared with the powder CoCuMnOx catalyst (P-CoCuMnOx, CuO as a minor impurity) without the addition of carbon microspheres, this newly developed nano-sized CoCuMnOx catalyst (N-CoCuMnOx) exhibited a more comparable activity and enhanced stability in comparison to commercial Pt/C catalyst in alkaline ORR electrochemical process. Moreover, this modified template-assisted calcination method can be further adopted to synthesize other single-phase multiple functional compounds.
2.3. Electrochemical measurements Electrochemical characterizations were performed on a CHI660A electrochemical workstation with a three-electrode system consisting of a glassy carbon electrode of 5 mm in diameter as the working electrode, a Pt foil as the counter electrode, and an Hg/HgO electrode as the reference electrode. All potential values were calibrated with respect to reversible hydrogen electrode (RHE) by E (RHE) = E (Hg/ HgO) + 0.92 V. For electrode preparation, P-CoCuMnOx, N-CoCuMnOx or commercial Pt/C (20 wt% Pt on Vulcan XC-72, Johnson Matthey) were dispersed by sonication for 30 min in ice-bath to form homogeneous ink (Note: 20 wt% of XC-72R Carbon was employed for PCoCuMnOx and N-CoCuMnOx catalysts ink to make a good electrochemical contact). The mixture is of 800 μl of ultrapure water, 200 μl of isopropanol, and 20 μl of Nafion solution (5.0 wt%). Then 20 μl of the catalysts ink was loaded onto the glassy carbon electrode and dried under ambient temperature with a catalyst loading of 0.5 mg/cm2. Cyclic voltammograms (CV) measurements were performed from 0.05 to 1.05 V with a scan rate of 50 mV/s in N2- and O2-saturated 0.1 M KOH solution, respectively. Rotating disk electrode (RDE) measurements were conducted at different rotating speeds from 400 to 2000 rpm at a scan rate of 5 mV/s, and chronoamperometry was carried out on a constant potential of 0.65 V in O2-saturated 0.1 M KOH solution. All ORR polarization curves were calibrated with LSV data tested in N2 to subtract the corresponding capacitance current. The electron transfer number in ORR can be calculated according to KoutechyLevich equation as follows:
2. Experimental 2.1. Materials and synthesis All starting materials were of analytical pure grade, purchased from commercial sources and used without further purification. Carbon spheres template (with an average diameter of ~500 nm, as shown in Fig. S1) in this work was prepared by means of hydrothermal carbonization of glucose at 160 °C according to a previous work [54]. CoCuMnOx nanoparticles (N-CoCuMnOx) were synthesized by a sacrificial template method followed by thermal annealing in air. In a typical process, 10 mmol of Cu(NO3)2·3H2O, Co(NO3)2·6H2O, Mn(NO3)2·4H2O and 0.15 g of carbon spheres were dissolved in 20 ml of anhydrous alcohol with the aids of ultrasonic dispersion and stirring, then heated in air at 60 °C for 48 h to yield a fluffy mixture powder. After annealing at 500 °C in air for 6 h, washing by DI water and anhydrous alcohol for several times and drying at 60 °C overnight, the powder was reground, pressed into pellets, and calcined for another 6 h to obtain the final NCoCuMnOx sample. For comparison, sub-micron CoCuMnOx powder sample (P-CoCuMnOx) was also collected using a similar synthetic process as described above without the addition of carbon spheres.
imeasured−1 = ik −1 + id−1 = ik −1 + Bω−1/2 B = 0.2nFCD 2/3υ−1/6 where imeasured and ik are the measured and kinetic-limiting current densities, ω is the rotation speed (rpm), n is the transferred electron number, F is the Faraday constant (96,485 C mol−1), C is the concentration of O2 in 0.1 M KOH solution (1.2 × 10−6 mol cm−3), D is the diffusion coefficient of O2 (1.9 × 10−5 cm2 s−1), υ is the kinematic viscosity (0.01 cm2 s−1). In addition, accelerated durability test (ADT) was carried out in the voltage range of 0.6–1.0 V (vs. RHE) for 1000 cyclic voltammetry cycles with a scan rate of 100 mV/s. Electrochemical Impedance Spectra (EIS) were further acquired in the constant voltage mode with the frequency ranging from 100 kHz to 1 Hz using a frequency response analyzer controlled by a potentiostat (Autolab PGSTAT-204) at open circuit potential.
