Model thiophene-decorated nickel porphyrins for tandem CO₂ reduction

Tandem systems that integrate CO-generating catalysts with copper have shown promise for enhanced carbon dioxide reduction reaction (CO₂RR) performance. Sulfur-containing single-atom catalysts are particularly effective for CO production; however, the role and positioning of sulfur in facilitating both CO₂-to-CO conversion and tandem CO₂RRs remain elusive. Here we show model thiophene-decorated nickel porphyrins as model single-atom catalysts that exhibit tandem activities in the CO₂RR. Spectroscopic and theoretical analyses reveal that thiophene substituents induce ligand holes, regulating the d orbitals and d-band centre of the nickel centre to reduce the reaction barrier and promote CO formation. Coupling these single-atom catalysts with a copper catalyst achieves a Faradaic efficiency of 74.3% and a partial current density of 445.8 mA cm⁻² for C₂ products in a neutral solution, a 46% improvement over bare copper. Operando studies confirm the formation of CO intermediates from the single-atom catalysts, highlighting their role in facilitating tandem catalysis. (Figure presented.).