Structure Engineering Enabled O-O Radical Coupling in Spinel Oxides for Enhanced Oxygen Evolution Reaction.

Developing cost-effective spinel oxide catalysts with both high oxygen evolution reaction (OER) activity and stability is crucial for advancing sustainable clean energy conversion. However, practical applications are often hindered by the activity limitations inherent in the adsorbate evolution mechanism (AEM) and the stability limitations associated with the lattice oxygen mechanism (LOM). Herein, we demonstrate structural changes induced by phase transformation in CoMn spinel oxides, which yield more active octahedral sites with shortened intersite distance. This structure optimization favors a direct O-O radical coupling mechanism, which circumvents the involvement of the *OOH intermediate and prevents overoxidation of the active sites, significantly enhancing both the OER activity and stability. Consequently, the optimized CoMn-400 catalyst exhibits an overpotential of 268 mV at 10 mA cm in 0.1 M KOH (310 mV for commercial RuO), and maintains negligible activity loss over 300 h' chronopotentiometry test at a current density of 100 mA cm. This simple strategy provides fundamental insights into transition metal oxide catalyst design and opens new possibilities for optimizing electrochemical energy conversion.