Stability and Degradation Mechanisms of Radiation-Grafted Polymer Electrolyte Membranes for Water Electrolysis

Abstract

Radiation-grafted membranes are a promising alternative to commercial membranes for water electrolyzers, since they exhibit lower hydrogen crossover and area resistance, better mechanical properties, and are of potentially lower cost than perfluoroalkylsulfonic acid membranes, such as Nafion. Stability is an important factor in view of the expected lifetime of 40 000 h or more of an electrolyzer. In this study, combinations of styrene (St), α-methylstyrene (AMS), acrylonitrile (AN), and 1,3-diisopropenylbenzene (DiPB) are cografted into 50 μm preirradiated poly(ethylene-co-tetrafluoroethylene) (ETFE) base film, followed by sulfonation to produce radiation-grafted membranes. The stability of the membranes with different monomer combinations is compared under an accelerated stress test (AST), and the degradation mechanisms are investigated. To mimic the conditions in an electrolyzer, in which the membrane is always in contact with liquid water at elevated temperature, the membranes are immersed in water for 5 days at 90 °C, so-called thermal stress test (TST). In addition to testing in air atmosphere tests are also carried out under argon to investigate the effect of the absence of oxygen. The water is analyzed with UV-vis spectroscopy and ion chromatography. The ion exchange capacity (IEC), swelling degree, and Fourier transform infrared (FTIR) spectra of the membranes are compared before and after the test. Furthermore, energy-dispersive X-ray (EDX) spectroscopic analysis of the membrane cross-section is performed. Finally, the influence of the TST to the membrane area resistance and hydrogen crossover is measured. The stability increases along the sequence St/AN, St/AN/DiPB, AMS/AN, and AMS/AN/DiPB grafted membrane. The degradation at the weak-link, oxygen-induced degradation, and hydrothermal degradation are proposed in addition to the "swelling-induced detachment" reported in the literature. By mitigating the possible paths of degradation, the AMS/AN/DiPB grafted membrane is shown to be the most stable membrane and, therefore, it is a promising candidate for a membrane to be used in a water electrolyzer.

Scaling the Graft Length and Graft Density of Irradiation‐Grafted Copolymers

“…argued that when ETFE was grafted with methyl acrylate, the long‐term swelling in hot water (85 °C) resulted in the detachment of the grafts from the base polymer, and the length of the grafted chains could be measured via gel permeation chromatography . The swelling approach, however, is reported to result in additional chain‐scission mechanisms, which questions the accuracy and selectivity of the analysis . Indeed, the complete lack of this approach in another but very similar work reported also by Enomoto et al.…”

Preparation and Characterization of PVA Alkaline Solid Polymer Electrolyte with Addition of Bamboo Charcoal

“…Compared to aqueous electrolyte (i.e., KOH), alkaline solid polymer electrolyte (ASPE), for use in nickel-hydrogen (Ni-MH) batteries, could provide solutions to the problems of high internal pressure upon charging [ 5 ], alkaline leakage [ 6 ], oxidation of negative electrode (hydrogen storage alloy) upon charge/discharge cycling [ 7 ] and high self-discharge rate [ 8 ]. Besides the ASPE features good processibility [ 9 ], and mechanical properties. To sum up, ASPE have been suggested to replace aqueous electrolytes [ 10 ].…”

Understanding Degradation Effects of Elevated Temperature Operating Conditions in Polymer Electrolyte Water Electrolyzers

“…Subtraction of η jR from E cell gives the iR-free cell voltage E iR .Thermal stress test.-Thermal stress tests with Nafion N117 membranes and CCMs were performed according to Albert et al 29. …”