2.2. Morphology and structural characterizations Morphology and microstructure of the samples were characterized by transmission electron microscopy (TEM) (JEOL, JEM-2011), highresolution TEM (HRTEM), and aberration-corrected scanning transmission electron microscopy (STEM) (JEOL, JEM-ARM200F) equipped with a CEOS probe aberration corrector. Phase structures of the samples were examined by X-ray diffraction (XRD) (RIGAKU, D/MX-IIIA) with Cu Kα radiation (λ = 1.54 Å) and Co Kα radiation (λ = 1.79 Å) which was chosen for the refinement analysis (carried out by the Rietveld method with the FULLPROF package) [55]. X-ray photoelectron spectroscopy (XPS) measurements were carried out on an ESCALAB 250Xi spectrometer (Thermo Scientific) with an internal standard (C 1 s peak at 284.4 eV) and a standard deviation of 0.2 eV. The concentration of every element was determined by inductive coupled plasma atomic emission spectrometry (ICP-AES) (Thermo Electron, IRIS Intrepid II
3. Results and discussion Carbon spheres as sacrificial templates have been widely used to fabricate hollow metal oxide microspheres, due to the rich surface functional groups which are available for metal ion adsorption [54]. It is even controllable for the formation of multiple-shell hollow structures with a specific number of shells by processing the metal ion loading for a wide range of metal oxide materials. However, to the best Fig. 1. Schematic illustration for the possible formation mechanism of quaternary spinel-type transition metal oxide N-CoCuMnOx.
1146
Applied Surface Science 487 (2019) 1145–1151
K. Huang, et al.
As previously mentioned, the surface valences distribution of cations in spinel transition metal oxides is highly relevant to their electrocatalytic performances, especially for ORR process. To illustrate this, Fig. 6 shows the XPS analysis results of N-CoCuMnOx, and all elements of Co, Cu, Mn and O have been identified (Fig. 6A). Moreover, the existence of mixed-valences for all transition metal atoms has been also confirmed, where two typical peaks in Co 2p 3/2 spectrum located at 779.8 eV and 781.3 eV correspond to Co2+ and Co3+ (Fig. 6B) [56], two peaks in Cu 2p 3/2 spectrum centered at 931.1 eV and 933.9 eV with another two shake-up satellite peaks (941.3 and 943.8 eV) can be attributed to Cu+ and Cu2+ (Fig. 6C) [57–59], and a dominant characteristic peak of Mn3+ at 641.9 eV (Mn4+ at 643.4 eV) exists in the high-resolution spectrum of Mn 2p 3/2 (Fig. 6D) [60], respectively. Considering the site preference of bivalent, trivalent and tetravalent cations driven by energy difference within the spinel structure as well as the MneCo active sits for ORR electro-catalysis, a possible general formula of N-CoCuMnOx can be expressed as (Cu+Cu2+) [Co2+Co3+Mn3+Mn4+]O4, where the cations within the square brackets are in octahedral sites and the outside cations occupy the tetrahedral sites [53]. Fig. 7 shows the oxygen reduction electro-catalytic performance of N-CoCuMnOx, P-CoCuMnOx and commercial Pt/C catalysts in 0.1 M KOH solution. In addition to the enhanced current density, cyclic voltammograms in Fig. 7A also suggest that no significant oxidation or reduction peak appears for N2-saturated electrolyte while additional metal cations reduction peak (Mn4+ → Mn3+) and oxidation peak (Mn3+ → Mn4+) can be observed for N-CoCuMnOx in O2-saturated electrolyte. This result indicates that the N-CoCuMnOx sample has been endowed with a superior ORR activity and surface-rich mixed-valence metal cations due to the significantly reduced size. As shown in Fig. 7B, the ORR polarization curve of N-CoCuMnOx