Single-atom catalysts of TM–porphyrin for alkali oxygen batteries: reaction mechanism and universal design principle

Abstract

Single-atom catalysts (SACs) have been intensively explored for many electrochemical reactions, but rarely in nonaqueous alkali oxygen batteries. A picture (activity trend, reaction mechanism and design principle) of SACs for nonaqueous alkali oxygen batteries remains to be built up. Here, using first-principles, we construct such a picture by systematically investigating the catalytic activities of SACs of transition metal–porphyrin (TM–porphyrin) in Li–O₂ batteries. Through fully exploring the possible reaction pathways, we reveal the reaction mechanism and chemical compositions of reaction products, and find that Fe/Co/Ni/Cu–porphyrin are promising cathode electrocatalysts for Li–O₂ batteries. The influences of various axial ligands on their catalytic performances are also studied. More importantly, based on the catalytic activities of free and axial ligand adsorbed Fe/Co/Ni/Cu–porphyrin, the adsorption free energy of LiO₂ is identified as a simple activity descriptor suitable for these cathode electrocatalysts. We further show that such a descriptor is also applicable for the catalytic activities of Fe/Co/Ni/Cu–porphyrin in Na–O₂ batteries. Our work not only provides a series of highly efficient SACs for alkali oxygen batteries, but also presents a universal design principle.