Nearly 100% selective and visible-light-driven methane conversion to formaldehyde via. single-atom Cu and W δ .

Direct solar-driven methane (CH 4 ) reforming is highly desirable but challenging, particularly to achieve a value-added product with high selectivity. Here, we identify a synergistic ensemble effect of atomically dispersed copper (Cu) species and partially reduced tungsten (W δ+ ), stabilised over an oxygen-vacancy-rich WO 3 , which enables exceptional photocatalytic CH 4 conversion to formaldehyde (HCHO) under visible light, leading to nearly 100% selectivity, a very high yield of 4979.0 μmol·g -1 within 2 h, and the normalised mass activity of 8.5 × 10 6  μmol·g -1 Cu ·h -1 of HCHO at ambient temperature. In-situ EPR and XPS analyses indicate that the Cu species serve as the electron acceptor, promoting the photo-induced electron transfer from the conduction band to O 2 , generating reactive •OOH radicals. In parallel, the adjacent W δ+ species act as the hole acceptor and the preferred adsorption and activation site of H 2 O to produce hydroxyl radicals (•OH), and thus activate CH 4 to methyl radicals (•CH 3 ). The synergy of the adjacent dual active sites boosts the overall efficiency and selectivity of the conversion process.