Proton conductivity and diffusion in molten nominally dry phosphonic acid

(H3PO3) were studied by 1H pulsed magnetic field gradient NMR and ac

impedance spectroscopy. The high intrinsic proton conductivity was found to be

the result of fast structure diffusion of protonic defects (Grotthuss mechanism)

which were present at high concentration (high degree of self-dissociation). The

proton transport behaviour was reminiscent to this of phosphoric acid, but slightly

higher correlations in the diffusion of protonic defects, as indicated by a higher

Haven ratio (~2.5 compared to ~1.5), and the lower rate of structure diffusion

(Grotthuss mechanism) compared to vehicle diffusion (~90% for phosphonic acid

compared to ~98% for phoshoric acid) were suggested to be the consequence of a

“weaker” hydrogen bond network formed by phosphonic acid compared to

phosphoric acid. But contrary to phosphoric acid, phosphonic acid may be

immobilized to organic structures by stable P–C bonds.

Proton Conductivity and Diffusion Study of Molten Phosphonic Acid H3PO3.

M.Schuster, K.D.Kreuer, H.Steininger, J.Maier: Solid State Ionics, 2008, 179[15-

16], 523-8