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 O 2 and carbon dioxide radical anions (•CO 2 − ) in situ formed on the Bi 2 S 3 composition (hole) through water oxidation and oxalic acid (OA) oxidative C–C cleavage, respectively. The shell‐yolk Z‐scheme Bi 2 S 3 /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 CO 2 ‐to‐CO reduction. Mechanistic investigations reveal that shell Bi 2 S 3 can cooperate with •OH generated/transferred from the yolk CdS‐Vs to mediate the efficient production of •CO 2 ‒ . Hollow microenvironment and electronic structure of the yolk CdS‐Vs can be manipulated by Vs to increase enrichment of •CO 2 − and favor its proton‐coupled electron transfer to produce CO. Bi 2 S 3 /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.