Building VS&Si-CuInS2/SiC Heterojunctions Mimicking Thylakoid for Artificial Photosynthesis-Dual-Vacancy-Assisted Mechanism.

Converting CO2 and water into value-added chemicals by mimicking plant photosynthesis is a promising strategy to mitigate CO2 concentration in the atmosphere. Herein, a series of hierarchical hollow VS&Si-CuInS2/SiC-X heterojunctions with abundant S and Si vacancies were designed, synthesized, and utilized for photoelectrocatalytic CO2 reduction in an aqueous KHCO3 solution. Our results reveal that the unique hierarchical hollow architecture, S and Si vacancies, and n-n heterojunction property synergistically contribute to CO2 reduction performance and selectivity to C2 products. In particular, the optimal heterojunction VS&Si-CuInS2/SiC-2 achieves a generation rate of 79.38 μM h-1 cm-2 for carbon-based products and a C2 selectivity of 83.63% for liquid products. Moreover, its total electron transfer rate (263.19 μM h-1 cm-2) is 3.60 times higher than that of VSi-SiC and 3.96 times higher than that of VS-CuInS2, respectively. DFT calculations indicate that the S and Si vacancies can evidently reduce the reaction barriers in the CO2 reduction, promoting the generation of crucial intermediates and facilitating the C-C coupling reaction on the catalyst surface. Based on the key intermediates *═C═O, *CHO, *COCHO, and *COCH3 detected through in situ FTIR spectroscopy and confirmed by DFT calculations, a dual-vacancy-assisted mechanism is proposed for photoelectrocatalytic CO2 reduction.