Basic Principles of PEM Structure and Operation

Principle 2.1 Stable Separation and Highly Selective Transport 

Principle 2.2 Water as Nature s Benign Proton Shuttle 

The prevailing class of PEMs exploits the unique properties of water as aproton solvent and shuttle. As a result of the high concentration of protons and the peculiar nature of hydrogen bonding, liquid water is an ideal medium for proton transport. As a blueprint for this fundamental principle, nature relies entirely on liquid water to facilitate proton transfer in intracellular energy transduction (Kuznetsov and Ultrup, 1999). 

The main physical property of a PEM is its proton conductivity (tpem or the proton resistance a 1 lapm-This property determines the heat loss, QpeM from Joule heating and the associated voltage loss, i]pem. 

The key material characteristic that is implanted into the material during chemical design and fabrication is the ion exchange capacity (lEC), defined as the number of moles of ion exchange sites per mass of dry polymer. It determines the volumetric charge density Ph+, resulting from excess protons. 

---