XPS Analysis of Polymer Membrane Degradation in PEMFCs

Abstract

An important challenge for proton exchange membrane fuel cells (PEMFCs) is the stability and durability of the membrane separator. In this study, fluoride ion emission rates were determined from fuel cell durability tests at different temperatures. Degraded membranes were removed after each test, and both the anode and cathode sides of degraded membranes were analyzed by X-ray photoelectron spectroscopy (XPS). The results show that degradation was accelerated by high temperature and that the decomposition of both sulfonic acid side chains and the poly(tetrafluoroethylene) backbone occurred. The degradation was more severe on the anode side, showing that at least half of the side groups were decomposed there. A multilayer membrane electrode assembly was also used to study degradation at different locations especially in the bulk membrane, which illustrates that the degradation also occurs there but is slower than that at the anode side. This result also indicates that the rate of membrane degradation slows with thicker membrane. Finally, an improved kinetic model of membrane degradation was proposed to explain the experimental results.

Effect of Mechanical Compression on Chemical Degradation of Nafion Membranes

“…1,[9][10][11][12][13][14]16 Fenton's Test is commonly employed to study the chemical-decomposition behavior of a membrane by monitoring the release of fluoride ions from the PFSA membrane's fluorocarbon chains. 1,7,[9][10][11][12][13][14] While it is known that chemical degradation changes the membrane's mechanical and other properties, 7,17,18 it is unknown as to whether concurrent mechanical and chemical stressors act independently or in concert to alter membrane degradation rates. Such combined stresses are expected to occur under actual operation due to simultaneous load and humidity changes.…”

“…These latter stressors originate from the deformation of the membrane due to cell assembly (constraint) and subsequent operational stresses driven by the hydration/dehydration of the constrained membrane. [1][2][3][4][5][6][7] To understand the impact of various stressors, accelerated stress tests (ASTs) are typically conducted with the aim of enhancing a single failure mode, 1,2,8 with Fenton's tests accelerating chemical degradation 7,[9][10][11][12][13][14] and relative-humidity (RH) cycling used for mechanical degradation. [1][2][3]6,8,15 However, failure mechanisms in operando are controlled by combination of chemical and mechanical stressors, which makes understanding any synergistic chemical/mechanical interactions of great importance.…”

Performance and degradation of Proton Exchange Membrane Fuel Cells: State of the art in modeling from atomistic to system scale

“…and subsequent decomposition to radical species is the main cause for chemical membrane degradation [280][281][282][283]. However, reports on the location of membrane degradation are contradictory: Degradation was observed at the anode [284,285] or at the cathode [286,287].…”

“…(zero dimensional) models are applied [280,281,299,300]. Further, 1D models for chemical degradation of the membrane were embedded in a simulated fuel cell environment [282,283].…”

Impact of Low Frequency Narrow Pulse Current on the Degradation of Proton Exchange Membrane Fuel Cells

“…It is necessary to keep the pressure difference between anode and cathode within a reasonable range, otherwise, the membrane can be damaged by excessive pressure difference . Chemical degradation of membrane can reduce the weight and thickness of membrane , , long‐term operating at low current or high temperature is the main reason for chemical degradation , , the narrow pulse current has nothing to do with low current or high temperature, thereby it cannot cause membrane chemical degradation. Insufficient hydrogen supply on the anode contributes high potential in local parts of cathode, which is the origin of carbon corrosion in catalyst layer on the cathode side , .…”