System level modeling and optimization of high temperature proton exchange membrane electrolyzer system considering recirculated hydrogen as carrier gas

High temperature proton exchange membrane electrolyzer cell is promising for hydrogen production using excess renewable power. However, system level simulation and optimization are lacking, which is critical for practical application. In this research, system level models are developed, considering the use of recirculated hydrogen and steam as carrier gases. It is found that the use of recirculated hydrogen shows higher efficiency than steam as a carrier gas due to lower thermal energy input, especially under the large steam stoichiometric excess ratio. Moreover, the effects of the working temperature and gas flow rate on the energy demand and energy efficiency are studied. The hydrogen recirculation system is more sensitive to the effects of temperature, and the steam carrier gas system has a lower thermoneutral voltage. Compared with the hydrogen recirculation system, the current density that corresponds to the optimal energy efficiency point of the steam carrier gas system is higher. At a gas flow rate of 0.015 mol s⁻¹, the current density at the optimal energy efficiency point of the hydrogen recirculation system is 7700 A m⁻², while that of the steam carrier gas system is 8800 A m⁻². The study can guide the integration of the electrolyzer system.