Polyoxometalate-Derived NiS-MoS ₂ and FeS-MoS ₂ Heterostructures Decorated on Reduced Graphene Oxide for Efficient Overall Water Splitting

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 (MxSy = FeS, NiS, CoS2) with MoS2 nanosheets, all of the heterostructures achieved obviously enhanced bifunctional activity due to the interfacial interaction and synergism between MxSy 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.