Selective Photoreduction of CO 2 to CH 4 Triggered by Metal-Vacancy Pair Sites.

Selectively achieving the photoreduction of carbon dioxide (CO 2 ) to methane (CH 4 ) 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 CH 4 . As an example, oxygen-deficient Nb 2 O 5 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 *CH 3 O intermediate, a key intermediate for CH 4 production, during the CO 2 photoreduction in oxygen-deficient Nb 2 O 5 nanosheets. Importantly, the built metal-vacancy pair sites regulate the *CH 3 O formation step as a spontaneous process, making the reduction of CO 2 to CH 4 the preferred method. Therefore, the oxygen-deficient Nb 2 O 5 nanosheets exhibit a CH 4 formation rate of 19.14 μmol g -1 h -1 , with an electron selectivity of ∼94.1%.