Effect of inserted Si p-n junction on GaN-based photo-electrochemical CO2 conversion system

We report on significantly improved GaN-based photo-electrochemical CO2 reduction system by inserting Si p-n junction. The device is introduced so as to raise the cathode potential which changes the reaction products qualitatively. It is discussed that the balance between cathode and anode reactions is essential to take the advantage of introduced device. We succeed in stoichiometric evaluation of oxygen evolution on the surface of GaN photo-electrode. When the reaction condition is optimized, we can realize the raised cathode potential, in which the chief reaction product of CO2 reduction changes from formic acid to hydrocarbons, such as methane (CH4) and ethylene (C2H4).