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Tektronix, Inc Touch, Test & Invent SMU를 활용한 전기화학적 특성 분석 (Keithley 2450 & 2460) 텍트로닉스 오연주 과장 Agenda • Introduction - Electrochemistry • Applications and Tests - Potentiometry - Voltammetry - Galvanostatic 2 Electrochemistry • Electrochemistry is the study of the interchange of chemical and electrical energy. • The branch of chemistry that is the study of: 1. the production of electricity by chemical reactions 2. chemical changes produced by electrical current • Evaluates oxidation-reduction (redox) reactions: transfer of electrons from reducing agent (gain of electrons) to oxidizing agent (loss of electrons) Because electrochemistry measurements often involve sourcing and measuring DC current and voltage, Keithley products can be used! 3 What is Electrochemistry? The study of electricity during a chemical reaction 1. Production of electricity by chemical reactions 2. Chemical changes that are produced by electrical current Electrochemistry measurements involve sourcing and measuring DC current and voltage. Keithley products are used! . Electrometers . Current Sources . Source Measure Units (SMU) . DMMs . 4200-SCS Parameter Analyzer Electrochemistry Applications . Batteries and Energy Storage . Fuel cells and energy conversion . Chemical & Biological sensors . Corrosion studies . Electrochemical deposition . Electroplating . Organic electronics – OLEDs, OTFTs . Physical and Analytical Electrochemistry . Nanomaterials . Photoelectrochemistry (dye sensitized solar cells) . University student labs Electrochemistry Methods Potentiometry, Voltammetry & Galvanostatic Analytical Chemistry: Electroanalytical Test Methods Test Method Description Potentiometry Measures the potential of a solution between 2 = Voltage vs. time electrodes Galvanostatic Measuring the cell's current that is consumed or = Current vs. time produced over time. Voltammetry Apply a varying potential and measure resulting = Voltage vs. Current current in a 3 electrode system. There are many types of voltammetry experiments depending on the potential waveform. 7 Potentiometry . Passively measures the potential of a solution between two electrodes . Requires two electrodes . A pH meters and electrometers are common equipment for measuring the potential . Common applications: – pH measurements – Ion Selective Electrode measurements. 8 Potentiometry . Potentiometry is the field of electro- analytical chemistry in which the potential is measured, with little current flow, between two electrodes. It is used to determine the concentration of analyte ions in a solution based on the Nerst equation (NOTE : an analyte is substance being analyzed.) . In terms of electrical measurements, voltages in the mV range are typically measured. Two applications for Potentiometry include PH measurements and Ion Selective Electrode measurements. pH Measurements The voltage difference between the glass electrode and reference electrode is related to the pH level. The resistance of the pH electrodes is typically about 100Mohm. To measure the voltage difference, use a pH meter or a voltmeter with high input impedance, like an electrometer. The pH meters automatically convert the voltage difference to a pH reading. From Wikipedia….. Voltammetry Voltammetry is the study of current as a function of the applied voltage usually requiring 3 electrodes. 1 working electrode 2 counter electrode 3 reference electrode - Counter electrode (2) passes all the current needed to balance the current observed at the working electrode (1) -Reference (3) acts as reference in measuring and controlling working (1) electrode’s potential -Voltage different between working (1) and reference (3) electrodes remains constant Voltammetry Many types of voltammetry……… •Linear Sweep Voltammetry •Staircase Voltammetry Linear sweep voltammetry- potential swept linearly with •Square wave Voltammetry time •Cyclic Voltammetry (otherwise known as CV) •Stripping Voltammetry Square wave potential sweep Cyclic Voltammetry (CV) In cyclic voltammetry, the electrode potential ramps linearly versus time as shown. This ramping is known as the experiment's scan rate (mV/s). The potential is applied between the reference electrode and the working electrode and the current is measured between the working electrode and the counter electrode. This data is then plotted as current (i) vs. potential (E). potential time This is called a voltammagram Interpreting the Voltammagram 14 