1. 1. POTENTIOSTAT, CIRCUITRY, E-T WAVEFORMS ANDELECTROCHEMICAL MEASUREMENTS(GROUP 2) GROUP MEMBERS MATRIC NUMBERNUR NADIAH BT 154982SAMSUDIN TUAN ZARITH FARHANA154922 BINTI TUAN ZAINUDDINMUNIRA BINTI MAZLAN 151847 NOOR AINI BINTI MD 154706 SAADSITI NUR ASMA BINTI151626 MOHD AYUBZALIKA AZREEN BINTI 153545ABD MANAN SUHAINIE BINTI ISMAIL153598
2. 2. ELECTROANALYTICAL METHOD Study an analyte by measuring the potential (volts)and/or current (amperes) in an electrochemical cellcontaining the analyte. 3 main categories : - potentiometry : the difference in electrodepotential is measured - AMPEROMETRY : the cell current ismeasured overtime - voltammetry : the cell current is measuredwhileactively altering the cellspotential.
3. 3. POTENTIOSTAT Potentiostat are amplifiers used to control a voltage between two electrode, a working electrode and a reference electrode, to a constant value~ Reference electrode is used to maintain a constant voltage referred to the potential of the hydrogen electrode~ Counter electrode is used to maintain a constant potential difference between the reference electrode and the working electrode
4. 4. Function of Potentiostat To measure the potential difference betweenthe working electrode and reference electrodewithout polarizing the reference electrode To compare the potential difference to apreset voltage and force a current through thecounter electrode towards the workingelectrode in order to counteract the differencebetween preset voltage and existing workingelectrode potential
5. 5. Characteristics of Potentiostat1) Control speed Speed of a potentiostat is measured in terms ofsmall - signal rise time, bandwidth rate. Potentiostats have bandwidths from 100 kHz tosome MHz.2) Accuracy The potentiostat counterbalances voltagedifference between set control voltage andexisting cell3) Current range and dynamics High currents are required from the potentiostat.
6. 6. 4) Noise In potentiostats, the most sensitive circuit is the inputstage, producing noise in the input resistor and the firstamplifier stage. Good potentiostats are equipped with low-noiseamplifiers.5) Stability
7. 7. VOLTAMMETRIC ANALYZER Advantages of the voltammetric analysis: i) High absolute sensitivity ii) Low cost of singular analysis iii) Multielement determination in one sample iv) Express analysis v) Safety for the operator vi) Excluding work with the metallic mercury(determination on the solid electrodes)
8. 8. POTENTIOSTATIC CIRCUITRY Referred also as control circuitry. Main purpose:i. To maintain a voltage between the reference electrode and the working electrodeii. To control the electro-chemical reactioniii. To deliver an output signal proportional to the WE current-Also provides the current to the counter electrode to balance the current required by WE
9. 9. VOLTAGE RAMP GENERATOR
10. 10. A circuit that generates a sweep voltage which increases linearly in value during one cycle of sweep, then returns to zero suddenly to start the next cycle. Voltage ramp generator is formed- feedback resistor of the inverting voltage amplifier is replaced by a capacitor. If the input voltage, V1 is constant and RC = 1s then the output voltage Vit after a time t is givenVo = Vo by: The output voltage rises steadily with time.
11. 11. OPERATIONAL AMPLIFIER Is an extremely versatile electronic device. Versatility stems from the very high voltagegain together with high input resistance andlow output resistance. Op-amp are direct coupled devices such thatthe input signal may be either AC or DC.
