Two-electron redox chemistry via single-atom catalyst for reversible zinc–air batteries

Rechargeable zinc–air batteries (ZABs) are considered to be one of the most sustainable alternative systems in a post-lithium-ion future owing to their lowest possible dependency on critical raw materials and high theoretical energy densities. However, their performance is still not up to par with their potential because of the sluggish kinetics of the oxygen reduction reaction. Here we report a single-atom catalyst design that transforms the sluggish four-electron oxygen reduction reaction into a fast two-electron pathway and enables a zinc peroxide (ZnO2) chemistry in ZABs. With accessible FeN2S2 active sites on mesoporous graphene, the catalyst serves to promote transport of electrolyte, oxygen and electron and confines the growth of ZnO2, which would otherwise form dead products. As a result, as-fabricated ZAB in a neutral electrolyte shows a voltage as high as 1.2 V at 0.2 mA cm−2, a high round-trip efficiency of 61% and an excellent operation stability beyond ∼400 h. This work provides guidelines for the rational design of multifunctional cathodes and would accelerate the adoption of sustainable batteries in the metal–air category. Rechargeable zinc–air batteries are a sustainable energy storage system, but their performance is not yet competitive. Now a mesoporous single-atom catalyst steers the sluggish four-electron oxygen reduction reaction pathway to a faster two-electron process and enables highly reversible zinc–air batteries.