The importance of non-ideality of protons and water in the open circuit potential modelling of redox flow battery aqueous electrolytes
File(s)
Published version
Author(s)
Sun, YuChen
Brandon, Nigel
Weiss, Dominik
Kucernak, Anthony
Type
Journal Article
Abstract
The non-ideality of electrolytes is commonly neglected in redox flow battery (RFB) modelling work. The neglect of activity coefficients introduces a discrepancy of up to 100 mV between the experimental open circuit potential (OCP) and model predicted reversible Nernstian potential, which propagates into inaccurate state of charge estimation and misinterpretation of thermodynamic efficiency. Due to the complex chemistry and the lack of thermodynamic data, activity coefficients of individual species in highly non-ideal electrolytes are often difficult to determine. In this work, proton and water activity values were calculated using geochemical numerical codes implementing the Pitzer theory, a semi-empirical thermodynamic model that accounts for the non-ideal behavior of ions in electrolyte solutions. The completed Nernst equation with corrected activity values has been elaborated for OCP comparison. An in-operando approach was proposed to measure the proton and water activities of strongly acidic electrolytes. The cell OCP of Hydrogen-Vanadium RFB (H2-V RFB) and Hydrogen-Manganese RFB (H2-Mn RFB) was measured and calculated to assess the electrochemical significance of proton and water non-ideality to the RFB model. With the measured activity data, the error between the experimental and calculated OCP values was reduced from 88-100 mV to 17–50 mV.
Date Issued
2026-01-01
Date Acceptance
2025-10-07
Citation
Journal of Power Sources, 2026, 661
ISSN
0378-7753
Publisher
Elsevier BV
Journal / Book Title
Journal of Power Sources
Volume
661
Copyright Statement
© 2025 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
License URL
Publication Status
Published
Article Number
238590
Date Publish Online
2025-10-16