Surface Electrostatic Gradient of Perovskite Boosts Metal in Situ Exsolution and CO ₂ Electrolysis in Solid Oxide Electrolyzer

The in situ exsolution of nanoparticles (NPs) has brought new opportunities for the application of perovskite-based catalysts in solid oxide electrolyzers. However, the kinetic driving force controlling cation migration and subsequent metal nucleation is not yet fully understood. Here we identified surface electrostatic gradient as the decisive kinetic factor in governing metal exsolution by treating La_0.3Ca_0.6Ti_0.9Mn_0.05Ni_0.05O_3-δ (LCTMN) with NaBH₄ of different concentrations. Multi-scale characterizations revealed that different spatial distribution of surface oxygen vacancy induced positive surface potential shift and established electrostatic gradients that attracted Ni²⁺ cations toward LCTMN surface, thereby driving Ni²⁺ migration and reduction. Moreover, theoretical calculations demonstrated that surface oxygen vacancies reduced Ni segregation energy and work function of LCTMN, elucidating the critical role of electronic redistribution in accelerating in situ exsolution. Consequently, treatment of LCTMN with 3.0 M NaBH₄ yielded a high-density dispersion of uniform Ni NPs with abundant strongly anchored interfacial sites for CO₂ adsorption and activation. Notably, it delivered maximal current density of 1.25 A cm^-2 and CO Faraday efficiency of 94.23%, coupled with a superior 100-hour stability, surpassing all counterparts. This study establishes a direct link between surface potential and exsolution kinetics, providing a universal paradigm for designing high-performance perovskites with desirable reactivity.