Research On The Theory And Application Of Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) is an in-situ electrochemical technology with both high special resolution and chemical sensitivity. It can be used to study charge transfer reactions at the solid/liquid interface and liquid/liquid interface, and can obtain rate constants of homogeneous and heterogeneous redox reaction. An advantage of this technology is that the SECM measurements are carried out under steady-state conditions, so that the complication caused by ohmic potential drop and charging current can be overcome, therefore, the reliability of the data was strengthened. Using the ultramicroelectrodes as the tip, SECM can also be a powerful tool to obtain images of different substrates immersed in electrolyte solution, and distinguish regions of different conductivity or electrochemical activity. It can also be used to investigate the complex biological processes, such as photosynthesis process, enzymatic reaction dynamics, biomacromolecule and so on. The combination of the traditional methods and SECM can provide macroscopic and microscopic information of substrate or sample. The study of electron transfer across self assembled monolayers (SAMs) interface has important significance for understanding complex physiological change process of organisms, because self assembled monolayers present an ideal model for the studies of biological membrane related to the many processes of life. Therefore, it is particularly important to discuss the quantitative analysis of SECM theory and study the kinetics of electron transfer at self-assembled monolayers interface.There are four parts in this paper, main contents are as follows:1. This paper reviewed the historical background of scanning electrochemical microscopy, introduced the instrumentation and working principle of SECM. Furthermore, the text described the developments in the working mode of SECM in recent decade and viewed its prospect. All contents are: (1) The historical background of scanning electrochemical microscopy; (2) The instrumentation and working principle of SECM; (3) Several working modes of SECM. 2. The platinum ultramicroelectrodes were fabricated by the method of electrochemical plated insulated film and electrochemical etching. Combining scanning electrochemical microscopy with cyclic voltammetry for characterize the ultramicroelectrodes,we obtained the effective radius and normalized shielding coefficient of the homemade probe electrode. Taking platinum ultramicroelectrodes as objects, we discussed in detail the electrochemical properties of ultramicroelectrodes.3. The diffusion equation and boundary conditions of the transient process, diffusion limited process and the dynamic processes in SECM experimental were discussed in this section. We summed up merits and demerits of the previous quantitative theoretical formula and treatment method. On this basis, we corrected the tip—substrate distance and given a reasonable method for treatment the approach curve. These methods are important guarantees for obtain more accurate kinetic parameters.4. This paper detailed analysis of the electron transfer kinetics process on self-assembled monolayer by SECM, and modified disadvantage of previous methods. Using self-assembled monolayers based on thiol-porphyrin (TPPO(CH₂)₁₂SH) as research object, the heterogeneous electron transfer rate constant can be obtained, and then verified the result with revised theory.