Oxygen functional group-mediated coupling mechanism between the oxygen reduction reaction and mass transport in microporous carbon-based catalysts.

Abstract

Hydrogen peroxide (H₂O₂) is a widely used environmentally benign bulk chemical. Electrocatalytic synthesis via the two-electron oxygen reduction reaction (2eORR) has emerged as a core green alternative to the traditional anthraquinone process, which suffers from high energy consumption, heavy pollution, and significant storage/transportation safety risks. Microporous carbon-based materials are recognized as the most industrially promising electrocatalysts for the 2eORR. However, most existing studies focus on modulating intrinsic catalytic activity through oxygen functional groups (OGs), while the strong coupling between OGs and mass transport in microporous systems is largely overlooked. The intrinsic structure-performance relationship among OGs, microporous structure, mass transport behavior, and catalytic performance remains incompletely elucidated, representing a critical bottleneck for optimizing microporous carbon-based catalysts. Herein, using commercial microporous activated carbon as the substrate, we achieved precise and controllable modulation of the type and content of surface OGs via liquid-phase H₂O₂ oxidation and high-temperature annealing, while preserving the pristine carbon matrix's microporous framework. Combining systematic characterizations, electrochemical measurements, DFT calculations, and EIS analysis, we comprehensively elucidated the OG-mediated reaction-mass transport coupling mechanism within micropores. Our results show that the synergistic effect between OGs and micropores has a negligible impact on intrinsic 2eORR activity. In contrast, the steric hindrance of OGs (especially carboxyl groups) significantly compresses the effective micropore size and markedly increases reaction mass transport resistance, which is identified as the dominant cause of performance degradation. A clear positive trend correlation exists between OC-O group content and both mass transport impedance and rotational speed sensitivity. On this basis, we propose "rotational speed sensitivity" as a novel electrochemical metric for quantitatively characterizing intrinsic mass transport resistance. This study provides theoretical guidance and a new methodology for the rational design of high-performance carbon-based catalysts for efficient H₂O₂ electrosynthesis.