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[en] The two-dimensional Saul’yev method of simulating processes at an ultramicrodisk electrode is compared with the fully implicit backward differentiation method started with a few backward implicit steps, and an alternating direction implicit method. 2D Saul’yev is convenient to program and although it is significantly slower in execution than the other two methods, it still executes in reasonable time, and yields equally good results with a suitable choice of discrete intervals, and despite its inherent propagation problem, and a certain restriction in the relationship of the spatial and temporal intervals. Saul’yev was implemented for the diffusion limited potential step experiment, as well as linear sweep voltammetry for a reversible system.
[en] Several ways of simulating time-dependent migration effects at an electrolytic liquid junction are explored, for a simple uni-univalent electrolyte, both with the full Nernst-Planck-Poisson (NPP) equation set and the reduced set from the electroneutrality condition (ENC) assumption. Using the NPP approach, the system can be simulated using all three variables (method ABψ), the two concentrations and the potential, or the two concentrations and the potential field (method ABE), or in principle by substituting for the potential field, thereby reducing to the two concentration variables (method AB). The two first methods are about equally efficient, whereas the latter method is seen to be quite inaccurate. Results at long times compare very well with the Henderson equation. Using the full NPP set, junction potentials are time-dependent but not when applying the ENC, where the potential rises to the Henderson value immediately. Results for KCl and HCl are presented, with left/right concentration ratios equal to 0.1 in both cases