obviously shifts towards higher potential and lies closer to that of Pt/C catalyst. The onset potential of N-CoCuMnOx is about 0.92 V vs. RHE, which is just 30 mV lower than that of Pt/C catalyst but 70 mV higher than that of P-CoCuMnOx. This advantage of N-CoCuMnOx has been further confirmed by Tafel analysis with a smaller Tafel slope of 67.3 mV dec−1 in comparison with P-CoCuMnOx (82.6 mV dec−1), as shown in Fig. 7C. By varying the rotating speed from 400 to 2000 rpm (Fig. 7D and E), the average numbers of electrons transferred per oxygen molecule involved in the N-CoCuMnOx, P-CoCuMnOx, and Pt/C catalysts for ORR are 3.84, 3.71, and 3.92, respectively, which suggests a dominant direct 4-electron reduction process for the N-CoCuMnOx catalyst (Fig. S4). In addition, a comparison between this study and the most recent relevant results is given in Table S1, which suggests that the N-CoCuMnOx catalyst exhibits a comparable ORR activity with other relevant catalysts, in terms of onset potential, half-wave potential, and Tafel slope. As for the durability, the chronoamperometric responses of different catalysts were further investigated (Fig. 7F). In contrast to the dramatic decrease in the current density of Pt/C catalyst, both N-CoCuMnOx and P-CoCuMnOx samples exhibit a relatively tardy loss. The relative current density of N-CoCuMnOx stays above 90% during the stability test, demonstrating a better stability of N-CoCuMnOx than both P-CoCuMnOx and Pt/C catalysts. Similar results have also been identified by accelerated durability tests. As shown in Fig. S5, reproducible ORR polarization curve of N-CoCuMnOx catalyst can be achieved after 1000 CV cycles. Therefore, this mixed metal spinel oxide N-CoCuMnOx can be regarded as an alternative candidate for non-precious ORR catalysts in alkaline electrolyte. As demonstrated by EIS analysis in Fig. S6, the enhanced ORR performance of N-CoCuMnOx can be attributed to the higher conductivity (smaller charge transfer resistance) corresponding to the facile charge transfer process between multiple valences metal cations and the increased specific surface area relative to P-CoCuMnOx (34.7 vs. 24.4 m2 g−1).
Fig. 2. XRD patterns of the sample prepared with (a) and without (b) carbon microspheres as templates.
of our knowledge, it has been rarely attempted to prepare metal oxides nanoparticles by taking the adsorption capacity of carbonaceous spheres. As illustrated in Fig. 1, we further developed a modified carbon spheres template method for the synthesis of quaternary spinel metal oxides, where a significant amount of metal ions such as Co2+, Cu2+ and Mn2+ can be adsorbed within the interior of the carbonaceous spheres, mixed and confined very well after further grinding in the mashed carbonaceous particles, and then yield transition metal oxide CoCuMnOx nanoparticles (N-CoCuMnOx) by annealing in air atmosphere. And this facile and effective strategy successfully bridges the mismatch in size between the final nano-sized products and micron carbon spheres template. To investigate the structure and morphology features, Fig. 2 shows the XRD patterns of N-CoCuMnOx and P-CoCuMnOx prepared with and without carbon spheres as templates, respectively. It is obvious that all main diffraction peaks at 2θ = 18.7°, 30.8°, 36.4°, 38.1°, 44.2°, 54.9°, 58.6° and 64.3° can well be indexed to CoCuMnOx (JCPDF#: 47-0324), while two additional diffraction peaks at 2θ = 35.6° and 38.7° corresponding to CuO crystal phase (JCPDF#:48-1548) are identified for PCoCuMnOx sample. This suggests that higher-purity of crystal phase can be obtained for N-CoCuMnOx