Boosting ORR Activity via Bidirectional Regulation of the Electronic Structure by Coupling MnO/Mn₃O₄ Composite Materials with N-Doped Carbon

Abstract

Suffering from poor conductivity and limited activity, manganese oxide was combined with carbon materials to promote electrocatalytic performance. Although the positive effects of the carbon composition strategy in performance promotion have been confirmed, the underlying mechanism involved remains unclear, which hinders the development of manganese oxide catalysts. Here, N-doped carbon (NC) shell-encapsulated MnO/Mn3O4 composite nanoparticles grown on NC nanorods were designed to catalyze the oxygen reduction reaction. The resulting MnO/Mn3O4@NC has excellent activity (E 1/2 = 0.853 V) and extraordinary durability, comparable to Pt/C. The MnO/Mn3O4 composite achieved an optimal eg occupancy of Mn3+. The NC shell formed in situ offers the electron transfer from MnO/Mn3O4 to the NC and results in bidirectional regulation of the electronic structure, forming electron-accumulated NC and Mn3+-rich manganese oxide systems. Electron accumulation on NC enhances the affinity for O2 adsorption, thereby significantly reducing the free-energy barrier for the ORR process. Furthermore, the NC shell formed in situ improves the electric conductivity and cycle durability of catalysts significantly. This paper fundamentally reveals the crucial role of the coupling effect between MnO/Mn3O4 and NC formed in situ in promoting catalysis and provides an efficient strategy for designing other metal oxide electrocatalysts.