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

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.