Development of Educational Tools Development of Educational Tools for PEM Fuel Cells for PEM Fuel Cells Vijay Ramani, Ruichun Jiang, Harold R. Kunz, Vijay Ramani, Ruichun Jiang, Harold R. Kunz, James M. Fenton James M. Fenton Department of Chemical Engineering Department of Chemical Engineering University of Connecticut University of Connecticut Storrs, CT Storrs, CT – – 06269, USA 06269, USA
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Development of Educational Tools for PEM Fuel Cellsjmfent/PEMFC Tutorial_final.pdfDevelopment of Educational Tools for PEM Fuel Cells. Vijay Ramani, Ruichun Jiang, Harold R. Kunz,
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Development of Educational Tools Development of Educational Tools for PEM Fuel Cellsfor PEM Fuel Cells
Vijay Ramani, Ruichun Jiang, Harold R. Kunz, Vijay Ramani, Ruichun Jiang, Harold R. Kunz, James M. FentonJames M. Fenton
Department of Chemical EngineeringDepartment of Chemical EngineeringUniversity of ConnecticutUniversity of ConnecticutStorrs, CT Storrs, CT –– 06269, USA06269, USA
- start from E = E1- sweep up to E = E2 - sweep down, back to E = E1
• Performed using a potentiostat• Fixed sweep rate - ~ 30mV/s• Faradaic current monitored
Typical CV at a fuel cell cathodeTypical CV at a fuel cell cathode
Working Electrode Potential (V)
0.0 0.2 0.4 0.6 0.8 1.0
Cur
rent
(A)
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
t
0 V
2H+ + 2 e H2
H2 2H+ + 2 e; Oxidation as E becomes more positive
2H+ + 2 e H2; Reduction as E becomes more negative
Overall Reaction:
Input Function
Output (Response)
0 s
(Area under peak)
(scan rate)*(210µC/cm2-Pt)*(Pt loading)ECA =
E0.8 V
Load Box
Single Cell
Flow Loop
Polarization experimentsPolarization experiments
Re=.04 mOhms/cm2 Correction by Using Io/Ia=~4.76 Current vs Voltage Data
300.00
400.00
500.00
600.00
700.00
800.00
900.00
0.00 500.00 1000.00 1500.00 2000.00 2500.00Current Density (mA/cm2)
Volta
ge (m
V)
Air Actual
4%Oxygen Actual
Oxygen Actual
Data AnalysisData Analysis
Polarization in PEM fuel cellsPolarization in PEM fuel cells
Current Density (mA/cm2)0 5 10 15 20 25 30 35
Cel
l Vol
tage
(V)
0.0
0.5
1.0
0.0
0.5
1.0
Pola
rizat
ion
(V)
Ideal Potential
Region of Activation Polarization(Reaction Rate Loss)
Total Loss
Region of Ohmic Polarization(Resistance Loss)
Region of Concentration Polarization
(Gas Transport Loss)
Cathode Loss
Membrane Internal Resistance Loss
Anode Loss
]/)ln[()(ln llemOCV iiicRRiibaEE −−+−−−=
VEOHeHOCathode
VEeHHAnode
red
red
23.1;44:
0;22:
022
20
=→++
=+→
+
+
(1.23 V)
Reactions:
Membrane resistanceMembrane resistance• Determined by using techniques such as current
interrupt and AC impedance spectroscopy. • Data then corrected as follows:
• Recall that the voltage drop across a resistor is given by V = IR :
mFreeiR iREEm
+=
Result of correctionResult of correction
E (V)
10000 i (mA/cm2) [log scale]
0
1
1
Original curve
Corrected curve
Various Stages of Correction for Current vs Voltage Data
R2 = 0.995
R2 = 0.999
R2 = 0.9993
0.00
100.00
200.00
300.00
400.00
500.00
600.00
700.00
800.00
900.00
1000.00
1.00 10.00 100.00 1000.00 10000.00 100000.00
Current Density (mA/cm2)
Volta
ge (m
V)
Air Corrected for RmAir ActualAir Corrected for Rm+ReOxygen Corrected for RmOxygen ActualOxygen Corrected for Rm+Re4% Oxygen Corrected for Rm4% Oxygen Actual4% Oxygen Corrected for Rm+ReO2 Corrected for ILAir Corrected for IL4% Corrected for ILLog. (O2 Corrected for IL)Log. (Air Corrected for IL)Log. (4% Corrected for IL)
• Contribution of Re is crucial in optimizing the structure of the electrode
• Re lowered by:- increasing the electrolyte content of the
electrode, - designing better gas diffusion layers that
permit water retentivity in the electrode• Not possible to directly separate out the contribution of
Re
The current ratioThe current ratio
• The ratio of the currents at a given (membrane resistance corrected) voltage when oxygen and air are used at the cathode
• Can be shown to equal the oxygen concentration ratio (~ 4.8) for first order kinetics
• The current ratio (C.R.) can be used to extract Re - rearrange data until iO2 / iAir = 4.8 at a given voltage.
