The kinetic Monte Carlo method is used to model the dynamic properties of proton diffusion in anhydrous proton conductors. The results have been discussed with reference to a two-step process called the Grotthuss mechanism. There is a widespread belief that this mechanism is responsible for fast proton mobility. We showed in detail that the relative frequency of reorientation and diffusion processes is crucial for the conductivity. Moreover, the current dependence on proton concentration has been analyzed. In order to test our microscopic model the proton transport in polymer electrolyte membranes based on benzimidazole C(7)H(6)N(2) molecules is studied.

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The kinetic Monte Carlo method is applied to examine effects of hydrostatic pressure on the benzimidazolium azelate (BenAze) proton conductivity. Following the experimental indications the recently proposed model has been modified to simulate the transport phenomena under moderate pressure, resulting in a very good agreement between numerical and experimental results. We demonstrate that the pressure-induced changes in the proton conductivity can be attributed to solely two parameters: the length of the hydrogen bond and the amplitude of lattice vibrations while other processes play a more minor role. It may provide an insight into tailoring new materials with improved proton-conducting properties. Furthermore, in high-pressure regime we anticipate the crossover from the increasing to decreasing temperature dependence of the proton conductivity resulting from the changes in the hydrogen-bond activation barrier with increased pressure.

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Structural relaxation and the role of molecular and proton dynamics in the electrolyte system, (NH 4 ) 4 H 2 (SeO 4 ) 3 (TeAHSe), are studied at ambient pressure, as a function of temperature and time, by using the solidstate 1 H NMR technique. Analysis of 1 H NMR spectra collected in the temperature range from 20 to 400 K yielded information about the dynamics of protons in the ordered and disordered crystalline TeAHSe phases. It has been shown that in the low-temperature phase TeAHSe is a proton conductor. In contrast, the electric charge carriers in the superionic phase are protons and NH 4 + ions. Therefore, the electrical conductivity in the superionic phase of TeAHSe is a combination of the chemical exchange of protons, proton diffusion within hydrogen bonds, and diffusion of ammonia cations in the bulk of the crystal. We also demonstrate that the enhanced charge transport in the superionic phase of TeAHSe mainly results from the NH 4 + cation diffusion process. The unique data from the time evolution of NMR spectra taken at a constant temperature just below the phase transition provide the first direct evidence of ammonium cations involvement in the lowtemperature structure recovery (structural relaxation). We proposed a scenario of the process of structural relaxation in the TeAHSe crystal as well as the origin of the phase transformation mechanism to the superionic stage.