Bird Nest-Like Fe₃O₄/CoO_x Nanosphere Heterojunctions with Amorphous/Crystalline Structure for Enhanced Electrochemical Oxygen Evolution

Developing efficient electrocatalysts is very important for water electrolysis technology to deal with the energy crisis. The oxygen evolution reaction (OER) in the semireaction of electrolytic water is a crucial step. Herein, we report a facial strategy to fabricate the bird nest-like Fe 3 O 4 /CoO x (BN-Fe 3 O 4 /CoO x ) nanosphere heterojunctions with amorphous/crystalline (a/c) structure through cation-exchange and subsequent calcination treatment in a reducing Ar/H 2 atmosphere. Owing to its unique structure and the electron state near the heterogeneous interface, the BN-Fe 3 O 4 /CoO x nanosphere exhibits a very competitive overpotential of 286 mV at the current density of 10 mA cm –2 for OER with a low Tafel slope of 55.51 mV dec –1 in 1.0 M KOH, and long-term durability for more than 20 h. This work may provide an idea and a convenient method for the preparation of a/c-heterostructure electrocatalysts.