Nitrogen Doping-Induced Structural Distortion in LaMnO3 Enhances Oxygen Reduction and Oxygen Evolution Reactions

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.