Origin of Spin‐State Precise Modulation for Enhanced Oxygen Evolution Activity: Effect of Secondary Coordination Sphere

Abstract The process of oxygen evolution reaction (OER) is crucial for energy storage and conversion, and the spin electronic structure of catalyst significantly influences its catalytic activity. Precisely regulating the spin electronic structures of metal active centers with intermediate spin (IS) states is challenging but important. This study presents a general method for achieving spin‐state precise modulation by altering the secondary coordination sphere (SCS) in Fe‐substituted LaCo 1‐ x Fe x O 3 perovskites, denoted as Co 6‐ y −[Co]−Fe y ( y = 0–6). The concentration‐dependent SCSs can precisely regulate the spin state of Co 3+ from high‐spin (HS) to IS and low‐spin (LS) state by tuning the Co─O binding energy of primary coordination sphere (PCS) to ≈567 KJ mol −1 . The binding energy demonstrates a strong negative correlation with the spin state of Co 3+ , serving as a quantitative descriptor for precise spin‐state modulation. Furthermore, a universal optimal doping concentration is proposed for generating IS‐state Co 3+ with the best OER activity, ranging from 1/( m +1) to 2/( m +1) in M‐doped ACo 1‐ x M x O y system with the coordination number of m . As a proof‐of‐concept, the LaCo 7/9 Fe 2/9 O 3 with IS Co 3+ exhibits significantly enhanced OER activity, almost six times higher than the control samples (without IS Co 3+ ). These findings provide new insights into spin‐state modulation for effective OER catalysts.