Oxidation-Reduction Reactions Oxidation-Reduction (redox) reactions involve a transfer of electronics. Oxidation involves a loss of electrons. Substances that have the ability to cause another substance to lose electrons are called oxidizing agents. Reduction involves a gain of electrons. Substances that have the ability to reduce another substance (cause to gain electrons) are called reducing agents. Example: hydrogen fluoride H2 + F2 = 2HF Oxidation Reaction Reduction Reaction 15 What is C-V used for? The information derived from a voltammagram will vary depending on the application. Some examples are: 1. Glucose sensor: The voltammagram may shift up and down on the Y-axis (current) depending relating the current to a glucose level. 2. Organic semiconductor material: The voltammagram will indicate the HOMO and LUMO levels of the material. This is analogous to the valence and conduction bands of traditional semiconductor material. 3. Battery materials: the voltammagram provides information on the quality of the material before charge/discharge cycling occurs. 16 Cyclic Voltammetry Measurements Cyclic voltammetry measurements are made using a 3-electrode system consisting of a voltage source, ammeter, and voltmeter. Commercially available instruments used to perform cyclic voltammetry are known as potentiostats. 17 Potentiostats Potentiostats are the most commonly used electrochemistry instruments. A potentiostat is the electronic hardware required to control a three electrode cell and run most electroanalytical experiments. The potentiostat includes software the electrochemistry tests. http://en.wikipedia.org/wiki/Potentiostat 18 Using a SourceMeter as a Potentiostat Model 2450 SourceMeter Electrochemical Cell Working Electrode Reference Electrode Counter Electrode The potentiostat operates by supplying current between the Working and Counter Electrodes such that the voltage difference between the Reference and the Counter Electrodes is constant. In the Source V, Measure I, 4-wire configuration, the SourceMeter will ensure that the voltage difference between Sense HI (Reference Electrode) and Sense LO (Counter Electrode) terminals is constant. 19 Using Model 2450 for C-V Script written to perform C-V using the Model 2450 Voltammagram generated by script downloaded into the box. Graphical display shows the image automatically. No computer needed. Scripts can be modified by user. Model 2450 SourceMeter 20 Model 2450 Screen Capture Voltammagram on Model 2450 SourceMeter 21 Galvanostatic . Similar to potentiostatic except current is forced and measured. Measuring the cell's current that is consumed or produced over time. Common applications – Galvanic Cycling (battery testing) – Galvanic Cell Testing (fuel cells) – Galvanic corrosion testing – Galvanic Deposition (depositing materials) 22 Galvanic Cycling Batteries change chemical energy into electrical energy. A lot of research to find ways to extend battery life and reduce battery costs. Looking for replacement for Li Ion batteries. Some of the tests performed include: • Galvanic Cycling (charge and discharge) • Cyclic Voltammetry (on material prior to performing cycling test) • Internal Resistance (use offset comp mode) • Electrochemical Impedance Spectroscopy (AC test) – characterize performance 23 Galvanic Cycling Battery Charge/Discharge SourceMeters are ideal for SourceMeter battery charge and Force HI discharge because they can both force and sink Sense HI current. A + V VB - The SourceMeter is VS configured to source Sense LO voltage. When charging Force LO and discharging the unit is in compliance, so it is essential in a constant current mode – galvanic. Battery charge and discharge cycling is often called galvanic cycling. 24 Galvanic Cycling Battery Charge/Discharge Charge Cycle Discharge Cycle SourceMeter SourceMeter Force HI Force HI i i A + A + V V - B - B VS VS Force LO Force LO SourceMeter in Source Mode SourceMeter in Sink Mode VS > VB VS < VB SourceMeter Functions as Power Supply SourceMeter Functions as Electronic Load Charge Current (i) is Positive Discharge Current (i) is Negative 25 Battery Discharge Plot Generated by Model 2460 2500 mAH D Cell Discharged at 2500 mA (1C) 1.4 1.35 1.3 1.25 1.2 1.15 1.1 Cell Voltage (Volts) Voltage Cell 1.05 1 0.95 0.9 0 0.2 0.4 0.6 0.8 1 Time (Hours) 26 App Note Available to Support Model 2450 or 2460 Battery Cycling and Cyclic Voltammetry November 2014 27 28 4 May 2015 .
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