Polymer electrolyte membrane degradation, severity

Electro-catalysts which have various metal contents have been applied to the polymer electrolyte membrane fuel cell(PEMFC). For the PEMFCs, Pt based noble metals have been widely used. In case the pure hydrogen is supplied as anode fuel, the platinum only electrocatalysts show the best activity in PEMFC. But the severe activity degradation can occur even by ppm level CO containing fuels, i.e. hydrocarbon reformates[l-3]. To enhance the resistivity to the CO poison of electro-catalysts, various kinds of alloy catalysts have been suggested. Among them, Pt-Ru alloy catalyst has been considered one of the best catalyst in the aspect of CO tolerance[l-3]. 

The scientific community has made great progress in increasing the durability of polymer electrolyte membrane fuel cell (PEMFC) systems, but durability must further increase before we can consider fuel cells economically viable [1]. As durability increases, new modes of fuel cell contamination and failure are exposed. We expect state of the art PEMFC systems to run for thousands of hours. This means that each sulfonate group in typical per-fluorosulfonic acid (PFSA) membranes used in today s PEMFC systems will associate with several million protons over the lifetime of the systems. Even if other cations replace only a small fraction of the protons entering the electrolyte membrane, these contaminant cations can build up in the system and degrade the fuel cell system performance over time. 

In a typical Pt/C catalyst, there are several modes of degradation that can occur through the oxidation of the carbon support. Figure 3.1 illustrates many of the mechanisms of performance loss in a PEMFC which are mainly due to the loss of TPB active sites. The first method (Figure 3.1a) in which TPB sites become inactive is from the loss of contact between the catalyst particles and the polymer electrolyte membrane. Detachment of the membrane, also known as membrane delamination, can be caused by the corrosion of the carbon support and can result in protons being unable to reach the platinum nanoparticles. This inevitably leads to lessening of the Pt utilization and catalytic activity of the MEA. 

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