Colloidal silver diphosphide (AgP₂) nanocrystals as low overpotential catalysts for CO₂ reduction to tunable syngas

Production of syngas with tunable CO/H₂ ratio from renewable resources is an ideal way to provide a carbon-neutral feedstock for liquid fuel production. Ag is a benchmark electrocatalysts for CO₂-to-CO conversion but high overpotential limits the efficiency. We synthesize AgP₂ nanocrystals (NCs) with a greater than 3-fold reduction in overpotential for electrochemical CO₂-to-CO reduction compared to Ag and greatly enhanced stability. Density functional theory calculations reveal a significant energy barrier decrease in the formate intermediate formation step. In situ X-ray absorption spectroscopy (XAS) shows that a maximum Faradaic efficiency is achieved at an average silver valence state of +1.08 in AgP₂ NCs. A photocathode consisting of a n⁺p-Si wafer coated with ultrathin Al₂O₃ and AgP₂ NCs achieves an onset potential of 0.2 V vs. RHE for CO production and a partial photocurrent density for CO at -0.11 V vs. RHE (j_{-0.11, CO}) of -3.2 mA cm^-2.