sample (further proved by the Rietveld refinement result as shown in Fig. S2), due to the homogeneous mixing of various metal ions with the aids of carbon spheres templates. Moreover, the transmission electron microscopy (TEM) images in Fig. 3 demonstrate that the randomly distributed and well crystallized N-CoCuMnOx particles exhibit small sizes of 5–20 nm (P-CoCuMnOx is in submicron size and agglomerated, as shown in Fig. S3) and a clear lattice fringe (d spacing of 0.25 nm) matching very well with (311) facets. The corresponding energy dispersive spectrometry (EDS) mapping of N-CoCuMnOx sample was further obtained and displayed in Fig. 4, where the uniform distributions of Co, Cu, Mn and O elements are in good accordance with the morphology features of selected nanoparticles. This result indicates a homogeneous distribution of different elements in N-CoCuMnOx nanoparticles. To further visualize the atomic-scale microstructure, aberration-corrected STEM image of a typical N-CoCuMnOx nanoparticle recorded along the [101] is shown in Fig. 5A. Based on the enlarged distribution of transition metal atoms in Fig. 5B and corresponding model in Fig. 5C, we can infer that 24 transition metal atoms as well as at most 32 oxygen atoms with octahedral and tetrahedral arrangements exist in a unit cell. Considering the result of elemental mass analysis by ICP, where the atom ratio in the NCoCuMnOx can be determined as Co: Cu: Mn: O = 1:0.98:1.01:3.86, the as-synthesized N-CoCuMnOx sample can be regarded as a pure phase of CoCuMnO4 with a certain amount of oxygen vacancies. 1147
Applied Surface Science 487 (2019) 1145–1151
K. Huang, et al.
Fig. 3. TEM (A, B) and HRTEM (C, D) images of N-CoCuMnOx nanoparticles.
Fig. 4. EDX mapping of N-CoCuMnOx (A) Co, (B) Cu, (C) Mn and (D) O. 1148
Applied Surface Science 487 (2019) 1145–1151
K. Huang, et al.
Fig. 5. (A) HRTEM image recorded along the [1 0 1] direction. (B) The position of the transition metal atoms in the HRTEM image where the transition metal atoms are shown in the pink spheres and the oxygen atoms are shown in the blue spheres. (C) Polyhedral view of the CoCuMnOx crystal structure projected along the [1 0 1] with the tetrahedra shown in pink and the octahedra shown in blue. The pink and blue spheres denote the tetrahedral and octahedral sites, respectively.
Fig. 6. (A) Full scan XPS spectrum of N-CoCuMnOx and high-resolution XPS spectra of (B) Co 2p 3/2, (C) Cu 2p 3/2, and (D) Mn 2p 3/2.
4. Conclusion
octahedral and tetrahedral sites. Moreover, we identified the enhanced ORR electro-catalytic performance of N-CoCuMnOx compared with PCoCuMnOx and commercial Pt/C catalysts in terms of activity and stability, suggesting N-CoCuMnOx as a rational candidate for low-cost and high-efficiency ORR catalysts.
In summary, we modified the conventional carbonaceous template method by an additional grinding process, and thus enabled the synthesis of highly phase-pure quaternary spinel oxide N-CoCuMnOx with a nano-size about 5–20 nm. Revealed by the measurements of XRD, TEM, STEM, EDX and XPS, all the transition-metal atoms are of mixed valences and distribute with a preferred location between
1149
Applied Surface Science 487 (2019) 1145–1151
K. Huang, et al.
Fig. 7. Cyclic voltammetry curves in N2-saturated (black line) and O2-saturated (red line) 0.1 M KOH (A), ORR activity (B), and Tafel slope (C) of N-CoCuMnOx, PCoCuMnOX and commercial Pt/C as ORR catalysts. LSV curves (D), Koutechy-Levich (K-L) plots at different electrodes (E) of N-CoCuMnOx, and the chronoamperometric response (F) of the CoCuMnOX catalysts and commercial Pt/C catalyst.
