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. This change decrease the potential barriers and allows 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.”