Abstract
Gallium nitride (GaN) has been shown to be a good photocatalyst for not only water splitting but also carbon dioxide (CO2) reduction. To verify the catalytic reaction involved in CO2 reduction, it is essential to confirm that the reaction products only come from dissolved CO,. Here, we report the results of (CO2)-C-13-labeling experiments on a GaN-Si based photoelectrochemical system for each reduction product. It was found that the C-13-based CO2 was almost completely converted to formic acid (HCOOH), methane, and ethylene when KCl was used as the electrolyte. In contrast, HCOOH from C-12 was observed when KHCO3 electrolyte was used, meaning that HCO3- in the electrolyte partly contributed to CO2 reduction. The energy conversion efficiency and Faradaic efficiency of the respective reduction processes in the present system are also discussed.