Quantitative Photo-Reforming of Biomass to CO Spurred by In Situ Protonation of Carbon Dioxide Radical Anions

Heterogeneous photocatalysis has emerged as a green solution for converting renewable biomass into biofuels and chemicals, though it typically suffers from unsatisfactory carbon utilization efficiency. Here, we present a "two-in-one" photoreduction strategy enabled by electron-rich Cd sites, both remote from and adjacent to sulfur vacancies (Vs). This strategy is highly selective for the reduction of O₂ and carbon dioxide radical anions (•CO₂ ^-) in situ formed on the Bi₂S₃ composition (hole) through water oxidation and oxalic acid (OA) oxidative C-C cleavage, respectively. The shell-yolk Z-scheme Bi₂S₃/CdS-Vs achieves complete photothermal catalytic upgrading of OA to CO with an unprecedented yield (1671 µmol g^-1 h^-1) and selectivity > 99%, outperforming state-of-the-art photocatalysts for CO₂-to-CO reduction. Mechanistic investigations reveal that shell Bi₂S₃ can cooperate with •OH generated/transferred from the yolk CdS-Vs to mediate the efficient production of •CO₂ ^‒. Hollow microenvironment and electronic structure of the yolk CdS-Vs can be manipulated by Vs to increase enrichment of •CO₂ ^- and favor its proton-coupled electron transfer to produce CO. Bi₂S₃/CdS-Vs exhibits good reusability and universality for converting various bio-organic acids into CO with 94%‒100% selectivity. Tailor-made versatile photocatalysts via vacancy engineering provide a viable avenue for the full-carbon upcycling of biomass and waste sources to biofuels.