Water Splitting Promotes the Proton-Coupled Electron Transfer Process for Selective Methane Photooxidation

Abstract The photocatalytic conversion of methane to formaldehyde under mild conditions is important for C1 chemistry and methane utilization, yet challenges such as reliance on noble metals and poor selectivity persist. Here, we report a noble-metal-free Fe-doped ZnO catalyst enriched with oxygen vacancies (OVs), where single-atom Fe and OVs synergistically lower the water dissociation barrier (0.15 vs. 0.52 eV on ZnO) to drive the proton-coupled electron transfer (PCET) process. Kinetic isotope effect experiments reveal that water dissociation is the rate-determining step, the acceleration of which is crucial for establishing a self-sustaining proton supply. In situ diffuse reflectance infrared Fourier transform spectroscopy and electron paramagnetic resonance confirm that PCET-mediated O2 reduction generates •OH, which selectively oxidize methane to formaldehyde via methanol intermediates. The optimized Fe0.05-ZnO achieves a formaldehyde yield of 29.00 μmol h−1 (89.45% selectivity), surpassing pristine ZnO by 4.12-fold while suppressing CO2 formation. This work provides mechanistic insights into proton-regulated photocatalytic alkane activation and solar-driven C1 conversion.