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| Hauptseite > Publikationsdatenbank > Combined high field and benchtop NMR studies of catalyst separation techniques on proton exchange membranes |
| Hauptseite > Publikationsdatenbank > Combined high field and benchtop NMR studies of catalyst separation techniques on proton exchange membranes |
| Poster (Panel discussion) | FZJ-2024-05345 |
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2024
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Please use a persistent id in citations: doi:10.34734/FZJ-2024-05345
Abstract: Proton exchange membrane (PEM) electrolysis is a promising technology for the large-scale production of green hydrogen using energy from renewable sources. PEMs are commonly based on perfluoroalkane sulfonic acid ionomers, i.e. polymers composed of a hydrophobic PTFE backbone and hydrophilic side chain with a sulfonic acid function. While PEM electrolyzers can be operated at high current densities and efficiencies, their industrial implementation is hindered by the high cost of the components, where catalysts and the PEM contribute a significant share. In addition, a PFAS ban is currently discussed by various governments. Thus, the PEM and catalysts must be used efficiently, and recycling of the materials at the end of their lifetime is incentivized. Current protocols for separation of the membrane-electrode-assembly (MEA) into PEM and catayst often involve isopropanol/water mixtures in combination with mechanical treatment [1]. However, the effect of the technique on the PEM properties has yet to be discussed in detail, as the incentive of separation was initially focused on the precious metal catalysts.This work presents two pathways for studying PEM materials by these separation techniques: First, a high field 19F MAS study focused on the structure and chemical composition of the ionomer, and second, a 1H benchtop NMR investigation utilizing proton diffusivity and relaxation experiments for assessment of the PEM. After separation treatment of the PEM, the 19F study revealed a significant loss of polar side chains in the ionomer in addition to less restricted polymer chain motions. These chemical and structural alterations suggest a loss of order in the ionomer structure, which is in line with the increased swelling behavior of the PEM after separation treatment. 1H PFG and relaxation studies support this conclusion, as both short- and long-range proton mobility increased significantly. Interestingly, the separation technique also led to the formation of two, non-exchanging proton diffusion regimes, indicating significant changes in the water transport behavior of the PEM. In conclusion, both high-field and low-field NMR studies contributed to new insights on the effect of membrane/catalyst separation techniques described in literature. While both methods are required for a comprehensive interpretation, 1H benchtop NMR proved capable as a low-cost and ease of use screening method.
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