Synthesis and optimization of proton exchange membranes by a pulsed plasma enhanced chemical vapor deposition technique

A pulsed plasma enhanced chemical vapor deposition technique, which involves alternative plasma “on” and plasma “off”, has been used to prepare sulfonated proton exchange membranes. Using such a plasma discharge technique, the degradation of monomer molecules can be well controlled, and the obtained membranes are found to be highly sulfonated. Compared with the commercial Nafion® 117, these plasma polymerized membranes contain higher contents of sulfonic acid groups and exhibit higher water uptake and IECs, comparable proton conductivity and activation energies for proton conduction, and low methanol permeability, which provide them with great potentials as PEMs for uses in direct alcohol fuel cells. In addition, the properties of the fabricated membranes are strongly dependent upon the conditions used for the membrane fabrication, such as the duty cycle and the partial pressure of monomers. For synthesis of membranes with desirable properties, the conditions used for the membrane fabrication should be well selected.