Asymmetric Site-Enabled O–O Coupling in Co3O4 for Oxygen Evolution Reaction

Abstract

The efficiency of hydrogen production from water electrolysis is mainly restricted by the sluggish oxygen evolution reaction (OER). The mainstream adsorbate evolution mechanism and lattice oxygen-mediated mechanism face a trade-off between performance and stability, while the diatomic oxygen mechanism (DOM) based on the O–O coupling provides a solution to overcome this limitation. However, the intrinsic principles that facilitate the O–O coupling remain unclear, which complicates material design. In this work, we use spinel Co₃O₄ as a model and identify that the asymmetric sites formed by the octahedral Co with O defects and the original octahedral Co are effective sites for O–O coupling. Based on this, we propose using the degree of asymmetry of the dual site as a descriptor to quantify the reaction free energy of rate-determining step along the DOM pathway, presenting a volcano plot relationship. Experimental validation shows that plasma-prepared Co₃O₄ enables O–O coupling, requiring only 287 and 420 mV overpotentials to achieve current densities of 10 and 1000 mA cm^–2 in 0.5 M H₂SO₄, respectively. This work demonstrates efficient sites for the OER along the DOM pathway in Co₃O₄, providing valuable insights for designing high-performance OER catalysts.