FOURIER-TRANSFORM SQUARE-WAVE VOLTAMMETRY

In this technique a potential excitation waveform is obtained by a sup erposition 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 tim e intervals 2n (where n = 2, 3, 4,...) times per square-wave cycle, an d the fast Fourier transform of the electrode response at each potenti al step is performed. This allows the electrode admittance to be calcu lated for various odd harmonic frequencies and plotted as a function o f the staircase potential. In addition, the average current at each po tential step as well as the even harmonic response generated by non-li nearity of the studied system can be obtained from collected data. The admittance data are almost identical with those obtained from traditi onal 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 N H4+/NH3 (aq) buffer on the static mercury electrode. Experimental resu lts were compared with those obtained by digital simulation. Diagrams of electronic circuits used in the experiments are also presented.