W–H Bond‐Mediated “Anti‐Overoxidation Valve”: 100% Formaldehyde Selectivity Among Detected Products in Photocatalytic Methane‐to‐Formaldehyde Conversion

Direct photocatalytic conversion of methane to formaldehyde is highly efficient, avoiding energy‐intensive methanol oxidation. However, its selectivity and activity are severely limited by uncontrollable over‐oxidation: Formaldehyde has lower C‐H dissociation energy than methane, prone to deep overoxidation to CO 2 . Herein, we report H/WO 2.72 hydrogenated nonstoichiometric tungsten oxide photocatalyst. At ambient temperature, it attains 100% HCHO selectivity over all detectable carbonaceous products at 30.94 µmol·h −1 , with 11‐fold higher activity than commercial WO 3 and outperforming most conventional photocatalysts. Operando spectroscopic studies and density functional theory (DFT) calculations reveal that surface W‐H bonds act as a kinetically gated “Anti‐Overoxidation valve,” W–H bonds are preferentially cleaved by reactive oxygen species (·OOH), as they are thermodynamically weaker than the C–H bonds in HCHO and its over‐oxidation intermediate (*HCOOH). Then the generated hydrogen radicals (H*) drive a reverse reduction pathway to convert the *HCOOH back to *HCHO, interrupting deep oxidation. Concurrently, hydrogenation optimizes the electronic structure of WO 2.72 , lowering the HCHO desorption barrier to facilitate timely product release. This work provides a dynamic strategy for complete selectivity in catalytic CH 4 conversion, emphasizing the value of precise kinetic pathway modulation for methane valorization.