The document discusses potentiostats, which are used to control the voltage between a working and reference electrode in electrochemical measurements. It describes the basic components and functions of a potentiostat, including maintaining a constant potential and delivering current. Voltammetry techniques that actively vary the cell potential are also summarized. Key aspects like accuracy, bandwidth, noise, and stability are important characteristics of potentiostats. Operational amplifiers and voltage ramp generators are important components of potentiostat circuitry used to control the electrochemical reaction and output current signals.

1. POTENTIOSTAT, CIRCUITRY, E-T
WAVEFORMS AND
ELECTROCHEMICAL
MEASUREMENTS
(GROUP 2)
GROUP MEMBERS MATRIC NUMBER
NUR NADIAH BT 154982
SAMSUDIN
TUAN ZARITH FARHANA 154922
BINTI TUAN ZAINUDDIN
MUNIRA BINTI MAZLAN 151847
NOOR AINI BINTI MD 154706
SAAD
SITI NUR ASMA‟ BINTI 151626
MOHD AYUB
ZALIKA AZREEN BINTI 153545
ABD MANAN
SUHAINIE BINTI ISMAIL 153598

2. ELECTROANALYTICAL
METHOD
 Study an analyte by measuring the potential (volts)
and/or current (amperes) in an electrochemical cell
containing the analyte.
 3 main categories :
- potentiometry : the difference in electrode
potential is measured
- AMPEROMETRY : the cell current is
measured over
time
- voltammetry : the cell current is measured
while
actively altering the cells
potential.

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 between
the working electrode and reference electrode
without polarizing the reference electrode
 To compare the potential difference to a
preset voltage and force a current through the
counter electrode towards the working
electrode in order to counteract the difference
between preset voltage and existing working
electrode potential

5. Characteristics of Potentiostat
1) Control speed
 Speed of a potentiostat is measured in terms of
„small - signal rise – time‟, bandwidth rate.
 Potentiostats have bandwidths from 100 kHz to
some MHz.
2) Accuracy
 The potentiostat counterbalances voltage
difference between set control voltage and
existing cell
3) Current range and dynamics
 High currents are required from the potentiostat.

6. 4) Noise
 In potentiostats, the most sensitive circuit is the input
stage, producing noise in the input resistor and the first
amplifier stage.
 Good potentiostats are equipped with low-noise
amplifiers.
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)

9. POTENTIOSTATIC CIRCUITRY
 Referred also as control circuitry.
 Main purpose:
i. To maintain a voltage between the reference
electrode and the working electrode
ii. To control the electro-chemical reaction
iii. 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

11. VOLTAGE RAMP GENERATOR

12.  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 given
Vo = Vo
by:
 The output voltage rises steadily with time.

13. OPERATIONAL AMPLIFIER
 Is an extremely versatile electronic device.
 Versatility stems from the very high voltage
gain together with high input resistance and
low output resistance.
 Op-amp are direct coupled devices such that
the input signal may be either AC or DC.

14. • All op-amp have two inputs connected in a
differential mode, so that output voltage:
V₀ =A(V₊ - V₋)
V₊ = voltage at non inverting input
V₋ = voltage at inverting input
A = open loop gain of the op-amp

15. Operational Amplifier (Op-Amp)
 Very high differential gain +V cc
In p u t 1
 High input impedance +
V o
 Low output impedance V d
O u tp u t
 Provide voltage changes 
In p u t 2
(amplitude and polarity)
R ~ in f
in -V R ~ 0 cc out
 Used in oscillator, filter
and instrumentation Vo  G dVd
 Accumulate a very high
G d : differenti al gain normally
gain by multiple stages 5
ver y large, say 10
Operational Amplifier

16. Single-Ended Input
+ • + terminal : Source
V o
• – terminal : Ground
~ V i • 0o phase change

+
V o • + terminal : Ground
• – terminal : Source
 • 180o phase change
~
V i
Operational Amplifier

17. Double-Ended Input
• Differential input
+
V d V o
• Vd  V  V
~ • 0o phase shift change
 between Vo and Vd
+
V o
~ V 1 
~
V 2
Operational Amplifier

18. Common-Mode Operation
• Same voltage source is +
applied V o
at both terminals 
• Ideally, two input are equally V i ~
amplified
• Output voltage is ideally
zero
due to differential voltage is
zero
• Practically, a small output
signal can still be measured
Operational Amplifier

19. Ideal Op-Amp Applications
Analysis 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 termainals
is zero +V in
V o

Rf
Ra
Operational Amplifier

20. Non-inverting Amplifier
(1) Kirchhoff node equation at V+
yields, V  V
V in +
 i V o

(2) Kirchhoff node V o
V   0 V   equation at V
 0 Rf
yields, a
R Rf Ra
(3) Setting V+ = V– yields
Vi Vi  Vo Vo Rf
 0 or  1
Ra Rf Vi Ra
Operational Amplifier

21. v+ v+
vi + vi +
vo R1 vo
R2 v-
v-
 
Ra Rf Ra Rf
Noninverting amplifier Noninverting input with voltage divider
Rf Rf R2
v o  (1  )vi v o  (1  )( )vi
Ra Ra R1  R 2
v+ v+
+ v i +
vi v
vo R 1
v-
o
v- R 2


Rf R f
Less than unity gain
Voltage follower
R2
vo  vi vo  vi
R1  R 2
Operational Amplifier

22. Inverting Amplifier
(1) Kirchhoff node equation at V+ Rf
yields, V   0 Ra

V o
(2) V in  V
Kirchhoff _nodeequation at V
V V
 o 0
V ~in +
yields, a
R Rf
(3) SettingV = fV– yields
Vo
+
R
Notice: The closed-loop gain Vo/Vin is
V in Ra dependent 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

23. COMPUTER READOUT
 Computer use digital signals (0 & 1) instead of analog
signals (0-10 V)
 Interfacing a potentiostat with a computer requires
translation back and forth
 Modern potentiostats have on-board DAC (digital to
analog converters) and ADC (analog to digital
converters)

24. External (strirrer, T, …)
01001010… 0-10 V
DAC
P-stat
ADC
10010100… 0-10 V
External ( spectro, pH, …)

25. DAC Digital to analog converter
-Defines the smallest possible step
- Multiple channels working as indipendent
function generators

26. ADC Analog to digital converter
-ADC is a digital filter
- Multi-channel ADC to convert several analog
signals into digital

27. ANALYTICAL SOFTWARE -
Autolab potentiostat

28. Autolab potentiostat
External (RDE, strirrer, T, …)
01001010… 0-10 V
DAC
01001010… 0-10 V
MODULE P-stat
10010100… 0-10 V
ADC
External (QCM, spectro, pH, …)

29. 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

30. 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 high
source resistance
 make fast measurements of small currents.
 useful for eliminating electrical interference,
especially line frequency noise.
 If the electrochemical cell is picking up electrical
noise from the environment, the additional use of
Faraday cage is strongly recommended

31. • Protect not just from static electrical charge but also from
electromagnetic waves; this is known as electromagnetic
shielding.
• This is how cars protect you from lightning: The charge is
conducted along the outer layer of the metal but does not

32. OXYGEN REMOVAL
 Most experiments require dissolved oxygen be
removed from the cell.
 This is because:
i. Electrochemically active across the cathodic
potential range
ii. 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 experiment
ii. A “blanket” of inert gas maintained above the
solution during the experiment

33. Both cells have a fritted sparge tube to allow
deoxygentation of the solution with inert gas