Which of three voltammetric methods, when applied to a reversible electrode reaction, can best cope with double-layer capacitance and severe uncompensated resistance?
The presence of uncompensated resistance and double-layer capacitance confounds the accurate measurements of the bulk concentration of electroreactant and the reversible half-wave potential from an experimental voltammogram. It is pertinent to ask which simple voltammetric technique-chronopotentiometry, linear-scan voltammetry, or potential-step voltammetry-is best able to confront these difficulties. We have carried out a modeling study in an attempt to answer this question. First, we devised an exact method of simulating each variety of reversible voltammogram, incorporating the effects of resistance and capacitance. Next, we developed an unprejudiced method of analyzing these voltammograms to recover both electrochemical parameters. Then we performed a sensitivity analysis on a very large number of simulated voltammograms by measuring the apparent half-wave potential and concentration when slightly erroneous values of resistance and capacitance were employed in the recovery step. Thereby we hoped to ascertain how uncertainty in the magnitudes of the two interfering electrical elements affects the measured values of the two electrochemical parameters. Basing conclusions on the sizes of the four sensitivity indices, we conclude, surprisingly, that linear-scan voltammetry, not chronopotentiometry, is most often the method of choice.
Department of Chemistry, Trent University, Peterborough, ON, Canada.
JC
Myland
KB
Oldham