1. The Effect of Cathode Stoichiometric
Ratio on PEMFC Performance in
Cold Operating Conditions
东 方 (Carl Cayabyab), Oakland University
蓝 天 (Jonathan Guidoboni), The George Washington University
任 龙 (Holden Ranz), Lafayette College
1
National Science Foundation
International Research Experience for Students 2011
快乐队

2.  Background
 Cold-start conditions and Stoichiometric ratio
 Project Design
 Methods and Procedures
 Equipment and Calibration
 Results
 Analysis
 Conclusions
2
Outline

3. Background
3
Proton exchange membrane fuel cell (PEMFC)
 Chemical energy  Electrical energy
 Hydrogen ions + Oxygen  Water
 Voltage difference makes current flow
 GDL – conductive carbon cloth or paper.
Porous material, gases pass through to
catalyst layer
 CCL – catalyst layer, encourage
separation of inlet gas atoms into ions /
electrons for easier and faster reaction

4. Interest
4
 Advantages: high power density, extremely low pollutant
emissions, and low operating temperature
Vehicle applications
 Reduce
dependence oil
 Lower harmful
emissions
 Hydrogen very
abundant
resource

5. Cold-start Conditions
5
 PEMFC normally operate at 70 to 80°C
 Cold climates, sub-freezing temperatures
 Ice blocks pores in membrane and GDL
 suppresses FC performance
 More difficult to start, especially on its own

6.  Actual / Theoretical
 Ratio of air  cathode  StC
 Ratio of hydrogen  anode  StA
6
Stoichiometric Ratio

7. Initially Relative Humidity
 Manipulated Variables
 Heating jacket voltage (V)  relative humidity (%)
 Flow rate (L/min)
 Applied current load (A)
 Controlled Variable
 Output cell voltage (V)
 Perform trials in both cold and room temp conditions
 Trend between relative humidity and cell performance
 Difference between cold and room temp conditions
7
Project Design
Hygrometer

8. Project Design - Redirected
8
Stoichiometry and Temperature
 Manipulated Variables
 Flow rate (L/min)  Stoichiometric ratio
 Temperature
 Applied current load (A)
 Controlled Variable
 Output cell voltage (V)
 Objectives
 trends between FC performance, StC, and temperature conditions
 Analyze behavior of the membrane and GDL at sub-freezing
temperatures.

9. Project Schematic

10. 1. Open nitrogen tank to 1MPa
2. Turn on water heater to 45°C
3. Check for leaks using soapy
water
4. Run water pump for 5 minutes
5. Turn off nitrogen gas. Hook up
air and hydrogen tanks.
Procedures

11. 6. Turn on multimeter and computer
program.
7. Open hydrogen and air tank to 1MPa
8. Adjust flow rates to an Stc of 2.5
9. Gather temperature readings every 30
seconds
10. Record voltage every 3 minutes and
increase current density. Change flow
rates as well.
Procedures

12. 11. Stop fuel cell once voltage change is small.
12. Save data. Flush out water with air for 5 minutes.
13. Repeat this for Stc ratios of 3 and 4
14. Repeat process for 0°C and -3°C.
Procedures

13.  Polyurethane Tubing (6mm OD)
 Fan
 Water Heater
 Insulation
 PEMFC
 Humidifier
Equipment

14.  Freezer (FYL-YS-108L)
 Rubber Plug
 2 Thermocouples
 Digital Thermometer
 Soapy Water
Equipment

15.  Digital thermometer accurate
 0.05°C Accuracy
 Calibrated 2 thermocouples
 Air inlet
 Hydrogen inlet
Calibration

16.  Methods of Calibration
 Water bath with varying temp
 Take temp readings at the same point
 Steady state
 Plot curves to find factor
Calibration

17. Calibration
y = 0.9876x - 0.8446
R² = 0.9998
0
10
20
30
40
50
60
70
80
0 20 40 60 80
AccurateDigitalTemp(°C)
Measured Thermocouple Temp (°C)
Thermocouple A
y = 0.9844x + 0.2978
R² = 0.9999
0
10
20
30
40
50
60
70
80
0 20 40 60 80
AccurateDigitalTemp(°C)
Measured Thermocouple Temp (°C)
Thermocouple B
Thermocouple C
Linear (Thermocouple C)
Thermocouple A:
Y=0.9876X-0.8446
Thermocouple B:
Y=0.9844X+0.2978

