Little is known about the electrolysis of supercritical water and what benefits it might offer in terms of hydrogen cost reduction [2,3]. In this work, experimental data was collected for supercritical water electrolysis and used to build an electrochemical model suitable for use under those conditions. The results of this model, combined with components of a previously published technoeconomic model for a high-temperature and pressure water electrolysis plant [4], indicate that while supercritical water electrolysis is achievable it is not the most economically efficient choice for hydrogen production. High-temperature and pressure water electrolysis performed under optimal conditions can be used to achieve higher economic efficiency when compared with contemporary water electrolysis solutions. Finally, a thorough optimization of the model presents a grim picture for achieving the US Department of Energy’s $2 kgH₂^-1 target through water electrolysis without government subsidy.

References:

[1] D. Todd, M. Schwager, W. Mérida, Thermodynamics of high-temperature, high-pressure water electrolysis, J. Power Sources. 269 (2014) 424–429. https://doi.org/10.1016/j.jpowsour.2014.06.144.

[2] H. Boll, E.. Franck, H. Weingärtner, Electrolysis of supercritical aqueous solutions at temperatures up to 800K and pressures up to 400MPa, J. Chem. Thermodyn. 35 (2003) 625–637. https://doi.org/10.1016/S0021-9614(02)00236-7.

[3] P.C. Ho, D.A. Palmer, Determination of ion association in dilute aqueous potassium chloride and potassium hydroxide solutions to 600°C and 300 MPa by electrical conductance measurements, J. Chem. Eng. Data. 43 (1998) 162–170. https://doi.org/10.1021/je970198b.

[4] T. Holm, T. Borsboom-Hanson, O.E. Herrera, W. Mérida, Hydrogen costs from water electrolysis at high temperature and pressure, Energy Convers. Manag. 237 (2021) 114106. https://doi.org/10.1016/j.enconman.2021.114106.