Microwave-assisted facile and rapid synthesis of layered metal hydroxide nanosheet arrays towards high-performance aqueous hybrid supercapacitors

Ceramics International 45 (2019) 20810–20817

Contents lists available at ScienceDirect

Ceramics International journal homepage: www.elsevier.com/locate/ceramint

Microwave-assisted facile and rapid synthesis of layered metal hydroxide nanosheet arrays towards high-performance aqueous hybrid supercapacitors

T

Guodong Xiaa,b, Sumei Wangb,* a b

Department of Material and Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan, 250353, China Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials (Ministry of Education), Shandong University, Jinan, 250061, China

A R T I C LE I N FO

A B S T R A C T

Keywords: Layered metal hydroxides Nanosheet arrays Microwave synthesis Hybrid supercapacitors Electrochemistry

Layered metal hydroxides (LMHs) have been extensively investigated due to their high surface area and excellent properties. However, rapid synthesis of LMHs, with desirable nanostructures and performance, is a challenging task. Herein, a novel microwave (MW)-assisted synthesis route is presented by employing household microwave oven to directly grow LMH nanosheet arrays (NSAs) on current collectors for binder-free electrodes in supercapacitors. Ni(OH)2 NSAs delivered a great capacitance of 2516 and 1273 F/g at 1 and 20 A/g, respectively. Furthermore, a Ni(OH)2//AC aqueous hybrid supercapacitor delivered a significantly large energy density up to 66.7 Wh/kg at 400 W/kg as well as good cycle stability of 85.2%. Moreover, the green and low-cost MW-assisted synthesis route can be adopted for other LMH NSAs, i.e., vertically aligned Cu2(OH)3NO3 NSAs. The excellent electrochemical performance of LMH NSAs can be attributed to the unique nanostructure, direct production of binder-free electrodes and highly efficient MW aqueous method. These results demonstrate the potential of MWassisted synthesis process for facile and rapid production of LMH NSAs with a wide variety of applications.

1. Introduction With the rapid demand for renewable energy technologies, costeffective energy storage devices are gaining increasing research attention to efficiently store renewable energy and counter the intermittent nature of renewable energy sources. The supercapacitor, as an efficient energy storage device, has aroused intensive research interest because of the combined advantages of batteries and capacitors, rendering excellent energy and power densities [1,2]. Supercapacitors (SCs) consist of electrical double layer capacitors employing carbon-based materials, and pseudocapacitors via reversible Faradaic reactions for charge storage. Carbonaceous materials exhibit excellent rate performance but relatively low capacitance for its only surface charge storage phenomenon. On the other hand, pseudocapacitors can be prepared by using a variety of materials, including transition metal compounds and conductive polymers [3,4]. In general, pseudocapacitive materials render significantly higher specific capacitance than carbonaceous materials, originating from redox reaction and intercalation. For example, Ni(OH)2 and CoOOH exhibited a great capacitance of ~2000 F/g, much larger than typical carbonaceous materials [5,6]. However, the low rate and cycling stability of pseudocapacitors are the major challenge for commercialization. Furthermore, compared with Li-ion batteries, supercapacitors possess the relatively

*

low energy density, which inhibits the large-scale utilization of SCs in diverse applications. Two-dimensional (2D) materials, including graphene, layered metal hydroxides (LMHs) and MXene, have attracted tremendous research interest because of their outstanding storage, optical, and electrical properties [7,8]. Among them, ultrathin LMH nanosheets, possessing large surface area, rich surface-active sites and tunable ion-intercalation behavior, have been widely investigated in the last decade [9–13]. Various LMHs have exhibited excellent performance in catalysis, batteries, and supercapacitors. In particular, Ni(OH)2, with the advantage of large theoretical capacitance (3750 F/g) and low cost, has been competitive electrode materials for high-capacitance supercapacitors [14]. However, their performance is still limited by the low rate and cycle stability. The properties of LMHs are highly influenced by the microstructure. Various LMH micro- and nanostructures, such as microspheres, nanosheets, hollow microspheres and nanotubes, have been synthesized. 2D layered nanostructures, i.e., nanosheets, can accelerate the diffusion of ions and improve electrochemical performance [15,16]. For instance, ultrathin mesoporous nanosheets of α-Ni(OH)2:F obtained a large capacitance of 1503 F/g [15]. However, LMHs are usually in the bulk powder form and require further processing, such as preparation of a mixture with binders and conductive agents, increasing the complexity

Corresponding author. E-mail address: [email protected] (S. Wang).

https://doi.org/10.1016/j.ceramint.2019.07.068 Received 15 June 2019; Received in revised form 2 July 2019; Accepted 6 July 2019 Available online 06 July 2019 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Ceramics International 45 (2019) 20810–20817

