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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. 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. 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. 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. 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. 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. 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. 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. VOLTAGE RAMP GENERATOR
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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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)
23. DAC Digital to analog converter-Defines the smallest
possible step- Multiple channels working as indipendentfunction
generators
24. ADC Analog to digital converter-ADC is a digital filter-
Multi-channel ADC to convert several analogsignals into
digital
25. ANALYTICAL SOFTWARE - Autolab potentiostat
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. 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. 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. 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. 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. Both cells have a fritted sparge tube to
allowdeoxygentation of the solution with inert gas