Photoelectrochemical production of formic acid and methanol from carbon dioxide on metal-decorated CuO/Cu2O-layered thin films under visible light irradiation

Abstract

As a cathode material for fuel generation from CO2 reduction in a photoelectrochemical system, layered CuO/Cu2O films were developed and their surfaces were decorated with transition metals (i.e. Ag, Au, Cd, Cu, Pb, and Sn). Deposition of the transition metals effectively enhanced CO2 conversion to fuel in terms of faradaic efficiency. In particular, Pb/CuO/Cu2O demonstrated outstanding performance among the transition metals: 0.524μmol/hcm2 for formic acid and 0.102μmol/hcm2 for methanol with 40.45% of total faradaic efficiency at −0.16V (vs. SHE), which was a higher potential than standard redox potentials of formic acid and methanol formation from CO2. Moreover, electrochemical impedance spectroscopy (EIS) showed that the deposition of the transition metals onto CuO/Cu2O electrode effectively generated photo-induced electron–hole pairs under visible light irradiation. However, fast performance degradations of the prepared electrodes were observed during the reactions as well as the disappearances of the photocurrents. X-ray photoelectron spectroscopy (XPS) results revealed that the outer CuO layer was readily reduced to Cu2O/Cu, and this compositional destruction was responsible for the degradation of the photocurrent by prohibiting transfers of the electrons (or holes) to the active sites.