Nitrogen doping-induced structural distortion in LaMnO₃ enhances oxygen reduction and oxygen evolution reactions

Abstract

Nitrogen-doped perovskites (LaMnO₃) were designed as bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Nitridation led to O-substitution in LaMnO₃, creating distortion in the LaMnO₃ structure and generating oxygen vacancies. N-doping facilitated an increase of Mn³⁺ content, enhancing ORR and OER activities. LaMnO₃ with 4 h of nitridation exhibits 3.35 and 1.75 times higher specific and mass activities in comparison to pristine LaMnO₃ (highest reported among perovskite oxides). The enhancement in catalytic activity is attributed to the increase of Mn³⁺ content and distorted Mn–O, leading to compressive strain. The substitution of N at the crystal lattice of perovskite stabilizes the intermediates through a combination of strain and charge modulation of the active Mn center, which causes the enhancement in ORR and OER performance. The bifunctional character of the catalyst was further evaluated for practical zinc–air battery applications in which nitrogen-doped LaMnO₃ undergoes steady operation up to 500 cycles in harsh industrial conditions of 6 M KOH.