Mechanism of Ionomer Degradation as a Consequence of Defective Anode PEMFC

Abstract

Defects in the various components of the membrane-electrode assembly (MEA), initially present or created during aging, are known to be responsible for the short lifetime PEMFC. Catalytic layer degradation has been identified as one of them [1]. However, the possible propagation of these defects to other components within a cell or a stack is not clear in the literature. To shed light on these phenomena, customized MEAs with a localized lack of anode active layer at two different locations -near the hydrogen inlet or outlet- were manufactured and tested with specific accelerated aging tests, combining high and low current and humidity cycles; these were specifically tailored to observe a possible propagation of the defects [2]. Local performance monitoring using a segmented cell revealed variations within the catalytic layers upstream and downstream of the defect. In order to better understand the impact of anode active layer defects on MEA components, localized physicochemical analyses were performed post mortem along the gas flow, with the main objective to identify possible degradations of the reinforced perfluorosulfonic acid (PFSA) membranes. Microscopic thickness measurements showed significant membrane thinning in the defective segments. Difference of these localized degradations between the monopolar plates rib and channel zones will be highlighted depending on the defect location i.e. at the inlet and outlet of hydrogen flow (Figure below). In the defective area, decrease of the Ion Exchange Capacity estimated by Raman analyses is pointed out for the reinforced PFSA layer. The PFSA chain degradation mechanism will be discussed, and, thus, the degradation rate will be calculated based on Raman and FTIR microscope and 19F NMR. For longer ageing time, the ionomer degradation is extended to an non-defective area. A propagation mechanism of the degradation will be proposed.[1] L, Dubau, et al. WIREs Energy and Environ. 2014, 3, pp. 540-560.[2] S, Touhami, et al. J. Power Sources. 2021, 481, pp. 228908-228917. Figure 1