PEEK-Reinforced Sulfonated Poly(phenylene sulfone)-Membrane for Water Electrolysis with Lower Gas Crossover and Lower Resistance Than N115
Authors: Qelibari Regina , Münchinger Andreas , Titvinidze Giorgi , Klose Carolin , Vierrath Severin 
Published: December 2024

Fluorine-free hydrocarbon polymers have the potential to be more environmentally friendly and cost-effective than current perfluorinated sulfonic acids (PFSA). These hydrocarbon polymers have a unique morphology that reduces gas transfer while maintaining high proton conductivity, making them a promising alternative to PFSA membranes in water electrolysis.[1] In an initial study, we demonstrate the potential of hydrocarbon membranes in electrolyzers using sulfonated polyphenylene sulfone (sPPS).[2] However, to achieve good performance, a high ion exchange capacity (2.17 - 3.57 meq/g) is required. This results in a high water uptake, which leads to membrane softening and detachment of the electrodes. In addition, excessive swelling makes upscaling, i.e., coating of the electrodes directly onto the membrane, impossible. To solve this problem, we have integrated a woven, open-mesh PEEK substrate (Fig.1, right).[3] The reinforced membrane shows a significant enhancement in the mechanical robustness and dimensional stability of the membrane, which leads to a strong reduction of water uptake from 294% to 115%. This allows direct casting of electrodes onto the membrane, an essential step for scaled production. Moreover, the reinforced membrane demonstrates a significantly lower electrical resistance of 70 mΩ cm² (versus 159 mΩ cm² for Nafion), attributed to its reduced thickness (74 µm compared to 127 µm) and higher ion exchange capacity. At the same time, the crossover is also strongly reduced as displayed in Figure 1. This leads to a better figure of merit, given by the ratio of conductivity to permeability, as shown in Figure 1 (right bottom), where crossover current densities are plotted over the high frequency resistance.[3]

Figure
1Illustration of the casting Process of the reinforced membrane and fabrication of a one side coated CCM (left). IV-curve of the PEEK-sPPS membrane and a Nafion 115 reference (top right) and the figure of merit for PEEK-sPPS and two reference membranes (N115 and N212).

Literature: [1] Miyake, J.; Taki, R.; Mochizuki, T.; Shimizu, R.; Akiyama, R.; Uchida, M.; Miyatake, K. Design of flexible polyphenylene proton-conducting membrane for next-generation fuel cells. Sci. Adv.
2017, 3(10), eaao0476. DOI: 10.1126/sciadv.aao0476

[2] Klose, C.; Saatkamp, T.; Münchinger, A.; Bohn, L.; Titvinidze, G.; Breitwieser, M.; Kreuer, K.; Vierrath, S. All‐Hydrocarbon MEA for PEM Water Electrolysis Combining Low Hydrogen Crossover and High Efficiency. Adv. Energy Mater.
2020, 10 (14), 1903995. DOI: 10.1002/aenm.201903995

[3] Qelibari, R.; Cruz Ortiz, E.; van Treel, N.; Lombeck, F.; Schare, C.; Münchinger, A.; Dumbadze. N.; Titvinidze, G.; Klose, C.; Vierrath, S. 74 µm PEEK-reinforced sulfonated poly(phenylene sulfone)-membrane for stable water electrolysis with lower gas crossover and lower resistance than Nafion N115. Adv. Energy Mater.
2023, 14 (5), 2303271. DOI: 10.1002/aenm.202303271

Figure 1