Aminopolysiloxane as Cu2O Photocathode Overlayer: Photocorrosion Inhibitor and Low Overpotential CO2-to-formate Selectivity Promoter

Cu2O, a photoactive p-type semiconductor based on earth-abundant elements, shows promising features for photoelectrochemical CO2 reduction reaction (PEC CO2RR). However, despite the broad light absorption and appropriate conduction band edge energy, it promptly undergoes photocorrosion in PEC CO2RR conditions. Herein, we evaluate an amine-functionalized polysiloxane (AF−PSi) as both protective layer and PEC CO2RR promoter via amine-CO2 adduct formation. Electrochemistry experiments and X-ray diffraction showed that photostability is significantly enhanced with AF−PSi overlayer. Electrolyses experiments under visible light irradiation indicated selective production of formate with faradaic efficiency of 61 % at low overpotential. Detailed in situ FTIR studies revealed that amine groups bind to CO2 to form carbamate species and that this process is favoured by cathodic polarization, confirming the dual role of AF−PSi layer.