The Impact of Hydration Dynamics on the Control of a PEM Fuel Cell Syed K. Ahmed  Donald J. Chmielewski Department of Chem...
Outline <ul><li>PEMFC Model  </li></ul><ul><ul><ul><li>Mat. & Energy Balances and Electrochemistry </li></ul></ul></ul><ul...
Polymer Electrolyte Membrane  Fuel Cell (PEMFC) Anode Electrolyte Cathode Generated power due to enthalpy released by the ...
Dynamic Model of PEMFC <ul><li>Parameters based on 1 kW scale. </li></ul><ul><li>Humidified hydrogen feed </li></ul><ul><l...
Material Balances in the Anode Gas Electrochemical Reaction Rate  ---->   Flux of Water to the Membrane  ---->
Material Balances in the Cathode Gas Electrochemical Reaction Rate  ---->   Flux of Water to the Membrane  ---->
Energy Balances   (Reaction Chamber Gases) Cathode Chamber Gas Anode Chamber Gas
Cooling Jacket Gas Solid Material Energy Balances   (Cooling Jacket and Solid Material)
Reaction, Heat & Power Rates Electrochemical Reaction Rates:  (molar generation per area of membrane) Heat Generation Rate...
Electrochemistry  <ul><li>Why we need it </li></ul><ul><ul><li>Reaction rates depend on  j ,  current </li></ul></ul><ul><...
Electrochemistry
Electrochemistry (Ideal Voltage) Nernst Potential:
Activation Loss:  Electrochemistry (Kinetic Losses) Exchange Current Density:
Ohmic Loss:  Membrane Thickness:  t mem   Ionic Conductivity:   Electrochemistry (Loss Due to Ionic Resistance)
Mass Transfer Loss: Electrochemistry (Mass Transfer Losses) Limiting Current Density:  Mass Transfer Coefficient:
Outline <ul><li>PEMFC Model  </li></ul><ul><ul><ul><li>Mat. & Energy Balances and Electrochemistry </li></ul></ul></ul><ul...
Hydration Model for MEA
Hydration Model for MEA
Water Transport in the Membrane ELECTRO-OSMOTIC DRAG DIFFUSION
Water Transport in the Membrane Water Flux Mechanisms:
Hydration Model for MEA <ul><li>Equations of Change: </li></ul>
Hydration Model for MEA <ul><li>Equations of Change: </li></ul>
Hydration Model for Membrane <ul><li>Boundary Conditions </li></ul>
Concentration Profiles
Water Fluxes Into the Membrane
Water Vapor at Membrane Surface
Water Vapor at Membrane Surface  Activity in Membrane:
Water Vapor at Membrane Surface  Activity in Membrane:  Activity in Gas:
Steady-State Water Content
Dynamic Model of PEMFC <ul><li>Parameters based on 1 kW scale. </li></ul><ul><li>Humidified hydrogen feed </li></ul><ul><l...
Membrane Conductivity   z )   z 
Ohmic Loss:   Electrochemistry (Loss Due to Ionic Resistance) Ionic Conductivity:    z )   z 
Outline <ul><li>PEMFC Model  </li></ul><ul><ul><ul><li>Mat. & Energy Balances and Electrochemistry </li></ul></ul></ul><ul...
Current Set-Point Tracking Transportation Applications
Current Controller
Current Controller
Current Controller
Current Controller
Current Controller
Current Controller
Water Fluxes Into the Membrane
Current Controller
Current/Temperature Controller
Current/Temperature Controller
Current/Temperature Controller
Current/Temperature Controller
Current/Temperature Controller
Feed-forward Controller
Feed-forward Controller
Feed-forward Controller
Feed-forward Controller
Feed-forward Controller
Water Content by the Cathode GDL
Feed-forward Controller
Conclusion <ul><li>What is the Impact of Hydration Dynamics on the Fuel Cell? </li></ul><ul><li>Fuel cell is unpredictable...
Acknowledgements <ul><li>Argonne National Laboratory </li></ul><ul><li>Department of Chemical &  </li></ul><ul><li>Environ...
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The Impact of Hydration Dynamics on the Control of a PEM Fuel Cell

