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EC-Lab products
Best Laboratory Practices
in Elect
Electrochemistry
E
ochemi try
Electronic conductor
Ionic conductor
Ox/Red
Set-up
CS-3A Cell Stand
To ccarry out these measurements, a potentiostat/galv
l anostat is used. Usually, a three-electrode
lv
setup is used i.e. Working Electrode (WE), Reference Electrode (RE) and Counter Electrode (CE).
A po
potentiostat/galv
l anostat applies/measures: a voltage between WE and RE,
lv
a current flow through WE and CE.
Shielding
in the Faraday cage and the cage must be connected to the
ground of the instrument. This creates an equipotential
shielding and eliminates any electromagnetic perturbation
that may come from the electrical grid or other “noise” sources
in your laboratory.
If the frequency of the grid is present in your data, you must
improve the cell shielding. When several devices are involved
in your experiment (RDE, thermostat...) make sure that
all instruments share the same Earth ground.
Sensors
Coatings
Fuel/solar cells
Materials
-
Techniques
Input
CV (Cyclic Voltammetry)
Unstirred
electrolyte
E
Sweep of voltage (forward and backward scan), the current is measured.
This allows the user to characterize the species and mechanism of interest.
Exp condition
Output
Time
A sinusoidal perturbation is applied to the cell (as potential or current) in
a range of frequencies. This allows the user to determine kinetic constants.
Typically, the resulting plot is a Nyquist plot i.e. -Im (Z) vs Re (Z).
Freq. 1
Freq. 2
E
Around
steady
state of
I vs E curve
Re(Z)
Time
Hydrodynamic steady-state voltammetry
Controlled
mass
transfer
E
A Rotating Disc Electrode (RDE) is employed to maintain a known
mass transfer rate of electroactive species from the bulk solution
to the electrode surface.
No mass
transport
limitations/
stirred
electolyte
Time
Time
2
3
1
2
with
-1
6
with
IL = 0.620 n F A D Ω ν [x]
Transport information
gained from RDE
experiments.
The Butler-Volmer equation:
I = I0 exp
log (I o )
Log (I )
Kinetic information
Anodic
Cathodic
αOnF
( RT
M n+
+n
e-
)
(E-Eeq) - I0 exp
-
n+
M
M
Eeq
M
e
+n
(
-αRnF
RT
EO:
R:
T:
n:
F:
[x]:
Potentiostat/galvanostat
Fourier
Transform
50 or 60 Hz
Frequency/Hz
Time
Decrease the inductive effects that result from
high current passing through your circuit by employing
“twisted pairs”. Twist the cables that carry current to
minimize electromagnetic effects which can affect your data.
Minimizing contact resistance: a 4-point connection to
an electrochemical device (battery, supercapacitor...) separates
the current-carrying lead from the voltage-sensing lead.
This ensures that there is no current passing through the
voltage-sensing lead and therefore, no voltage drop exists
and the “true” potential is measured.
Do not use extension cables: extension cables, especially
unshielded ones, can add inductive effects to EIS measurements.
Current
Current
Voltage
Voltage
L
R: resistance (Ω)
P: power (W) P = E i
W: energy (J) W = E i t
IL:
n:
F:
A:
D:
Ω:
Levich current (A)
number of exchanged electrons
Faraday constant (96,487 C mol-1)
electrode area (cm²)
diffusion coefficient (cm² s-1)
angular rotation rate of the electrode (rad s-1)
1 rpm = 2π/60 rad s-1
ν: kinematic viscosity (cm² s-1)
[x]: concentration of the species x (mol cm-³)
10-3 mol cm-³ = 1 mol L-1
Inductive effect
due to extended cables
)
I0: exchange current (A)
αx: charge transfer coefficient
R: perfect gas constant (8.315 J K-1 mol-1)
T: temperature (K)
n: number of exchanged electrons
F: Faraday constant (96,487 C mol-1)
Eeq: equilibrium potential in the standard conditions (V)
E: applied potential (V)
E
Place WE close to the RE: this will help to minimize the ohmic
CE
drop RΩI(t) across the electrolyte. If not set up properly, the result
is that the control voltage is different from the measured voltage.
EIS is recommended to measure the true ohmic drop of your cell.
Warning: if the ohmic drop is significant theoretical models
cannot be applied to your system.
