SLOW FORMATION OF AN EXTRA-VISCOUS IONIC LAYER AT PLATINUM MICROELECTRODES DURING VOLTAMMETRIC OXIDATION OF UNDILUTED DIMETHYLFORMAMIDE

A minimum appears on the steady-state anodic voltammetric waves of und iluted dimethylformamide (DMF) and its concentrated solutions in aceto ne and propylene carbonate. The magnitude of the minimum obtained in u ndiluted DMF depends strongly on the experimental time scale and was e xamined using chronoamperometry and normal pulse-and reverse pulse vol tammetry. The rate of formation of the minimum is much lower compared to that of reaching the steady state. The experiments done and the fac t that the minimum vanishes at the potential where water is oxidized f avor a concept that the ionic product in the ionic liquid at the surfa ce of the Pt microelectrode is being hydrated and this leads to extra viscosity of the layer. The process is slow, since the rate of hydrati on is determined by diffusion of traces of water from the bulk. The pr oducts of oxidation of DMF are rather soluble, as found by long range reverse pulse voltammetry. This technique is apparently also useful fo r the estimation, in situ, of the water content in DMF.