Key Features:
- No of Pages: 69
- No of Chapters: 05
- References Included
- Diagrams Included
- Illustrative pictures included
Introduction:
Abstract
The need to produce high quality films at low and normal atmospheric pressure had led to the adaptation of electrochemical methods in thin film deposition. This project “Design and Construction of a two electrode potentiostat” is aimed at improving on the cost effectiveness of commercially available three electrode potentiostat, for thin film fabrication in Physics Department as the department does not have any working deposition system. The two electrode potentiostat was designed and constructed to realize an electronic module. The module was interfaced to a computer unit using a lab view software program, the results obtained indicated that the two electrode potentiostat electronic design produced the required voltage range for thin film deposition. The system though needs optimization will be of great use in the thin film preparation for research purposes.
Table of Content
TABLE OF CONTENTS
Cover page i
Title page ii
Certification iii
Dedication iv
Acknowledgement v
Abstract vi
Table of content vii
List of Figure xii
List of table xiv
CHAPTER ONE
INTRODUCTION 1
1.1 Background History 1
1.2 Aims and Objectives 2
1.3 Significance of the study 3
1.4 Scope of the study 4
CHAPTER TWO
LITERATURE REVIEW 5
2.1 Electrochemistry 5
2.2 The Potentiostat 6
2.2.1 The Potentiostat and History 7
2.2.2 Problems Encountered in Potentiostat 8
2.3 Applications of Potentiostats 9
2.3.1 Potentiostats for use in corrosion studies 9
2.3.2 Potentiostats for use in biosensor applications 10
2.3.3 Potentiostats in electrodeposition of thin films 11
2.3.4 Potentiostats in electrochemical energy Sources 12
2.4 Characteristics of Potentiostats 13
2.4.1 Control Speed 13
2.4.2 Accuracy 14
2.4.3 Current Range and Dynamics 14
2.4.4 Noise 14
2.4.5 Stability 15
2.5 Electrodes 15
2.5.1 Counter Electrodes 16
2.5.2 Reference Electrode 16
2.5.3 Working Electrode 17
2.6 Two-Electrode versus Three-Electrode 17
2.6.1 Two- Electrode Experiment 17
2.6.2 Three Electrode Experiments 19
CHAPTER 3
MATERIALS, METHODS AND TECHNIQUES 21
3.1 Materials/circuit components 21
3.1.1 Diode 21
3.1.2 Capacitor 23
3.1.3 Resistor 24
3.1.5 Tl074 Operational Amplifier 25
3.1.6 L7905 Negative Fixed Voltage Regulators 27
3.1.7 L7805 Positive Fixed Voltage Regulators 28
3.1.8 The Arduino Microcontroller 30
3.2 Electrodes 37
3.3.1 Working Electrode 38
3.3.2 Reference Electrode 38
3.4 Two Electrode Setup 38
3.5 Description and Operating Principles Of The Two Electrode Potentiostat
Circuit Diagrams 39
3.5.1 Power Supply and Conditioning Circuit 39
3.5.2 Signal Pre-Amplifier and Voltage Conditioning Circuit 40
3.5.3 Signal Post-Amplifier Output and Conditioning Circuit 41
3.5.4 Signal Output Processing Circuit 42
3.6 Features of The Finished Three Electrode Potentiostat 45
CHAPTER 4
4.1 Software Features 46
4.2 Operating Procedures 47
4.3 Software Development IDE Used for the Programming 51
4.4 Serial Port Using Visual Basic .Net For Windows Software Development 52
4.5 Checking the Virtual Serial Port Connection 53
4.6 Testing Of the Potentiostat 53
4.7 Discussion 54
CHAPTER 5
5.1 Conclusion 55
5.2 Recommendation 55
References 56
Introduction
Electrochemistry is the science which deals with the conversion of matter to electricity and/ or electricity of matter (Kyvstakovsky, 1910). A large part of this field deals with the study of chemical changes caused by the passage of an electric current and the production of electrical energy by chemical reaction (Bard and Faulkner, 2001). In fact, the field of electrochemistry is one which covers a huge array of different phenomena (e.g. corrosion and electrophoresis), devices (electrochromic display, electroanalytic sensors, batteries and fuel cells) and technologies (the electroplating of metals and the large scale production of aluminum and chlorine).
