Unveiling the Overlooked Role of Alcoholic Sacrificial Agents in Photocatalytic H2O2 Synthesis: Beyond Hole Scavenging to Proton Donation

Abstract Two-electron oxygen reduction (2e– ORR) offers a green route for photocatalytic H2O2 synthesis, yet severe charge recombination restricts its efficiency. Alcoholic sacrificial agents are widely adopted to address this issue, but their transformation mechanism and exact contributions beyond hole capture remain poorly verified. In this work, we employed sodium anthraquinone sulfonate (SAS) as a model photocatalyst to systematically investigate the role of alcoholic sacrificial agents. The presence of alcohols substantially increased the H2O2 yield, with anhydrous methanol affording a maximum accumulated concentration of 98.2 mM, which is 818.3 times higher than that obtained in pure water. Two quantitative strategies (HRP-ABTS enzymatic colorimetry and FeCl2-based colorimetry) were adopted to exclude interfering signals, and the authentic generation of H2O2 was further validated via 31P NMR, 1H NMR, and MnO2 decomposition experiments. Then, deuterium isotope tracing revealed that all hydrogen atoms in the generated H2O2 originate exclusively from the methyl α-H of methanol rather than hydroxyl groups. Through quenching experiments, EPR spectroscopy, and in-situ FTIR analysis, we elucidated the transformation pathway of methanol on the catalyst surface. Furthermore, two common metal-containing and metal-free photocatalysts (NH2-MIL-125(Ti) and g-C3N4) were synthesized for verification, both exhibiting remarkably enhanced H2O2 productivity in alcoholic media. Via atomic-level proton tracking, this work overturns the conventional viewpoint that sacrificial agents contribute to promoting H2O2 generation by scavenging holes to promote charge separation and identifies the participation of methyl α-H in H2O2 generation. The elucidated reaction mechanism and alcohol conversion pathway offer valuable guidance for the rational design of high-performance photocatalysts toward efficient H2O2 photosynthesis.