Alternating current voltammetry of electrode reactions with constant surface activity: Application to electrolysis of molten electrolytes

Analytic solutions are derived for the alternating current voltammetry (ACV) harmonic waveforms of electrodeposition and gas evolution reactions where the surface activity of the reduced species R is constant. Reversible and quasi-reversible charge transfer kinetics are considered, as well as the effects of ohmic drop and double layer charging. It is shown that ohmic drop produces a characteristic distortion of the waveform envelopes, resulting in the emergence of waveform extrema in the higher harmonics that are distinct from those of the conventional ACV theory of soluble redox couples. A quantitative connection is made between the peak potential of the second harmonic and the electrode reaction parameters. The analytic solutions agree well with measurements of the fundamental, second, and third harmonic waveforms of Pb electrodeposition on liquid Pb and of Cl2 evolution on graphite in molten PbCl2-NaCl-KCl at 700 °C