Experimental and Theoretical Investigations of Shunt Currents between Alkaline Water Electrolyzers

Abstract

A pivotal component of national climate strategies is the transition of the energy sector from fossil fuels to green energy. In this context, electrochemical processes will play a significant role in the future, requiring electrochemical systems with high efficiency and maximum system life cycles.1,2 For industrial electrochemical systems capital and operating costs are often reduced by a system design with a shared and circulating electrolyte supply providing ionically conductive cell-to-cell pathways. Under such conditions, parasitic ion migration occurs between adjacent cells, known as shunt currents.3,4 Shunt currents can have severe implications, such as decrease in faraday efficiency, material corrosion or interferences with instrumentation 3,5,6.To ensure high efficiency and maximum system life cycle, shunt current estimation is of high importance for the design of electrochemical multi-cell systems. A widely used approach in the literature is the theoretical, model-based approach using equivalent circuit models for shunt current determination7–9. Only a few publications demonstrate experimental determination methods 10,11. Furthermore, most shunt current studies in the field of electrochemistry focus on redox flow batteries.This work shows an innovative experimental approach for direct shunt current measurements between two alkaline water electrolysis cells with shared and circulating electrolyte feed under various conditions. The flow field design enables the insertion of reference electrodes into the flow cells for direct measurement of the potential differences between adjacent electrodes. Combined with the experimental data of the ionic tube resistances, the cell-to-cell shunt currents were accurately determined. Furthermore, an equivalent circuit model was created, fed with experimental data and validated with measured results. After successful validation the model was extended to electrolysis systems with more than two cells.Experimental data and simulations are in good agreement. The conducted experiments show the impact of temperature, cell voltage and tube manifold geometry on shunt current formation between alkaline water electrolyzers. Simulations performed are carried out to calculate shunt currents as a function of these parameters in large multi-cell systems. Furthermore, efficiency losses and corrosion processes as a result of shunt currents are estimated based on the results of this work.Literature Baños R, Manzano-Agugliaro F, Montoya FG, Gil C, Alcayde A, Gómez J. Optimization methods applied to renewable and sustainable energy: A review. Renew Sustain Energy Rev. 2011;15(4):1753-1766. doi:10.1016/j.rser.2010.12.008Yan Z, Hitt JL, Turner JA, Mallouk TE. Renewable electricity storage using electrolysis. Proc Natl Acad Sci U S A. 2020;117(23):12558-12563. doi:10.1073/pnas.1821686116Delgado NM, Monteiro R, Cruz J, Bentien A, Mendes A. Shunt currents in vanadium redox flow batteries – a parametric and optimization study. Electrochim Acta. 2022;403:139667. doi:10.1016/j.electacta.2021.139667Kaminski EA, Savinell RF. A Technique for Calculating Shunt Leakage and Cell Currents in Bipolar Stacks Having Divided or Undivided Cells. J Electrochem Soc. 1983;130(5):1103-1107. doi:10.1149/1.2119891Yin C, Guo S, Fang H, Liu J, Li Y, Tang H. Numerical and experimental studies of stack shunt current for vanadium redox flow battery. Appl Energy. 2015;151:237-248. doi:10.1016/j.apenergy.2015.04.080Pletcher D, Walsh FC. Industrial Electrochemistry. Springer Science & Business Media; 2012.Schaeffer JA, Chen L Der, Seaba JP. Shunt current calculation of fuel cell stack using Simulink®. J Power Sources. 2008;182(2):599-602. doi:10.1016/j.jpowsour.2008.04.014Wandschneider FT, Röhm S, Fischer P, Pinkwart K, Tübke J, Nirschl H. A multi-stack simulation of shunt currents in vanadium redox flow batteries. J Power Sources. 2014;261:64-74. doi:10.1016/j.jpowsour.2014.03.054Ye Q, Hu J, Cheng P, Ma Z. Design trade-offs among shunt current, pumping loss and compactness in the piping system of a multi-stack vanadium flow battery. J Power Sources. 2015;296:352-364. doi:10.1016/j.jpowsour.2015.06.138Rous̆ar I, Cezner V. Experimental Determination and Calculation of Parasitic Currents in Bipolar Electrolyzers with Application to Chlorate Electrolyzer. J Electrochem Soc. 1974;121(5):648. doi:10.1149/1.2401878Fink H, Remy M. Shunt currents in vanadium flow batteries: Measurement, modelling and implications for efficiency. J Power Sources. 2015;284:547-553. doi:10.1016/j.jpowsour.2015.03.057