Anhydrous proton-conducting membrane based on poly-2-vinylpyridinium dihydrogenphosphate for electrochemical applications.

Anhydrous electrolytes with high proton conductivity and adequate chemical stability in the temperature range of 120-180 °C can be very useful in electrochemical devices such as fuel cells, sensors, and electrolyzers. Developing such proton-conducting materials has been challenging. We have fabricated and characterized the performance of such membranes, based on poly-2-vinylpyridinium dihydrogenphosphate (P2VP-DHP), that can operate in the range of 105-180 °C under anhydrous conditions. The ionic conductivity of the membrane was 0.01 S cm(-1) at 140 °C. Proton conduction occurs by ionization of the quaternary ammonium group and by Grotthus-type transport that involves the rapid rotation of the dihydrogenphosphate anion. The activation energy for proton transport was 50 kJ/mol. The transport number of the proton was measured by impedance spectroscopy and potential-step techniques. The measured value was in the range of 0.17-0.20. A membrane-and-electrode assembly using the P2VP-DHP was tested as an electrochemical hydrogen pump. This demonstration shows the advantage of membranes based on a polymer amine salt in electrochemical applications that require operating under water-free conditions. Weight loss measurements at 120 °C in air confirmed the thermal and oxidative stability of the membrane. The properties of the P2VP-DHP membrane reported here provide the basis for further development of proton-conducting polymer electrolyte membranes for operating temperatures above 100 °C in anhydrous environments.