in Wiley InterScience (www.interscience.wiley.com).Steady state, hydrodynamic voltammetry is a well-established technique to measure the rate of mass transport of an electroactive species to, or from, a solid surface electrode in an aqueous electrolyte. Limiting current measurements during the reduction of ferricyanide (hexacyanoferrate III ) ion at a nickel rotating disc electrode (RDE) are critically considered, and the accuracy of the technique is quantitatively assessed. The importance of surface pretreatment, type of indifferent electrolyte, and the effect of sunlight are considered. Limiting current values can show large deviations from the values predicted by the Levich equation for laminar flow to a polished RDE when unsuitable conditions are employed, despite the appearance of well-defined limiting current plateaux. Using appropriate pretreatment and experimental procedures, the averaged mass transport coefficients or limiting currents values can be obtained, which are close to the values predicted by the Levich equation for laminar flow to a hydrodynamic smooth RDE. 2008 American Institute of Chemical Engineers AIChE J, 54: [802][803][804][805][806][807][808][809][810] 2008 Keywords: activation of electrodes, convective diffusion, electrochemical mass transport, ferricyanide hexacyanoferrate(III) ion, nickel electrode surfaces, limiting current, rotating disc electrode, pretreatment of electrode surfaces, RDE, voltammetry IntroductionThe establishment of any electrochemical processes requires feasibility and process design studies. These preliminary works are normally carried out on pilot-scale laboratory electrolysers or in small laboratory electrochemical cells, and are essential to design the electrochemical reactor. The successful scale-up from laboratory to industry depends in great measure on the guidance obtained from the results of these investigations and from the continuous evaluation of the process after being implemented. The limiting currentThe most important figures of merit to be determined during the preliminary studies are often the current efficiency,

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