Bifunctional Electrocatalyst Spinel Oxide Co₂GeO₄ and Ni₂GeO₄ with High Oxygen Evolution Reaction and Oxygen Reduction Reaction Activity

Bifunctional catalysts for oxygen evolution reduction (OER) and oxygen reduction reaction (ORR) are key renewable energy technologies including metal–air batteries and water splitting. In this work, a solid-state sintering approach was employed to prepare spinel-structured bimetallic oxides Co₂GeO₄ and Ni₂GeO₄ with remarkable bifunctional catalytic activity. Compared to Ni₂GeO₄ and Co₃O₄, Co₂GeO₄ demonstrates a larger density of oxygen vacancies, leading to an increased abundance of active sites and superior OER and ORR activities. Electrochemical measurements were carried out in alkaline media, the material requiring a mere overpotential of 263 mV to attain a current density of 10 mA cm⁻². Moreover, Co₂GeO₄ exhibited exceptional stability, maintaining a stable potential for 40 h at a current density of 1 mA cm⁻². The calculation revealed that the high stability is attributed to the robust Ge-O bonds, which stabilize the Ge-O4 tetrahedrons within the spinel framework. This study possesses significant potential in guiding the development of highly efficient bifunctional electrocatalysts for both OER and ORR.