Phosphonic acid-based membranes as proton conductors prepared by a pulsed plasma enhanced chemical vapor deposition technique

Among the electrolyte membranes for proton conduction in hydrogen production systems and fuel cells, phosphonic acid-based membranes are promising because of their advantage as good proton conductors in anhydrous medium which allows their use in systems operating at high temperature (80-150 degrees C) which is not the case of sulfonic acid-based ones such as the well-known Nafion (R) commercial membrane. In this study, a plasma polymerization process using a continuous or pulsed glow discharge has been implemented to prepare original Plasma Enhanced Chemical Vapor Deposition (PECVD also called plasma polymerization) phosphonic acid-based membranes using dimethyl allylphosphonate as a single precursor. The structural and proton transport properties of such membranes have been correlated with the plasma parameters in the deposition of films. The membranes prepared by pulsed plasma deposition method exhibit a better proton conductivity than that of membranes prepared by continuous plasma deposition method, in direct relation with their specific structural properties. The optimal plasma membrane, obtained in a pulsed 100 W plasma discharge, has shown specific resistance to proton conduction twice less than Nafion (R) 212 one which is great for the final applications of such membrane.