Noble Metal-Free High-Entropy Oxide/Co-N-C Bifunctional Electrocatalyst Enables Highly Reversible and Durable Zn-Air Batteries

Abstract

Noble metal-free electrocatalysts for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are crucial to rechargeable metal-air batteries. Nanoporous high-entropy spinels have recently been studied as bifunctional ORR/OER electrocatalysts due to the adjustable surface electronic structure and catalytic activity. In this work, we adjust catalytic activities of HEO by varying the composition and proportion of the metal elements and find an optimal seven-component AlNiCoFeCrMoV prepared by a scalable two-step dealloying strategy. The seven-component HEO is highly active for OER while it exhibits a relatively poor ORR activity, much worse than the commercial Pt/C. Thus, the highly ORR active Co-N-C is rationally integrated with the seven-component HEO to construct a highly bifunctional HEO/Co-N-C nanocomposite electrocatalyst. Importantly, when used in a Zn-air battery, small charge/discharge voltage differences and ultralong lifespan (at 2, 5, 10 mA cm -2 ) can be achieved. This work highlights the rapid screening and rational design of highly bifunctional catalysts by function integration in multicomponent high-entropy system.

Keywords: composites, OER/ORR, metal-air batteries