Membrane Degradation Mechanisms in PEMFCs

Abstract

Nafion membrane degradation was studied in a polymer electrolyte membrane fuel cell ͑PEMFC͒ under accelerated decay conditions. Fuel cell effluent water was analyzed to determine the fluoride emission rate. Experimental findings show that formation of active oxygen species from H 2 O 2 decomposition or the direct formation of active oxygen species in the oxygen reduction reaction are not the dominating membrane degradation mechanisms in PEMFCs. Instead, membrane degradation occurs because molecular H 2 and O 2 react on the surface of the Pt catalyst to form the membrane-degrading species. The source of H 2 or O 2 is from reactant crossover through the membrane. The reaction mechanism is chemical in nature and depends upon the catalyst surface properties and the relative concentrations of H 2 and O 2 at the catalyst. The membrane degradation rate also depends on the residence time of active oxygen species in the membrane and volume of the membrane. The sulfonic acid groups in the Nafion side chain are key to the mechanism by which radical species attack the polymer.

Membrane Durability and Degradation under Dry Fuel Cell Operation Conditions

“…The studies on the membrane degradation in PEM fuel cell operation have been carried out and some fundamental understandings on the failure mechanisms have been reported (8)(9)(10)(11)(12)(13)(14)(15)(16)(17) …”

“…There are many studies regarding membrane degradation and failure mechanisms under different fuel cell operation conditions (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17). The main causes for membrane failures are: 1) chemical/electrochemical degradation; 2) cation contamination; 3) mechanical stress from hydration/dehydration and pressure difference; 4) manufacture defects.…”

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.…”

Local Impact of Pt Nanodeposits on Ionomer Decomposition in Polymer Electrolyte Membranes

“…Chemical degradation is linked to the attack of the weak bonds in ionomer side chains by radical species. The main type of radical species, hydroxyl radicals, is formed by the reaction of hydrogen peroxide, H 2 O 2 , at impurities such as Fe 2+ [12,13], which are present in small amounts due to the dissolution of end plates in contact with humidified oxygen and hydrogen [14][15][16]. H 2 O 2 -the main chemical compound responsible for chemical PEM degradation-is the product of surface reactions of H 2 and O 2 at PITM [17][18][19][20][21][22][23].…”

“…The net rate of H 2 O 2 formation at PITM depends on the size, shape, and distribution of Pt nanoparticles in the membrane and local reaction conditions around particles, determined by temperature, electrical potential, reactant concentrations, pH, and RH [12][13][14][15][16][17][18][24][25][26][27][28][29][30][31].…”