Ni-modified Co3O4 with competing electrochemical performance to noble metal catalysts in both oxygen reduction and oxygen evolution reactions

The commercial viability of zinc-air batteries (ZABs) depends upon the availability of cost-effective and high-performance bifunctional electrocatalyst, which can simultaneously accelerate both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Noble metal catalysts suffer from poor cycling stability and cost ineffectiveness. Here we report on a Ni-modified spinel Co3O4 catalyst, which exhibits competing electrochemical properties to Pt/C in ORR and to RuO2 in OER. A ZAB cell fabricated with the catalyst as cathode and Zn as anode exhibits a specific capacity of 803 mAh/g and a cycling stability of 240 h at 5 mA cm−2, comparable to commercial noble metal catalysts. Computational calculations reveal that Ni partially substitutes tetrahedral Co sites in spinel Co3O4 to induce the formation of oxygen vacancies, which play an important role in hindering peroxide formation and enhancing electron conductivity. The presence of Ni in Co3O4 also weakens the interaction between surface Co and OH*, lowering the overpotentials of ORR and OER.