12. 12. All op-amp have two inputs connected in a differential mode, so that output voltage:V =A(V - V)V = voltage at non inverting inputV = voltage at inverting inputA = open loop gain of the op-amp
13. 13. Operational Amplifier (Op-Amp) Very high differential gain +V cc In p u t 1 High input impedance+V o Low output impedanceV dO u tp u t Provide voltage changes In p u t 2(amplitude and polarity) R ~ in fin -V R ~ 0cc out Used in oscillator, filterand instrumentation Vo G dVd Accumulate a very high G d : differenti al gain normallygain by multiple stages5ver y large, say 10 Operational Amplifier
14. 14. Single-Ended Input + + terminal : SourceV o terminal : Ground~V i 0o phase change +V o + terminal : Ground terminal : Source 180o phase change ~ V iOperational Amplifier
15. 15. Double-Ended Input Differential input+V d V o Vd V V~ 0o phase shift changebetween Vo and Vd+V o~ V 1 ~V 2Operational Amplifier
16. 16. Common-Mode Operation Same voltage source is +appliedV oat both terminals Ideally, two input are equally V i ~amplified Output voltage is ideallyzerodue to differential voltage iszero Practically, a small outputsignal can still be measured Operational Amplifier
17. 17. Ideal Op-Amp ApplicationsAnalysis Method :Two ideal Op-Amp Properties:(1) The voltage between V+ and V is zero V+ =V(2) The current into both V+ and V termainalsis zero +V inV o RfRa Operational Amplifier
18. 18. Non-inverting Amplifier(1) Kirchhoff node equation at V+yields, V V V in+iV o (2) Kirchhoff node V o V 0 V equation at V0Rfyields, aR RfRa(3) Setting V+ = V yieldsVi Vi VoVoRf 0 or 1Ra Rf ViRa Operational Amplifier
19. 19. v+ v+vi+vi+voR1voR2v- v- Ra Rf RaRfNoninverting amplifier Noninverting input with voltage dividerRfRf R2 v o (1 )vi v o (1 )()viRaRa R1 R 2v+ v+ + v i + vi v vo R 1 v-ov-R 2 RfR fLess than unity gain Voltage follower R2vo vi vo viR1 R 2Operational Amplifier
20. 20. Inverting Amplifier(1)Kirchhoff node equation at V+Rf yields, V 0 Ra Vo(2)V in V Kirchhoff _nodeequation at V V V o0 V ~in+ yields, a RRf(3)SettingV = fV yieldsVo+R Notice: The closed-loop gain Vo/Vin isV in Radependent upon the ratio of two resistors, and is independent of the open-loop gain. This is caused by the use of feedback output voltage to subtract from the input voltage.Operational Amplifier
21. 21. COMPUTER READOUT Computer use digital signals (0 & 1) instead of analogsignals (0-10 V) Interfacing a potentiostat with a computer requirestranslation back and forth Modern potentiostats have on-board DAC (digital toanalog converters) and ADC (analog to digitalconverters)
22. 22. External (strirrer, T, )01001010 0-10 VDAC P-statADC10010100 0-10 V External ( spectro, pH, )
23. 23. DAC Digital to analog converter-Defines the smallest possible step- Multiple channels working as indipendentfunction generators
24. 24. ADC Analog to digital converter-ADC is a digital filter- Multi-channel ADC to convert several analogsignals into digital
25. 25. ANALYTICAL SOFTWARE - Autolab potentiostat
26. 26. Autolab potentiostat External (RDE, strirrer, T, ) 010010100-10 V DAC 01001010 0-10 V MODULE P-stat 100101000-10 V ADC External (QCM, spectro, pH, )
27. 27. Autolab potentiostat other D/A modules Scangen module: true linear scan generator Generates an analog scan (no staircase) with scan rates up to 250,000 V/s FRA module: frequency response analyzer Digital to analog sine wave generator
28. 28. FARADAY CAGE 3 conditions:- Very small currents are to be measured(current down to a few picoamperes)- The electrolyte has low conductivity- The reference electrode system has highsource resistance make fast measurements of small currents. useful for eliminating electrical interference,especially line frequency noise. If the electrochemical cell is picking up electricalnoise from the environment, the additional use ofFaraday cage is strongly recommended
29. 29. Protect not just from static electrical charge but also fromelectromagnetic waves; this is known as electromagneticshielding. This is how cars protect you from lightning: The charge isconducted along the outer layer of the metal but does not
30. 30. OXYGEN REMOVAL Most experiments require dissolved oxygen be removed from the cell. This is because:i. Electrochemically active across the cathodic potential rangeii. Very likely to react with products formed by electron transfer To remove the dissolved oxygen:i. The solution is purged with an inert gas (N2 or Ar) for 5 10 mins prior to the experimentii. A blanket of inert gas maintained above the solution during the experiment
31. 31. Both cells have a fritted sparge tube to allowdeoxygentation of the solution with inert gas