The structure of the electrical double layer in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) near a basal plane of graphite was investigated by molecular dynamics simulation. The calculations were performed both for an uncharged graphite surface and for positively and negatively charged ones. It is found that near an uncharged surface the ionic liquid structure differs from its bulk structure and represents a well-ordered region, extending over approximately 20 A from the surface. Three dense layers of ca 5 A thick are clearly observed at the interface, composed of negative ions and positively charged rings. It is established that in the first adsorption layer the imidazolium ring in the [BMIM]+ cation tends to be arranged in parallel to the graphite surface at a distance of 3.5 A. The [PF6]- anion is oriented in such a way that the phosphorus atom is at a distance of 4.1 A from the surface and triplets of fluorine atoms form two planes parallel to the graphite surface. Ions adsorbed at the uncharged surface are arranged in a highly defective 2D hexagonal lattice and the corresponding lattice spacing is approximately four times larger than that of the graphene substrate. The influence of the electrode potential on the distribution of electrolyte ions and their orientation has also been investigated. Increase in the electrode potential induces broadening of the angle distribution of adsorbed rings and a shift of the most probable tilt angle towards bigger values. It was shown that there are no adsorbed anions on the negatively charged surface (sigma = -8.2 microC cm(-2)), but the surface concentration of adsorbed cations on the positively charged surface (sigma = +8.2 microC cm(-2)) has a nonzero value. In addition, the influence of the surface charge (+/- sigma) on the volume charge density and electric potential profiles in an electrolyte was studied. The differences in the cation and anion structure result in the fact that the integral capacitance of the electrical double layer depends on the electrode polarity and equals C = 4.6 microF cm(-2) at sigma = -8.2 microC cm(-2) and C = 3.7 microF cm(-2) at sigma = +8.2 microC cm(-2).

A comparative modelling of pulsed-corona and silent discharges for removal of NO x , N y O x , SO 2 , CO and CH 2 O using operating equipment is presented. The main purpose is to compare, by modelling, the energy efficiency on removal of toxic impurities between two types of discharges at similar gas composition and temperature. Three different gas compositions: diesel engine exhaust, methane combustion products and pollutant air are considered. The simulation is based on an approximate mathematical model for plasma cleaning of a waste gas. The influence of non-uniform species distributions arising from a great number of streamer or microdischarge channels in a discharge chamber is taken into account. The modelling is carried out for a pulse series, considering after each discharge pulse the chemical and diffusion processes inside and outside the streamer trace. The distinctions of the cleaning processes in the pulsed-corona and barrier discharges are presented. It is also recommended when each of the examined discharges should be used.

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The TiO2/electrolyte interface was investigated as a key element of dye-sensitized solar cells (DSSCs). The influence of cations such as lithium (Li+), 1,2-dimethyl-3-propylimidazolium (DMPIM+), and tetrabutylammonium (TBA+) on the double-layer structure in acetonitrile-based electrolyte at the anatase (101) surface was studied by molecular dynamics (MD) simulation. The calculations were performed for the uncharged surface as well as for the negatively charged one, which imitated TiO2 nanocrystals with excess electron density under light irradiation. It was shown that acetonitrile molecules form a self-assembled monolayer on the anatase (101) surface, inhibiting adsorption/desorption of both cations and anions. The effective dipole moments of acetonitrile molecules in the monolayer are directed away from the surface and produce a potential drop across the interface of ∼1.3 V. The characteristic time for the reversible adsorption/desorption process of Li+ cations occurs in the second time range. The MD simulations show that cationic species have a strong effect on the electrolyte structure both in bulk and at the interface. In particular, a significant influence of cations on the density distribution of I– at the interface was found. This result suggests that the mechanism, by which cations affect the dye regeneration kinetics, consists of the local change of I– density in the region where the −NCS groups of ruthenium dyes (involved in the regeneration process) are located.

The influence of temperature on the structure and dynamics of the [BMIM][PF(6)] ionic liquid/graphite interface has been investigated by molecular dynamics simulations. The performed simulations cover a 100 K wide temperature interval, ranging from 300 K to 400 K. It was shown that the magnitudes of density peaks of anions in the vicinity of the surface decrease with increasing temperature while in the case of cations anomalous temperature behaviour of the density profile is observed: the magnitude of the second peak of cations increases with the increase of temperature. To characterize interface dynamics the local self-diffusion coefficients D(x) of ions in the normal direction to the surface and the residence time of ions in the first and second interfacial layer have been estimated. It was shown that the local self-diffusion coefficients in the vicinity of the surface correlate with the local ion density; the maxima of the function D(x)(x) for the cations (anions) coincide with the regions of reduced cation (anion) density and vice versa. Finally, the influence of temperature on the screening potential in the vicinity of a charged graphite surface has been studied. It was shown that the increase of temperature from 300 K to 400 K induces the decrease of the potential drop across the interface that implies the increase of the capacitance of the electrical double layer.