A single-atom COF/CdS S-scheme photocatalyst for COF thickness-dependent CO2 photoreduction

• • The Co SA-TT-COF/15 wt% CdS heterojunction with 50.5 nm TT-COF thickness achieves a CO production rate of 14157 μmol g−1 h−1 and 90.9% selectivity, representing a top-tier performance among COF-based photocatalysts, which is critical for industrial-scale solar fuel synthesis. • • The S-scheme heterojunction design enhances the built-in electric field and promotes charge separation, as evidenced by femtosecond transient absorption spectroscopy, leading to accelerated charge transfer kinetics and reduced recombination losses, essential for practical efficiency. • • The optimized TT-COF thickness (50.5 nm) balances active site density and accessibility, directly influencing the CO2 photoreduction rate; this thickness-dependent behavior provides a design guideline for maximizing catalytic output. • • The integration of Co single atoms into the COF matrix increases CO2 adsorption and activation, lowering energy barriers, as confirmed by theoretical calculations, which is pivotal for achieving high selectivity and conversion rates under mild conditions.