Identifying an Alternative Hydride Transfer Pathway for CO2 Reduction on CdTe(111) and CuInS2(112) Surfaces

Abstract To ascertain if CdTe(111) and CuInS 2 (112) photoelectrodes exhibit the same carbon dioxide (CO 2 ) reduction mechanism as found for GaP, with adsorbed 2‐pyridinide (2‐PyH –* ) as active intermediate, the feasibility of 2‐PyH –* formation on these surfaces must be assessed. Via density functional theory, we conclude that although thermodynamically possible, 2‐PyH −* formation on CdTe(111) or CuInS 2 (112) is hindered kinetically. A different CO 2 reduction pathway, distinct from GaP's mechanism, must be operative. We predict that surface hydride (H −* ) readily forms on CdTe(111) and CuInS 2 (112) and direct surface hydride transfer (HT) to CO 2 dominates over transfer to adsorbed pyridine (Py * ). Direct HT to CO 2 has a large thermodynamic driving force and zero activation barrier on both surfaces. This reaction becomes slightly more spontaneous with adjacent Py * on both surfaces, rationalizing experiments where Py slightly enhances CO 2 reduction on CdTe and CuInS 2 . We thus conclude, Py is largely a spectator in CO 2 reduction on these electrodes, unlike its key role as hydride shuttle on GaP. HT from H −* to CO 2 also competes effectively with hydrogen evolution on these two surfaces, explaining the observed selectivity for CO 2 reduction over hydrogen evolution. Finally, formic acid readily adsorbs on CuInS 2 (112), which may facilitate the observed methanol formation.