<p>Photocatalytic hydrogen production from anhydrous methanol is dynamically regulated by oxygen concentration, challenging the conventional paradigm that oxygen suppresses H₂ evolution. This study demonstrates that introducing 10 vol% oxygen into the Pt/TiO₂ system enhances the hydrogen production rate from 289.17 to 1189.46 μmol/h by acting as an electron acceptor to accelerate interfacial charge transfer at the semiconductor-cocatalyst-solution interface. Under anaerobic conditions, hole-driven methanol oxidation dominates the reaction, yielding ~ 100% formaldehyde selectivity. Limited proton generation arises from methanol’s low ionization degree, hindering hydrogen evolution. Oxygen addition shifts the mechanism to superoxide radical (·O₂⁻) dominance, reducing photogenerated electron accumulation and promoting carrier separation. This overcomes the kinetic limitation of proton deficiency in anhydrous media. Excess oxygen (&gt; 10 vol%) triggers over-oxidation of methanol/formaldehyde to formic acid, CO, and CH₄, decreasing H₂ selectivity. Radical scavenging experiments reveal that ·O₂⁻ becomes the primary reactive species with oxygen, outperforming holes and hydroxyl radicals. These findings establish oxygen as a dual-function regulator of electron transfer and product selectivity, offering strategies for optimizing photocatalytic hydrogen evolution systems.</p>