Facile Electrochemical Synthesis of Highly Efficient Copper-Cobalt Oxide Nanostructures for Oxygen Evolution Reactions

Nanostructured copper-cobalt oxide (Cu_xCo_3-xO₄, CCO) electrodes are grown directly on conducting substrates via electrochemical deposition; then, various factors (e.g., oxygen vacancies, electrochemically active surface area, and electrical conductivity) affecting their electrocatalytic activity for oxygen evolution reactions (OERs) are studied. The observed OER performance decreases when increasing the annealing temperature due to the nanostructure deformation and agglomeration and the decreased number of oxygen vacancies, electrochemically active surface area, and electrical conductivity. An optimized nanopetal structure of Cu_xCo_3-xO₄ (x = 0.95, annealed at 200 °C) shows a considerably high Faradaic efficiency (∼93%) with a remarkably low overpotential (∼230 mV) at a benchmark current density (J) of 10 mA cm^-2; at the same J in an alkaline solution (1 M KOH) for OER, it also exhibits high durability (up to 100 h). This study provides a complete guide for designing efficient and robust spinel-type CCO electrocatalysts through a facile electrochemical route.