Constructing dual-channel charge transfer pathways in ternary heterojunctions for promoting carbon dioxide conversion

Compared with binary heterojunctions, ternary heterojunctions can orchestrate multi-level charge transport pathways. In this study, a series of ternary heterojunctions IEF-11@TiO₂@Cu-X (I@T@Cu-X) with the synergistic effects of a Z-type heterojunction and a Schottky junction are successfully architected, and the synergistic effects are corroborated by surface photovoltage (SPV) measurements, in-situ X-ray photoelectron spectroscopy (XPS), and hydroxyl radical (·OH) detection experiments. The coexistence of the dual heterojunction structures fosters dual-channel charge transfer pathways, effectively facilitating the separation and migration of photogenerated electron-hole pairs, as confirmed by comparisons of photocurrent and electrochemical impedance (EIS) measurements between I@T@Cu-X and other prepared catalysts. Consequently, the prepared photocatalysts are evaluated in the solid-gas mode without the addition of photosensitizers or sacrificial agents under different CO₂ concentrations. In pure CO₂, among all prepared photocatalysts, the highest CO formation rate reaches 45.9 μmol·g^-1·h^-1, and CH₄ appears as a new product with the highest formation rate of 11.1 μmol·g^-1·h^-1. Subsequently, by varying Cu NPs loading amount and conducting selective poisoning experiments on Cu sites, Cu NPs are confirmed to serve as the active centers for CH₄ generation. Notably, this ternary heterojunction also exhibits excellent photocatalytic performance under low-concentration CO₂ (LC-CO₂) conditions, with the highest CO formation rate of 36.9 μmol·g^-1·h^-1 and a CH₄ yield of 1.6 μmol·g^-1·h^-1, which is likely due to the efficient separation and migration of photogenerated electron-hole pairs. The above results confirm that Cu sites are the active centers for CH₄ generation and validate the rationality and efficiency of the dual-channel charge transfer pathways. This study demonstrates a practical pathway for the direct photoconversion of CO₂ into CO and CH₄ using solar energy, establishing a sustainable strategy for CO₂-to-fuel conversion.