Degradation of Polymer-Electrolyte Membranes in Fuel Cells

Abstract

In this work, chemical degradation is studied using highly controlled measurements of the fluoride ion release from subscale cells in degrading environments using perfluorosulfonic-acid-based membrane electrode assemblies, primarily with cast, 25μm (1mil) thick membranes. Effects of key variables, such as oxygen concentration, relative humidity (RH), temperature, and membrane thickness on the fluoride ion emission rate (FER) are described under open-circuit decay conditions. Some of the observed trends are expected or consistent with previous observations, such as decreasing FER with decreasing temperature and increasing RH. Other trends observed are not expected, such as a logarithmic decrease of FER with oxygen concentration and increasing FER with increasing membrane thickness. Cross-sectional transmission electron microscopy analysis of decayed membranes indicates a surprisingly homogeneous distribution of small Pt particles ( ∼3to20nm in diameter), presumably from dissolution and migration from the cathode. The experimental results are consistent with radical generation at these Pt particles from crossover hydrogen and oxygen, subsequent radical migration, and polymer attack. The response of the FER to new experimental conditions in this study suggests that the attack can exist at any plane within the membrane, not just the “Xo” plane of maximum Pt precipitation.

Kinetic study of Nafion degradation by Fenton reaction

“…The tearing of PEMs induces the crossover of both oxygen and hydrogen, decreasing cell efficiency. In addition, this oxygen leakage accelerates the degradation of the PEM at the anode caused by the production of hydrogen peroxide (H 2 O 2 ) [11][12][13][14][15][16][17][18][19][20][21][22][23]. Research on the degradation mechanisms of PEMs shows that the main damage to the polymers is the result of attack by the reactive oxygen species of free radicals such as hydroxyl radicals [3,24,25].…”

Catalyst, Membrane, Free Electrolyte Challenges, and Pathways to Resolutions in High Temperature Polymer Electrolyte Membrane Fuel Cells

“…Nafion TM /PTA (phosphotungstic acid) operating on hydrogen/oxygen at ambient pressure achieve 0.6 V at 180 mA/cm 2 for an operating temperature of 120 • C [35], and Nafion TM -Teflon Zr(HPO 4 ) operating on hydrogen/oxygen at 120 • C achieved 0.6 V at 400 mA/cm 2 [32]. While performance is significantly lower than PEM Nafion TM performance when operated at 80 • C and ambient pressure with saturated reactants, it is roughly equivalent to the performance of Nafion TM /phosphoric acid [36], however there are little to no data on the durability of these membranes at fuel-cell operating conditions Durability of the membrane has been studied by numerous researchers [37][38][39][40][41]. Degradation of Nafion TM has been separated into the following three mechanisms: chemical, thermal, and mechanical.…”

The Model of Stress Distribution in Polymer Electrolyte Membrane

“…Here S pl is the platform active surface area, 2 O C is the inlet oxygen concentration, 2 O U is the oxygen utilization, n ch is a number of the channels in the platform. The vapor concentrations at the membrane/GDL interfaces, C M/AGDL (y, z, t) and C M/CGDL (y, z, t) are obtained from the steady state concentrations for the low and high load cycle steps (j = j min and j = j max ).…”