Constructing defect-rich S-doped NiMoO4/Ni3S2 2D/2D heterostructures as highly efficient and stable bifunctional electrocatalysts for overall water splitting

The development of economical, efficient, and durable bifunctional catalyst for overall water splitting is an attractive and challenging task. Herein, a novel defect-rich 2D/2D heterostructure is constructed by vertically growing S-doped NiMoO4 (NiMoO4-S) nanosheets on nickel sulfide (Ni3S2) nanosheet arrays supported on nickel foam (NF) using a two-step hydrothermal method. Benefiting from the hierarchical sheet-on-sheet heterogeneous nanostructure and abundant oxygen vacancies for more active sites, efficient electronic/mass transfer, and fast gas release, the synthesized NiMoO4-S/Ni3S2/NF electrode exhibits excellent electrocatalytic performance for HER (110 mA cm -2 = 107 mV) and OER (150 mA cm -2 = 285 mV). The alkaline water electrolyzer with NiMoO4-S/ Ni3S2/NF as the positive and negative electrodes can provide a current density of 10 mA cm-2 with the potential of 1.52 V, which is below that of the commercial Pt||RuO2/NF system or many other reported systems. More importantly, the alkaline water electrolyzer offers a current density of 100 mA cm-2 at 1.85 V with outstanding durability of over 50 h. This research points to a promising route in designing transition metal-based bifunctional electrocatalysts for large-scale energy conversion applications.