1 Introduction

In electrochemical and electroanalytical chemistry, fast scanning cyclic voltammetry (FACV) has been developed for the purpose of detecting electroactive substances and transient changes around electrodes for a certain need. This method was first used to activate carbon fiber microelectrodes, but the formal establishment as a method was also attributed to the contribution of R.M. Wightma et al. R.M. Wightma et al. Developed this voltammetric method for monitoring transient changes in neurotransmitters in animal annoyances. It is compared with other voltammetry in most of the time the electrode is not responding to the potential. At some point, the electrode potential suddenly swept at a very fast rate, the response current is proportional to the reactant concentration; due to the extremely fast scanning speed (typically tens of thousands of volts / second, there are also up to 105V / S and 106V / S this Scanning speed, and the upper limit of the scanning speed is still increasing), the thickness of the diffusion layer is extremely small, so the fast scanning voltammetry can provide the information of the reaction substance directly adjacent to the electrode. Although fast scan cyclic voltammetry was originally used to monitor transient changes in the electroactive material surrounding an electrode, the current application of this method to electrochemical and electroanalytical chemistry goes well beyond that, in other areas such as rapid electron transport Reaction kinetics, reaction mechanism and many other aspects of the application has been very good, this article on the fast scanning cyclic voltammetry and its application in the electrochemical make an introduction.

2 fast scanning cyclic voltammetry of the basic characteristics

Fast scan cyclic voltammetry and conventional cyclic voltammetry compared to significant differences, both of the requirements of the experimental conditions are not the same.

2.1 Potentiostat

Due to the extremely high scanning speed of fast scanning cyclic voltammetry experiments, which is usually tens of thousands of volts per second or even higher, commercially available potentiostats are very difficult to reach such a high scanning speed, such as PAR M370 electrochemical system only Can reach 100V / S, and PA RM270 electrochemical system maximum sweeping speed is only 40 V / S. Therefore, the potentiometer must be assembled according to the actual requirements.

2.2 recorder

Due to the extremely high scanning speed, it has been difficult for a typical recorder to record cyclic voltammograms during scanning. Under normal circumstances with the oscilloscope to observe the waveform changes during scanning, it is best to use an oscilloscope with storage capabilities to record, and then send the data to the computer for processing.

2.3 to eliminate the charging current

Since the electric double layer charging current is proportional to the scanning speed v and the Faraday current is proportional to the scanning speed V 1/2 under the diffusion control, the charging current will be very high when the scanning speed is very high, and the signal-to-noise ratio This will certainly affect the measurement of Faraday's current. Therefore, the influence of the charging current must be eliminated.

2.4 electrode

The electrode used in the fast scan cyclic voltammetry must be a microelectrode or a microelectrode. Mainly Pt microelectrode, carbon fiber microelectrode and gold microelectrode; shape mainly in the disc-shaped, but also columnar and ribbon. The benefits of using the microelectrode are: First, because the microelectrode produces a smaller current, which can eliminate the impact of iR drop; second is due to the microelectrode double-layer capacitance is small, so you can reduce the electrolytic cell time constant to Reduce the double layer charge current interference. For the disk electrode, cell constant and iR drop decrease with decreasing electrode radius.

2.5 iR drop correction

In the fast scanning cyclic voltammetry, although the microelectrode with a smaller iR drop is used, it can only reduce the influence of iR drop to a certain extent. When the scanning speed reaches tens of KV / S or MV / S, the current flowing through the system will also be larger. At this time, the influence of iR drop must be corrected. Especially when some surface reactions are studied, the correction of iR drop appears Particularly important.

3 fast scanning cyclic voltammetry in electrochemical applications

3.1 Rapid electron transfer reaction rate constant determination

The determination of heterogeneous electron transfer rate constants is a very important part of the electrode kinetics. With the rate constants of each reaction, the reaction mechanism of the electrode can be further analyzed. A convenient and simple method of determining electron transfer rate constants in electrochemical chemistry is cyclic voltammetry.

3.2 Reaction intermediates and reaction mechanism of the study

In the study of reaction mechanism, some reaction intermediates exist very short time, slow scanning cyclic voltammetry can not be studied, only by using other methods such as field spectroscopy, paramagnetic resonance and other methods to study it. The fast scanning cyclic voltammetry in this area has played a significant role. Fast scanning cyclic voltammetry is also very useful in the study of some complex reaction mechanisms. For example, in general, the reaction mechanism of the conductive polymer monomer in the initial stage of electrochemical polymerization is relatively complicated because it involves many intermediates and its research is also difficult.

3.3 surface reaction process research

The adsorption process that takes place at the electrode / solution interface is a very important process because the adsorption process changes the structure of the electrode double layer, which in turn affects the electrochemical reactions that occur at the electrode. An important parameter of the adsorption process is adsorption The rate constant, due to the adsorption process is very fast, the rate constant is large, in the conventional electrode and slow scan speed, the adsorption rate constant can be measured up to only 1000S-1. With the advent of ultra-microelectrodes and fast scanning voltammetry, up to 500,000S-1 can be measured.

3.4 in bio-electrochemical applications

In animals, certain biological substances such as neurotransmitters decay rapidly and the concentration fluctuates over time, with rapid scanning voltammetry is very convenient for its detection. Since the electrode used in this method is a microelectrode, it can perform in vivo analysis and provide information on the substance directly adjacent to the electrode. In addition, fast-scanning voltammetry has also shown its specific function in some studies that simulate biological processes in vitro, such as the study of certain enzymatic reactions.

3.5 Other

In addition to the above applications, fast scan cyclic voltammetry is also useful in other aspects such as determining the standard electrode potential of unstable electrochemical systems and in studying different electrochemical properties of certain compounds due to their configuration changes Response and so on. The theoretical study of cyclic scan voltammetry is not as rapid as its application. The theory behind fast scan cyclic voltammetry is still the theory of slow scan cyclic voltammetry.