Contaminant species, transport continuity

Deployment of MDPs, which are solid solutions of a transport-active species (typically in the range 30-50 wt %) in an inert host polymer, embodies the concept of full compositional control of mobility (53), Transport molecules are chosen with the aim of rendering accidental contaminants electrically inactive. The concentration of small molecules controls drift mobility. Appropriate choice of a compatible host polymer can then focus on mechanical properties and environmental stability. MDPs are limited by phase separation, crystallization, and leaching by contact with the development system, cleaning solvent, etc. These problems continue to motivate the search for single-component transport polymers. 

All three major components of an ME A, membrane, catalyst, and diffusion medium, can be contaminated by foreign species during PEMFC operation. Contamination of the diffusion medium usually lowers its hydrophobicity, which leads to water transport problems and can potentially create a continuous liquid path from the membrane to the gas flow channel. Foreign ionic contaminants can directly migrate to the membrane via this liquid path. Consequently, faster contamination may occur under this condition. Since diffusion medium contamination does not directly cause more severe membrane degradation, the discussion of the contamination issue will focus on two aspects membrane contamination and catalyst contamination. 

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