Mass transfer at gas-evolving electrodes

The first school began with Venczel s dissertation in Zurich in 196190 on the transport of ferric ion to an electrode evolving hydrogen gas from one molar sulfuric acid. Venczel found that mass transfer increased rapidly with the onset of gas evolution. Ibl and Venczel26 reported mass transfer at gas-evolving electrodes as Nemst boundary layer thicknesses that are functions of gas evolution rate... 

Stephan, K., and Vogt, H., 1979, A model for correlating mass transfer data at gas evolving electrodes, Electrochim. Acta, 24 11-18. 

Janssen and Hoogland (J3, J4a) made an extensive study of mass transfer during gas evolution at vertical and horizontal electrodes. Hydrogen, oxygen, and chlorine evolution were visually recorded and mass-transfer rates measured. The mass-transfer rate and its dependence on the current density, that is, the gas evolution rate, were found to depend strongly on the nature of the gas evolved and the pH of the electrolytic solution, and only slightly on the position of the electrode. It was concluded that the rate of flow of solution in a thin layer near the electrode, much smaller than the bubble diameter, determines the mass-transfer rate. This flow is affected in turn by the incidence and frequency of bubble formation and detachment. However, in this study the mass-transfer rates could not be correlated with the square root of the free-bubble diameter as in the surface renewal theory proposed by Ibl (18). 

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