Modulated MOF-derived tunable size mesoporous nitrogen-doped carbons as model catalysts for efficient oxygen reduction

Integrating tunable and uniform nanosizes and ordered mesoporous structures into MOF-derived carbons remains a challenge, while imprecise morphological control also hinders clarifying microstructure-catalytic activity relationships, limiting rational design of high-performance MOF-derived electrocatalysts. In this work, we developed a one-step modulator approach to synthesize ordered mesoporous rod-shaped MOF-545-x precursors, with their lengths tunable from microns to nanometers. After direct carbonization, MNC-x retained the rod-shape and mesoporous structures. Considering that length is the most significant variable across the MNC-x series, these materials acted as ideal model catalysts to unravel the connection between particle size and the utilization efficiency of electrocatalytic active sites during ORR. Electrochemical tests demonstrated that MNC-250 nm, which has the shortest length, delivered superior ORR activity, achieving half-wave potentials of 0.861 V in alkaline electrolyte and 0.713 V in acidic electrolyte. This superiority was attributed to its larger electrochemical surface area, lower charge transfer resistance, and more accessible active sites. Additionally, first-principles calculations further clarified the potential ORR catalytic mechanism centered on the dominant C1 active sites. This study provides a straightforward strategy for regulating the particle size of ordered mesoporous MOF precursors and their derived carbon-based electrocatalysts, offering valuable insights for developing high-performance catalysts in catalytic reactions.