Electrode kinetics by hydrodynamic voltammetry—study of ferrous-ferric, ferrocyanide-ferricyanide and iodide-iodine systems

Using rotated and circulatory electrolysis cells, rate parameters of electrode processes have been determined at stationary conical and cylindrical platinum microclectrodes in flowing solutions, under judiciously controlled hydrodynamic conditions. Virtually ideal laminar flow was maintained at velocities up to 700 cm/s. Normally reversible d.c. current/voltage waves were made “irreversible in shape”, due to enhancement of convective mass transfer. Thus specific electron-transfer rate constants, ranging up to an estimated limit of 10 cm/s, could be evaluated by a simple and unambiguous “wave analysis” procedure. The electro-oxidation of iodide to iodine, in perchloric acid in the absence of triiodide, is governed by second-order kinetics. A mechanism is proposed to account for this remarkable finding.