Scientists usually make electrochemical analysis and measurements on chemical systems for a variety of reasons. They may be interested in obtaining thermodynamic data about a reaction. They may also want to generate an unstable intermediate such as a radical ion and study its rate of decay or its spectroscopic properties. They may also seek to analyze a solution for trace amounts of a metal ion or organic species. In these examples, electrochemical methods are employed as a tool in the study of chemical systems in just the same way that spectroscopic methods are frequently applied. There are also investigations in which the electrochemical properties of the system themselves are of primary interest, for example, in the design of a new power source or for the electrosynthesis of some new product many electrochemical methods have been devised. Their applications require an understanding of the fundamental principle of electrode reactions and the electrical properties of the electrode-electrolyte interfaces.
And this electrochemistry phenomenon is further understood through experiments and research with the use of potentiostat. The potentiostat could even be taken as the greatest tool in electrochemistry. This potentiostat device with its different mode of operation has proved to be very useful as it can measure and control electrical characteristics like resistance, current and voltage in changing chemical reactions of electrodes in an electrolyte.
Potentiostats have been very important in almost every electrochemical research and experiment, and can be applied to different uses with varying configurations such as two electrodes, three- electrode or four- electrode as may be needed.
2.2 THE POTENTIOSTAT
From time immemorial, in the history of scientific and technological inventions, there have been many instances when two or more people independently or individually created or discovered an invention or concept at almost the same time. But for several reasons one of the inventors takes all the credit for that invention. This was so in the telephone, the integrated circuit and even calculus in mathematics. A very rare instance is an invention that was developed by two different scientists in two different fields and these inventions have been in use for years without investigators or users of the invention being aware of the other applications. This happened with the potentiostat and the voltage clamp which are basically similar instrument but whose actual applications are quite different.
Both the potentiostat and the voltage clamp operate on the principle of negative feedback control. Both instruments employ an amplifier in a feedback arrangement to control the voltage (or electrode potential) in an electrolytic cell or biological specimen. In their simplest forms, they are essentially of the same circuit (Harrar, 2014).
2.2.1 THE POTENTIOSTAT AND HISTORY
In the early 1940s, Archie Hickling at The University of Leicester, England, who was working in the field of electrochemistry, invented the potentiostat and coined the apt name of the device (Hickling ,1942). He used the potentiostat to control the voltage of an electrode while performing electrolysis in an electrolytic cell (Harrar, 2014).
Also, in the late 1940s at the University of Chicago, Kenneth Cole with the help of George Marmont, invented electronic circuit called the voltage clamp (Huxley, 1996) which was used to investigate ionic conductors in nerves. Concurrently, the voltage clamp technique was adopted by Alan Hodgkin, Andrew Huxley and Bernard Katz at Cambridge University in England for their research in this field. In 1963, Hodgkin and Huxley were awarded the noble price in physiology or medicine for this work.
Further development of potentiostatic and voltage clamp instrument from the simple circuits described here has proceeded in parallel. The first circuit used amplifiers that were assembled from the individual electronics components (resistors, capacitors and vacuum tubes). Some early potentiostats also use mechanical servomechanisms. The advent during the 1950s of commercially available plug in modular amplifiers called operational amplifiers (Philbrick, 2013) quite advanced instrument incorporating the integrated-circuit operational amplifiers. Operational amplifiers are now commercially available for many specialized applications in electrochemistry and electrophysiology. These instruments embody features that enable measurement of electric current during voltage control or control of the current instead of voltage. Operational amplifiers are incorporated in the measurement of impendence, buffering, current measurement and resistance (Harrar, 2014).
