Classical molecular dynamics simulations of proton conduction were used to provide insight into potential improvements of proton conductivity in polyelectrolyte membranes. For the simulations the reactive force field for water was used, which allowed bond dissociation of water, acids and hydronium ions. The effects were shown to be fundamental relevance for the diffusion of protons in membranes. One and two-dimensional conductors, and a Nafion membrane were modelled in the simulations. The two-dimensional model imitates a metal phosphate; the one-dimensional model imitates an idealized pore of hydrated Nafion membranes. The molecular dynamics simulations of proton conductivity of the metal phosphate showed the dissociation of the acid POH groups and their participation in the proton transport. Several simulations were performed with acids of different strength and the effect of the acid’s strength on the diffusion and on the conductivity was analyzed. The importance of the ion coupling on the conductivity was firstly proved in tubes, which imitate an ideal pore inside a membrane. Afterwards, the coupling was investigated in a real hydrated Nafion membrane by a non-equilibrium molecular dynamics simulation. The results suggested a soliton-like behavior for proton conductivity in membranes.

Theoretical Simulations of Proton Conductivity: Basic Principles for Improving the Proton Conductor. Hofmann, D.W.M., Kuleshova, L.N., D’Aguanno, B.: Journal of Power Sources, 2010, 195[23], 7743-50