Understanding the Mechanism of the Oxygen Evolution Reaction with Consideration of Spin

Abstract: The oxygen evolution reaction (OER) with its intractably high overpotentials is the rate-limiting step in many devices, including rechargeable metal–air batteries, water electrolysis systems and solar fuel devices. Correspondingly, spin state transitions from spin singlet OH–/H2O reactants to spin triplet O2 product have not yet received enough attention. In view of this, this article will discuss electron behaviours during OER by taking into consideration of spin attribute. The main conclusion is that, regardless of the possible adopted mechanisms (the adsorbate evolution mechanism or the lattice oxygen mechanism), the underlying rationale of OER is that three in four electrons being extracted from adsorbates should be in the same spin direction before O=O formation, superimposing high requirements on the spin structure of electrocatalysts. Therefore, upon fully understanding of the OER mechanism with considerations of spin, the awareness of the coupling between spin, charge, orbital and lattice parameters is necessary in the optimization of geometric and electronic structures in transition metal systems. Based on this, this article will discuss the possible dependency of OER efficiency on the electrocatalyst spin configuration, and the relevance of well-recognized factors with spin, including the crystal field, coordination, oxidation, bonding, the eg electron number, conductivity and magnetism. It is hoped that this article will clarify the underlying physics of OER to provide rational guidance for more effective design of energy conversion electrocatalysts. Graphic Abstract: [Figure not available: see fulltext.]