On the Lattice Oxygen Evolution Mechanism: Avoiding Pitfalls

The oxygen evolution reaction (OER) is often designated as the enigma in water electrolysis because the development of active and stable OER catalysts is a challenging and formidable task. While ab initio theory in the density functional theory approximation initially focused on the mechanistic description via the OH, O, and OOH adsorbates, in recent years the lattice oxygen evolution reaction (LOER) mechanism attracted increasing attention, given that the LOER is seen as the main reason for catalyst instability under anodic potential conditions. The present concept article critically analyzes the LOER and indicates pitfalls in the interpretation of this mechanistic pathway. A method to assess the energetics of the LOER in relation to conventional OER mechanisms by the compilation of free-energy diagrams is introduced, which may contribute to enhance our understanding of the competing LOER and OER on the atomic scale. Further works are urgently needed to comprehend the interrelationship for the evolution of gaseous oxygen from the electrolyte or the crystal lattice.