1 / 16

Lecture 6. Mass Transport

Lecture 6. Mass Transport . Diffusive Transport Reaction drives transport Limiting current density Concentration affects Nernst voltage Concentration affects reaction rate Concentration loss explained on j-V curve. Fuel Cell Performance Curve. Reversible Voltage (Chapter 2).

tamika
Télécharger la présentation

Lecture 6. Mass Transport

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 6. Mass Transport Diffusive Transport • Reaction drives transport • Limiting current density • Concentration affects Nernst voltage • Concentration affects reaction rate • Concentration loss explained on j-V curve

  2. Fuel Cell Performance Curve Reversible Voltage (Chapter 2) Activation Loss (Lecture 4) Ohmic Loss (Lecture 5) Cell voltage(V) Cell voltage(V) Cell voltage(V) Current Density (A/cm2) Current Density (A/cm2) Current Density (A/cm2) Concentration Loss (Lecture 6) Net Fuel Cell Performance Cell voltage(V) Cell voltage(V) Current Density (A/cm2) Current Density (A/cm2)

  3. Convection and Diffusion a) Convection b) Diffusion

  4. Flow Channel GDL H2 H2 H+ c0H2 DiffusionLayer Concentration c*H2 Flow Channel Electrode Distance Both Convection and Diffusion Are Important in FCs H2 O2 Anode Electrolyte Cathode

  5. Reaction Drives Diffusion Flow Channel GDL Catalyst Electrolyte Reactants (R) In JR jrxn JP Products (P) Out Reaction in catalyst layer consumes R, generates P c0R JR c*P Concentration JP c0P c*R d

  6. c*P c*R Reaction Drives Diffusion CatalystLayer Flow Channel Anode Electrode c0R Concentration c0P d Distance

  7. Reaction Drives Diffusion j

  8. Limiting Current Density • High • Large • Small

  9. Concentration Affects Nernst Voltage =

  10. Concentration Affects Nernst Voltage when j << jL, is negligible; when j → jL, is increase sharply.

  11. Concentration Affects Reaction Rate j We only need to concentrate on the high-current density region where the concentration effects become pronounced. j =

  12. Concentration Affects Reaction Rate = From concentration effects On Nernst voltage we have: + Combine both effects: = c

  13. Concentration Loss and j-V Curve

  14. Concentration Loss and j-V Curve

  15. 1.2 Cell voltage(V) Reactant depletion (C*R < C0R) yields concentration loss (ηconc) Theoretical EMF or Ideal voltage Concentration Loss jL = 1.0A jL = 1.5A jL = 2.0A 0.5 1.0 2.0 Current (A)

  16. Recap • Convection vs. Diffusion • Convection dominates in the flow channels • Diffusion dominates in the electrode/catalyst (GDL) • Reactant depletion leads to jL = limiting current density • jL = max operating j for fuel cell; determined when CR* = 0 • jL = nFDeff(CR0/d) • High jL = GOOD • hconc = Loss due to CR* < CR0 • hconc = cln[jL/(jL-j)] • Decrease hconc by increasing jL

More Related