Vapor pressure and specific electrical conductivity in the H2O–LiH2PO4–LiPO3 system—a novel electrolyte for water electrolysis at elevated temperature

Rolf W. Berg*, Aleksey Valerievich Nikiforov, Niels J. Bjerrum

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Lithium dihydrogen phosphate, LiH2PO4 (LDP), was studied for water electrolysis at elevated temperatures. It is shown that pure LDP, melting at ~ 224 °C and with correct DSC and X-ray diffraction diagram, in presence of sufficient humidity is stable up to 360 °C. Both solid and liquid LDP is structurally disordered and superprotonic conducting with conductivities reaching 0.48 S*cm−1, when determined in sealed conductivity cells. The vapor pressure above LDP, pure and mixed with LiPO3 or H2O, was determined by means of Raman spectroscopy based on N2 as internal reference gas. Pressures up to ~ 20 bar at 350 °C were found and conductivities are given for solid and liquid states. Water splitting by electrolysis, 2H2O ➔ 2H2 + O2, was demonstrated by Raman spectroscopy at ~ 225 °C and ~ 4.2 bar with Pt/W electrodes, thus showing that molten LDP has a significant potential for elevated temperature water electrolysis with high efficiency.
Original languageEnglish
JournalIonics
Volume27
Issue number2
Pages (from-to)703–719
ISSN0947-7047
DOIs
Publication statusPublished - 2021

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