Photoelectrochemical reduction of CO2 at p-InP electrode in copper particle-suspended methanol

The photoelectrochemical reduction of CO2 in copper particle-suspended methanol was studied by using a p-type InP photoelectrode. In the absence of copper particles, only formic acid and carbon monoxide were formed during the photoelectrochemical reduction of CO2, and the formation of hydrocarbons could not be observed. However, hydrocarbons were formed on the addition of copper particles into the catholyte. The current efficiencies of methane and ethylene were better below 273 K than at ambient temperature (288 K). The maximum Faradaic efficiencies of methane and ethylene were rf = 0.56% and 0.80%, respectively. The total current efficiency of hydrocarbons became maximum at 263 K, and the maximum efficiency was rf = 1.21%. On the basis of these observations, it was realized that it is possible to roughly change and control the reduction product distribution by the addition of metal particles into the catholyte during the photoelectrochemical reduction of CO2. This research can contribute to the large-scale manufacture of useful organic products from readily available and cheap raw materials, e.g., the manufacture of CO2-saturated methanol from industrial absorbers (the Rectisol process).