G. Xia and S. Wang

of electrode preparation process. Moreover, the binder- and conductive agent-containing electrodes render inferior electrochemical performance due to limited electrochemically active surface sites. To overcome these issues, binder-free electrodes can be efficiently prepared by directly growing the active material on current collectors. Unlike powder materials, the directly-grown nanostructure arrays avoid the utilization of binder and complex electrode fabrication process [5,17,18]. Therefore, numerous studies have investigated the preparation of LMH-based binder-free electrodes. For instance, Cu(OH)2/ FeOOH nanotube based microsupercapacitors have demonstrated a superior capacitance of 58 mF/cm2 [19]. Moreover, in-situ prepared αNi(OH)2 nanosheets, via a low-cost solution-based process, achieved a large capacitance of ~1760 F/g [5]. Therefore, in-situ fabricated nanostructures render considerable potential towards cost-effective energy applications. Furthermore, LMHs can be prepared by different techniques, such as chemical precipitation, hydro/solvothermal process, electrodeposition, microwave (MW) -assisted hydrothermal/solvothermal method, and chemical bath deposition [20–23]. MW-assisted techniques are considered promising due to their unique advantages of less time, reduced energy consumption and their ability to synthesize desirable morphologies of LMHs. For instance, MW-processed ultrathin Ni(OH)2:Fe nanosheets have exhibited superior performance as water oxidation electrocatalysts [24]. However, most of the previous reports have utilized the expensive microwave-assisted hydrothermal and digestion equipment, which are not economical and desirable for scalable production. Therefore, the synthesis of 2D LMHs by facile, large-scale and low-cost synthesis route is still a challenging task. Herein, we report efficient MW-assisted synthesis of 2D LMH NSAs by using a household microwave oven and demonstrate the electrochemical performance of directly grown LMHs, with Ni(OH)2 as a typical example, on NFs as effective binder-free electrodes. Apart from the less time and energy consumption, the Ni(OH)2 nanosheets rendered a significantly better electrochemical performance than previous Ni(OH)2 nanostructures. Furthermore, aqueous asymmetric supercapacitors (ASCs) with Ni(OH)2 NSA realized a superior energy density of 66.7 Wh/kg at 400 W/kg. Moreover, the proposed synthesis approach can be extended to prepare other LMH NSAs, i.e., Cu2(OH)3NO3 nanosheets have been synthesized as a proof of concept. Therefore, the proposed MW-assisted synthesis route is a promising method of preparing metal hydroxide NSAs for a variety of electrochemical devices.

Fig. 1. (a) The scheme of MW aqueous process for LMH NSAs. SEM images of (b) MW-10, (c) MW-15, (d) MW-20 Ni(OH)2 NSAs. (e) XRD pattern of MW-15 Ni(OH)2 NSAs.

2. Experiment

scanning electronic microscopy (SEM) and JEM-2100F transmission electron microscopy (TEM). The surface group was checked by a Thermo Scientific Nicolet 710 spectrometer. The surface chemical states were analyzed via an X-ray photoelectron spectrometer (ESCALAB 250). The active material loading was measured by a microbalance after vacuum drying the samples. The mass amount of Ni(OH)2 MW-10, MW15 and MW-20 samples was found to be ~0.96, 1.24, 1.37 mg/cm2, respectively. The mass amount of Cu2(OH)3NO3 was about 1.40 mg/ cm2. Electrochemistry properties were measured through an electrochemical workstation (Vertex C) with 1 M aqueous KOH electrolyte. The capacitance, energy and power density of supercapacitors were estimated similarly with standard methods in previous reports [5,18,19].

2.1. MW-assisted growth of LMH NSAs

3. Results and discussion

The commercial nickel foam (NF), used as a current collector, was precleaned with 3 M HCl for 0.5 h, and then cleaned by deionized (DI) water and vacuum dried. In a typical reaction, 12 mmol of nickel nitrate and 24 mmol of hexamethylenetetramine (HMT) were mixed with 50 mL of DI water in 200 mL glass bottle. The solution was continuously stirred for 1 h to produce a transparent green solution. Then, NF substrate was immersed in the solution. The glass bottle was placed into a domestic Galanz MW oven with MW irradiation frequency of 2.45 GHz and power of 280 W for 10, 15 and 20 min, which are denoted as Ni (OH)2 MW-10, MW-15 and MW-20, respectively. The as-obtained Ni (OH)2 samples deposited on NFs were taken out from the glass bottle and ultrasonically cleaned, followed by overnight vacuum drying. Similar to Ni(OH)2 NSAs, Cu2(OH)3NO3 NSAs were synthesized by employing 10 mmol of copper nitrate and 20 mmol of HMT as the precursors. Herein, the MW irradiation was carried out for 10 min.

