Quantifying π-electron delocalization as a universal descriptor for ORR activity in MN4 catalysts

Abstract

The development of high-performance transition metal and nitrogen co-doped carbon (M−N−C) catalysts for the oxygen reduction reaction (ORR) hinges on identifying robust and quantitative descriptors for catalytic activity. In this study, we introduce the π-electron delocalization factor (Δπ) in the carbon basal plane as a universal and quantitative descriptor for ORR activity. By combining experimental data and density functional theory (DFT) calculations, we demonstrate that Δπ systematically tunes the d-orbital energy levels of MN₄ active sites, particularly the d_z² orbital, which governs the adsorption of oxygen intermediates and influences the rate-determining step of the ORR. A linear correlation between Δπ and ORR kinetics across different metal centers (Fe, Mn, Co, Ni) highlights the pivotal role of π-electron delocalization in optimizing the metal–oxygen interaction. This study provides a novel framework for quantifying catalytic performance and offers an efficient strategy for the rational design and screening of next-generation M−N−C catalysts with enhanced ORR activity.