The reactor design for photoelectrochemical hydrogen production

The heat transfer and flow characteristics of a photoelectrochemical (PEC) hydrogen generation reactor are investigated numerically. Four different reactor designs are considered in this study. The solar irradiation is separated into short and long wavelength parts depending on the energy band gap of the photoelectrode used. While short wavelength part is used to generate electron and hole pairs, the long wavelength part is used to heat the system. Because the energy required for splitting water decreases as temperature is increased, heating the reactor by using the long wave energy increases the system efficiency. Thus, how the long wavelength energy is absorbed by the reactor is very important. The results show that more long wavelength energy kept inside the reactor can increase the solar-to-hydrogen efficiency, η_SH. For Fe₂O₃ photoelectrode, careful reactor design can increase η_SH by 11.0%. For design D under 4000 W/m² irradiation and a quantum efficiency of 30%, η_SH is found to be 14.1% and the hydrogen volume production rate is 166 L/m² h for Fe₂O₃. Effects of several parameters on the PEC hydrogen reactor are also discussed.