The facile and rapid MW-assisted synthesis of metal hydroxide NSAs is schematically illustrated in Fig. 1a. The metal nitrate and HMT were dissolved to produce a clear solution, transferred into a domestic MW oven and irradiated for different times, which resulted in the in-situ synthesis of vertically aligned LMH NSAs. The porous and conductive NF favored the release of gas bubbles and applied as the current collector. In particular, the in-situ growth of LMHs on NFs simplified the fabrication of electrodes and significantly improved electrochemical properties. During MW-assisted synthesis, HMT provided the alkaline environment to form hydroxides [5,25,26]. Moreover, HMT produced a robust structure due to the excellent chelating effect, resulting in α-Ni (OH)2 nanostructure with good electrochemical properties and high stability in strong alkali solutions [25]. Compared with MW hydrothermal process, the present MW-assisted process avoided the utilization of expensive microwave-hydrothermal equipment and utilized the commonly used low-cost kitchen MW oven to prepare the desired nanostructures. As shown in Fig. 1b-d, the surface of NF has been fully covered by vertically aligned NSAs, forming a hierarchical 3D web-like structure, which consists of 2D nanosheets. The resulting 2D Ni(OH)2 nanosheets

2.2. Characterization The phase was measured through Rigaku Smartlab X-ray diffraction (XRD) equipment. The structure was measured using Hitachi S-5000

20811

Ceramics International 45 (2019) 20810–20817

G. Xia and S. Wang

Fig. 2. (a-c) TEM images and (d) SAED patterns of MW-15 Ni(OH)2 NSAs.

Fig. 3. (a) FTIR and (b-d) XPS spectra of MW aqueous-processed Ni(OH)2 MW-15 NSAs.

originated from its intrinsic layered structure. With the support of NFs, Ni(OH)2 nucleated and grew on NFs to form the vertically aligned 3D NSAs. The hierarchical 3D structure provides enriched electrochemically active surface sites and facilitates the electrolyte diffusion, resulting in enhanced electrochemical performance. With the increase of MW processing time from 10 to 20 min, the pore size increased from a few hundreds of nanometers to several micrometers. Moreover, Ni (OH)2 MW-15 sample exhibited the most dense and uniform NSAs due to the medium pore size and nanosheets thickness. The interconnected Ni(OH)2 nanosheets array provides abundant open spaces and

pathways for the efficient transmission of electrons and ions, which would render excellent properties. As presented in Fig. 1e, the major diffraction peaks correspond to the JCPDS file 22-0444 of α-Ni(OH)2. Moreover, any impurity phase has not been observed, which implies that α-Ni(OH)2 pure phase was successfully obtained using the proposed MW-assisted rapid and facile aqueous approach. The (001) peak exhibited a slight shift towards the lower angle, which can be ascribed to the presence of charge-balancing anions, including water molecules and nitrate ions, between the sheets, as confirmed by FTIR analysis.

20812

Ceramics International 45 (2019) 20810–20817

G. Xia and S. Wang

Fig. 4. CV curves of (a) MW-10, (b) MW-15, and (c) MW-20 Ni(OH)2 NSAs. (d) CV curves at 50 mV/s. (e) The dependence of current density on the square root of scan rate for Ni(OH)2 MW-15 sample.

TEM images in Fig. 2a-b reveal the web-like structure with interlaced nanosheets, which is consistent with the above SEM results. Some nanosheets look flocculent, which suggests the ultrathin Ni(OH)2 nanosheets. In addition, some observed black lines perhaps correspond to the edges or intersections of the nanosheets. Furthermore, these lines are extremely thin (~10 nm), which also confirms the ultrathin nanosheets of Ni(OH)2. Fig. 2c exhibits clear lattice fringes, indicating the crystalline nanosheets. The average lattice spacing is 0.372 nm, corresponding to the (002) planes of α-Ni(OH)2. As exhibited in Fig. 2d, the bright rings, from outside to inside, can be indexed to (300), (004), (103) and (110) planes of polycrystalline α-Ni(OH)2. Fourier transform infrared spectroscopy (FTIR) spectrum is shown in Fig. 3a. The absorption peaks at 3354 and 647 cm−1 correspond to typical OH− vibration, originating from the interlayered H-bonded water molecules. The absorption band at ~2911 cm−1 represents -CH2 vibrations, whereas the band at 1637 cm−1 refers to δ-H2O vibrations, implying absorbed H2O in the interlayers. Furthermore, the absorption peak at 1384 cm−1 corresponds to NO3– vibrations due to the intercalation of nitrate ions. Two weak absorption peaks at 2365 and 1194 cm−1 belong to CO32− vibrations. These results suggest that some anions have been inserted into the interlayer spacing to maintain charge neutrality. As presented in Fig. 3b, the wide-range X-ray photoelectron spectrum (XPS) of Ni(OH)2 MW-15 sample consists of C 1s, O 1s and Ni 2p

