Recent advances in non-precious metal M-N-C-based composites as bifunctional electrocatalysts for rechargeable zinc-air batteries

Abstract

Non-precious single-atom M-N-C catalysts (M-N-C SACs) have attracted great attention due to their extreme metal utilization efficiency (100% in idea situation) and high activity for oxygen reduction reaction (ORR). However, their catalytic activity for oxygen evolution reaction (OER) is still unsatisfactory due to the lack of suitable active sites, which limited its commercial application in rechargeable zinc-air batteries (ZABs). Coupling the M-N-C SACs with an additional OER-active component has been confirmed as an efficient strategy to achieve bifunctional oxygen electrocatalysis.In this paper, we summarised the recent progress of non-precious metal M-N-C SACsbased composites as bifunctional electrocatalysts for rechargeable ZABs. The principle for oxygen electrocatalysis is generalized, and the structure-activity relationship between M-N-C SACs and OER-active components is also highlighted and discussed in detail. The prospects and main challenges for bifunctional oxygen electrocatalysts in ZABs are reviewed. This review aims to provide a deep insight and valuable reference for the development of a bifunctional oxygen electrocatalyst for rechargeable ZABs.This mechanism is referred to as the adsorption evolution mechanism (AEM).Similar to the ORR process, the theoretical minimum overpotential for the OER through AEM pathway on a single site is limited to 0.37 V by the scaling relations. In recent years, it has also been discovered that the OER can proceed through other mechanisms, thereby bypassing the limitations imposed by the scaling relations in the AEM pathway.The more extensively studied ones are the lattice oxygen mechanism (LOM) and the oxide path mechanism (OPM), [23] as shown in the Figure 4.