A circuit based on the current feedback operational amplifier was constructed to accomplish on-line ohmic drop compensation in ultrafast cyclic voltammetry. Firstly, its characteristics were confirmed experimentally on dummy cells. Then the reduction of anthracene in acetonitrile, a classical test example with very fast electron-transfer kinet-ics, was examined to prove them too. The results showed that this circuit could afford excellent ohmic drop com-pensation so that the undistorted voltammograms up to 2.2 MVs-1 scan rate can be recorded, and 2.5 MVs-1 if 5% error is tolerated.
Based on the perfect ohmic drop compensation by online electronic positive feedback, ultrafast cyclic voltammetry with asymmetrical potential scan is achieved for the first time, with the reduction of anthracene acting as the test system. Compared with the traditional cyclic voltammetry utilizing symmetrical triangular waveform as the excitation one, the new method allows a simpler approach to mechanistic analysis of ultrafast chemical reactions coupled with a charge transfer. And perhaps more important, it also provides a way to eliminate the interference of the adsorbed product in dynamic monitoring. 2007 Zhi Yong Guo. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
A novel idea of in-cell iR compensation was proposed by using a four-electrode electrochemical system, which was consisted of two working electrodes, one reference electrode （RE） and one auxiliary electrode （AE）. One of the two working electrodes was called the auxiliary working electrode （AWE）, which was directly connected to the ground. Another working electrode was used as a regular working electrode （WE） for electrochemical testing. The reference electrode was set in a frit close to the AWE for potential sampling. The other electrodes, WE, RE and AE, were connected to a conventional potentiostat of three-electrode system for electrochemical measurements. A linear narrow electrochemical cell was designed for setting AE at one end and AWE with RE at another end, and setting WE in between AE and AWE. In this way, a positive feedback potential was generated at the working electrode from the solution resistance and the current flow in the solution. An formal iR compensation over 100%, as high as 500%, had been achieved without potential oscillation. The electrochemical cell design, the principle of the in-cell iR compensation, and the preliminary voltammetric characterization by using the redox reaction of ferrocyanide anions were reported.
Ultrafast cyclic voltammetry was used to study the redox behavior of a gold electrode in acetonitrile. The direct electrochemical evidence of the dissociation and adsorption behavior of acetonitrile at gold electrodes was found. It could be stated that two consecutive redox paths are involved, each with a special adsorption state acting as the reaction intermediate. The mean value, obtained of the electron-transfer rate constant of the second path, was 1.3 × 10^5 s^-1 with a standard deviation of 0.24 × 10^5 s^-1.
A unique method for preparing a coaxial dual-microelectrode sensor by vaporizing the nano-thickness Au layer on the DNA modified carbon fiber micro-column electrode was illustrated. The dual-electrode showed particular merit for determination in biological systems.
A universal simulator capable of simulating virtually any user-defined electrochemical/chemical problems in one-dimensional diffusion geometry was developed based on an exponentially expanding grid modification of the existing network approach. Some generalized reaction-diffusion governing equations of an arbitrary electrochemical/chemical process were derived, and program controlled automatic generation of the corresponding PSPICE netlist file was realized. On the basis of the above techniques, a universal simulator package was realized, which is capable of dealing with arbitrarily complex electrochemical/chemical problems with one-dimensional diffusion geometry such as planar diffusion, spherical diffusion, cylindrical diffusion and rotational disk diffusion-convection processes. The building of such a simulator is easy and thus it would be very convenient to have it updated for simulations of newly raised electrochemical problems.
