Cluster Models for Studying CO₂ Reduction on Semiconductor Photoelectrodes

Sunlight-powered CO₂-photoelectroreduction is a promising and potentially sustainable route to recycle CO₂ byproducts back into energy-dense liquid fuels. One of the most intriguing processes known to date is the pyridinium-catalyzed CO₂ reduction on p-type GaP photoelectrodes, where conversion to methanol has reported faradaic efficiencies nearing 100 %. Modeling this reactive environment requires understanding energetics of differently charged species at semiconductor electrodes, so we develop a cluster model and benchmark binding energies from it to those from Kohn-Sham density functional theory calculations that employ periodic boundary conditions. We then use this cluster model to theoretically predict structures and binding energies for charged and neutral adsorbates on the GaP(110) surface with and without the presence of van der Waals interactions and implicit solvation. We discuss the relative magnitudes of binding energy contributions for different adsorbates considered relevant in this CO₂ reduction process and provide details showing pitfalls when using cluster models.