EC-Lab products Best Laboratory Practices in Electrochemistry · Best Laboratory Practices -...
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agence-connivence - 1404011 EC-Lab products Electro-analytical Corrosion Battery testing Supercapacitors Applications Sensors Coatings Fuel/solar cells Materials Ox/Red Red/Ox ±n e - Electronic conductor Ionic conductor in Electrochemistry Best Laboratory Practices - y a d a r a F cage: the electrochemical cell should be placed 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. Shielding - e c a l P WE close to the RE: this will help to minimize the ohmic drop R Ω I(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. - : e c n a i l p m o C 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). - e c n a d e p m I 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. - E R selection: select the appropriate RE according to your application (pH, chloride free, temperature). Cell Geometry Set-up CE WE RE Capacitor Pt wire I(t) V(t) = E(t) + R Ω I(t) Frit Input Exp condition Output Sweep of voltage (forward and backward scan), the current is measured. This allows the user to characterize the species and mechanism of interest. CV (Cyclic Voltammetry) E Time I E Unstirred electrolyte Time E I E Controlled mass transfer 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. Hydrodynamic steady-state voltammetry The log of absolute value of current vs potential is plotted to extract kinetic constants. Tafel Plot Time E log |I| E No mass transport limitations/ stirred electolyte 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. Chrono-amperometry/potentiometry Time Eor I Time I or E Unstirred electrolyte 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). EIS (Electrochemical Impedance Spectroscopy) Sinus (Eor I) Time Freq. 1 Freq. 2 -Im(Z) Re(Z) Around steady state of I vs E curve Bio-Logic SAS 1, rue de l’Europe - 38640 Claix France Phone: +33 476 98 68 31 Fax: +33 476 98 69 09 www.bio-logic.info - g n i g a r e v A : 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. - g n i r e t l i F : 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. Data Processing Eand I Time Ox + ne - Red Variables The Redox reaction: E: measured potential (V) I: current (A) Q: charge (C or A s) Q = i t 1 C = 1 mA h/3.6 R: resistance (Ω) P: power (W) P = E i W: energy (J) W = E i t Reminder with E O : equilibrium potential in the standard conditions (V) 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 ) [x]: concentration of the species x (mol cm - ³) 10 -3 mol cm - ³ = 1 mol L -1 E eq = E O + RT In [Ox] nF [Red] The Nernst equation: Thermodynamic information I L = 0.620 n F A D 2 3 Ω 1 2 ν -1 6 [x] with I L : Levich current (A) n: number of exchanged electrons F: Faraday constant (96,487 C mol -1 ) A: electrode area (cm²) D: diffusion coefficient (cm² s -1 ) Ω: 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 V(t): controlled potential E(t): actual potential R Ω I(t): ohmic drop The Levich equation: Transport information gained from RDE experiments. with I 0 : 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 ) E eq : equilibrium potential in the standard conditions (V) E: applied potential (V) I = I 0 exp ( α O nF (E-E eq ) ) - I 0 exp ( -α R nF (E-E eq ) ) RT RT The Butler-Volmer equation: Log ( I ) E E eq log ( I o ) M M n + + ne - M n + + ne - M Kinetic information - 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. Hardware Configuration Signal Processing Frequency/Hz 1e +10 1e +8 1e +6 1e +4 1e +2 1 1e -2 1 10 100 1e +3 10e +3 100e +3 1e +6 3e +6 |Z|/Ω Ultra Low Current option Standard configuration Contour plot in different configurations where: ΔZ < 1% Z Δϕ < 1% ϕ Typical Techniques Faraday cage Potentiostat/galvanostat to ground CS-3A Cell Stand SP-200 E Time |FT E | Frequency/Hz 50 or 60 Hz - e s a e r c e D 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. Hg/Hg 2 Cl 2 Hg/HgSO 4 Ag/AgCl Hg/HgO Ag/AgNO 3 Alkaline solutions Aqueous Hydrofluoric acid Organic media Sea water Risk of damage Not recommended Acceptable Recommended Proper Cell Connection - g n i z i m i n i M 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. - o D not use extension cables: extension cables, especially unshielded ones, can add inductive effects to EIS measurements. Current Voltage Current Voltage -Im(Z) Re(Z) Inductive effect due to extended cables R C L Magnitude Frequency Cut-off frequency Anodic Cathodic Fourier Transform
Transcript of EC-Lab products Best Laboratory Practices in Electrochemistry · Best Laboratory Practices -...
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ectrochemistry is a science that studies emical reactreactr ions which take place at the interface
etween an electronic conductor (electrode) d an ionic conductor (er (er lectrolyte).carry out these measurements, a potentiostat/galvlvl anostat is used. Usually, a three-electrode up is used i.e. Working Electrode (WE), Reference Electrode (RE) and Counter Electrode (CE).
potentiostat/galvlvl anostat applies/measures: a voltage between WE and RE, a current flow through WE and CE.
ectrochemical techniques are highly sensitive methods and precautions must be taken prevent collection of false or erroneous data resulting from experimental errors.
