Synergistic Integration of AuCu Co-Catalyst with Oxygen Vacancies on TiO₂ for Efficient Photocatalytic Conversion of CO₂ to CH₄

Abstract

Photocatalytic reduction of CO₂ toward eight-electron CH₄ product with simultaneously high conversion efficiency and selectivity remains great challenging owing to the sluggish charge separation and transfer kinetics and lack of active sites for the adsorption and activation of reactants. Herein, a defective TiO₂ nanosheet photocatalyst simultaneously equipped with AuCu alloy co-catalyst and oxygen vacancies (AuCu-TiO_2-<i>x</i> NSs) was rationally designed and fabricated for the selective conversion of CO₂ into CH₄. The experimental results demonstrated that the AuCu alloy co-catalyst not only effectively promotes the separation of photogenerated electron-hole pairs but also acts as synergistic active sites for the reduction of CO₂. The oxygen vacancies in TiO₂ contribute to the separation of charge carriers and, more importantly, promote the oxidation of H₂O, thus providing rich protons to promote the deep reduction of CO₂ to CH₄. Consequently, the optimal AuCu-TiO_2-<i>x</i> nanosheets (NSs) photocatalyst achieves a CO₂ reduction selectivity toward CH₄ up to 90.55%, significantly higher than those of TiO_2-<i>x</i> NSs (31.82%), Au-TiO_2-<i>x</i> NSs (38.74%), and Cu-TiO_2-<i>x</i> NSs (66.11%). Furthermore, the CH₄ evolution rate over the AuCu-TiO_2-<i>x</i> NSs reaches 22.47 μmol·g^-1·h^-1, which is nearly twice that of AuCu-TiO₂ NSs (12.10 μmol·g^-1·h^-1). This research presents a unique insight into the design and synthesis of photocatalyst with oxygen vacancies and alloy metals as the co-catalyst for the highly selective deep reduction of CO₂.