  Oxygen evolution reaction (OER) with intractable high overpotential is the
rate-limiting step for rechargeable metal-air battery, water electrolysis
systems, and solar fuels devices. There exists a spin state transition from
spin singlet OH-/H2O reactant to spin triplet O2 product, which has not
received enough attention yet. In this perspective, we attempt to retrospect
electron behaviours during the whole OER process, with the consideration of
spin attribute. Regardless of the adopted mechanisms by different
electrocatalysts, for example, adsorbate evolution mechanism (AEM) or lattice
oxygen mechanism (LOM), the underlying rationale is that active sites have to
extract three in four electrons with the same spin direction before the
formation of O=O. This spin-sensitive nature of OER superimposes additional
high requirements on the electrocatalysts, especially on the spin structure, to
compliment the fast electron transfer in the interface with spin selection and
smoothly delivery afterwards. When optimizing the geometric and electronic
structures catering for the spin-sensitive OER, awareness of the couplings
between spin, charge, orbital and lattice is necessary. Some spin-correlated
physical properties, such as (1) crystal field, (2) coordination, (3)
oxidation, (4) bonding, (5) eg electron number, (6) conductivity and (7)
magnetism, are also discussed briefly. It is hoped that our perspective could
shed lights on the underlying physics of the slow kinetics of OER, providing a
rational guidance for more effective energy conversion electrocatalysts
designs.
