Ultrahigh Selectivity of 95.78% for Visible Photocatalytic CO₂-to-CH₄ Conversion on Cu-Modulated Cs₄CdBi₂Cl₁₂ Microcrystals

The conversion of CO2 to CH4 by using solar energy represents a promising carbon-neutral process. Nonetheless, some critical issues, including the inherent stability of CO2, the presence of erratic intermediates, and intricate electron transfer processes, pose significant challenges to the photocatalytic conversion of CO2 to CH4. Therefore, how to introduce specific active metals as an innovative site has been recognized as one effective approach to improve the photocatalytic performance of catalysts. Here, we designed and incorporated Cu sites into Cs4CdBi2Cl12 microcrystals for the first time, aiming to produce CH4 with high selectivity by adjusting the CO2 reduction pathway. Among the synthesized microcrystals, the Cs4Cd0.8Cu0.2Bi2Cl12 exhibited superior visible photocatalytic performance, achieving CO and CH4 yields of 1.54 and 8.78 μmol/g, respectively, with CH4 electron selectivity as high as 95.78%. Additionally, we utilized in situ Fourier transform spectroscopy to elucidate the mechanism underlying the photoreduction of CO2 to CH4. By introducing a novel active site, this study opens up a new avenue for the development of photocatalysts featuring highly selective reduction of CO2 to CH4.