Surface/Interface Engineering of Hierarchical MoO2/MoNi4@Ru/RuO2 Heterogeneous Nanosheet Arrays for Alkaline Water Electrolysis with Fast Kinetics

Comprehensive Summary Realizing the hydrogen economy by water electrolysis is an attractive approach for hydrogen production, while the efficient and stable bifunctional catalysts under high current densities are the bottleneck that limits the half‐cell reactions of water splitting. Here, we propose an approach of hydrothermal and thermal annealing methods for robust MoO 2 /MoNi 4 @Ru/RuO 2 heterogeneous cuboid array electrocatalyst with multiplying surface‐active sites by depositing a monolayer amount of Ru. Benefiting from abundant MoO 2 /MoNi 4 @Ru/RuO 2 heterointerfaces, MoO 2 /MoNi 4 @Ru/RuO 2 heterogeneous cuboid array electrocatalysts effectively drive the alkaline water splitting with superior hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances. The synthesized MoO 2 /MoNi 4 @Ru/RuO 2 has high HER activity, which realizes the working overpotentials of 48 mV at 50 mA·cm –2 , further achieving overpotentials of 230 mV for industry‐level 1000 mA·cm –2 in alkaline water electrolysis. Moreover, it also showed an enhanced OER activity than commercial RuO 2 with a small overpotential of 280 mV at 200 mA·cm –2 in alkaline media. When building an electrolyzer with electrodes of (–)MoO 2 /MoNi 4 @Ru/RuO 2 IIMoO 2 / MoNi 4 @Ru/RuO 2 (+), a cell voltage of 1.63 V and 1.75 V is just required to support the current density of 200 mA·cm –2 and 500 mA·cm –2 in alkaline water electrolysis, much lower than that of the electrolyzer of (–)Pt/CIIRuO 2 (+). This work demonstrates that MoO 2 /MoNi 4 @Ru/RuO 2 heterogeneous nanosheet arrays are promising candidates for industrial water electrolysis applications, providing a possibility for the exploration of water electrolysis with a large current density.