A generalized one-step in situ formation of metal sulfide/reduced graphene oxide nanosheets toward high-performance supercapacitors

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 two-dimensional 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 capacitances of 1526 and 988 F g−1 at 2 and 20 A g−1, respectively. The supercapacitors based on CoNi2S4/rGO showcase an operation potential window of 1.6 V, and energy density of 54.8 W h kg−1 at the power density of 798 W kg−1. The capacitance retention of the supercapacitor is about 93.7% after 8000 cycles at 3 A g−1. 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.