Polyoxometalate-Derived NiS-MoS₂ and FeS-MoS₂ Heterostructures Decorated on Reduced Graphene Oxide for Efficient...

Developing a feasible approach to improve both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performance of MoS₂ is important for the utilization of low-cost and earth-abundant non-noble metals toward efficient water splitting. Herein, we report a hydrothermal strategy to construct binary metal sulfide heterostructures supported on reduced graphene oxide (RGO) by utilizing polyoxometalates as precursors. By integrating the transition-metal sulfides (M_xS_y = FeS, NiS, CoS₂) with MoS₂ nanosheets, all of the heterostructures achieved obviously enhanced bifunctional activity due to the interfacial interaction and synergism between M_xS_y and MoS₂. Consequently, the NiS-MoS₂/RGO and FeS-MoS₂/RGO catalysts exhibited the lowest overpotentials at the current density of 10 mA cm^-2, which required only 132 mV for the HER and 231 mV for the OER, respectively. More importantly, a low cell voltage of 1.58 V was achieved for delivering an overall water-splitting current density of 10 mA cm^-2 by assembling the NiS-MoS₂/RGO and FeS-MoS₂/RGO into an electrolyzer. This work provides a feasible strategy for designing bimetal heterostructures to improve the water splitting performance of MoS₂-based catalysts.