Acknowledgments
density, Nano Energy 51 (2018) 513–523. [5] X.T. Wang, Y. Cui, T. Li, M. Lei, J.B. Li, Z.M. Wei, Recent advances in the functional 2D photonic and optoelectronic devices, Adv. Opt. Mater. 7 (2019) 1801274. [6] Y. Wang, Y. Song, Y. Xia, Electrochemical capacitors: mechanism, materials, systems, characterization and applications, Chem. Soc. Rev. 45 (2016) 5925–5950. [7] S. Lin, X.P. Bai, H.Y. Wang, H.L. Wang, J.N. Song, K. Huang, C. Wang, N. Wang, B. Li, M. Lei, H. Wu, Roll-to-roll production of transparent silver nanofiber network electrode for flexible electrochromic Smart windows, Adv. Mater. 29 (2017) 1703238. [8] Q. Wang, X. Li, L.Y. Wu, P.F. Lu, Z.F. Di, Electronic and Interface properties in graphene oxide/hydrogen-passivated Ge heterostructure, Phys. Status Solidi RRL 13 (2019) 1800461. [9] K. Bi, D.Q. Yang, J. Chen, Q.M. Wang, H.Y. Wu, C.W. Lan, Y.P. Yang, Experimental demonstration of ultra-large-scale terahertz all-dielectric metamaterials, Photonics Res 7 (2019) 457–463. [10] J. Wei, F.W. Guo, X. Wang, K. Xu, M. Lei, Y.Q. Liang, Y.C. Zhao, D.S. Xu, SnO2-inpolymer matrix for high-efficiency perovskite solar cells with improved reproducibility and stability, Adv. Mater. 30 (2018) 1805153. [11] K. Bi, X.Y. Wang, Y.N. Hao, M. Lei, G.Y. Dong, J. Zhou, Wideband slot-coupled dielectric resonator-based filter, J. Alloys Compd. 785 (2019) 1264–1269. [12] W.W. Zhong, S.J. Shen, S.S. Feng, Z.P. Lin, Z.P. Wang, B.Z. Wang, Facile fabrication of alveolate Cu2-xSe microsheets as a new visible-light photocatalyst for discoloration of rhodamine B, Crystengcomm 20 (2018) 7851–7856. [13] Q. Zhao, Z. Yan, C. Chen, J. Chen, Spinels: controlled preparation, oxygen
This work was financially supported by National Natural Science Foundation of China (Grant nos. 61874014, 61874013, 51572032, 51572073, 51672074, 61674019, 61574020), and Open Fund of State Key Laboratory of Information Photonics and Optical Communications (Beijing University of Posts and Telecommunications, China). References [1] L.Y. Wu, P.F. Lu, R.G. Quhe, Q. Wang, C.H. Yang, P.F. Guan, K.S. Yang, Stanene nanomeshes as anode materials for Na-ion batteries, J. Mater. Chem. A 6 (2018) 7933–7941. [2] H.J. Yang, L. Geng, Y.T. Zhang, G. Chang, Z.L. Zhang, X. Liu, M. Lei, Y.B. He, Graphene-templated synthesis of palladium nanoplates as novel electrocatalyst for direct methanol fuel cell, Appl. Surf. Sci. 466 (2019) 385–392. [3] W.W. Zhong, W.G. Tu, S.S. Feng, A.J. Xu, Photocatalytic H-2 evolution on CdS nanoparticles by loading FeSe nanorods as co-catalyst under visible light irradiation, J. Alloys Compd. 772 (2019) 669–674. [4] K. Bi, M.H. Bi, Y.N. Hao, W. Luo, Z.M. Cai, X.H. Wang, Y.H. Huang, Ultrafine coreshell BaTiO3@SiO2 structures for nanocomposite capacitors with high energy
