Oxygen-Vacancy Rich Co3O4/CeO2 Interface for Enhanced Oxygen Reduction and Evolution Reactions

Oxygen reduction and evolution reactions (ORR and OER, respectively) are the two most extensively studied reactions in electrochemistry. Herein, we report the synthesis of Co3O4/CeO2/GNP (GNP = graphene nanoplatelet) electrocatalyst for ORR and OER that exhibits an early onset potential (0.85 V) and half-wave potential (E-1/2) of 0.69 V for ORR. The reported catalyst is highly durable with 87.6% retention of its initial current after a 6 h chronoamperometry test compared to 72.5% by Pt/C. It exhibits a negligible shift of E-1/2 after 10,000 potential cycles for ORR. Heterogeneous oxide/oxide interfaces, oxygen vacancies and semicrystalline nature are inferenced to play a dominant role in altering the collective catalytic efficiency of Co3O4/CeO2/GNP. High concentration of oxygen vacancy defects (68%) in Co3O4/CeO2/GNP is presumed to play a dominant role here. The catalyst is bifunctional for ORR and OER with a bifunctionality index of 0.98 V and operates at an overpotential of eta(10) = 440 mV for OER. Ex situ X-ray absorption studies indicate an increased average oxidation state of Co by 15% in Co3O4/CeO2/GNP compared to Co3O4/GNP, aiding in preserving its inherent catalytic nature of spinel Co3O4.