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The Polymer Electrolyte Membrane Fuel Cell (PEMFC) has been projected to be the fuel cell of choice for future automotive applications. Among the most challenging aspect of this application is the occurrence of severe and frequent changes in power demand. From a dynamic perspective, it is frequently assumed that the thermal phenomenon possesses the largest time constant and determines response times. In a recent effort, [1], we analyzed PEMFC control issues using this thermal dominant perspective, and concluded that consideration of the faster time-scale phenomena (electrochemical and species flow) will be critical to successful controller design.
In the PEMFC literature, the subjects of water management and flooding are frequently stated as key issues in the design and operation of these systems. Recent studies on the dynamics of membrane hydration [2, 3] suggest that the time constant of this phenomenon is just a bit faster than that of the thermal characteristics. In this paper we will present two dynamic models central to understanding the water management / flooding issue. The first considers membrane hydration and shows how the interplay between electro-osmotic drag and back-diffusion will determine ionic conductivity. Additionally, we will illustrate how over-hydration of the membrane will lead to liquid water being ejected from the membrane to the Gas Diffusion Layer (GDL). The second model focuses on the GDL and illustrates how capillary forces govern the evolving distribution of liquid water in the GDL and how this eventually leads to a blocking of oxygen transfer through the GDL and to the electrochemical reaction site ( i.e., flooding). Finally, this expanded dynamic model will be employed in an updated analysis of closed-loop performance.

[1] K.C. Lauzze and D.J. Chmielewski, "Power Control of a Polymer Electrolyte Membrane Fuel Cell" Ind. Eng Chem Res., in press, 2006.

[2] Y. Wang and C-Y. Wang, "Transient analysis of polymer electrolyte fuel cells," Electrochimica Acta, vol 50, pp 1307-1315, 2005.

[3] D. Song, Q. Wang, Z-S. Liu and C. Huang, "Transient analysis for the cathode gas diffusion layer of PEM fuel cells," J. of Power Sources., in press, 2005.

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  • Current set point
  • Voltage of cell trying to decrease to incr current
  • Add 3 rd graph membrane reistance? Reaseon for failure
  • Animation show water going out,num2str(convert num into string)
  • Backup shows time plot of water cont in memb
  • Explain resistance due to flux of water out, driving force is Concentration due to the activity changes
  • Add temperature of solid as a result
  • To solve for add Temp control
  • With current sp
  • Show temp controlled
  • Add here the results of the F rates going down
  • Add here the results of the F rates going down
  • To solve flow rates
  • Show that its more power than before by adding prev. plots
  • Show progression of Current and Power, then show flowrates.. in 1, 2, 3(only flow) slides Why phenomena..bam:Membrane Resistance
  • Show progression of Current and Power, then show flowrates.. in 1, 2, 3(only flow) slides Why phenomena..bam:Membrane Resistance
  • What is resistance so high, cuz, temp of solid is hig, which causes surface concentr inverse of T-sol, thus fluxes showing water exiting…
  • Show alternative method by seeing inside the fule cell, show animation, check it, num2str, strcat
  • Horiz align, tsol with Ch2o-mem-prof-@ca/gdl vs. time
  • The Impact of Hydration Dynamics on the Control of a PEM Fuel Cell