peaks. The Ni 2p spectrum in Fig. 3c is fitted into four peaks. The main peaks at 873.2 and 855.6 eV correspond to Ni 2p1/2 and Ni 2p3/2, respectively. The peaks located at ~878.9 and 861.4 eV can be assigned to two shake-up peaks. Fig. 3d shows the O 1s spectrum, consisting of three main peaks. The highest intensity band at 531.4 eV corresponds to OH− groups, which dominate the composition. The peak at 532.6 eV is attributed to water (H2O) molecules. One should note that the inserted water molecules may improve electrochemical performance. The lowest intensity band at 530.2 eV corresponds to M-O bonding, which suggests that the possible existence of minor NiO. The contribution of OH− groups, H2O molecules and M-O has been calculated from the O 1s spectrum and found to be 62.3, 21.9 and 15.8%, respectively. The high percentage of OH− groups indicates the production of Ni(OH)2 via the MW assisted rapid and facile synthesis. Furthermore, MW aqueous-processed Ni (OH)2 NSAs were directly employed as binder-free electrodes, which substantially simplified the device fabrication process. Fig. 4a, b and 4c present the cyclic voltammetry (CV) of MW-10, MW-15, and MW-20 Ni (OH)2 electrodes, respectively. The measured voltage window is 0–0.6 V (vs. Hg2Cl2/Hg). With the increasing scan rate, CV curves did not exhibit any substantial change of the shape, which indicates the good reversibility of electrodes. Furthermore, the almost same current values of the redox peaks infered that the redox reaction is reversible. The reversible electrochemical reaction is from the reaction between Ni

20813

Ceramics International 45 (2019) 20810–20817

G. Xia and S. Wang

Fig. 5. GCD curves of (a) MW-5, (b) MW-10 and (c) MW-15 Ni(OH)2 NSAs. (d) GCD curves at 1 A/g. (e) rate capability of Ni(OH)2 NSAs.

Fig. 6. EIS curves of MW aqueous-processed Ni(OH)2 NSAs.

(OH)2 and NiOOH. There are a pair of redox peaks, representing the pseudocapacitive charge storage behavior of Ni(OH)2 NSAs. With the increase of scan rate, cathodic and anodic peaks moved towards higher and lower potentials, respectively. One should note that the ions cannot completely diffuse into electrodes at a larger scan rate, resulting in a larger potential to carry out the electrochemical reactions. It is revealed in Fig. 4d that the area of CV curves, proportional to the capacitance, followed the given order: MW-15 > MW-10 > MW20 Ni(OH)2 NSA electrodes. The maximum CV area of MW-15 electrode

is result from the uniform and dense NSA structure, which offered abundant active sites, accelerated the ionic diffusion and resulted in optimal specific capacitance. Fig. 4e presents the linear relationship between maximum redox current and the square root of scan rate, which indicates that the electrochemical reactions are primarily dominated by the diffusion-control processes. This further indicates the good reversibility and fast ionic diffusion rate of Ni(OH)2 MW-15 electrode. As exhibited in Fig. 5, all galvanostatic charge/discharge (GCD)

20814

Ceramics International 45 (2019) 20810–20817

G. Xia and S. Wang

Fig. 7. (a) CV, (b) GCD, (c) Ragone plot and (d) cycle curves of MW-15 Ni(OH)2 NSAs//AC aqueous hybrid supercapacitor.