EC-Lab products
Electro-analytical Corrosion Battery testing Supercapacitors
Applications
ElectchbeanTo csetA po
Electto p
Sensors Coatings Fuel/solar cells Materials
Ox/Red
Red/Ox±n e-
Electronic conductor Ionic conductor
in Electrochemistryin Ein Elect ochemi tryBest Laboratory Practices
- yadaraF cage: the electrochemical cell should be placed 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.
Shielding
- ecalP WE close to the RE: this will help to minimize the ohmic 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.
- :ecnailpmoC 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).
- ecnadepmI 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.
- ER selection: select the appropriate RE according to your application (pH, chloride free, temperature).
Cell Geometry
Set-up
CE WE RE
Capacitor
Pt wire
I(t)
V(t) = E(t) + RΩI(t)
Frit
Input Exp condition Output
Sweep of voltage (forward and backward scan), the current is measured. This allows the user to characterize the species and mechanism of interest.
CV (Cyclic Voltammetry)
E
Time
I
E
Unstirred electrolyte
Time
E I
E
Controlled mass transfer
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.
Hydrodynamic steady-state voltammetry
The log of absolute value of current vs potential is plotted to extract kinetic constants.
Tafel Plot
Time
E log
|I|
E
No mass transport limitations/ stirred electolyte
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.
Chrono-amperometry/potentiometry
Time
E or
I
Time
I or E
Unstirred electrolyte
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).
EIS (Electrochemical Impedance Spectroscopy)
Sinu
s (E
or I
)
Time
Freq. 1 Freq. 2
-Im(Z
)
Re(Z)
Around steady state of I vs E curve
Bio-Logic SAS1, rue de l’Europe - 38640 ClaixFrancePhone: +33 476 98 68 31 Fax: +33 476 98 69 09
www.bio-logic.info
- gnigarevA : 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.
- gniretliF : 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.
Data Processing
E a
nd I
Time
Ox + ne- Red VariablesThe Redox reaction: E: measured potential (V)I: current (A)Q: charge (C or A s) Q = i t
1 C = 1 mA h/3.6
R: resistance (Ω)P: power (W) P = E iW: energy (J) W = E i t
Reminder
with EO: equilibrium potential in the standard conditions (V)R: perfect gas constant (8.315 J K-1 mol-1)T: temperature (K)n: number of exchanged electronsF: Faraday constant (96,487 C mol-1)[x]: concentration of the species x (mol cm-³)
10-3 mol cm-³ = 1 mol L-1
Eeq = EO +RT
In [Ox]
nF [Red]
The Nernst equation:
Thermodynamic information
IL = 0.620 n F A D23 Ω 12 ν
-16 [x] with IL: Levich current (A)
n: number of exchanged electronsF: Faraday constant (96,487 C mol-1)A: electrode area (cm²)D: diffusion coefficient (cm² s-1)Ω: 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
V(t): controlled potentialE(t): actual potentialRΩI(t): ohmic dropThe Levich equation:
Transport information gained from RDE experiments.
with I0: exchange current (A)αx: charge transfer coefficientR: perfect gas constant (8.315 J K-1 mol-1)T: temperature (K)n: number of exchanged electronsF: Faraday constant (96,487 C mol-1)Eeq: equilibrium potential in the standard conditions (V)E: applied potential (V)
I = I0 exp (αOnF
(E-Eeq)) - I0 exp (-αRnF
(E-Eeq))RT RT
The Butler-Volmer equation:
Log
(I)
E Eeq
log
(Io) M M
n + + ne-M n + + ne - M
Kinetic information
- 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.
Hardware Configuration
Signal Processing
Frequency/Hz
1e+10
1e+8
1e+6
1e+4
1e+2
1
1e-2
1 10 100 1e+3 10e+3 100e+3 1e+6 3e+6
|Z|/
Ω
Ultra Low Current option
Standard configuration
Contour plot in different configurations where:
∆Z< 1%
Z
∆ϕ < 1%ϕ
Typical Techniques
Faraday cage Potentiostat/galvanostat
to ground
CS-3A Cell Stand
STIR PURGE
ON
OFF
REMOTE
SLOW FAST
STIR
ON
OFF
REMOTE
OPEN CLOSE
SP-200
Reset
B
S2
S3
Term
USB
Ethernet10/100 BaseT
P2
Reset
B
S2
S3
Term
USB
Ethernet10/100 BaseT
P2
E
Time
|FT E
|
Frequency/Hz
50 or 60 Hz
- esaerceD 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.
Hg/Hg2Cl2 Hg/HgSO4 Ag/AgCl Hg/HgO Ag/AgNO3
Alkaline solutionsAqueousHydrofluoric acidOrganic mediaSea water
Risk of damage Not recommended Acceptable Recommended
Proper Cell Connection- gniziminiM 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.
- oD not use extension cables: extension cables, especially unshielded ones, can add inductive effects to EIS measurements.
Current
Voltage
Current
Voltage
-Im(Z
)
Re(Z)
Inductive effect due to extended cables
R
C
L
Mag
nitu
de
Frequency
Cut-off frequency
Anodic Cathodic
Fourier Transform
