This work focuses on photoelectrochemical CO2 reduction at a Cu/Cu2O electrode (1 x 1 cm(2)). 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-center dot). 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-center dot, CH3 center dot, and OH center dot radical species generated in situ. The medium pH was identified as a key variable in the selectivity of the methanol formation. (C) 2014 Elsevier B.V. All rights reserved.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)