Design and Construction of a Two Electrode Potentiostat
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 CONTENTS
Cover page i
Title page ii
Table of content vii
List of Figure xii
List of table xiv
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
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
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
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
5.1 Conclusion 55
5.2 Recommendation 55
During the year 1950, metallurgist and physio-chemist tried to bring some light into a fascinating electrochemical phenomenon (Bard and Faulkner, 2001) called electrochemistry.
Electrochemist discovered that if an iron electrode is dropped into diluted sulphuric acid (electrolyte), it will instantly start to corrode and if another electrode which will not corrode is inserted into the same electrolyte e.g. Platinum and iron electrode is connected to the negative pole of the current source and the platinum electrode to the positive pole of the current source, the iron dissolves will slow down or even stop depending on the voltage applied. This phenomenon was discovered already in the 17th century by Sir Humphery Davy. When the iron electrode is connected to the positive pole and the voltage increased from very low value to higher ones, the dissolution grows exponentially with increasing voltage. Above a certain current limit depending on the electrode area, the electrolytic composition and temperature, it is found that current suddenly drops to a very low value and the iron electrode stops to dissolve. This phenomenon was detected by Michael Faraday which he called ‘passivity’. Although, this phenomenon has been an object of controversy since then a better understanding of this phenomenon was possible after the invention of the potentiostat.
Although potentiostats are the foundation of modern electrochemical research, they have seen relatively little application in resource poor setting such as undergraduate laboratory courses and the developing world (Aaron et al, 2011). One reason for low penetration of potentiostat is their cost as even the least expensive potentiostat sells for more than a thousand dollars. Inexpensive electrochemical workstations could prove useful in educational laboratories, increasing access to electrochemical based analytical techniques. But with this project work, constructing a potentiostat will not even cost up to a hundred thousand naira as locally sourced material and electronic components available on the shelf will be used.
1.2 AIMS AND OBJECTIVES
This project work is done so as to produce a cheap electrochemical analytical device which can be interfaced with dedicated computer software for real time recording and plotting of experimental results.
1.3 SIGNIFICANCE OF THE STUDY
This device is a basic device used in electrochemical research which includes.
Electroplating: Used in electroplating experiments.
Biosensors: Used in microbial sensors for testing DNA and other proteins in the health sector.
It is also used in the health sector as a sensor that can be used to test for sugar level in diabetics.
Energy source: Used to create electrochemical source of energy as in fuel cells super caps, batteries etc.
Thin film deposition: Used for the deposition of thin films, characterizing of properties of the thin films used in solar cells.
1.4 SCOPE OF THE STUDY
The two-electrode potentiostat or bipotentiostat is basically an operational amplifier circuit in conjunction with an electrochemical case which comprises of the electrodes dipped into an electrolyte. It is a device which controls the potential between a pair of electrodes (working electrode and reference electrode) while measuring current flow. It is a control and measuring device. It comprises of an electric circuit which controls the potential across the cell by increasingly sensing changes in the resistance, varying according to the current supplied to the system; a higher resistance will result in a decreased current and vice-versa, in order to keep the voltage constant as described by Ohm’s law.
Most early potentiostats could function independently providing output through a physical data trace. Modern potentiostats are designed to interface with a personal computer and operate through a dedicated software package. This automated software allows rapid shifting between experiments and experimental condition. This computer allows data to be stored and analyzed more effectively rapidly and accurately than historic methods.
The potentiostat to be designed involves electrodes in electrolyte which is activated by the following circuits or sections:
Control amplifier: This amplifies the potential between the working and reference electrodes.
Electrometer: This measure the potential difference between the working and reference electrodes.
Current -to- voltage converter: This measures the current flow.
This device is to be interfaced with operating system software on the computer so that results can be easily recorded in real time by measuring, recording and plotting of results into tables and graphs respectively. In this work it will be shown how this device can be designed, constructed and applied in electrochemical research.