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Monitoring and Modeling of Compression Creep of Perfluorosulfonic Acid Membranes for Electrolyzers

Water-splitting electrolyzers are a key technology for enabling the hydrogen economy and reshaping the renewable energy landscape. Among the most viable candidates for the low-temperature electrolyzers is the proton-exchange membrane (PEM) water-splitting electrolyzers (PEMWEs), which uses an ion-conductive polymer solid-electrolyte. For PEMWEs to be commercially viable, PEMs must perform over long operational times in liquid environments under compression and therefore must exhibit good mechanical stability when hydrated. [1-2]. While a hydrated environment is an intrinsic result of the operation and membrane’s conductive function, it undermines PEM stability. [3] PEMs are under unique mechanical stresses due to differential pressure affecting the active area, and high sealing pressures to prevent off-board leaks, thus, high differential pressure in PEMWEs makes compressive creep a great concern. [4] However, mechanical stability of PEMs is commonly characterized by tensile testing [5], the applicability of which to electrolyzers or technologies with similar cell designs is unclear. Using compression and compression creep data of hydrated PEMs in situ and in controlled temperature [6], this work develops a material model to describe PEM under device-relevant operation.
 An important aspect of PEM design consideration is the stability of membrane, especially under conditions relevant to operation, such as, in a liquid environment with varying range of temperatures (50 to 80 °C). While hydration, pressure, and temperature are used as design parameters for optimizing electrolyzers performance, their role in durability is not established [5]. This creates a gap between performance and lifetime assessment of membranes for electrolyzers. Thus, there is need for a model that could capture membrane durability by accounting for performance operators. This study identifies compression creep as a potential material stability metric that can account for the operation-dependent variables, such as pressure, dehydration, and temperature, and provides guidance for better assessment of membrane lifetime in electrolyzers and similar electrochemical devices.
 Our results show compressive response of perfluorosulfonic acid (PFSA) membranes is significantly different than tensile behavior in both dry and hydrated states [6]. Moreover, PEMs exhibit creep response under compression with continuous decrease in its thickness over 24 hours, with a dependence on the applied pressure and temperature [6]. This work demonstrates the importance of studying the mechanical properties of PEMs under compression, which is more relevant to the stress-states the membrane undergoes during operation in an electrolyzer and similar electrochemical devices.
 
 References
 
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 [2] K. E. Ayers et al., “Research Advances towards Low Cost, High Efficiency PEM Electrolysis,” ECS Trans., vol. 33, no. 1, pp. 3–15, 2010, doi: 10.1149/1.3484496.
 [3] A. Kusoglu, S. Savagatrup, K. T. Clark, and A. Z. Weber, “Role of mechanical factors in controlling the structure-function relationship of PFSA ionomers,” Macromolecules, vol. 45, no. 18, pp. 7467–7476, 2012, doi: 10.1021/ma301419s.
 [4] C. Cropley and T. Norman, “DEPARTMENT OF ENERGY A Low-Cost High-Pressure Hydrogen Generator,” System, 2008.
 [5] A. Kusoglu and A. Z. Weber, “New Insights into Perfluorinated Sulfonic-Acid Ionomers,” Chem. Rev., vol. 117, no. 3, pp. 987–1104, 2017, doi: 10.1021/acs.chemrev.6b00159.
 [6] C. Arthurs and A. Kusoglu, “Compressive Creep of Polymer Electrolyte Membranes: A Case Study for Electrolyzers,” ACS Appl. Energy Mater., vol. 4, no. 4, pp. 3249-3254. Mar. 2021, doi: 10.1021/acsaem.0c03024.