S-Block Potassium Single-atom Electrocatalyst with K-N4 Configuration Derived from K+ /Polydopamine for Efficient Oxygen Reduction.

Abstract

Currently, single-atom catalysts (SACs) research mainly focuses on transition metal atoms as active centers. Due to their delocalized s/p-bands, the s-block main group metal elements are typically regarded as catalytically inert. Herein, an s-block potassium SAC (K-N-C) with K-N4 configuration is reported for the first time, which exhibits excellent oxygen reduction reaction (ORR) activity and stability under alkaline conditions. Specifically, the half-wave potential (E1/2 ) is up to 0.908 V, and negligible changes in E1/2 are observed after 10,000 cycles. In addition, the K-N-C offers an exceptional power density of 158.1 mW cm-2 and remarkable durability up to 420 h in a Zn-air battery. Density functional theory (DFT) simulations show that K-N-C has bifunctional active K and C sites, can optimize the free energy of ORR reaction intermediates, and adjust the rate-determining steps. The crystal orbital Hamilton population (COHP) results showed that the s orbitals of K played a major role in the adsorption of intermediates, which was different from the d orbitals in transition metals. This work significantly guides the rational design and catalytic mechanism research of s-block SACs with high ORR activity.