Green combustion synthesis of Co₃O₄-CoO heterostructures for efficient alkaline oxygen evolution reaction

Replacing noble metal-based OER electrocatalysts demands economical and high-performance alternatives for energy saving industrial applications. This study explores an innovative combustion synthetic technique to produce a Co₃O₄-CoO (CoOPE-600) heterophase using pomegranate peel extract as a green source of fuel. The optimized CoOPE-600 electrocatalyst showed outstanding electrochemical performance for oxygen evolution reaction (OER), requiring an overpotential of 231 mV to achieve 10 mA cm^-2. The kinetics of CoOPE-600 electrolysis was examined via impedance analysis, demanding a very small activation energy of 5.2 kJ mol^-1 compared to Co₃O₄-600 (6.4 kJ mol^-1) to complete the reaction, as supported by an Arrhenius plot. The combined contribution of CoO and Co₃O₄ phases increased the catalytically active surface area to expose abundant active sites, increased oxygen vacancies and promoted intimate contact between CoOPE-600 and the electrolyte to facilitate charge transfer around Co active sites for remarkable activity. An alkaline-/solar-driven electrolyzer fabricated with the anode CoOPE-600 required 1.56 V along with notable long-term stability, indicating promising prospects for practical applications. The current research provides a novel green approach for the synthesis of an efficient non-precious electrocatalyst for water splitting.