18. Ideal Flow Rate Calculations
𝑣 = 𝐼
𝑛𝐹
where 𝑣 = molar flow rate of reactant (mol/s),
𝑛 = moles of electrons per mole of reactant (mol e-/mol),
𝐹 = Faraday’s constant = 96485 C/mol.
𝐼 = 𝑖 ∗ 𝐴𝑟𝑒𝑎 = current load on the fuel cell (A),
𝑖 = current density (A/cm2),
and 𝐴𝑟𝑒𝑎 = active area of the fuel cell = 32 cm2 (FC1), 16 cm2 (FC2)
𝐻2 2𝐻+
+ 2𝑒−
1
2 𝑂2 + 2𝐻+ + 2𝑒− 𝐻2 𝑂
𝑛H2 = 2
𝑛H2 = 4

19. Flow Rates for Stc values
Air M= 0.0288479 kg/mol
ρ = 1.205 kg/m3
Ideal Q (L/min) Actual Q (L/min)
i (A/cm2) I (A) v (mol/s) ṁ (kg/s) 1 MEA 2 MEA Stc = 2.5 Stc = 3 Stc = 4
0.05 1.6 1.974E-05 5.695E-07 0.028 0.057 0.142 0.170 0.227
0.1 3.2 3.948E-05 1.139E-06 0.057 0.113 0.284 0.340 0.454
0.15 4.8 5.922E-05 1.709E-06 0.085 0.170 0.425 0.510 0.681
0.2 6.4 7.897E-05 2.278E-06 0.113 0.227 0.567 0.681 0.907
0.25 8 9.871E-05 2.848E-06 0.142 0.284 0.709 0.851 1.134
0.3 9.6 1.184E-04 3.417E-06 0.170 0.340 0.851 1.021 1.361
0.35 11.2 1.382E-04 3.987E-06 0.198 0.397 0.992 1.191 1.588
0.4 12.8 1.579E-04 4.556E-06 0.227 0.454 1.134 1.361 1.815
Hydrogen M= 0.002 kg/mol
ρ = 0.08375 kg/m3
Ideal Q (L/min) Actual Q (L/min)
i (A/cm2) I (A) v (mol/s) ṁ (kg/s) 1 MEA 2 MEA Stc = 1.5
0.05 1.6 8.291E-06 1.658E-08 0.012 0.024 0.036
0.1 3.2 1.658E-05 3.317E-08 0.024 0.048 0.071
0.15 4.8 2.487E-05 4.975E-08 0.036 0.071 0.107
0.2 6.4 3.317E-05 6.633E-08 0.048 0.095 0.143
0.25 8 4.146E-05 8.291E-08 0.059 0.119 0.178
0.3 9.6 4.975E-05 9.950E-08 0.071 0.143 0.214
0.35 11.2 5.804E-05 1.161E-07 0.083 0.166 0.249
0.4 12.8 6.633E-05 1.327E-07 0.095 0.190 0.285
Considerations: Active area = 32 cm2, fuel cell has 2 membranes
Assumptions: Air is 79% N2 and 21% O2, gas is flowing at NTP (20°C and 1 atm), constant density

20. Data Collection

21. Output voltage at 0.1 A/cm2
21
FC Performance Results
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 20 40 60 80 100 120 140 160
Voltage(V)
Time (s)
(ii) Cold Start, 0°C
Stc = 2.5 Stc = 3 Stc = 4
1.4
(iii) Cold Start, -3°C
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 20 40 60 80 100 120 140 160
Voltage(V)
Time (s)
(i) Room Temperature
Stc = 2.5 Stc = 3 Stc = 4
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 20 40 60 80 100 120 140 160
Voltage(V)
Time (s)
(ii) Cold Start, 0°C
Stc = 2.5 Stc = 3 Stc = 4
1.4
(iii) Cold Start, -3°C
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 20 40 60 80 100 120 140 160
Voltage(V)
Time (s)
(i) Room Temperature
Stc = 2.5 Stc = 3 Stc = 4
Δ ≈ 0.1 V
Δ ≈ 0.08 V
Δ ≈ 0.9 V
Δ ≈ 0.08 V
Δ ≈ 0.07 V
Δ ≈ 0.03 V
Δ ≈ 0.06 V
Δ ≈ 0.06 V
Output voltage at 0.15 A/cm2
**Fluctuations most likely due to flow rate adjustments when switching between current loads

