Synergistic Tuning of CoO/CoP Heterojunction Nanowire Arrays as Efficient Bifunctional Catalysts for Alkaline Overall Water Splitting

Abstract Bifunctional electrocatalysts with superior activity and durability are of great importance for electrocatalytic water splitting. Herein, hierarchical structured CoO/CoP heterojunctions are successfully designed as highly efficient and freestanding bifunctional electrocatalysts toward overall water splitting. The unique microstructure combining two‐dimensional nanosheets with one‐dimensional nanowires enables numerous exposed active sites, shortened ion‐diffusion pathways, and enhanced conductivity, significantly improving performance. Such freestanding electrodes achieve high current density over 400 mA cm−2 at low overpotentials and have exceptional electrocatalytic activity as well as long‐term durability for both hydrogen and oxygen evolution reactions under alkaline conditions. Remarkably, a high current density of 20 mA cm−2 is generated at a low cell voltage of 1.56 V in an alkaline water electrolyzer, originating from synergistic interactions between CoO and CoP exposing active sites and facilitating charge transfer and enhancing kinetics. This work provides new insight into designing low‐cost but high‐performance bifunctional electrocatalysts for practical water splitting.