The effect of oxygen-containing functional groups on oxygen reduction reaction activity in carbon-based catalysts

The development of efficient metal-free carbon-based catalysts for the oxygen reduction reaction (ORR) is critical for advancing fuel cell technologies. Although defects and oxygen-containing functional groups are both recognized as important factors influencing ORR activity, the specific contribution of oxygen functionalities remains insufficiently understood. Herein, hollow carbon spheres (HCSs) with tunable graphitization degree and oxygen content were rationally designed to decouple the effects of structural defects and surface functionalities on ORR performance. Electrochemical measurements reveal that the optimized HCS-900-3 catalyst delivers half-wave potentials of 0.784 V and 0.556 V (vs. RHE) in alkaline and acidic media, respectively. Remarkably, HCS-900-3 exhibits outstanding durability, showing no negative shift in half-wave potential after 3500 cycles in 0.1 M KOH, as well as excellent tolerance to methanol in both alkaline and acidic environments. Comprehensive structural and electrochemical analyses demonstrate that the superior ORR performance originates from the synergistic effects of a high degree of graphitization and residual oxygen-containing functional groups, particularly C–O–C structures, which modulate the local electronic structure of adjacent carbon atoms and promote ORR kinetics. This work provides mechanistic insights into oxygen-functionalized carbon catalysts and offers a rational strategy for designing high-performance metal-free ORR electrocatalysts.