Hydrogen evolution on miniaturized electrodes studied byelimination voltammetry

Elimination voltammetry with linear scan (EVLS) in connection with mini- and micro-electrodes provides useful information about the character and kinetics of processes at electrode/electrolyte interfaces. The EVLS resulting in the elimination of certain selected voltammetric current components is a simple mathematical procedure based on the different dependencies of these currents on the scan rate (1-5). EVLS improves voltammetric results important for electroanalysis and helps to study the electrode processes often accompanied by adsorption and structural changes of studeid electroactive species. Based on the experiment related to the hydrogen evolution, we show that the EVLS is capable of detecting the effect of sperical diffusion associated with both the scan rates and the size of an electrode drop. A mechanically renewed mercury drop electrode with variable radius was realized using a pulse generator connected to a valve and a minitapper (6, 7). Linear sweep voltammetric (LSV) measurements were performed with an Autolab System PGSTAT 302N (EcoChemie, Utrecht, The Netherlands) connected to a Metrohm 663 VA Stand (Metrohm, Zurich, Switzerland) and a personal computer with the NOVA (version 1.5, EcoChemie) software for the measurement control and data evaluation. It was found that for small size drops the diffusion layer is thick and the non-stationary linear diffusion results into stationary spherical diffusion, which is independent of scan rate. The EVLS experiment confirmed the assumption that spherical diffusion can be expressed as the partial kinetic component and therefore, for this study the functions eliminating the kinetic current component were selected. The effect of spherical diffusion on the miniaturized electrodes was also discussed using the extended Cottrell equation (8), which contains the correction term for this effect.