curves exhibited obvious voltage plateaus, suggesting the typical faradaic characteristics. Fig. 5d reveals the Ni(OH)2 MW-15 electrode rendered the longest discharge time, which corresponds to the maximum capacitance. The calculated capacitance of Ni(OH)2 MW-10, MW15 and MW-20 electrodes was 2024, 2516 and 1476 F/g, respectively. One should note that the GCD curves and corresponding capacitances are in agreement with the CV observations. The achieved capacitance of Ni(OH)2 MW-15 NSAs is comparable or superior to those of reported Ni (OH)2-based nanostructures [27,28], which could be result from the insitu growth of ultrathin nanosheets on NFs, improving the ionic diffusion and electron transfer processes. Furthermore, MW-assisted synthesis route can substantially reduce the processing time and energy consumption, which favors the large-scale preparation of LMHs for energy storage applications. As revealed in Fig. 5e, the capacitance decreased with increasing current density due to the relatively slow ionic diffusion. As the current density increased, the electrolyte ions gained less time to penetrate the active sites and the layers of the electrode material, leading to inferior capacitance. Ni(OH)2 MW-15 NSAs achieved a relatively large capacitance of 2516 and 1273 F/g at 1 and 20 A/g, respectively. One should note that Ni(OH)2 MW-15 does not contain a conductive additive, and the rate performance would be enhanced through introduction of a conductive agent including graphene or Mxene. The electrochemical impedance spectroscopy (EIS) curves are exhibited in Fig. 6. The nearly vertical frequency response curves suggest the high diffusion ability of electrolyte ions into the electrodes. Rs and Rct correspond to series and charge transfer resistances, respectively. The high-frequency intercept provides Rs value. The fitted Rs values of Ni(OH)2 MW-10, MW-15 and MW-20 electrodes are 1.23, 1.22 and 1.07 Ω, respectively. The diameter of the high-frequency quasi-semicircle, as shown in enlarged Nyquist plots in Fig. 6b, corresponds to Rct. The fitted Rct values of Ni(OH)2 MW-10, MW-15 and MW-20 electrodes are 1.37, 0.22 and 1.91 Ω, respectively. Clearly, Ni(OH)2 MW-15 electrode has exhibited the lowest Rct, which explains the achieved superior performance. To demonstrate the practical applications, an aqueous hybrid supercapacitor has been prepared with Ni(OH)2 MW-15 and activated carbon (AC). The capacitance of AC is about 278 F/g at 1 A/g. As shown

in Fig. 7a, the large voltage window is 1.6 V, result from the combined contributions of Ni(OH)2 and AC. One should note that the CV curves did not exhibit any obvious distortion at high scan rates, which indicates the excellent capacitive performance. Fig. 7b reveals the calculated capacitance of Ni(OH)2//AC supercapacitor at 0.5, 1, 2, 3, 5 and 10 A/g is 187.6, 181.5, 127.5, 105.4, 88.8 and 65.0 F/g, respectively. As revealed in the Ragone plot (Fig. 7c), Ni(OH)2//AC supercapacitor obtained a great energy density of ~66.7 Wh/kg at ~400 W/ kg. Furthermore, at a very large power density of 8000 W/kg, an energy density of 23.1 Wh/kg was obtained. The energy density of present Ni (OH)2//AC is higher than or comparable to those of previous Ni(OH)2 supercapacitors [29–34]. Moreover, MW aqueous synthesis approach is rapid, low-cost and facile, making it highly promising for scalable fabrication. The cyclic performance of Ni(OH)2//AC device has been assessed by carrying out GCD testing at 2 A/g during 5000 cycles. Fig. 7d shows Ni(OH)2//AC aqueous hybrid supercapacitor resulted in the superior cycle stability of 85.2%. The increase of capacitance during 1000 cycles perhaps results from the activation process of electrodes. Hence, MW aqueous-processed Ni(OH)2 NSA electrodes exhibit great potential in energy storage applications. To demonstrate the generic nature of MW-assisted synthesis route, copper hydroxide NSAs have also been prepared by using the same protocol and Cu(NO3)2 precursor. Fig. 8a and b shows the XRD pattern and SEM image of MW-processed copper hydroxide NSAs. The XRD peaks correspond with the standard JCPDS file 45-0594 of Cu2(OH)3NO3, which indicates that NO3−-infiltrated copper hydroxide has been successfully synthesized. One should note that the previous studies have also reported the formation of Cu2(OH)3NO3 instead of Cu (OH)2 [35,36]. It has been demonstrated that the double hydroxyl salts, i.e., Cu2(OH)3NO3, also possess layered structure, which is promising for electrochemical energy storage applications [37]. Cu2(OH)3NO3 has also shown the vertically aligned nanosheet arrays, as shown in Fig. 8b. Therefore, the proposed MW-assisted synthesis route can be utilized to fabricate desirable nanostructures of other layered metal hydroxides. Fig. 8c exhibits the typical CV curves of Cu2(OH)3NO3 NSA electrode. The CV curves exhibited two obvious redox peaks because of the Faradic reactions between Cu2(OH)3NO3 and Cu(OH)2. The GCD curves of Cu2(OH)3NO3 NSA electrode exhibit non-linear shape, which can be

20815

Ceramics International 45 (2019) 20810–20817

G. Xia and S. Wang

Fig. 8. (a) XRD, (b) SEM image, (c) CV curves, (d) GCD curves and (e) dependence of capacitance on current density of MW aqueous-processed Cu2(OH)3NO3 NSAs.

