Proton Mobilities in Phosphonic Acid-Based Proton Exchange Membranes Probed by 1H and 2H Solid-State NMR Spectroscopy

Two novel phosphonic acid-based dry proton exchange membrane materials that may allow for fuel cell operation above 100 degrees C have been prepared and characterized via solid-state H-1 and H-2 MAS NMR spectroscopy. We obtained information on both the nature of hydrogen bonding and local proton mobilities among phosphonic acid moieties. In particular, H-2 MAS NMR line shape analysis yielded apparent activation energies of the underlying motional processes. Using this approach, we have investigated both a model compound and a novel PEM system. It was found that the relation of estimated hydrogen-bond strength and local proton mobility accessible by solid-state NMR and bulk proton conductivity is complex. Improvements through admixture of a second component with protogenic groups are suggested.