Hierarchical NiCo2O4 Hollow Microcuboids as Bifunctional Electrocatalysts for Overall Water‐Splitting

Abstract Bifunctional electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline electrolyte may improve the efficiency of overall water splitting. Nickel cobaltite (NiCo2O4) has been considered a promising electrode material for the OER. However, NiCo2O4 that can be used as an electrocatalyst in HER has not been studied yet. Herein, we report self‐assembled hierarchical NiCo2O4 hollow microcuboids for overall water splitting including both the HER and OER reactions. The NiCo2O4 electrode shows excellent activity toward overall water splitting, with 10 mA cm−2 water‐splitting current reached by applying just 1.65 V and 20 mA cm−2 by applying just 1.74 V across the two electrodes. The synthesis of NiCo2O4 microflowers confirms the importance of structural features for high‐performance overall water splitting.