Stabilizing oxygen-deficient Mn sites active in seawater oxidation

Abstract

This study presents the engineering of a sustainable electrode for unpurified seawater electrolysis, featuring Ca-doped manganese oxide nanorods anchored on a Ni(OH)₂ microarray. The designed electrode demonstrates enhanced stability through the stabilization of Mn³⁺ species and optimized interaction, effectively mitigating the overpotential barrier of MnO_x from 310 mV to 250 mV during seawater oxidation. Ca doping induces surface oxygen vacancies, crucial for stabilizing Mn³⁺ species. The synthesized electrode exhibits distinctive characteristics, including increased surface Mn³⁺ concentration via charge state manipulation, micro and mesopores for a high specific surface area with unique hydrophilic and aerophobic properties, and strong Brønsted basicity and Lewis's acidity due to Ca doping, facilitating efficient charge transfer via effective covalent bond formation with anions. The modified catalyst demonstrated 100% faradaic efficiency for seawater electrolysis, required a low input voltage of 1.68 V to deliver a current density of 500 mA cm⁻², and sustained this performance for over 100 hours without degradation or hypochlorite formation.