Investigation of the Impact of Chloride Contamination on Degradation in PEM Water Electrolyzer Cells

Abstract

Polymer electrolyte membrane water electrolysis (PEMWE) is a promising technology for hydrogen production from renewable energy sources. However, current systems require ultra-pure water (>18 MΩ*cm) and fail in the presence of impurities like dissolved ions or chemical contaminants [1,2]. Due to the cost of purification and local scarcity of groundwater, there is a rising interest in creating electrolyzers that can function using water of inferior quality [3]. Additionally, feedwater used in offshore applications that is generated by the desalination of seawater still contains low amounts of ionic contaminants [4].Among the most detrimental impurities responsible for performance loss in PEMWE, Cl− is present in high concentrations in both, sea- and potable water [3]. Cl− can reduce the efficiency of the electrolysis process by accelerating component degradation and lower the purity of the produced hydrogen. A competing reaction between the oxygen evolution reaction (OER) and the chlorine evolution reaction (CER) results in the formation of gaseous chlorine that lowers the quality of the produced hydrogen gas. Additionally, Cl− blocking layers can form on the catalyst surfaces which result in a reduced electrochemical surface area. For PEM fuel cells, a technology facing related problems, Cl− adsorption has also been reported to accelerate the formation of hydrogen peroxide [5], promoting chemical degradation of the PFSA-based membrane.The scope of this work is to quantify the reduction of efficiency based on different Cl− concentrations in the feedwater of a PEMWE cell. Therefore, a single cell PEMWE with commercial catalyst coated membranes (CCMs) is exposed to different concentrations of Cl−. The PEMWE single cell is operated up to 100 h and investigated by various characterization techniques, including in-situ and ex-situ cell tests. Electrochemical performance characterization by means of polarization behaviour and impedance spectroscopy is carried out throughout a range of currents (0.01 A cm− 2 to 3.0 A cm− 2) at 60°C. Furthermore, the fluoride emission rate (FER) is monitored during the experiments and optical investigation of the CCMs is carried out after the tests. Based on this complementary investigation, a deeper insight into degradation phenomena associated with Cl− contamination in PEMWE cells is presented. Feng, Q.; Yuan, X.; Liu, G.; Wei, B.; Zhang, Z.; Li, H.; Wang, H. A Review of Proton Exchange Membrane Water Electrolysis on Degradation Mechanisms and Mitigation Strategies. Journal of Power Sources 2017, 366, 33–55, doi:10.1016/j.jpowsour.2017.09.006.Kuhnert, E.; Hacker, V.; Bodner, M. A Review of Accelerated Stress Tests for Enhancing MEA Durability in PEM Water Electrolysis Cells. International Journal of Energy Research 2023, 2023, 1–23, doi:10.1155/2023/3183108.Becker, H.; Murawski, J.; Shinde, D.V.; Stephens, I.E.L.; Hinds, G.; Smith, G. Impact of Impurities on Water Electrolysis: A Review. Sustainable Energy Fuels 2023, 7, 1565–1603, doi:10.1039/D2SE01517J.Bacquart, T.; Moore, N.; Wilmot, R.; Bartlett, S.; Morris, A.S.O.; Olden, J.; Becker, H.; Aarhaug, T.A.; Germe, S.; Riot, P.; et al. Hydrogen for Maritime Application—Quality of Hydrogen Generated Onboard Ship by Electrolysis of Purified Seawater. Processes 2021, 9, 1252, doi:10.3390/pr9071252.Katsounaros, I.; Meier, J.C.; Mayrhofer, K.J.J. The Impact of Chloride Ions and the Catalyst Loading on the Reduction of H2O2 on High-Surface-Area Platinum Catalysts. Electrochimica Acta 2013, 110, 790–795, doi:10.1016/j.electacta.2013.03.156.