Molecule-Derived Coatings Improve The Selectivity and Durability of CO2 Reduction on Chalcogenide Photocathodes

Direct solar-driven conversion of carbon dioxide to chemicals and fuels requires identification of efficient, durable, and selective photocathodes. Chalcogenide p-type semiconductors, exemplified by chalcopyrite Cu(In,Ga)Se₂ (CIGS), have been effectively deployed as photocathodes. However, selectivity toward CO₂ reduction and durability of the commonly used CdS buffer layer remain unsolved challenges. We have demonstrated that for the wide band gap CuGa₃Se₅ chalcopyrite absorber these challenges are well addressed by an organic coating generated in situ from an N,N′-(1,4-phenylene)bispyridinium ditriflate salt in the electrolyte. The molecular additive provides a 30-fold increase in selectivity toward CO2R products compared to the unmodified system and lowers Cd corrosion at least 10-fold. This dual functionality highlights the promise of hybrid solid-state-molecular photocathodes for enabling durable and efficient solar fuel systems. This presentation will highlight the variations in product selectivity and durability observed for different combinations of coatings derived from molecular precursors in the electrolyte with photocathodes including CuGa₃Se₅ and Cu(In,Ga)Se₂, with and without CdS buffer layers.