PHYSICOCHEMICAL CONSEQUENCES OF GENERATING A THIN-LAYER OF IONIC LIQUID AT MICROELECTRODE SURFACE IN UNDILUTED REDOX LIQUID

Very-thin layers of ionic liquids are formed at microelectrode surface s during electrolysis of undiluted redox liquids containing only suppo rting electrolyte at a low concentration. The layers consist of ionic product and counterion coming from supporting electrolyte. Formation o f ionic-liquid layer leads to increased viscosity, changes in activity coefficients, and thus to changes in diffusion coefficients of all sp ecies involved in the electrode process. This engenders also a specifi c type of convection. Exchange of one supporting electrolyte for anoth er may change dramatically the physicochemical properties of the gener ated ionic layer and, in consequence, the magnitude of the electrochem ical response of an undiluted substance. A computational model for pre dicting the phenomena mentioned above is presented. An important step in the model is extension of the concentration dependence of diffusivi ties to concentrations corresponding to ionic liquids. The calculation s done have shown a substantial influence of counterion volume on the electrochemical behavior of undiluted redox liquids even if the counte rions are present at a very-low concentration. The consequences of cha nging supporting electrolyte concentration are also included in the mo del. The theoretical predictions were compared with experimental data obtained for undiluted nitrobenzene and methanol. The model can be use d for both transient and steady-state responses.