In situ fabrication of atomically adjacent dual-vacancy sites for nearly 100% selective CH 4 production

The photocatalytic CO 2 -to-CH 4 conversion involves multiple consecutive proton–electron coupling transfer processes. Achieving high CH 4 selectivity with satisfactory conversion efficiency remains challenging since the inefficient proton and electron delivery path results in sluggish proton–electron transfer kinetics. Herein, we propose the fabrication of atomically adjacent anion–cation vacancy as paired redox active sites that could maximally promote the proton- and electron-donating efficiency to simultaneously enhance the oxidation and reduction half-reactions, achieving higher photocatalytic CO 2 reduction activity and CH 4 selectivity. Taking TiO 2 as a photocatalyst prototype, the operando electron paramagnetic resonance spectra, quasi in situ X-ray photoelectron spectroscopy measurements, and high-angle annular dark-field-scanning transmission electron microscopy image analysis prove that the V Ti on TiO 2 as initial sites can induce electron redistribution and facilitate the escape of the adjacent oxygen atom, thereby triggering the dynamic creation of atomically adjacent dual-vacancy sites during photocatalytic reactions. The dual-vacancy sites not only promote the proton- and electron-donating efficiency for CO 2 activation and protonation but also modulate the coordination modes of surface-bound intermediate species, thus converting the endoergic protonation step to an exoergic reaction process and steering the CO 2 reduction pathway toward CH 4 production. As a result, these in situ created dual active sites enable nearly 100% CH 4 selectivity and evolution rate of 19.4 μmol g −1 h −1 , about 80 times higher than that of pristine TiO 2 . Thus, these insights into vacancy dynamics and structure–function relationship are valuable to atomic understanding and catalyst design for achieving highly selective catalysis.