Abstract
We report on a qualitatively improved photoelectrochemical CO2 reduction system which makes it possible to convert CO2 into hydrocarbons. The key is the tandem photoelectrode, which consists of AlGaN/GaN and Si device with p-n junction. The Si device is located on the back of AlGaN/GaN structure and acts as activation layer that raises cathode potential. Use of a Cu cathode results in change of the main reaction products from CO and HCOOH to hydrocarbons such as CH4 and C2H4. The energy conversion efficiency to hydrocarbons from CO2 is estimated to be 0.046% under irradiation with concentrated solar light.