Selective Photoreduction of CO₂ to CH₄ Triggered by Metal-Vacancy Pair Sites

Selectively achieving the photoreduction of carbon dioxide (CO₂) to methane (CH₄) remains a significant challenge, which primarily arises from the complexity of the protonation process. In this work, we designed metal-vacancy pair sites in defective metal oxide semiconductors, which anchor the reactive intermediates with a bridged linkage for the selective protonation to produce CH₄. As an example, oxygen-deficient Nb₂O₅ nanosheets are synthesized, in which the niobium-oxygen vacancy pair sites are demonstrated by X-ray photoelectron spectroscopy and electron paramagnetic resonance spectra. In situ Fourier transform infrared spectroscopy monitors the *CH₃O intermediate, a key intermediate for CH₄ production, during the CO₂ photoreduction in oxygen-deficient Nb₂O₅ nanosheets. Importantly, the built metal-vacancy pair sites regulate the *CH₃O formation step as a spontaneous process, making the reduction of CO₂ to CH₄ the preferred method. Therefore, the oxygen-deficient Nb₂O₅ nanosheets exhibit a CH₄ formation rate of 19.14 μmol g^-1 h^-1, with an electron selectivity of ∼94.1%.