Spatially Resolved Quantification of Ionomer Degradation in Fuel Cells by Confocal Raman Microscopy. Issue 7 (1st January 2019)

• Record Type: Journal Article
• Authors: Böhm, Thomas; Moroni, Riko; Breitwieser, Matthias; Thiele, Simon; Vierrath, Severin
• Is Part Of: Journal of the Electrochemical Society. Volume 166:Issue 7(2019)
• Page Start: F3044
• Page End: F3051
• Publication Date: 2019-01-01
• Subjects: Fuel Cells -- ionomer -- membrane degradation -- Nafion; Electrochemistry -- Periodicals; 541.3705
• DOI: 10.1149/2.0051907jes
• Languages: English
• ISSNs: 0013-4651

Abstract

Abstract : Ionomer membranes are crucial components of many electrochemical devices. In this work, confocal Raman microscopy is employed to characterize Nafion ionomers quantitatively in pristine status and after usage as a proton exchange membrane in a fuel cell. Confocal Raman microscopy allows non-destructive thickness and equivalent weight measurements of Nafion with a 95% confidence interval of ±13 g mol −1 at an equivalent weight of 1000 g mol −1, which is significantly more accurate than previously reported methods. Characterization can be performed at a spatial resolution better than 2 μm, providing insights into local membrane degradation after fuel cell operation. Membrane thinning to less than 40% of the initial thickness of Nafion NR-211 occurs after a 100 h open circuit voltage hold, accompanied by an anisotropic increase of the equivalent weight from 1035 g mol −1 to an average of 1200 g mol −1 . Most pronounced increases are found close to the anode. Further, the characterization of a Nafion XL membrane shows that its microporous reinforcement is represented as increased equivalent weight with local heterogeneities within the membrane. These results show that confocal Raman microscopy is a valuable tool to investigate ionomers that are used as ion exchange membranes in electrochemical devices.