• Iterative procedure, best done using a spreadsheet
Effect of REffect of Re e correctioncorrection
Various Stages of Correction for Current vs Voltage Data
R2 = 0.995
R2 = 0.999
R2 = 0.9993
0.00
100.00
200.00
300.00
400.00
500.00
600.00
700.00
800.00
900.00
1000.00
1.00 10.00 100.00 1000.00 10000.00 100000.00
Current Density (mA/cm2)
Volta
ge (m
V)
Air Corrected for RmAir ActualAir Corrected for Rm+ReOxygen Corrected for RmOxygen ActualOxygen Corrected for Rm+Re4% Oxygen Corrected for Rm4% Oxygen Actual4% Oxygen Corrected for Rm+ReO2 Corrected for ILAir Corrected for IL4% Corrected for ILLog. (O2 Corrected for IL)Log. (Air Corrected for IL)Log. (4% Corrected for IL)
E (V)
i (mA/cm2) [log scale]
1 10000 0
1Re corrected data – note that the
mass transport effects are not eliminated
Substrate DiffusionSubstrate Diffusion• Need to determine limiting current • May be done by guessing value for iL, and plotting
data as:
V vs.
• The value of iL that yields a linear data fit should be the true limiting current (since other losses are accounted for, Tafel behavior should be seen)
)/1/( liii −
Effect of substrate diffusion correctionEffect of substrate diffusion correction
Various Stages of Correction for Current vs Voltage Data
R2 = 0.995
R2 = 0.999
R2 = 0.9993
0.00
100.00
200.00
300.00
400.00
500.00
600.00
700.00
800.00
900.00
1000.00
1.00 10.00 100.00 1000.00 10000.00 100000.00
Current Density (mA/cm2)
Volta
ge (m
V)
Air Corrected for RmAir ActualAir Corrected for Rm+ReOxygen Corrected for RmOxygen ActualOxygen Corrected for Rm+Re4% Oxygen Corrected for Rm4% Oxygen Actual4% Oxygen Corrected for Rm+ReO2 Corrected for ILAir Corrected for IL4% Corrected for ILLog. (O2 Corrected for IL)Log. (Air Corrected for IL)Log. (4% Corrected for IL)
i (mA/cm2) [log scale]
1 10000 0
1Linearization obtained with
iterative il estimation
Reacting DiffusionReacting Diffusion
• If oxygen reduction reaction entirely activation controlled:
• Data should have a theoretical Tafel slope (70mV/decade at 80°C) – if 1st order B-V kinetics are followed
• Any deviation– due to uncorrected diffusion losses (e.g. in electrodes)
• These losses may be determined by estimating difference between theoretical Tafel line and corrected data
Effect of correctionEffect of correction
E (V)“Corrected data”
i (mA/cm2) [log scale]
1 10000 0
1
Theoretical Tafel slope assuming 1st order B-V
kinetics
Various Stages of Correction for Current vs Voltage Data
R2 = 0.995
R2 = 0.999
R2 = 0.9993
0.00
100.00
200.00
300.00
400.00
500.00
600.00
700.00
800.00
900.00
1000.00
1.00 10.00 100.00 1000.00 10000.00 100000.00
Current Density (mA/cm2)
Volta
ge (m
V)
Air Corrected for RmAir ActualAir Corrected for Rm+ReOxygen Corrected for RmOxygen ActualOxygen Corrected for Rm+Re4% Oxygen Corrected for Rm4% Oxygen Actual4% Oxygen Corrected for Rm+ReO2 Corrected for ILAir Corrected for IL4% Corrected for ILLog. (O2 Corrected for IL)Log. (Air Corrected for IL)Log. (4% Corrected for IL)
Correction was not performed for this data set
RecapRecap
• Original data from test stand• Correct for membrane resistance• Correct for electrode ionic resistance – current
ratios• Estimate limiting current – air or 4% O2 data• Correct for substrate diffusion – iterative –
determine value of iL that yields linear fit• Deviation between corrected curve and
theoretical Tafel behavior: losses due to diffusion in electrode
Typical resultsTypical resultsRe=.04 mOhms/cm2 Correction by Using Io/Ia=~4.76 Current vs Voltage Data
300.00
400.00
500.00
600.00
700.00
800.00
900.00
0.00 500.00 1000.00 1500.00 2000.00 2500.00
Current Density (mA/cm2)
Volta
ge (m
V)
Air Actual
4%Oxygen Actual
Oxygen Actual
Various Stages of Correction for Current vs Voltage Data
R2 = 0.995
R2 = 0.999
R2 = 0.9993
0.00
100.00
200.00
300.00
400.00
500.00
600.00
700.00
800.00
900.00
1000.00
1.00 10.00 100.00 1000.00 10000.00 100000.00
Current Density (mA/cm2)
Volta
ge (m
V)
Air Corrected for RmAir ActualAir Corrected for Rm+ReOxygen Corrected for RmOxygen ActualOxygen Corrected for Rm+Re4% Oxygen Corrected for Rm4% Oxygen Actual4% Oxygen Corrected for Rm+ReO2 Corrected for ILAir Corrected for IL4% Corrected for ILLog. (O2 Corrected for IL)Log. (Air Corrected for IL)Log. (4% Corrected for IL)