Balance between oxygen 2p holes and oxygen vacancies for optimal water oxidation

Abstract

The emergence of the lattice oxygen-mediated mechanism (LOM) has triggered a paradigm shift in oxygen evolution reaction (OER) research from conventional metal-centered catalysis to the reactivity of lattice oxygen sites. In LOM scenario, one viewpoint is that the degree of metal-oxygen covalency controls the OER activity, while the other argument suggests the determining factor is oxygen vacancy. However, metal-oxygen covalency has a competing relationship with oxygen vacancy. Herein, it is demonstrated that the intrinsic OER activity of cobaltite perovskites would be more accurately described by considering two competing factors on the O sites, i.e., oxygen 2p hole (an indicator of metal-oxygen covalency) and oxygen vacancy simultaneously. The increment in oxygen 2p hole favors the LOM route but weakens the hydroxide affinity, whereas moderate oxygen vacancy mitigates the undesirable effects of high oxygen 2p hole. Specifically, the Sr₀.₉Y₀.₁CoO3-δ catalyst among Sr₁₋ₓYₓCoO₃ system has an ideal balance between oxygen 2p hole and oxygen vacancy, catalyzes OER via LOM, showing the optimal intrinsic activity. The proposed dual-parameter descriptor offers a coherent explanation for the OER activity of cobaltite perovskites, and more importantly, it would shed light on future design of efficient OER electrocatalysts under the classic Sabatier principle.