Thermodynamic analysis of the efficiency of high-temperature steam electrolysis system for hydrogen production

High-temperature steam electrolysis (HTSE), a reversible process of solid oxide fuel cell (SOFC) in principle, is a promising method for highly efficient large-scale hydrogen production. In our study, the overall efficiency of the HTSE system was calculated through electrochemical and thermodynamic analysis. A thermodynamic model in regards to the efficiency of the HTSE system was established and the quantitative effects of three key parameters, electrical efficiency (ηel), electrolysis efficiency (ηes), and thermal efficiency (ηth) on the overall efficiency (ηoverall) of the HTSE system were investigated. Results showed that the contribution of ηel, ηes, ηth to the overall efficiency were about 70%, 22%, and 8%, respectively. As temperatures increased from 500 °C to 1000 °C, the effect of ηel on ηoverall decreased gradually and the ηes effect remained almost constant, while the ηth effect increased gradually. The overall efficiency of the high-temperature gas-cooled reactor (HTGR) coupled with the HTSE system under different conditions was also calculated. With the increase of electrical, electrolysis, and thermal efficiency, the overall efficiencies were anticipated to increase from 33% to a maximum of 59% at 1000 °C, which is over two times higher than that of the conventional alkaline water electrolysis.