Low‐Spin‐Induced Optimization of Intermediate Adsorption in Selenium‐Incorporated Layered Double Hydroxides for Enhanced Electrochemical Water Splitting

The rational manipulation of spin configurations in cobalt-based electrocatalysts offers a viable strategy for optimizing oxygen and hydrogen evolution activities. Nevertheless, the intermediate spin (IS) configuration of Co²⁺ sites, featuring partially occupied d orbitals, triggers suboptimal adsorption with oxygenated species. In this work, selenium incorporation into CoCr layered double hydroxides (LDH) is demonstrated to induce spin-state transition, activating inert sites and stabilizing the low-spin (LS) Co²⁺ configuration. The low spin-state materials exhibit superior electrocatalytic activity, requiring overpotentials of merely 284.0 and 130.0 mV for oxygen and hydrogen evolution reactions, respectively, at 10 mA cm^-2, while maintaining excellent durability over 168 h. The lowered e_g occupancy in low-spin Co²⁺ results in electronic asymmetry and enhances electron density at the metal center. This electronic configuration facilitates robust Co 3d-O 2p orbital hybridization, which enhances the adsorption of oxygenated intermediates by elevating the d-band center toward the Fermi level, optimizing adsorption energetics. Moreover, low-spin Co²⁺'s paired d-orbital electron configuration minimizes high-energy antibonding e_g orbital occupancy, enhancing crystal lattice stability. Overall, this work establishes that spin state modulation in transition metals significantly lowers reaction energy barriers, offering a promising strategy for developing high-performance electrocatalysts.