Enhancing oxygen evolution reaction via hydrogen plasma treatment: Unveiling the functionality of CN defects and the role of Fe in NiFe Prussian blue analogs

The rational design of electronic and vacancy structures is crucial to regulating and enhancing electrocatalytic water splitting. However, creating novel vacancies and precisely controlling the number of vacancies in existing materials systems pose significant challenges. Herein, a novel approach to optimize the concentration of the CN vacancy (V_CN) in the NiFe Prussian blue analog (PBA) nanocubes is designed by incorporating the H₂ or O₂ plasma treatment. The relationship between the V_CN and catalysis is analyzed, and results show that a moderate concentration of V_CN (6.5%) can enormously enhance oxygen evolution reaction (OER) activity of NiFe PBA. However, an excessive amount of V_CN disrupts the crystal structure and hinders the transportation of charge carriers, consequently leading to inferior OER. Furthermore, the V_CN significantly activates the activity of Fe sites, inducing preferential adsorption of OH⁻ on Fe sites, followed by adsorption on Ni sites, thereby optimizing the reaction pathway and significantly promoting OER performance. In addition, V_CN also suppresses Fe leaching, giving the catalyst excellent durability. This study reveals the feasibility of creating unconventional defects in nanomaterials and precisely controlling the number of vacancies for diverse catalytic and energy applications.