Triple roles of Ni(OH)2 promoting the electrocatalytic activity and stability of Ni3S4@Ni(OH)2 in anion exchange membrane water electrolyzers

Developing high performance and durable electrocatalysts is crucial for the practical application of large-scale water splitting under high current density. Here, we constructed a Mott–Schottky heterojunction bifunctional electrocatalyst coating of Ni3S4 with Ni(OH)2 thin film supported on Ni foam substrate (Ni3S4@Ni(OH)2) for anion exchange membrane water electrolyzers (AEMWEs). Remarkably, the η500 is as low as 274.6 mV toward the hydrogen evolution reaction and 423.8 mV toward the oxygen evolution reaction. AEMWEs deliver a stable performance that achieves current densities of 500 and 1000 mA cm−2 at a cell voltage of 1.84 and 1.95 V, respectively. In particular, the Ni3S4@Ni(OH)2 exhibits durable stability for 100 h at 500 mA cm−2 without significant degradation and uses 0.75 kW·h of electricity less than commercial Ni foam electrode to produce each standard cubic meter of hydrogen gas at 500 mA cm−2. The excellent performance is ascribed to the triple roles of Ni(OH)2, which prevent the inner Ni3S4 from decomposing during the reaction process, promoting the dissociation of water and formation of adsorbed hydrogen intermediate and accelerating electron transfer ability due to the Mott–Schottky heterojunction between Ni(OH)2 and Ni3S4. This work sheds light on the development of advanced bifunctional electrocatalysts based on non-precious transition metals for AEMWEs.