Dual-Gas Activation Nanodomains Enable Solar-Powered Selective Methane Conversion.

Photocatalytic oxidation of methane to formaldehyde at concentrations compatible with direct fuel-cell use remains a critical yet unmet challenge. Here we introduce a "dual-gas coadsorption domain" architecture discovered through a high-throughput screen of 37 earth-abundant transition metals and their oxides. Reduced nickel oxide (NiO1-x) emerged as the optimal co-catalyst, decorating the pore edges of vacancy-rich porous ZnO (pZnO). Oxygen vacancies in pZnO act as oxygen pumps, while adjacent NiO1-x nanoclusters chemisorb and polarize methane, lowering the C-H activation barrier and steering the radical cascade toward methyl hydroperoxide instead of methanol. Methyl hydroperoxide quantitatively decomposes to formaldehyde, delivering 28.5 mmol g-1 (3 mM in solution, 88.5% selectivity). An outdoor reactor powered only by natural sunlight (peak 72.8 mW cm-2) produced 12.3 mmol g-1 formaldehyde in 6 h without detectable by-products. The concentrated effluent feeds an alkaline formaldehyde fuel cell directly-no purification-co-generating 0.2 kWh of electricity and valuable formate at a peak power density of 32.6 mW cm-2. The work establishes a scalable, solar-driven pathway for simultaneous methane valorization and on-site energy conversion.