Influence of viscosity on chronoamperometry of reversible redox system on rough and nanoparticles deposited Pt electrode: Aqueous/glycerol and RTIL medium

•Theory for chronoamperometry on rough electrode is validated with experiments.•Contributions from ohmic loss and double layer charging are accounted.•Experiments were carried out for two systems - in glycerol + water mixture and ionic liquid.•Enhanced viscosity induces delay and dilation in roughness influenced time regime.•A modified method of microscopic area determination in viscous medium is proposed.

Recently developed theories allow us to predict expected electrochemical response from quantitative surface texture information obtained from various microscopies. We generalized power spectrum based chronoamperometry theory involving species with unequal diffusion coefficient of electroactive species in presence of uncompensated solution resistance. Chronoamperometric response in two viscous media, like ionic liquid and glycerol, is studied and it shows strong influence of electrode roughness up to longer time scales. Measurements were carried out for two reversible charge transfer systems: (i) solution of Fe(CN)63− and Fe(CN)64− in 3 M NaNO3 at various compositions of glycerol and (ii) ferrocene in [bmim][BF4] RTIL. Viscous medium induces suppression in growth of diffusion length which allows us to see enhanced and prolonged roughness effect in chronoamperometry. It is found that the enhanced viscosity: (i) induces delay, through enhanced ohmic contribution, in the onset of anomalous regime and (ii) causes dilation in roughness influenced time regime (the enlargement of roughness influenced region). These two effects allow determination of microscopic area from short time chronoamperometric data which is not possible in non-viscous aqueous medium. The corrections in the chronoamperometric current for the electric double layer and the random convective flow are also accomplished.