Manipulating the spin configuration by topochemical transformation for optimized intermediates adsorption ability in oxygen evolution reaction

The underlying spin-related mechanism remains unclear, and the rational manipulation of spin states is challenging due to various spin configurations under different coordination conditions. Therefore, it is urgent to study spin-dependent oxygen evolution reaction (OER) performance through a controllable method. Herein, we adopt a topochemical reaction method to synthesize a series of selenides with e_g occupancies ranging from 1.67 to 1.37. The process begins with monoclinic-CoSeO₃, featuring a distinct laminar structure and Co-O₆ coordination. The topochemical reaction induces significant changes in the crystal field's intensity, leading to spin state transitions. These transitions are driven by topological changes from a Co-O-Se-O-Co to a Co-Se-Co configuration, strengthening the crystalline field and reducing e_g orbital occupancy. This reconfiguration of spin states shifts the rate-determining step from desorption to adsorption for both OER and the hydrogen evolution reaction (HER), reducing the potential-determined step barrier and enhancing overall catalytic efficiency. As a result, the synthesized cobalt selenide exhibits significantly enhanced adsorption capabilities. The material demonstrates impressive overpotentials of 35 mV for HER, 250 mV for OER, and 270 mV for overall water splitting, indicating superior catalytic activity and efficiency. Additionally, a negative relation between e_g filling and OER catalytic performance confirms the spin-dependent nature of OER. Our findings provide crucial insights into the role of spin state transitions in catalytic performance.