Hierarchical Co9S8@In2.77S4 Heterojunction for Efficient Photocatalytic Reduction of CO2 to Syngas

Photocatalytic reduction of CO2 to solar fuels is recognized as a promising route to address environmental and energy issues. However, there exist two challenges of insufficient CO2 activation and fast charge carrier recombination, impeding this conversion. Herein, a hierarchical Co9S8@In2.77S4 (CoS@InS) heterojunction is developed by the in situ growth of the In2.77S4 nanosheets on the Co9S8 nanotubes for efficient photocatalytic reduction of CO2 to syngas in an aqueous reaction system with [Ru(bpy)3]Cl2 serving as a photosensitizer and triethanolamine as a sacrificial agent. In addition to the promoted charge separation and transfer, the strong interfacial electric field formed in this heterojunction tunes the p-band center of In active sites toward the Fermi level. Accordingly, the adsorption of the key intermediate *COOH is enhanced, and the energy barrier of *CO desorption is reduced. Besides, the hierarchical hollow structure enhances light utilization and mass transfer, increases the specific surface area, and provides abundant reaction sites. As a result, the hierarchical CoS@InS heterojunction exhibits superior activity. The optimized heterojunction yields CO and H2 production rates as high as 83,648 and 28,635 μmol g–1 h–1, respectively, with an apparent quantum yield of 5.60% at 450 nm.