Stable CO₂ reduction under natural air on Ni–Sn hydroxide photocatalyst with dynamic renewable oxygen vacancies

Abstract Advanced photocatalysts are highly desired to activate the photocatalytic CO₂ reduction reaction (CO₂RR) with low concentration. Herein, the NiSn(OH)₆ with rich surface lattice hydroxyls was synthesized to boost the activity directly under the natural air. Results showed that terminal Ni–OH could serve as donors to feed protons and generate oxygen vacancies (V_O), thus beneficial to convert the activated CO₂ (HCO₃ ⁻) mainly into CO (5.60 μmol g⁻¹) in the atmosphere. It was flexible and widely applicable for a stable CO₂RR from high pure to air level free of additionally adding H₂O reactant, and higher than the traditional gas–liquid–solid (1.58 μmol g⁻¹) and gas–solid (4.07 μmol g⁻¹) reaction system both using high pure CO₂ and plenty of H₂O. The strong hydrophilia by the rich surface hydroxyls allowed robust H₂O molecule adsorption and dissociation at V_O sites to achieve the Ni–OH regeneration, leading to a stable CO yield (11.61 μmol g⁻¹) with the enriched renewable V_O regardless of the poor CO₂ and H₂O in air. This work opens up new possibilities for the practical application of natural photosynthesis.