Electrochemical techniques including polarography 1, cyclic voltammetry 2, double potential step 3, reverse current chronopotentiometry 4 and rotating disc and ring~tisc electrodes 5 have been used for the determination of the rates of those homogeneous chemical reactions following electron transfer which regenerate the electroactive species, i.e. catalytic reactions: electrode
While all these techniques are successful at mercury electrodes, the non-steady state methods are subject to complications when applied to systems at solid electrodes owing to rapid alterations in the electrode surface which can occur when changing the potential, e.9. adsorption of substrates or formation of oxides. Furthermore, the above techniques are normally restricted to the study of chemical reactions with pseudo first order rate constants in the range 1-103 s-1.
In this paper we describe a steady state technique, requiring only simple apparatus, which is suitable for the rapid determination of the rates of slower reactions with pseudo first order rate constants in the range 10-a-10-1 s-~. The principle of this method is that in cells with a large electrode area to solution volume ratio (A/V), it is possible to reach an equilibrium where the rate of generation of the oxidising or reducing agent at the electrode surface is balanced by its rate of removal by reaction with the substrate in the bulk of the solution ; the steady state current will be shown to be directly related to the rate of the homogeneous chemical reaction. A very high A/V ratio is advantageous since it allows the equilibrium to be reached rapidly. The theory and apparatus were tested using the osmium(VIII)-methanol reaction in aqueous potassium hydroxide 6.
Recently, Kalvoda 7 has reported the use of a similar technique but his experimental approach and analysis of the results are markedly different to that described here.
EXPERIMENTAL
The cell used in this work is shown diagramatically in Fig. . The working