Ionomer Degradation in Electrodes of PEM Fuel Cell

Conference · Sat Jan 01 04:00:00 EST 2011

OSTI ID:1013118

Borup, Rodney L ^[1]

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1. Los Alamos National Laboratory

Although PEMFC Membrane Electrode Assembly (MEA) durability related studies have increased dramatically since 2004, studies on ionomer degradation of the composite electrodes has received far less attention than that of the proton exchange membranes, electrocatalysts, and catalyst supports. The catalyst layer ionomer unavoidably gets involved in other components degradation processes since it is subjected to exposure to different operating effects, including the presence of the catalyst, catalyst support, and the porous nature of the electrode layer which includes 2-phase flow. PEMFC durability issues cannot be fully resolved without understanding the contribution of ionomer degradation in electrode to the performance decay in life time. However, addressing the impact of changes to the catalyst layer ionomer during durability tests is experimentally difficult mainly because of the need to separate the ionomer in the electrode from other components during chemical, electrical and materials characterization. The catalyst layer ionomer is essentially chemically identical to the membrane ionomeric material, and is composed of low atomic number elements, making characterization difficult. In the present work, MEAs with different Nafion ionomer types: stabilized and non-stablized ionomer in the electrode layer (Type I) and mixed membrane/ionomer MEAs (Type II) were designed to separate ionomer degradation from membrane degradation, as shown in Figure (1a) and (b) respectively. Stabilized and non stabilized ionomers were 5% Nafion{reg_sign} solutions (Ion Power, New Castle, Delaware). The non-stabilized version is the typical Nafion chemical structure with carboxylic acid (-COOH) end groups; these end groups are thought to be a susceptible point of degradative peroxide attack. The stabilized version replaces the -COOH end groups with -CF{sub 3} end groups to prevent peroxide attack at the end groups. Type I MEAs were designed to compare ionomer degradation and its effect on performance decay. Since F{sup -} ions are released only from PFSA based membranes, and not from non-PFSA based membranes, Type II MEAs use a hydrocarbon membrane with no fluorine with a PFSA (Nafion{reg_sign}) ionomer in the catalyst layer for FER measurements. Any F{sup -} ions measured will then have come only for the catalyst layer ionomer during degradation experiments. Type II MEAs allow more detailed chemical characterization exclusively of the catalyst layer ionomer to better understand its degradation.

• Research Organization: Los Alamos National Laboratory (LANL)
• Sponsoring Organization: DOE/LANL
• DOE Contract Number: AC52-06NA25396
• OSTI ID: 1013118
• Report Number(s): LA-UR-11-10545
• Country of Publication: United States
• Language: English

Related Subjects

ATOMIC NUMBER
CARBOXYLIC ACIDS
CATALYST SUPPORTS
CATALYSTS
DECAY
ELECTROCATALYSTS
ELECTRODES
Energy Conservation
Consumption
& Utilization (32)
Energy Sciences
FLUORINE
FUEL CELLS
HYDROCARBONS
MEMBRANES
PERFORMANCE
PEROXIDES
PROTONS