Microstructure-dependent magnetic property and oxygen evolution activity in LaMnO3+δ electrocatalysts

A series of perovskite-type LaMnO 3 (LMO) electrocatalysts (LMO-4, LMO-6, and LMO-8) with different oxygen contents (δ) has been successfully prepared by regulating the sintering temperature and time under nitrogen vs. air atmosphere sintered sample (LMO-0). We investigated the effects of microstructural features such as oxygen vacancies, adsorbed oxygen (O ads ), δ value, Mn 3+ /Mn 4+ ratio, and Mn-O bond lengths on their magnetic performance and oxygen evolution reaction (OER) activity and its intrinsic correlation mechanism. The nitrogen induces crystal structure transition from tripartite phase (LMO-0) to orthorhombic phase and increases the adsorbed oxygen (O ads ) content with the variation of annealing conditions. LMO-0 with a high δ-value and high Mn 4+ ratio exhibits a predominantly Mn 3+ -O-Mn 4+ ferromagnetic double-exchange interaction. Among the samples, LMO-0 exhibits the optimal OER activity with the lowest apparent kinetic slope and charge transfer resistance, which is attributed to its highest Mn 4+ ratio, oxygen vacancy content, and most significant electrochemically active area.