A generalized one-step in situ formation of metal sulfide/reduced graphene oxide nanosheets toward high-performance supe
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Published online 8 July 2020 | https://doi.org/10.1007/s40843-020-1371-y
A generalized one-step in situ formation of metal sulfide/reduced graphene oxide nanosheets toward high-performance supercapacitors 1†
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Kaiyang Zhang , Yuanhao Wei , Jun Huang , Yingbo Xiao , Weizu Yang , Ting Hu , 1* 1,2* Kai Yuan and Yiwang Chen ABSTRACT Metal sulfides are promising candidates for supercapacitors, but their slow reaction kinetics hinders their electrochemical performance. Large electrochemical surface area and combination with conductive carbon are potential methods to improve their capacitive performance. However, seeking for a generalized and simple approach to prepare twodimensional composites of metal sulfide and conductive carbon for supercapacitors is challengeable. Herein, a generalized and facile one-step pyrolysis method was designed for in situ growth of cobalt nickel sulfides (CoNi2S4) on reduced graphene oxide (rGO) nanosheets (CoNi2S4/rGO) under mild conditions. The as-prepared CoNi2S4/rGO materials possess the nanoparticles-on-nanosheets structure, which is effective to provide a myriad of active sites and optimized electron/ion diffusion pathway. Benefiting from those advantages, the resultant CoNi2S4/rGO electrodes exhibit impressed specific −1 −1 capacitances of 1526 and 988 F g at 2 and 20 A g , respectively. The supercapacitors based on CoNi2S4/rGO showcase an operation potential window of 1.6 V, and energy density of −1 −1 54.8 W h kg at the power density of 798 W kg . The capacitance retention of the supercapacitor is about 93.7% after −1 8000 cycles at 3 A g . Moreover, a series of metal sulfide/rGO hybrids are obtained by this generalized strategy, which could be extended to construct electrode materials for various energy devices. Keywords: metal sulfide, reduced graphene oxide, in situ growth, two-dimensional, supercapacitors
INTRODUCTION Developing sustainable energy resources is one of the 1 2 3
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significant channels to meet the challenge of fossil fuel overconsumption [1–4]. Supercapacitors (SCs) have attracted extensive attentions due to their special advantages including high security, low cost, high power density and long discharging/charging cycles [5–8]. However, the feature of low energy density restricts further development of SCs [9–11]. Adopting high capacitance materials is an effective way to expanding energy 2 density of SCs according to the equation E=0.5CV , where C and V are the specific capacitance and voltage window of the devices, respectively [12–14]. Transitional metal sulfides possess higher capacitance than their oxide counterparts because of the lower electronegativity of sulfur, rendering them promising candidates for SCs [15– 17]. Especially, mixed metal sulfides such as NiCo2S4 [18– 20], MnCo2S4 [21], CuCo2S4 [22] possess much more significant electrochemical activity and specific capacitance in contrast to single-metallic sulfides because of the synergistic effect among different components [23,24]. Ternary nickel cobalt sulfides (NCSs), a typical
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