22.  Output voltages essentially the same for 0.1 and 0.15
A/cm2 at different Stc
22
FC Performance Results
Output voltage at 0.1 A/cm2 Output voltage at 0.15 A/cm20
0.2
0.4
0.6
0.8
1
0 20 40 60 80 100 120 140 160
Voltage(V)
Time (s)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 20 40 60 80 100 120 140 160
Voltage(V)
Time (s)
(iii) Cold Start, -3°C
Stc = 2.5 Stc = 3 Stc = 4
0
0.2
0.4
0.6
0.8
1
0 20 40 60 80 100 120 140 160
Voltage(V)
Time (s)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 20 40 60 80 100 120 140 160
Voltage(V)
Time (s)
(iii) Cold Start, -3°C
Stc = 2.5 Stc = 3 Stc = 4

23. FC Performance – Polarization Curves
 Initial loss due to activation of the fuel cell
 Linear loss due to resistance
 End loss due to concentration
0.0 0.2 0.4 0.6 0.8
0.2
0.4
0.6
0.8
1.0Voltage(V)
Current Density (A/cm
2
)
Experimental data
Numerical results
Activation
Loss
Ohmic Loss
Concentration
Loss

24. Experimental Polarization Curves
 Polarization curves mostly
linear  Ohmic losses
 At room temp and 0°C,
2.5<3<4
 At -3°C curves nearly identical
 Approximate current densities
resulting in failure:
 Room temp – I ≈ 0.33 A/cm2
 0°C – I ≈ 0.30 A/cm2
 -3°C – I ≈ 0.31 A/cm2

25. 25
Ice Formation?
After Room Temp Trial
-water present in the form of foggy
condensate
After Cold Temp Trial
-small droplets and ice crystal
formation

26.  Cathode stoichiometric ratio affects fuel cell
performance at room temperature and cold
conditions
 Increase in Stc at room temp and 0°C corresponds to
increase in output voltage
 Current densities ≥0.1 A/cm2
 FC performance hardly affected by Stc changes at -3°C
 Linear polarization curves indicate resistance losses
 Ice formation inside gas lines creates blockages
 FC stops generating electricity
26
Conclusions

27.  Flow meter instability and inaccuracy
 Tendency to get stuck
 Inability to maintain constant operating temperature of
the PEMFC
 Duration of membrane humidification prior to testing
Recommendations
 Calibrate glass flow meters using digital meters
 Use the heat exchange line in fuel cell to cool/maintain
operating temperature
 Use a hot water bath to try to control relative humidity
27
Sources of Error

28.  Kang Mi et al. Experimental Study on Dynamic
Characteristics of Proton Exchange Membrane Fuel Cells
(PEMFC) under Subzero Temperatures.
 Shanhai Ge et al. Characteristics of subzero startup and
water/ice formation on the catalyst layer in a polymer
electrolyte fuel cell.
 Jer-Huan Jang et al. Effects of operating conditions on the
performances of individual cell and stack of PEM fuel cell.
 US Department of Energy, http://www.energy.gov/.
28
References

29.  China is awesome.
 Flow chart of attitude
29
The China Experience
Before China…
Meh
In China…
快乐 !
Thought of leaving…

30. First Impressions
 Huge
 Lots of people
 Crazy cab drivers
 Water closet
 A lot of biking (crazy bikers)
30

31. Places Visited
 Beijing Zoo
 Temple of Heaven
 Summer Palace
 Tianamen Square
31

32. Places Visited
 Great Wall
 Shanghai
 Xi’an
32

33. Foods
33

34. Foods
34

35. Activities with Students
 Ping Pong
 Badminton
 Basketball
 Chinese Chess
35

36. China Experience
 Exposure to research
 Communication with Chinese
students
 Learning the language
 Making new friends
36