Spin State Engineering of Active Sites in Oxygen Electro‐Catalysis

ABSTRACT The sluggish kinetics of oxygen electro‐catalysis, encompassing both oxygen evolution (OER) and reduction (ORR) reactions constitute a major bottleneck for energy conversion and storage devices like water electrolyzers and rechargeable metal‐air batteries. The spin state transitions from singlet ground‐state OH − /H 2 O reactants to triplet ground‐state O 2 products in OER (and vice versa in ORR) play a critical role in catalytic performance. This review presents an in‐depth exploration of spin state engineering of active sites in oxygen electro‐catalysts. We begin by elucidating the origin of spin states based on crystal field theory and the distinctions among low‐spin (LS), intermediate‐spin (IS) and high‐spin (HS) configurations. Subsequently, we discuss strategies for modulating spin states of active sites, supported by examples from oxygen electro‐catalysis. Advanced characterization techniques, including x‐ray absorption/Emission spectroscopy (XAS/XES), magnetic susceptibility measurements, electron paramagnetic resonance (EPR), Mössbauer spectroscopy, and density functional theory (DFT)/molecular dynamic (MD) simulations, are critically analyzed. Finally, we propose future research directions to advancing spin‐state‐related electrocatalysis.