Room temperature oxygenated groups addition in carbon materials via ozone oxidation for boosting electrochemical H2O2 production

The crucial yet delicate 2e- oxygen reduction reaction (ORR) for producing the green chemical H2O2 relies on the uniform coordination environment of the active sites, such as oxygenated groups in metal-free carbon material catalysts. However, conventional harsh carbon material synthesis methods inevitably introduce structural defects and alter morphology, hindering the precise control of active site formation. Herein, we developed the ozone oxidation method under controlled reaction conditions to precisely modify carbon materials at room temperature. Through controlling the ozonation of reaction time, concentration, temperature, and relative humidity, we find the mild method allows us to precisely add active carboxyl group (-COOH) without forming structural defects. Electrochemical tests reveal that the optimal catalyst with the highest -COOH content exhibits the most outstanding mass activity of 164 A/g at 0.65 V and the highest H2O2 selectivity of 91 %. The density functional theory calculations demonstrate that the carbon sites directly connected to -COOH possess the optimized binding strength of *OOH intermediate to favor the two-electron oxygen reduction process. This work offers a novel approach to precisely and gently control carbon surface groups while preserving the structural morphology through ozone gas treatment, which can be readily applied to other material designs.