The concept to utilize an ion-conducting polymer membrane as a solid po- mer electrolyte offers several advantages regarding the design and operation of an electrochemical cell, as outlined in Volume 215, Chapter 1 (L. Gubler, G.G. Scherer). Essentially, the solvent and/or transport medium, e.g., H O, 2 + for the mobile ionic species, e.g., H for a cation exchange membrane, is taken up by and con?ned into the nano-dimensional morphology of the i- containingdomainsofthepolymer.Asaconsequence, aphaseseparationinto a hydrophilic ion-containing solvent phase and a hydrophobic polymer ba- bone...