2.2.2 PROBLEMS ENCOUNTERED IN POTENTIOSTAT
Although the electronic circuits of potentiostat and voltage clamp are very similar, the laboratory apparatus and experiments using them are quite different. Nevertheless, some problems that complicate the experiment are present in both fields. Electrophysiologists are always dealing with extremely small electrodes which have high resistance that may introduce errors in potential control (Harrar, 2006). Certain investigations using potentiostat also employ small working electrodes, and when more exact potential control are required, solution resistances exist that many have to be compensated, particularly at the working electrode (Roe, 1996).
There are also many electrical capacitance effects that complicate the measurement. First of all, a cell membrane constitutes an electrical capacitance that must be charged before the desired potential is established. This is analogous to potentiostatic work in which the working electrode/solution double layer capacitance must first be charged. There is also stray capacitance in both electrolytic and voltage damp arrangement that can influence the measurement of high speed signals. (Roe, 1996). Data interpretation in electrophysiology may also be complicated because of the micro electrode contact at a point (Harrarr, 2014). In both electrochemistry and electrophysiology quite sophisticated instrumentation has been designed to deal with all these problems.
2.3 APPLICATIONS OF THE POTENTIOSTAT
2.3.1 POTENTIOSTAT IN CORROSION STUDIES
During the late 70’s and early 80’s, corrosion specialist began to discover that electrochemical instruments would be valuable problem solving tools. When manufacturers began to produce more compact and easy-to-use instruments, they became even more popular. The proliferation of books, papers and articles on the advantages of electrochemical corrosion measurements make it clear that electrochemical instrumentation is becoming a significant part of the corrosion specialist repertoire.
Because of the rapid expansion of the literature, newcomers are learning that electrochemical instruments can help solve away of their most tedious and persistent corrosion problems (Autolab, 2015)
Corrosion is a process involving electrochemical oxidation and reduction reaction (Autolab, 2015). It makes sense that electrochemical methods can be used to study or measure corroding system.
More especially, when a metal is immersed in a given solution, electrochemical reaction characteristics of the metal- solution interface occur at the surface of the metal causing the metal to corrode. These reactions create an electrochemical potential called the corrosion potential or the open circuit potential (measured in volts) at the metal- solution interface since the corrosion potential is determined by the specific chemistry of the system, it is a characteristics of the specific metal-solution system.
The corrosion potential ECORR of the metal-solution interface cannot be directly measured. Since all voltage measuring devices measure a potential energy difference. ECORR can only be compared to the potential of a known reference system Eref and can only be indirectly measured.
Hence, the need of an electrode that has been used for corrosion work and in recent years most corrosion specialist has been using a single type of electrode. The Saturated Calomel Electrode (SCE) (Autolab, 2015)
2.3.2 POTENTIOSTAT IN BIOSENSOR APPLICATION
Portable biosensors have become essential to the world of medicine, a need that materialized due to an ever increasing population and as a means to provide health care for all. In 1962, Leyland Clark of the Children’s Hospital Research Foundation in Cincinnati, developed the first biosensor but it was not until 1975 that his discovery was commercialized (Clark, 1991). Today, that first biosensor, better known as the glucose monitor has provided millions of diabetics with independence allowing them to monitor their disease at home, thereby decreases their need for medical attention. The glucose monitor has also provided an immerse aid to the government and health system considering that more than 20 people are diagnosed with diabetics every hour of every day (C.D. Association, 2009).
A biomarker is a substance, often a protein which is indicative of the onset on predisposition of diseases (Javanmad et. al., 2009). A biosensor is a device that is used for the detection of such biomarkers. Because electrochemical detection methods such as cycle voltammetry can be used to confirm the presence of analytes or biomarker within a solution (Loncaric, 2009) these methods hold great potential in the creation of new biosensors.
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