ascribed to the typical pseudocapacitive behavior of LMHs (Fig. 8d). At 1 A/g, Cu2(OH)3NO3 NSA electrode resulted in a discharge time of ~370 s, corresponding to a capacitance of 317.2 F/g. Even at 20 A/g, the Cu2(OH)3NO3 NSA electrode still rendered a specific capacitance of 184 F/g (Fig. 8e). The obtained performance is comparable with those of reported copper hydroxide electrodes [38,39]. These results indicate the superior performance of Cu2(OH)3NO3 NSA via the present MW aqueous process. The superior electrochemical performance of LMH NSAs can be ascribed to several reasons: (1) the interconnected NSAs with abundant active sites, (2) enhanced electrolyte access to the active material, (3) increased ionic diffusion due to the layered structure and (4) effective electron transfer process due to the in-situ growth of active material on NFs. The achieved excellent performance of LMH NSA electrodes is also highly dependent on the present MW process. The utilization of polar water solvent results in rapid MW-assisted synthesis because the microwave can heat water to ~100 °C in few minutes, which is much quicker than other heating methods, i.e., drying oven. Therefore, the excellent properties resulted from the unique nanostructure, direct contact between LMH NSAs and conductive NFs, and efficient MW aqueous route.

4. Conclusion In short, we demonstrated a rapid and facile microwave-assisted aqueous synthesis approach to directly grow LMH NSAs on NFs as efficient electrodes in supercapacitors. Compared to the conventional processes, the proposed MW-assisted synthesis approach rendered obvious advantages, including rapid growth, facile equipment and lowcost, making it a promising choice for large-scale fabrication of LMH NSAs with vertical nanosheets on the conductive foams. The MW-processed Ni(OH)2 NSAs rendered a great capacitance of 2516 F/g under 1 A/g. Furthermore, an aqueous hybrid supercapacitor, consisting of Ni (OH)2 and AC, delivered a high energy density of 66.7 Wh/kg under 400 W/kg. Moreover, the present hybrid device exhibited excellent cycle stability of 85.2% after 5000 cycles. The short reaction time, green solution processing and superior electrochemical performance indicate the promise of MW-assisted synthesis approach for the largescale and cost-effective synthesis of energy materials. We believe that the present work offers a novel synthesis route to obtain LMH NSAs and provides a cost-effective strategy to design high-performance nanostructures for diverse applications.

20816

Ceramics International 45 (2019) 20810–20817

G. Xia and S. Wang

Acknowledgements This work was supported by the National Natural Science Foundation of China (No. 61106086), Natural Science Foundation of Shandong Province (No. ZR2019MF031, No. ZR2015FM009) and National-level College Students Innovative Entrepreneurial Training Plan Program (No. 04120482).

[19]

[20]

[21]