1150
Applied Surface Science 487 (2019) 1145–1151
K. Huang, et al.
[14] [15] [16]
[17]
[18]
[19]
[20]
[21]
[22]
[23] [24]
[25]
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37] H.N. Cong, K.El. Abbassi, P. Chartier, Electrocatalysis of oxygen reduction on polypyrrole/mixed valence spinel oxide nanoparticles, J. Electrochem. Soc. 149 (2002) A525–A530. [38] L. Hu, L. Wu, M. Liao, X. Hu, X. Fang, Electrical transport properties of large, individual NiCo2O4 nanoplates, Adv. Funct. Mater. 22 (2012) 998–1004. [39] C. Fu, G. Li, D. Luo, X. Huang, J. Zheng, L. Li, One-step calcination-free synthesis of multicomponent spinel assembled microspheres for high-performance anodes of Liion batteries: a case study of MnCo2O4, ACS Appl. Mater. Interfaces 6 (2014) 2439–2449. [40] S. Jiang, Y. Sun, H. Dai, P. Ni, W. Lu, Y. Wang, Z. Li, A facile enhancement in battery-type of capacitive performance of spinel NiCo2O4nanostructure via directly tuning thermal decomposition temperature, Electrochim. Acta 191 (2016) 364–374. [41] A.M.M. Durka, S.A. Antony, A novel synthesis, structural, morphological, and optomagnetic characterizations of magnetically separable spinel CoXMn1-X Fe2O4 (0 ≤ X ≤ 1) nano-catalysts, J. Supercond. Nov. Magn. 27 (2014) 2841–2857. [42] L. Zhang, Y. Wang, H. Jiu, W. Zheng, J. Chang, Controllable synthesis of spinel nano-CoMn2O4 via a solvothermal carbon templating method and its application in lithium ion batteries, Electrochim. Acta 182 (2015) 550–558. [43] M.H. Habibi, M. Mardani, Synthesis and characterization of Bi-component ZnSnO3/ Zn2SnO4 (perovskite/spinel) nano-composites for photocatalytic degradation of intracron blue: structural, opto-electronic and morphology study, J. Mol. Liq. 238 (2017) 397–401. [44] J. Wan, X. Chen, Z. Wang, X. Yang, Y. Qian, A soft-template-assisted hydrothermal approach to single-crystal Fe3O4 nanorods, J. Cryst. Growth 276 (2005) 571–576. [45] Y. Song, R.M. Garcia, R.M. Dorin, H. Wang, Y. Qiu, E.N. Coker, W.A. Steen, J.E. Miller, J.A. Shelnut, Synthesis of platinum nanowire networks using a soft template, Nano Lett. 7 (2007) 3650–3655. [46] B. Liu, H. Shioyama, H. Jiang, X. Zhang, Q. Xu, Metal-Organic Framework (MOF) as a template for syntheses of nanoporous carbons as electrode materials for supercapacitor, Carbon 48 (2010) 456–463. [47] Y. Sun, B.T. Mayers, Y. Xia, Template-engaged replacement reaction: a one-step approach to the large-scale synthesis of metal nanostructures with hollow interiors, Nano Lett. 2 (2002) 481–485. [48] Z. Wang, X. Li, Y. Yang, Y. Cui, H. Pan, Z. Wang, B. Chen, G. Qian, Highly dispersed β-NiS nanoparticles in porous carbon matrices by a template metal-organic framework method for lithium-ion cathode, J. Mater. Chem. A 2 (2014) 7912–7916. [49] J.J. Miao, L.P. Jiang, C. Liu, J.M. Zhu, J.J. Zhu, General sacrificial template method for the synthesis of cadmium chalcogenide hollow structures, Inorg. Chem. 46 (2007) 5673–5677. [50] M. Yang, G. Zhang, C. Wu, Z. Chang, X. Sun, X. Duan, Preparation of multi-metal oxide hollow sphere using layered double hydroxide precursors, Chin. J. Chem. 30 (2012) 2183–2188. [51] S. Tang, S. Vongehr, X. Meng, Controllable incorporation of Ag and Ag-Au nanoparticles in carbon spheres for tunable optical and catalytic properties, J. Mater. Chem. 20 (2010) 5436–5445. [52] S.J. Kim, C.W. Na, I.S. Hwang, J.H. Lee, One-pot hydrothermal synthesis of CuOZnO composite hollow spheres for selective H2S detection, Sensors Actuators B Chem. 168 (2012) 83–89. [53] C. Wei, Z. Feng, G.G. Scherer, J. Barber, Y. Shao Horn, Z.J. Xu, Cations in octahedral sites: a descriptor for oxygen electrocatalysis on transition metal spinels, Adv. Mater. 