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 elec trochemical investigation of nanosecond time scales by allowing the recordi ng of ohmic drop-free voltammograms at scan rates in the megavolt per secon d range. This range of scan rate corresponds to the development of diffusio n layers having only a few nanometers thickness. The principle and properti es of the potentiostat are first demonstrated analytically based on a simpl ified equivalent circuit for the conditions used in this study (v < 5 MV s( -1)). The validity of this simplified analytical approach is then tested an d 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 establi sh that the potentiostat behaves excellently up to slightly above 2 MV s(-1 ). These results were then confirmed by examination of the reduction voltam metry of anthracene in highly concentrated (0.9 M) supporting electrolyte t o avoid interference with transport in the double layer, since usual suppor ting electrolyte concentrations would produce double layers of the same thi cknesses as the diffusion layers that are created in this range of scan rat es. These tests confirmed the results of the above investigations and final ly demonstrated that this potentiostat allows the recording of undistorted voltammograms up to 2.25 MV s(-1). (C) 2000 Elsevier Science S.A. All right s reserved.