Rotating two-ring electrodes as a tool for electrochemical investigations of gas-evolving reactions

Abstract

It is shown that two concentric ring electrodes located on a rotating disc surface can be used as an instrument for chemical and electrochemical analysis of gas-evolving reactions up to rates of gas evolution from the inner ring of 140 ml h-1 cm-2 for a rotation speed of 2950 rev. min-1. A linear dependence between the inner ring current generating a certain species, and outer ring current of detection of that species, is found with a collecting effeciency of 17% up to a gas evolution rate of 27 ml h-1 cm-2. The same value is obtained without gas generation in the ferrocyanide-ferricyanide redox system. After a transition period from 27 to 40 ml h-1 cm-2, the collecting efficiency coefficient attains another constant value of 11%. It is suggested that the two linear parts of the plot pertain to a laminar mass transfer regime (17%) and a turbulent regime (11%) for the collecting of reaction products. However, in view of the results reported earlier1, which indicate that there is no change in the hydrodynamic situation on the inner ring electrode for gas generation rates up to 250 ml h-1 cm-2, this method is recommended for electrochemical analysis even under conditions of extremely high rates of generation of gaseous bubbles from the electrode surface, the turbulence affecting the operation of the detecting electrode, but only in a well deffned and reproducible, manner.