References [22] [1] W. Guo, C. Yu, S. Li, X. Song, H. Huang, X. Han, Z. Wang, Z. Liu, J. Yu, X. Tan, J. Qiu, A universal converse voltage process for triggering transition metal hybrids in situ phase restruction toward ultrahigh-rate supercapacitors, Adv. Mater. (2019) 1901241. [2] Y. Zhang, Y. Zhang, Y. Zhang, H. Si, L. Sun, Bimetallic NiCo2S4 nanoneedles anchored on mesocarbon microbeads as advanced electrodes for asymmetric supercapacitors, Nano-Micro Lett. 11 (2019) 35. [3] X. Bai, D. Cao, H. Zhang, Constructing ZnCo2O4@LDH Core–Shell hierarchical structure for high performance supercapacitor electrodes, Ceram. Int. 45 (2019) 14943–14952. [4] X. Zhang, R. Zhang, C. Xiang, Y. Liu, Y. Zou, H. Chu, S. Qiu, F. Xu, L. Sun, Polydopamine-assisted formation of Co3O4-nanocube-anchored reduced graphene oxide composite for high-performance supercapacitors, Ceram. Int. 45 (2019) 13894–13902. [5] L. Li, G. Xia, W. Yu, K. Lu, A. Zhang, S. Wang, Low-energy hydrothermal fabrication of α-Ni(OH)2 nanosheet arrays as efficient electrodes for sustainable supercapacitors, Sustain. Mater. Technol. 20 (2019) e00085. [6] D. Zhang, X. Kong, Y. Zhao, M. Jiang, X. Lei, CoOOH ultrathin nanoflake arrays aligned on nickel foam: fabrication and use in high-performance supercapacitor devices, J. Mater. Chem. A 4 (2016) 12833–12840. [7] H. Liu, T. Yu, D. Su, Z. Tang, J. Zhang, Y. Liu, A. Yuan, Q. Kong, Ultrathin Ni-Al layered double hydroxide nanosheets with enhanced supercapacitor performance, Ceram. Int. 43 (2017) 14395–14400. [8] M. Shao, R. Zhang, Z. Li, M. Wei, D.G. Evans, X. Duan, Layered double hydroxides toward electrochemical energy storage and conversion: design, synthesis and applications, Chem. Commun. 51 (2015) 15880–15893. [9] H. Yin, Z. Tang, Ultrathin two-dimensional layered metal hydroxides: an emerging platform for advanced catalysis, energy conversion and storage, Chem. Soc. Rev. 45 (2016) 4873–4891. [10] D. Zhang, H. Wang, G. Chen, H. Wan, N. Zhang, X. Liu, R. Ma, Post-synthesis isomorphous substitution of layered Co–Mn hydroxide nanocones with graphene oxide as high-performance supercapacitor electrodes, Nanoscale 11 (2019) 6165–6173. [11] B. Jia, R. Hao, Z. Huang, P. Hu, L. Li, Y. Zhang, L. Guo, Creating ultrathin amorphous metal hydroxide and oxide nanosheet libraries, J. Mater. Chem. A 7 (2019) 4383–4388. [12] X. Chen, X. Zhong, B. Yuan, S. Li, Y. Gu, Q. Zhang, G. Zhuang, X. Li, S. Deng, J.g. Wang, Defect engineering of nickel hydroxide nanosheets by Ostwald ripening for enhanced selective electrocatalytic alcohol oxidation, Green Chem. 21 (2019) 578–588. [13] J. Yu, Q. Wang, D. O'Hare, L. Sun, Preparation of two dimensional layered double hydroxide nanosheets and their applications, Chem. Soc. Rev. 46 (2017) 5950–5974. [14] W. He, H. Qiu, J. Meng, B. Liu, J. Cui, Y. Zhang, Microwave-assisted synthesis of nano petal-like α-Ni(OH)2/RGO and its electrochemical performance, J. Alloy. Comp. 788 (2019) 183–190. [15] N. Hussain, W. Yang, J. Dou, Y. Chen, Y. Qian, L. Xu, Ultrathin mesoporous F-doped α-Ni(OH)2 nanosheets as an efficient electrode material for water splitting and supercapacitors, J. Mater. Chem. A 7 (2019) 9656–9664. [16] H. Tong, S. Yue, F. Jin, L. Lu, Q. Meng, X. Zhang, Honeycomb-like NiCo2O4@Ni (OH)2 supported on 3D N−doped graphene/carbon nanotubes sponge as an high performance electrode for Supercapacitor, Ceram. Int. 44 (2018) 3113–3121. [17] D. Ba, Y. Li, Y. Sun, Z. Guo, J. Liu, Directly grown nanostructured electrodes for high-power and high-stability alkaline nickel/bismuth batteries, Sci. China Mater. 62 (2019) 487–496. [18] J. Lin, Y. Liu, Y. Wang, H. Jia, S. Chen, J. Qi, C. Qu, J. Cao, W. Fei, J. Feng, Designed

[23]

[24]

[25]

[26]

[27] [28]

[29]

[30]

[31]

[32]

[33]

[34] [35]

[36]

[37]

[38]

[39]

