Carbon dioxide adsorption and activation on gallium phosphide surface monitored by ambient pressure x-ray photoelectron spectroscopy

Abstract

Gallium phosphide (GaP) is a promising catalyst material used in the photo-electrochemical carbon dioxide (CO₂) reduction reaction (CO₂RR). However, experimental data needed to interpret the interactions between CO₂ and GaP at their interfaces must be gathered in order to develop advanced GaP based catalysts for the CO₂RR. Here we used ambient pressure x-ray photoelectron spectroscopy to characterize the surface chemistry at 298 K on the GaP surface exposed to CO₂ alone and in the presence of H₂O under both dark and illuminated conditions. We found that a carbonate-like configuration is stable on the GaP surface exposed solely to 0.35 Torr CO₂. Shining solar light promoted the CO₂ dissociation process on the surface while negligibly influencing the CO₂ adsorption configuration on GaP. Based on the surface chemistry change under dark and illuminated conditions, we propose a CO₂ dissociation pathway on GaP. We also found that linear physisorbed CO₂ formed on the surface of GaP when 0.35 Torr CO₂ is co-dosed with 0.35 Torr H₂O. Co-dosing H₂O with CO₂ also created a surface dipole, which is further influenced by solar light illumination. This work provides a fundamental atomic level understanding of how CO₂ adsorption and activation happened on the GaP surface and how it was further influenced by solar light.