Store or catalyze? The M–O bond decides

Abstract

The nature of the metal–oxygen (M–O) bond is a key electronic factor that decides if an oxide/hydroxide serves as a charge-storage medium or an electrocatalyst. When the M–O bond is highly ionic and electronically stable, oxygen remains inactive. In this case, the material stores charge through fast, reversible metal-centered redox, which is typical of battery-like and pseudocapacitive behavior. On the other hand, increasing M–O covalency changes the electronic environment. Antibonding states become accessible, oxygen becomes chemically active, and the M–O unit can perform the bond-making and bond-breaking steps needed for catalytic activity. Small, intentional changes in M–O covalency—such as doping, defect engineering, oxidation-state tuning, or lattice strain—can switch materials between these two modes. These changes decrease the potential barriers and allow for the formation of oxygen-evolving intermediates. This view brings these findings together in a clear framework where M–O covalency acts as a switch between “store” and “react.”