Variable-Temperature Microelectrode Voltammetry:  Application to Diffusion Coefficients and Electrode Reaction Mechanisms

An apparatus for the measurement of steady-state microelectrode voltammetry at elevated temperatures is described. The scope of this experimental approach as a method for the determination of diffusion coefficients at variable temperatures in the case of simple one-electron processes is demonstrated. Diffusion coefficients over a range of temperatures are derived for N, N, N ‘, N ‘-tetramethylphenylenediamine in both acetonitrile and water solvents, tris-4-bromophenylamine in acetonitrile, and ferrocene in acetonitrile and dimethylformamide from which activation energies for diffusion are obtained. Diffusion coefficient values are used to derive Stokes−Einstein radii for each species in solution. The electroreductions of o -bromonitrobenzene in dimethylformamide and 9-chloroanthracene in acetonitrile are studied as a function of temperature and activation energies estimated for carbon−halide bond cleavage in the corresponding radical anions.