-
Impedance of RE: the effect is significant especially in EIS
measurement. The impedance should be low. If the impedance
of the reference is too high, you may have to change the frit tip or
even change the reference electrode. In some cases, for high
frequency measurements a platinum wire and capacitor must be
added to the RE.
I(t)
Hg/HgSO4
Not recommended
Ag/AgCl
Frit
V(t) = E(t) + RΩI(t)
V(t): controlled potential
E(t): actual potential
RΩI(t): ohmic drop
your application (pH, chloride free, temperature).
Hg/Hg2Cl2
RE
Pt wire
RE selection: select the appropriate RE according to
Alkaline solutions
Aqueous
Hydrofluoric acid
Organic media
Sea water
Risk of damage
WE
Capacitor
Compliance: this is the voltage between the WE and CE. This can
be decreased if the CE and RE are close enough and if the surface
area of the CE is bigger than the surface area of the WE. This is
relevant when the solvent used is not highly conductive (DMSO, DMF).
-
R
C
Re(Z)
-
equilibrium potential in the standard conditions (V)
perfect gas constant (8.315 J K-1 mol-1)
temperature (K)
number of exchanged electrons
Faraday constant (96,487 C mol-1)
concentration of the species x (mol cm-³)
10-3 mol cm-³ = 1 mol L-1
(E-Eeq)
with
REMOTE
Faraday cage
Hg/HgO
Acceptable
Ag/AgNO3
Recommended
Signal Processing
1e+10
Hardware Configuration
- Specifications: check if E/I expected are in agreement
with the configuration of the instrument (resolution/
accuracy). Low or high current options may be required.
Contour plot in different
configurations where:
Ultra Low Current
option
1e+8
∆Z
< 1%
Z
1e+6
1e+4
∆ϕ
< 1%
ϕ
Standard configuration
1e+2
1
1e-2
1
Data Processing
www.bio-logic.info
Bio-Logic SAS
1, rue de l’Europe - 38640 Claix
France
Phone: +33 476 98 68 31
Fax:
+33 476 98 69 09
- Averaging: if the data is too noisy, averaging may be employed.
The noise changes as the square root of the averaging.
Thus, to decrease the noise by a factor of two, four times more
data points must be averaged.
10
100
1e+3 10e+3 100e+3
Frequency/Hz
1e+6 3e+6
- Filtering: some instruments offer low-pass filters as part
of the hardware and can be turned on or off by the user.
Low-pass filters allow signals with frequencies
below the cut-off frequency to be measured.
Time
Cut-off frequency
Frequency
agence-connivence - 1404011
RT
[Ox]
In
nF
[Red]
E: measured potential (V)
I: current (A)
Q: charge (C or A s) Q = i t
1 C = 1 mA h/3.6
OFF
REMOTE
|Z|/Ω
The Levich equation:
Eeq = EO +
Variables
to ground
CLOSE
E and I
Thermodynamic information
Red
OFF
OPEN
Magnitude
The Nernst equation:
Ox + ne-
-
Time
Reminder
The Redox reaction:
P2
ON
Cell Geometry
E
Unstirred
electrolyte
E or I
Apply a potential/current respectively and follow the change over time,
the user may add a species that will modify the response in current or
in potential of the electrode.
-
I or E
Chrono-amperometry/potentiometry
Term
S3
FAST
ON
E
I
E
The log of absolute value of current vs potential is plotted to extract
kinetic constants.
log |I|
Time
Tafel Plot
B
Reset
USB
SLOW
PURGE
STIR
Proper Cell Connection
-
-Im(Z)
Sinus (E or I)
EIS (Electrochemical Impedance Spectroscopy)
10/100 BaseT
S2
STIR
I
Typical
Electro-analytical
Corrosion
Battery testing
Supercapacitors
Ethernet
Faraday cage: the electrochemical cell should be placed
-
Elect
ectrochemical techniques are highly sensitive methods and precautions must be taken
to p
prevent collection of false or erroneous data resulting from experimental errors.
Applications
SP-200
|FTE|
Red/Ox
E
±n e-
-Im(Z)
Elect
ectrochemistry is a science that studies
chemical react
r
ions which take place at the interface
beetween an electronic conductor (electrode)
and an ionic conductorr (electrolyte).