29 (2017) 1606800. [54] M. Sevilla, A.B. Fuertes, The production of carbon materials by hydrothermal carbonization of cellulose, Carbon 47 (2009) 2281–2289. [55] D.L. Bish, S.A. Howard, Quantitative phase analysis using the Rietveld method, J. Appl. Crystallogr. 21 (1988) 86–91. [56] M.C. Biesinger, B.P. Payne, A.P. Grosvenor, L.W.M. Lau, A.R. Gerson, R.S.C. Smart, Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Cr, Mn, Fe, Co and Ni, Appl. Surf. Sci. 257 (2011) 2717–2730. [57] S. Ramamurthy, R.D. Davidson, N.S. McIntyre, J.T. Francis, A. McBride, A.M. Brennenstuhl, A. Roberts, Mechanisms for pitting corrosion in alloy N04400 as revealed by imaging XPS, ToF-SIMS and low-voltage SEM, Surf. Interface Anal. 33 (2002) 29–34. [58] R.S. Vishwanath, S. Kandaiah, Metal ion-containing C3N3S3 coordination polymers chemisorbed to a copper surface as acid stable hydrogen evolution electrocatalysts, J. Mater. Chem. A 5 (2017) 2052–2065. [59] L.H. Zhang, C. Zheng, F. Li, D.G. Evans, X. Duan, Copper-containing mixed metal oxides derived from layered precursors: control of their compositions and catalytic properties, J. Mater. Sci. 43 (2008) 237–243. [60] Y. Zhou, S. Sun, S. Xi, Y. Duan, T. Sritharan, Y. Du, Z.J. Xu, Superexchange effects on oxygen reduction activity of edge sharing [CoxMn1-xO6] Octahedra in spinel oxide, Adv. Mater. 30 (2018) 1705407.
reduction/evolution reaction application, and beyond, Chem. Rev. 117 (2017) 10121–10211. V. Augustyn, P. Simon, B. Dunn, Pseudocapacitive oxide materials for high-rate electrochemical energy storage, Energy Environ. Sci. 7 (2014) 1597–1614. L. Croguennec, M.R. Palacin, Recent achievements on inorganic electrode materials for lithium-ion batteries, J. Am. Chem. Soc. 137 (2015) 3140–3156. H. Wang, R.P. Liu, Z.M. Cui, X.J. Lv, Y.T. Li, X. Li, S. Xin, R. Zhang, M. Lei, Z.Q. Lin, Hollow porous spinel ZnMnCoO4 microspheres with a high oxygen reduction activity, Joule 2 (2018) 337–348. P. Stelmachowski, A.H.M. Videla, K. Ciura, S. Specchia, Oxygen evolution catalysis in alkaline conditions over hard templated nickel-cobalt based spinel oxides, Int. J. Hydrog. Energy 42 (2017) 27910–27918. A.H.M. Videla, P. Stelmachowski, G. Ercolino, S. Specchia, Benchmark comparison of Co3O4 spinel-structured oxides with different morphologies for oxygen evolution reaction under alkaline conditions, J. Appl. Electrochem. 47 (2017) 295–304. R.A.M. Esfahani, L.M.R. Gavidia, G. García, E. Pastor, S. Specchia, Highly active platinum supported on Mo-doped titanium nanotubes suboxide (Pt/TNTS-Mo) electrocatalyst for oxygen reduction reaction in PEMFC, Renew. Energy 120 (2018) 209–219. R.A.M. Esfahani, S.K. Vankova, A.H.A. Monteverde Videla, S. Specchia, Innovative carbon-free low content Pt catalyst supported on Mo-doped titanium suboxide (Ti3O5-Mo) for stable and durable oxygen reduction reaction, Appl. Catal. B Environ. 201 (2017) 419–429. C. Wei, R.R. Rao, J. Peng, B. Huang, I.E. Stephens, M. Risch, Y. Shao-Horn, Recommended practices and benchmark activity for hydrogen and oxygen electrocatalysis in water splitting and fuel cells, Adv. Mater. 