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Table of known degradation processes
 
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Degradation process 
Qualitative effect on the fuel cell
Assumed mechanisms

Membranes

Loss of sulphuric acid groups

Reduction of the ion conducti­vity / loss of electrochemical performance

Attack of free radicals / local overheating

Ion exchange of protons with metallic ions (from other components)

Reduction of the ion conducti­vity / loss of electrochemical performance

Ion exchange, poisoning of the ionomer

Loss of fluorine à change of membrane properties:

Stability, swelling, hydro­phobicity

Not clear

Not clear

Deposition of metal in the membrane

Electrical short-circuit of the cell

Ion diffusion and deposition

Formation of crevices

Breakdown of the fuel cell

Mechanical stress on the fixing points of the mem­brane due to length changes depending on the water balance (wet-dry-cycles)

Formation of localized leakages

Loss of performance, breakdown of the fuel cell

Mechanical damaging

Local overheating

Mechanical changes of the thickness

Accelerated breakdown of the fuel cell

Dissolution of membrane materials/decomposition

Catalysts

Structure change of catalyst:
Agglomeration of catalyst particles

Loss of the dispersive dis­tribution / loss of specific surface catalyst area-à loss of electrochemical performance

Ostwald ripening,

dissolution and re-deposition

Oxidation of the carbon support of the catalysts

Thinning of electrodes / influence on performance not clear

Local electrochemical ele­ments with corrosion poten­tial (critical states open potential + fuel starvation)

Alteration of the compo­sition of platinum alloy catalysts

Change of the reaction mechanism à loss of electrochemical performance

Potential depending dissolution of alloy materials

Poisoning of catalysts by dissolved species from other components

Loss of catalytic activity à loss of electrochemical performance

Change of the surface properties and composition

Poisoning of the catalyst by fuel/air components

Loss of catalytic activity à loss of electrochemical perfor­mance (irreversible/reversible depending on the poisoning component)

Change of the surface properties and composition à blocking of active sides

Movement of the catalyst material in the electrical field/loss of electro­chemical performance

à loss of electrochemical performance

Dissolution and re-deposition of the catalyst and diffusion of ions in the electrical field

Reactive layer

Loss of particles in reaction layer

Not clear, maybe loss of active surface area/decrease of the Pt utilization / loss of electro­chemical performance

Mechanical erosion into gas water flow

Partially decomposition of the PTFE in the reactive layer

Loss of hydrophobicity / altered water balance

Not clear

Delamination from the membrane

Increase of contact resistance / loss of electrochemical performance

Induced by wet/dry cycles and the changes of the membrane dimension (mechanical stress)

Delamination from the GDL

Increase of the contact resistance / loss of electro­chemical performance

Not clear, maybe induced by the formation of liquid water at the interface

Thinning of the reactive layer

Deterioration of mass transport properties

Carbon corrosion by local undersupply of fuel or air (by liquid water)

Gas diffusion layers

Loss of particles from the micro porous layers

Change of the structureà alteration of the transport properties in the GDL

Mechanical erosion

Partially decomposition of the PTFE

Loss of hydrophobicity / alternated water balance

Not clear

Bipolar plates

Change of the surface composition of metallic bipolar/endplates

Change of hydrophobicity / hydrophobic character / altered water balance

Adsorption of polar groups on the surface

Surface deposition of species from other compo­nents / Dissolution of surface com­ponents

Corrosion of metallic bipolar plates: Formation / growing of passive films on bipolar plates on anode or cathode side

Increasing contact resistance between bipolar plates and gas diffusion layers / loss of electrochemical performance

change of hydrophobicity / altered water balance

Change of the porosity on the surface

Corrosion of sealing materials and deposition in the reactive layer

Loss of electrochemical performance

Adsorption of surface species

Italic font: degradation process is influenced by water