Study And Application Of A Novel Electrochemical Measurement System Based On Measuring The Interface Potential

The solid/solution interface widely occurs in nature,and deals with our vital processes. daily livings,industry,and interdisciplinary research and engineering.Understanding of interface phenomena at the solid/solution interface is of paramount importance for interpreting some problems in electrochemistry,colloid science,surface science,and biophysics,and has been a topic of intensive research.Measurement of interface potential at the interface region is a significant avenue to study the interface phenomena.It is of imporatance to develop some highly effective techniques for measuring interface potential at the solid/solution interface.In this dissertation,a new electrochemical measurement system is proposed for measuring the interface potential at the solid/solution interface.Based on the distinct measurement principle of the system,two topic measurement modes containing zero current potentiometry and amperometric techniques are developed.By using these two modes,the pH sensitive property of the polyaniline film and the surface acid-base property of carboxylic MWNTs are investigated,respectively.The chief contributions of the author are as follows:1) A solid electrode is connected in series between the terminal points of the working electrode and the counter electrode of a potentiostat.The electrode and a reference electrode are immersed in the electrolyte solution,thereby establishing a new electrochemical system. The theoretical and experimental studies show that the distinct connection excludes the possibility of the current passing through the interface of the electrode and solution and the electrolyte solution.The circuit current only flows inside the electrode,and its value rests with the electronic property of the electrode,the applied potential controlled by the potentiostat and the interface potential at the interface of the electrode/solution.When different controlled-potential techniques such as linear sweep voltammetry,square wave voltammetry,different pulse voltammetry and amperometry,are used in the new electrochemical measurement system,various current-potential curves and current-time curves are recorded.In these profiles,the potential and current are the input and output parameters,respectively.They are two detectable physical data in nature.Meanwhile.the interface potential depends strongly on the properties of the sensing surface and the solution composition.It is a latent chemical variable whose information can be drawn from the profiles by measuring the shift of the potential or current with the change of the solution composition. Based on measuring the potential shift at the same current level and the variation of the current at the same potential level,two new measurement modes,zero current potentiometry and amperometric measurement are proposed for the study of the interface phenomena at the solid/solution.2) With the new electrochemical system,a linear sweep potential is applied:the resulting curve I-E of current versus potential is recorded.In the curve I-E,the applied potential when the current is zero is defined as zero current potential E_zcp,which can be used as a key parameter for indicating interface potential at the sensor/solution interface.The corresponding technique to measure zero current potential is named as zero current potentiometry.The measurement principle and the performance of the proposed approach are discussed on the examples of measuring the interface potential at several interfaces without specific adsorption.Zero current potentiometry offers rapidity,high stability,and high accuracy compared to open circuit potentiometry.Zero current potentiometry has been used for investigating the pH sensitivity of the polyaniline film and surface acid-base property of the carboxylic groups terminated MWNTs.The results are consitent with the literatuers.These studies may provide a promising way for the development of the new potentiometric pH sensors.3) A new amperometric mode is proposed based on the use of the amperometric technique in the new electrochemical system.When the applied potential is fixed,the curve of current versus time is recorded.The relationship of the current and the solution compostion provides the therotical basis for the amperometric mode in investigating interface phenemena. The pH sensitive property of the polyaniline film has been investigated using the new amperometric mode,and the result is in agreement with the previous reports.Based on this work,a polyaniline film based amperometric pH sensor has been developed,and a polyaniline film pH switch of current direction has been designed.Different from the classic amperometric measurements based on the study of the redox reactions at the electrode,the new mode actually employ the amperometric technique to measure the interface potential variation.The new mode exhiblits high stability,accuracy,selectivity,sensitivity and a short time.This study may offer an effective means of the development of amperometric sensors and the design of the electrochemical molecular switches.