31 (2019) 1806296. X. He, S.Z. Luan, L. Wang, R.Y. Wang, P. Du, Y.Y. Xu, H.J. Yang, Y.G. Wang, K. Huang, M. Lei, Facile loading mesoporous Co3O4 on nitrogen doped carbon matrix as an enhanced oxygen electrode catalyst, Mater. Lett. 244 (2019) 78–82. Y. Eunjoo, Z. Hao, Li-air rechargeable battery based on metal-free graphene nanosheet catalysts, ACS Nano 5 (2011) 3020–3026. X. Bo, Y. Zhang, M. Li, A. Nsabimana, L. Guo, NiCo2O4 spinel/ordered mesoporous carbons as noble-metal free electrocatalysts for oxygen reduction reaction and the influence of structure of catalyst support on the electrochemical activity of NiCo2O4, J. Power Sources 288 (2015) 1–8. F.M. Courtel, H. Duncan, Y. Abu-Lebdeh, I.J. Davidson, High capacity anode materials for Li-ion batteries based on spinel metal oxides AMn2O4 (A = Co, Ni, and Zn), J. Mater. Chem. 21 (2011) 10206–10218. H. Zhang, X. Tian, C. Wang, H. Luo, J. Hu, Y. Shen, A. Xie, Facile synthesis of RGO/ NiO composites and their excellent electromagnetic wave absorption properties, Appl. Surf. Sci. 314 (2014) 228–232. P. Lavela, J.L. Tirado, C. Vidal-Abarca, Sol-gel preparation of cobalt manganese mixed oxides for their use as electrode materials in lithium cells, Electrochim. Acta 52 (2007) 7986–7995. Y. Xu, W. Bian, J. Wu, J.H. Tian, R. Yang, Preparation and electrocatalytic activity of 3D hierarchical porous spinel CoFe2O4 hollow nanospheres as efficient catalyst for oxygen reduction reaction and oxygen evolution reaction, Electrochim. Acta 151 (2015) 276–283. L. Wang, X. Zhao, Y. Lu, M. Xu, D. Zhang, R.S. Ruoff, K.J. Stevenson, J.B. Goodenough, CoMn2O4 spinel nanoparticles grown on graphene as bifunctional catalyst for lithium-air batteries, J. Electrochem. Soc. 158 (2011) A1379–A1382. A. Serov, N.I. Andersen, A.J. Roy, I. Matanovic, K. Artyushkova, P. Atanassov, CuCo2O4 ORR/OER Bi-functional catalyst: influence of synthetic approach on performance, J. Electrochem. Soc. 162 (2015) F449–F454. Y. Liang, H. Wang, J. Zhou, Y. Li, J. Wang, T. Regier, H. Dai, Covalent hybrid of spinel manganese-cobalt oxide and graphene as advanced oxygen reduction electrocatalysts, J. Am. Chem. Soc. 134 (2012) 3517–3523. Y. Sharma, N. Sharma, G.V.S. Rao, B.V.R. Chowdari, Lithium recycling behaviour of nano-phase-CuCo2O4 as anode for lithium-ion batteries, J. Power Sources 173 (2007) 495–501. L. Osmieri, A.H.M. Videla, M. Armandi, S. Specchia, Influence of different transition metals on the properties of Me–N–C (Me = Fe, Co, Cu, Zn) catalysts synthesized using SBA-15 as tubular nano-silica reactor for oxygen reduction reaction, Int. J. Hydrog. Energy 41 (2016) 22570–22588. L. Osmieri, R. Escudero-Cid, M. Armandi, P. Ocón, A.H.M. Videla, S. Specchia, Effects of using two transition metals in the synthesis of non-noble electrocatalysts for oxygen reduction reaction in direct methanol fuel cell, Electrochim. Acta 266 (2018) 220–232. P. Stelmachowski, A.H.M. Videla, T. Jakubek, A. Kotarba, S. Specchia, The effect of Fe, Co, and Ni structural promotion of Cryptomelane (KMn8O16) on the catalytic activity in oxygen evolution reaction, Electrocatalysis 9 (2018) 762–769. Y. Liang, H. Wang, J. Zhou, Y. Li, J. Wang, T. Regier, H. Dai, Covalent hybrid of spinel manganese-cobalt oxide and graphene as advanced oxygen reduction electrocatalysts, J. Am. Chem. Soc. 134 (2012) 3517–3523.
1151