CO₂ Enrichment Boosts Highly Selective Infrared-Light-Driven CO₂ Conversion to CH₄ by UiO-66/Co₉S₈ Photocatalyst

Photocatalytic CO₂ reduction to high-value chemicals is an attractive approach to mitigate climate change, but it remains a great challenge to produce a specific product selectively by IR light. Hence, UiO-66/Co₉S₈ composite is designed to couple the advantages of metallic photocatalysts and porous CO₂ adsorbers for IR-light-driven CO₂-to-CH₄ conversion. The metallic nature of Co₉S₈ endows UiO-66/Co₉S₈ with exceptional IR light absorption, while UiO-66 dramatically enhances its local CO₂ concentration, revealed by finite-element method simulations. As a result, Co₉S₈ or UiO-66 alone does not show observable IR-light photocatalytic activity, whereas UiO-66/Co₉S₈ exhibits exceptional activity. The CH₄ evolution rate over UiO-66/Co₉S₈ reaches 25.7 µmol g^-1 h^-1 with ca.100% selectivity under IR light irradiation, outperforming most reported catalysts under similar reaction conditions. The X-ray absorption fine structure spectroscopy spectra verify the presence of two distinct Co sites and confirm the existence of metallic Co─Co bond in Co₉S₈. Energy diagrams analysis and transient absorption spectra manifest that CO₂ reduction mainly occurs on Co₉S₈ for UiO-66/Co₉S₈, while density functional theory calculations demonstrate that high-electron-density Co1 sites are the key active sites, possessing lower energy barriers for further protonation of *CO, leading to the ultra-high selectivity toward CH₄.