CYCLIC VOLTAMMETRIC WAVE-SHAPES FOR MICRODISK ELECTRODES - COUPLED EFFECTS OF SOLUTION RESISTANCE, DOUBLE-LAYER CAPACITANCE, AND FINITE ELECTROCHEMICAL KINETICS

Cyclic voltammograms at microdisk electrodes that account for the effects of solution resistivity, rho-OMEGA, double-layer capacitance, C(dl), and electrochemical kinetics have been simulated by using the explicit Hopscotch algorithm and a conformally mapped space-grid. The latter procedure, in particular, provides an efficient means of simulating voltammograms at slower potential scan rates where radial, rather than linear, diffusion predominates. Simulated voltammetric waveshapes as a function of scan rate are reported for systematic variations in rho-OMEGA, C(dl), and the standard electrochemical rate constant k(s), both separately and together. The waveshape description utilizes both the anodic-cathodic potential peak separation, DELTA-E(p), and the halfwave potential for the forward scan in relation to the formal potential, (E1/2-E(f)). The latter waveshape parameter is suitable for analyzing voltammograms where the influence of radial diffusion is sufficient to yield largely sigmoidal, rather than peaked, waveshapes. While the use of high scan rates enhances the effect of electrode kinetics upon the voltammetry, the deleterious coupled influence of rho-OMEGA and C(dl) is also maximized under these conditions, especially for larger C(dl) values. At slower scan rates, however resistive/capacitance distortions are often attenuated greatly, while substantial kinetic information remains due to the enhanced mass transport associated with radial diffusion. The examination of voltammetric waveshapes over a wide range of scan rates, together with proper consideration of resistance/capacitance effects, therefore constitutes a desirable tactic for evaluating rapid electrode kinetics using microdisk electrodes. Representative simulation results are provided as a guide to such procedures, and as a means of assessing the degree of error involved if resistance/capacitance effects are neglected.