Photochromic single atom Ag/TiO2 catalysts for selective CO2 reduction to CH4

Photocatalytic production of CH4 from CO2 and H2O is recognized as one of the most sustainable approaches to address the environmental and energy crises. However, this strategy is severely plagued by the poor activity and low selectivity due to the inefficient electron production, inadequate proton supply and insufficient stabilization of the key intermediates. Herein, a new design concept of photochromic single atom photocatalysis is proposed to overcome these issues simultaneously. As a prototype, single Ag atoms anchored TiO2 nanoparticles reveal rapid and macroscopic photochromic behavior upon light irradiation, which is attributed to the trapping of photogenerated electrons. The generated colored state effectively suppresses the combination of photogenerated carriers and improves their migration. Further mechanistic analyses suggest that the isolated Ag atoms act as the dominant active sites to capture CO2 and stabilize the key C1 intermediate, while the adjacent Ti sites promote the activation of H2O for the generation of more protons, thereby together providing highly active sites to boost the production of CH4 instead of CO. As a result, an extraordinary activity of 46.0 μmol g−1 h−1 and an ultrahigh electron selectivity of ∼91% for CH4 production are achieved. The proposed all-in-one design concept, especially the macroscopic electron-trapping photochromism, opens a new avenue to substantially enhance the yield efficiency of photogenerated electrons to accelerate various photocatalytic reduction reactions.