Less active CeO2 regulating bifunctional oxygen electrocatalytic activity of Co3O4@N-doped carbon for Zn–air batteries

Abstract

Non-precious bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play a pivotal role in regenerative fuel cells and rechargeable metal–air batteries. In this contribution, less active CeO₂ is introduced for regulating the ORR/OER bifunctional activity of Co₃O₄@N-doped carbon (NC). The introduced CeO₂ plays essential roles in increasing the surface contents of Co²⁺, Co³⁺ and N species in CeO₂/Co₃O₄@NC for ORR/OER processes, while still maintaining hierarchical porosity and large specific surface area. Furthermore, the surface acid–base properties for the adsorption of oxygen molecules (for the ORR) and activation of water molecules (for the OER) and the charge transfer efficiency are also improved by the introduced CeO₂. As a result, significantly enhanced ORR/OER bifunctional activity is achieved for the optimal and desired electrocatalyst, i.e., CeO₂/Co₃O₄@NC. Its bifunctional activity is comparable or even superior to that of the benchmarked 20 wt% Pt/C (for the ORR) and IrO₂ (for the OER), respectively. In the applications of Zn–air batteries, the battery with CeO₂/Co₃O₄@NC still exhibits higher performance than the battery with mixed 20 wt% Pt/C + IrO₂, due to its outstanding bifunctional activity toward the ORR and OER.