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

Abstract

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.

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