Engineering heterostructured and hierarchical CoP/CoFeP nanosheet for effective oxygen evolution reaction in alkaline freshwater and seawater

Oxygen evolution reaction (OER) with sluggish kinetics plays a crucial role in the field of renewable energy conversion, and it is urgent but still challenging to develop highly active and stable OER electrocatalysts. Herein, heterostructured and hierarchical transition metal phosphide (CoP/CoFeP) nanosheet is prepared as a highperformance OER electrocatalyst. Strong electronic interaction is observed between CoP and CoFeP, which could regulate the electronic structure and promote the generation of high-valence cobalt. The hierarchical architecture is beneficial to enlarging the surface area. Consequently, CoP/CoFeP only needs an overpotential of 211 and 274 mV to afford a current density of 10 and 400 mA cm-2, respectively. Moreover, CoP/CoFeP could maintain superior electrocatalytic activity in alkaline seawater, which achieves 400 mA cm-2 with a potential lower than the thermodynamic potential of chloride oxidation. This work provides a deep understanding on the heterostructured transition metal phosphides for electrocatalytic OER and opens up a novel avenue to prepare highly active electrocatalysts.