Sulfides/3D reduced graphene oxide composite with a large specific surface area for high-performance all-solid-state pseudocapacitors

Exploring highly efficient electrode materials is crucial for advancing clean energy storage devices such as pseudocapacitors (PCs). Transition-metal sulfides (TMSs), typically involving conventionally stoichiometric ternary components (such as NiCo2S4 and Ni2CoS4), are suggested as promising electrode nanomaterials for PCs. Herein, a large-specific-surface-area NiS2/CoS2 composite anchored on three-dimensional reduced graphene oxide (NiS2/CoS2/3DGO) is prepared by the sulfuration of a needle-like NiCo-hydroxycarbonate precursor grown on the 3DGO support. The NiS2/CoS2/3DGO composite is endowed with the following advantages: CoS2 and NiS2 composite, a large specific surface area (200.48 m(2) g(-1)) and narrow mesoporous size distribution, as well as high conductivity. The composite electrode indeed delivers a highly attractive capacitance of 2451 F g(-1) at 1 A g(-1), which is comparable or superior to most TMS electrodes reported previously. Furthermore, the all-solid-state NiS2/CoS2/3DGO//activated carbon for PCs achieves a decent energy density and power density at 1 A g(-1), and an attractive reversible capacitance retention of 97.2% after 5000 cycles at the high current density of 20 A g(-1). Such an improvement strategy can be extended for constructing diverse transition-metal sulfides and phosphides as electrode materials for energy storage.