Ru single atoms induce surface-mediated discharge in Na-O2 batteries

Abstract

Sodium (Na) O2 batteries have high energy density and low cost. However, high polarization, complex discharge products, and low Coulombic efficiency (CE) lead to poor cyclability. Here, we proposed an atomically dispersed Ru catalyst on nitrogen-doped graphene for Na-O2 batteries. The catalysts enable the discharge to proceed via a surface-mediated route, which leads to uniform deposition of Na2-xO2 and low polarization during recharge. The first-principle calculation revealed that Ru-N4 complex in the catalyst has strong chemical adsorption to intermediate superoxides, facilitating uniform deposition and enhancing rapid kinetics. In contrast, Ru nanoparticles, despite the catalytic activity, induce bulk deposition via a solution-mediated route because the exposed graphene surface shows weak interaction to superoxides, thereby lowering CEs and cyclability. In brief, the atomically-dispersed Ru catalyst endows Na-O2 batteries with excellent electrochemical properties via a surface-mediated discharge.