    1. 1. The Impact of Hydration Dynamics on the Control of a PEM Fuel Cell Syed K. Ahmed Donald J. Chmielewski Department of Chemical and Environmental Engineering Illinois Institute of Technology Presented at the Annual Meeting of the AIChE: November 2006
    2. 2. Outline <ul><li>PEMFC Model </li></ul><ul><ul><ul><li>Mat. & Energy Balances and Electrochemistry </li></ul></ul></ul><ul><ul><ul><li>Membrane Model </li></ul></ul></ul><ul><li>Controller Analysis </li></ul><ul><ul><ul><li>Feedback Control </li></ul></ul></ul><ul><ul><ul><li>Feedback/Feed-forward Control </li></ul></ul></ul>
    3. 3. Polymer Electrolyte Membrane Fuel Cell (PEMFC) Anode Electrolyte Cathode Generated power due to enthalpy released by the reaction: H 2 + ½ O 2  H 2 O (  H ~ 58 kcal/mole H 2 ) N 2 N 2 N 2 H 2 H 2 H 2 H 2 H 2 H 2 O 2 O 2 O 2 H + e - e - O 2 N 2 N 2 O 2 O 2 H + H + H + H 2 O H 2 O H 2 O H 2 O H 2 O H 2 O
    4. 4. Dynamic Model of PEMFC <ul><li>Parameters based on 1 kW scale. </li></ul><ul><li>Humidified hydrogen feed </li></ul><ul><li>Air cooling is assumed. </li></ul>
    5. 5. Material Balances in the Anode Gas Electrochemical Reaction Rate ----> Flux of Water to the Membrane ---->
    6. 6. Material Balances in the Cathode Gas Electrochemical Reaction Rate ----> Flux of Water to the Membrane ---->
    7. 7. Energy Balances (Reaction Chamber Gases) Cathode Chamber Gas Anode Chamber Gas
    8. 8. Cooling Jacket Gas Solid Material Energy Balances (Cooling Jacket and Solid Material)
    9. 9. Reaction, Heat & Power Rates Electrochemical Reaction Rates: (molar generation per area of membrane) Heat Generation Rate: (per area of membrane) Power Generation Rate: (electrical energy generation rate per area of membrane)
    10. 10. Electrochemistry <ul><li>Why we need it </li></ul><ul><ul><li>Reaction rates depend on j , current </li></ul></ul><ul><ul><li>Heat Generation depen on current </li></ul></ul><ul><li>Need E cell </li></ul>
    11. 11. Electrochemistry
    12. 12. Electrochemistry (Ideal Voltage) Nernst Potential:
    13. 13. Activation Loss: Electrochemistry (Kinetic Losses) Exchange Current Density:
    14. 14. Ohmic Loss: Membrane Thickness: t mem Ionic Conductivity:  Electrochemistry (Loss Due to Ionic Resistance)
    15. 15. Mass Transfer Loss: Electrochemistry (Mass Transfer Losses) Limiting Current Density: Mass Transfer Coefficient:
    16. 16. Outline <ul><li>PEMFC Model </li></ul><ul><ul><ul><li>Mat. & Energy Balances and Electrochemistry </li></ul></ul></ul><ul><ul><ul><li>Membrane Model </li></ul></ul></ul><ul><li>Controller Analysis </li></ul><ul><ul><ul><li>Feedback Control </li></ul></ul></ul><ul><ul><ul><li>Feedback/Feed-forward Control </li></ul></ul></ul>
    17. 17. Hydration Model for MEA
    18. 18. Hydration Model for MEA
    19. 19. Water Transport in the Membrane ELECTRO-OSMOTIC DRAG DIFFUSION
    20. 20. Water Transport in the Membrane Water Flux Mechanisms:
    21. 21. Hydration Model for MEA <ul><li>Equations of Change: </li></ul>
    22. 22. Hydration Model for MEA <ul><li>Equations of Change: </li></ul>
    23. 23. Hydration Model for Membrane <ul><li>Boundary Conditions </li></ul>
    24. 24. Concentration Profiles
    25. 25. Water Fluxes Into the Membrane
    26. 26. Water Vapor at Membrane Surface
    27. 27. Water Vapor at Membrane Surface Activity in Membrane:
    28. 28. Water Vapor at Membrane Surface Activity in Membrane: Activity in Gas:
    29. 29. Steady-State Water Content
    30. 30. Dynamic Model of PEMFC <ul><li>Parameters based on 1 kW scale. </li></ul><ul><li>Humidified hydrogen feed </li></ul><ul><li>Air cooling is assumed. </li></ul>
    31. 31. Membrane Conductivity   z )  z 
    32. 32. Ohmic Loss: Electrochemistry (Loss Due to Ionic Resistance) Ionic Conductivity:   z )  z 
    33. 33. Outline <ul><li>PEMFC Model </li></ul><ul><ul><ul><li>Mat. & Energy Balances and Electrochemistry </li></ul></ul></ul><ul><ul><ul><li>Membrane Model </li></ul></ul></ul><ul><li>Controller Analysis </li></ul><ul><ul><ul><li>Feedback Control </li></ul></ul></ul><ul><ul><ul><li>Feedback/Feed-forward Control </li></ul></ul></ul>
    34. 34. Current Set-Point Tracking Transportation Applications
    35. 35. Current Controller
    36. 36. Current Controller
    37. 37. Current Controller
    38. 38. Current Controller
    39. 39. Current Controller
    40. 40. Current Controller
    41. 41. Water Fluxes Into the Membrane
    42. 42. Current Controller
    43. 43. Current/Temperature Controller
    44. 44. Current/Temperature Controller
    45. 45. Current/Temperature Controller
    46. 46. Current/Temperature Controller
    47. 47. Current/Temperature Controller
    48. 48. Feed-forward Controller
    49. 49. Feed-forward Controller
    50. 50. Feed-forward Controller
    51. 51. Feed-forward Controller
    52. 52. Feed-forward Controller
    53. 53. Water Content by the Cathode GDL
    54. 54. Feed-forward Controller
    55. 55. Conclusion <ul><li>What is the Impact of Hydration Dynamics on the Fuel Cell? </li></ul><ul><li>Fuel cell is unpredictable and a better controller needs to be attached </li></ul>
    56. 56. Acknowledgements <ul><li>Argonne National Laboratory </li></ul><ul><li>Department of Chemical & </li></ul><ul><li>Environmental Engineering, IIT </li></ul>

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