Ohmic drop compensation in cyclic voltammetry at scan rates in the megavolt per second range: access to nanometric diffusion layers via transient electrochemistry

A new concept of a three-electrode potentiostat involving positive feedback compensation of ohmic drop is discussed. This potentiostat allows the electrochemical investigation of nanosecond time scales by allowing the recording of ohmic drop-free voltammograms at scan rates in the megavolt per second range. This range of scan rate corresponds to the development of diffusion layers having only a few nanometers thickness. The principle and properties of the potentiostat are first demonstrated analytically based on a simplified equivalent circuit for the conditions used in this study (v < 5 MV s(-1)). The validity of this simplified analytical approach is then tested and further investigated by precise simulations of the electronic properties of the real circuit, and then by experimental tests on RC dummy cells or on dummy cells equipped with a pseudo-faradaic impedance. These tests establish that the potentiostat behaves excellently up to slightly above 2 MV s(-1). These results were then confirmed by examination of the reduction voltammetry of anthracene in highly concentrated (0.9 M) supporting electrolyte to avoid interference with transport in the double layer, since usual supporting electrolyte concentrations would produce double layers of the same thicknesses as the diffusion layers that are created in this range of scan rates. These tests confirmed the results of the above investigations and finally demonstrated that this potentiostat allows the recording of undistorted voltammograms up to 2.25 MV s(-1). (C) 2000 Elsevier Science S.A. All rights reserved.