Why and when does lattice oxygen participate in oxygen evolution?

Why does lattice oxygen contribute to the oxygen evolution reaction (OER) in some oxides and hydroxides, while remaining completely inactive in others that seem to have similar electronic properties? This Perspective argues that lattice oxygen redox does not occur merely due to high metal valence or strong metal-oxygen covalency. It only takes place when two linked conditions are met: (i) the oxidation of transition metals reaches an electronic saturation point that adds oxidative charge to oxygen ligands, and (ii) the lattice can structurally adapt to oxygen removal and vacancy healing during turnover. We demonstrate that various surface-engineering strategies-such as doping, creating heterostructures, modifying interlayers, and anchoring single atoms-work together by lowering charge-transfer energy, improving TM-O covalency, and making additional metal oxidation less stable. However, only materials with enough lattice flexibility can turn this electronic state into functional lattice oxygen redox. By separating the electronic basis of oxygen hole formation from the structural need for vacancy accommodation, this Perspective offers a chemistry-based framework that clarifies both the development and the scarcity of the lattice oxygen mechanism in OER catalysts.