The synergy of low S-vacancy and Cu sites in Cu-In₄SnS₈ promotes the favorable conversion of CO₂ to ethanol with full selectivity

Direct photocatalytic CO₂ conversion to C₂ products holds notable potential, but this technology is still limited by the high thermodynamic energy and sluggish kinetics. By introducing Cu in In₄SnS₈ catalyst, we here developed low S vacancies and chemical reactive sites photocatalysts Cu-In₄SnS₈, enabling photocatalytic CO₂ to ethanol with full selectivity. Minor electron paramagnetic resonance peak intensity and large formation energy for S-vacancy suggest Cu introduction suppresses S vacancies formation. Low S vacancies photocatalysts Cu-In₄SnS₈ possess excellent carrier transfer and separation ability by the steady photoluminescence and transient fluorescence characteristic results. Furthermore, in situ, FTIR measurements confirmed ethanol formation via the presence of the intermediates *COOH, *CO, *OCCO(H), and *OCH₂CH₃. Also, theory calculations reveal that Cu efficiently reduces the energy barriers of the rate-limiting steps of *COOH and *COH, and promotes C-C coupling and multi-proton coupled electron transfer processes by co-adsorption and asymmetric charge distribution effects. As a result, the optimized sample achieves 0.73 μmol h⁻¹ CH₃CH₂OH generation with full selectivity.