20817

formation of NiO@C@Cu2O hybrid arrays as battery-like electrode with enhanced electrochemical performances, Ceram. Int. 43 (2017) 15410–15417. J.-Q. Xie, Y.-Q. Ji, J.-H. Kang, J.-L. Sheng, D.-S. Mao, X.-Z. Fu, R. Sun, C.-P. Wong, In situ growth of Cu(OH)2@FeOOH nanotube arrays on catalytically deposited Cu current collector patterns for high-performance flexible in-plane micro-sized energy storage devices, Energy Environ. Sci. 12 (2019) 194–205. W. Ma, L. Wang, J. Xue, H. Cui, A bottom-up strategy for exfoliation-free synthesis of soluble α-Ni(OH)2 monolayer nanosheets on a large scale, RSC Adv. 6 (2016) 85367–85373. X. Zhang, S. Wang, L. Xu, T. He, F. Lu, H. Li, J. Ye, Controllable synthesis of crosslinked CoAl-LDH/NiCo2S4 sheets for high performance asymmetric supercapacitors, Ceram. Int. 43 (2017) 14168–14175. H. Liu, T. Yu, D. Su, Z. Tang, J. Zhang, Y. Liu, A. Yuan, Q. Kong, Ultrathin Ni-Al layered double hydroxide nanosheets with enhanced supercapacitor performance, Ceram. Int. 43 (2017) 14395–14400. D.-K. Cho, I.-K. Park, Evolution of structural and chemical properties of CoAl-based layered double hydroxides grown on silicon substrate, Ceram. Int. 44 (2018) 8556–8561. K. Yan, M. Sheng, X. Sun, C. Song, Z. Cao, Y. Sun, Microwave synthesis of ultrathin nickel hydroxide nanosheets with iron incorporation for electrocatalytic water oxidation, ACS Appl. Energy Mater. 2 (2019) 1961–1968. B.-H. Liu, S.-H. Yu, S.-F. Chen, C.-Y. Wu, Hexamethylenetetramine directed synthesis and properties of a new family of α-nickel hydroxide Organic−Inorganic hybrid materials with high chemical stability, J. Phys. Chem. B 110 (2006) 4039–4046. Y. Li, H. Peng, X. Wei, P. Xiao, Controlled growth of hierarchical nickel and cobalt hybrid inorganic–organic nanosheet-supported nanowires for energy storage, CrystEngComm 19 (2017) 1555–1563. J.J. William, I.M. Babu, G. Muralidharan, Spongy structured α-Ni(OH)2: facile and rapid synthesis for supercapattery applications, Mater. Lett. 238 (2019) 35–37. F. Liu, X. Chu, H. Zhang, B. Zhang, H. Su, L. Jin, Z. Wang, H. Huang, W. Yang, Synthesis of self-assembly 3D porous Ni(OH)2 with high capacitance for hybrid supercapacitors, Electrochim, Acta 269 (2018) 102–110. H. Qiu, S. An, X. Sun, H. Yang, Y. Zhang, W. He, Excellent performance MWCNTsGONRs/Ni(OH)2 electrode for outstanding supercapacitors, Ceram. Int. (2019), https://doi.org/10.1016/j.ceramint.2019.06.059. D. Wang, B. Guan, Y. Li, D. Li, Z. Xu, Y. Hu, Y. Wang, H. Zhang, Morphologycontrolled synthesis of hierarchical mesoporous α-Ni(OH)2 microspheres for highperformance asymmetric supercapacitors, J. Alloy. Comp. 737 (2018) 238–247. L. Jiang, Y. Qiu, P. Luo, Y. Yu, Nickel hydroxide-impregnated and -coated carbon nanotubes using an easily manipulated solvothermal route for supercapacitors, Ceram. Int. 42 (2016) 11634–11639. J. Zhao, S. Huang, L. Song, Z. Zhao, Gas-liquid diffusion synthesis of different Ni (OH)2 nanostructures for their supercapacitive performance, Chem. Phys. (2019) 110395. T. Xia, X. Zhang, J. Zhao, Q. Li, C. Ao, R. Hu, Z. Zheng, W. Zhang, C. Lu, Y. Deng, Flexible and conductive carbonized cotton fabrics coupled with a nanostructured Ni (OH)2 coating for high performance aqueous symmetric supercapacitors, ACS Sustain. Chem. Eng. 7 (2019) 5231–5239. L. Liu, Y. Hou, Y. Gao, N. Yang, J. Liu, X. Wang, Co doped α-Ni(OH)2 multipledimensional structure electrode material, Electrochim. Acta 295 (2019) 340–346. A.C. Cardiel, K.J. McDonald, K.-S. Choi, Electrochemical growth of copper hydroxy double salt films and their conversion to nanostructured p-type CuO photocathodes, Langmuir 33 (2017) 9262–9270. S.K. Padhi, S.N. Gottapu, M.G. Krishna, Electron-beam irradiation induced transformation of Cu2(OH)3NO3 nanoflakes into nanocrystalline CuO, Nanoscale 8 (2016) 11194–11201. Y. Ma, J. Chu, Z. Li, D. Rakov, X. Han, Y. Du, B. Song, P. Xu, Homogeneous metal nitrate hydroxide nanoarrays grown on nickel foam for efficient electrocatalytic oxygen evolution, Small 14 (2018) 1803783. P. Chang, H. Mei, Y. Zhao, W. Huang, S. Zhou, L. Cheng, 3D structural strengthening urchin-like Cu(OH)2-Based symmetric supercapacitors with adjustable capacitance, Adv. Funct. Mater. (2019) 1903588. Z. Zhai, Y. You, L. Ma, D. Jiang, F. Li, H. Yuan, M. Zheng, W. Shen, One-step in situ self-assembly of cypress leaf-like Cu(OH)2 nanostructure/graphene nanosheets composite with excellent cycling stability for supercapacitors, Nanoscale Res. Lett. 14 (2019) 167.