Photoelectrochemical reduction of CO2 on Cu/Cu2O films: Product distribution and pH effects

• Photoelectrochemical CO2 reduction at a Cu/Cu2O electrode.
• Formation of methanol, ethanol, formaldehyde, acetaldehyde, and acetone.
• A reaction scheme is presented to account for the product evolution.
• The medium pH was identified as a key variable in the product distribution.

This work focuses on photoelectrochemical CO2 reduction at a Cu/Cu2O electrode (1 × 1 cm2). The formation of methanol, ethanol, formaldehyde, acetaldehyde, and acetone was monitored during UV–visible radiation for 3 h at +0.20 V (vs. Ag/AgCl reference); 80% of the initial CO2 was removed. In this process, the photogenerated electrons in the p-type Cu2O semiconductor reduced CO2 (CO2 + e− → CO2−). Subsequent reaction involved radical species that originated during photolysis and dictated the product distribution observed. Methanol formation prevailed for a short period (<30 min); acetaldehyde and acetone were the main products after a longer accumulation period (>120 min). A reaction scheme is presented to account for the product evolution and reactions with the H, CH3, and OH radical species generated in situ. The medium pH was identified as a key variable in the selectivity of the methanol formation.