FOURIER-TRANSFORM SQUARE-WAVE VOLTAMMETRY

In this technique a potential excitation waveform is obtained by a superposition of a small amplitude square-wave modulation on a staircase function. The square-wave cycle is repeated several times (usually 16) at each potential step. The electrode response is sampled at even time intervals 2n (where n = 2, 3, 4,...) times per square-wave cycle, and the fast Fourier transform of the electrode response at each potential step is performed. This allows the electrode admittance to be calculated for various odd harmonic frequencies and plotted as a function of the staircase potential. In addition, the average current at each potential step as well as the even harmonic response generated by non-linearity of the studied system can be obtained from collected data. The admittance data are almost identical with those obtained from traditional ac voltammetric experiments, but the equipment is less expensive and the experiments are run much faster and provide more information. The technique was tested by studying kinetics of Cd2+ reduction from NH4+/NH3 (aq) buffer on the static mercury electrode. Experimental results were compared with those obtained by digital simulation. Diagrams of electronic circuits used in the experiments are also presented.