Ionic mass transfer in flowing solutions

Abstract

Several electrochemical reactions under ionic mass-transfer rate-control have been studied on cylindrical electrodes forming part of electrolysis cell. The electrodeposition of copper and the redox reactions for the ferro-ferricyanide systems have been examined, in each case with a large excess of a suitable inert electrolyte. The influences of concentration of the reacting species, rate of flowing, viscosity and diffusivity, height of the working electrode, temperature, and distance between anode and cathode, were studied under streamline-flow conditions. The data are fitted by the dimensionless equation Sh = 0·525 . eR_d^1/2 . Sc^1/3 . (hd)^3/4. The temperature dependence of the kinetic constant yielded the following experimental heats of activation (a) for copper ion deposition 4800 ± 200 cal/mole (b) for ferricyanide reduction, 3400 ± 200 cal/mole (c) for ferrocyanide oxidation, 3700 ± 200 cal/mole. Since the kinetic constant increases when the flow rate is increased and also when the electrode height is decreased, a departure from reversibility has been observed for the redox system reaction when suitable experimental conditions are chosen.