Dual electronic-spin engineering in cobalt-doped CdS: Photocatalytic pathway switching from competing H2 evolution to selective CO2 reduction

The photocatalytic reduction of CO 2 over CdS faces significant challenges due to dominant hydrogen evolution competition and inefficient CO 2 activation. Herein, a magnetic cobalt-doping strategy is proposed that fundamentally restructures the surface reaction dynamics of CdS, effectively switching the photocatalytic pathway from H 2 evolution to CO 2 reduction. It is demonstrated that cobalt incorporation markedly suppresses charge recombination while increasing the population of photogenerated electrons available for CO 2 activation. Density functional theory calculations uncover two critical doping effects: an upshifted d-band center that optimizes CO 2 adsorption and activation energetics, and a substantially reduced energy barrier for the formation of rate-determining COOH* intermediate. Crucially, the introduced cobalt species induce pronounced spin polarization, which facilitates the separation of charge carriers. This spin effect can be further amplified under an external magnetic field to improve photocatalytic performance. The synergistic interplay of these effects endows Co-doped CdS with an exceptional CO production rate of 2322.8 μmol g −1  h −1 under visible light irradiation and magnetic field application – a 10.9-fold enhancement over pristine CdS. This work pioneers a novel paradigm that concurrently addressing thermodynamic (reaction pathway), kinetic (energy barrier), and electronic-spin (charge separation) factors, providing new design principles for breaking activity-selectivity trade-offs in photocatalytic CO 2 reduction systems.