Beyond Volcano Top of Transition Metal‐Based Electrocatalysts Triggered by Spin State Modulation

Abstract Although modulating the spin state of transition metal (TM)‐based catalysts has emerged as a strategy to improve the sluggish kinetics of oxygen evolution reaction (OER), the quantitative correlation between spin state and OER activity remains elusive, especially at the experimental level. This hinders the rational design of high‐performance electrocatalysts. Here, ferromagnetic CoSe 2 polycrystalline nanoparticles by hydrothermal and vapor anion exchange methods are synthesized. Zn with various concentrations is doped to regulate the spin quantum number ( S ) of Co. The results show that the saturation magnetization of Co 0.9 Zn 0.1 Se 2 , as a macroscopic feature of S , exhibits a remarkable 18‐fold enhancement from 0.74 to 14.2 emu g −1 . Such enhanced S achieves an extraordinary enhancement of OER activity by 448%, surpassing its traditional volcano top. Meanwhile, the OER activity demonstrates a strong linear relationship with S , clarifying the effect of total S in bulk on the surface active sites. This work systematically quantifies the spin‐catalysis relationship and formulates the guidelines for precision design of spin‐optimized electrocatalysts.