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Journal of Applied Electrochemistry

, Volume 11, Issue 2, pp 145–152 | Cite as

Transient analysis of a flow-through porous electrode at the limiting current

  • P. S. Fedkiw
Papers

Abstract

The equations governing the transients in the concentration, current and potential response of a porous flow-through electrode at the limiting current for a single reactant in a well-supported electrolyte have been solved. It was assumed that a potentiostatic step was applied to an electrode with a uniform feed concentration. The dispersive flux of reactant was assumed to be negligible but double-layer charging effects were taken into consideration. If the double-layer time constant is much less than the fluid residence time (νC/ɛϰ ≪ 1), it is quantitatively shown that the capacitive current may be neglected in interpreting the current-time response of the electrode when examined in the fluid residence time frame. If the entire electrode is to operate at the limiting current, it is quantitatively shown that the solution phase ohmic drop can become significant early in the transient such that secondary reactions may become important. The ability to interpretI versust data in terms of the limiting current species mass transfer coefficient is removed under these conditions. The results support the qualitative arguments made by Newman and Tiedemann in their comprehensive review article on porous flow-through electrodes. Finally, it is shown that ln(Faradaic current) versust can be approximately linear in a limited time span, although no useful information can be obtained from such a plot.

Keywords

Mass Transfer Coefficient Secondary Reaction Transient Analysis Feed Concentration Porous Electrode 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Nomenclature

a

specific interfacial area (cm2cm−3)

c

concentration (mol cm−3)

cF

feed concentration (mol cm−3)

C

double-layer capacitance (F cm−2)

D0

reactant diffusion coefficient (cm2 s−1)

F

Faraday's constant (Coulomb/equivalent)

i2

solution phase current density (A cm−2)

I

dimensionless total current density (Equation 9)

km

mass transfer coefficient (cm s−1)

L

electrode length (cm)

n

number of electrons transferred in reaction

(Pe)B

bed Péclet number,v/aD0

SR

stoichiometric coefficient of reactant

(Sh)B

bed Sherwood number,εkm/aDo

t

time (s)

T

dimensionless time,tυ/εL

υ

superficial bed velocity (cm s−1)

x

streamwise co-ordinate (cm)

z

dimensionless streamwise co-ordinate,x/L

ε

bed porosity

τR

fluid residence time,Lε/υ

τC

double-layer time constant,aL2C/κ

κ

solution phase conductivity (ohm−1 cm−1)

η

overpotentialφ1–φ2 (V)

gh0

overpotential atz=0 (V)

gf1

matrix phase potential (V)

gf2

solution phase potential (V)

Φ2

dimensionless solution phase potential,φ2κSR/(-εnFD0CF)

(i)

condition att=0 (as superscript)

(ss)

steady-state condition (as superscript)

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References

  1. [1]
    A. K. P. Chu, M. Fleischmann and G. J. Hills,J. Appl. Electrochem. 4 (1974) 323.Google Scholar
  2. [2]
    J. Newman and W. Tiedemann, in ‘Advances in Electrochemistry and Electrochemical Engineering’ Vol. 11, (edited by H. Genscher and C. Tobias) Wiley Interscience, New York (1978).Google Scholar
  3. [3]
    P. S. Fedkiw,PhD Dissertation, University of California, Berkeley, USA, December (1978).Google Scholar
  4. [4]
    J. Newman and W. Tiedemann,AIChE J. 21 (1975) 25.Google Scholar
  5. [5]
    F. A. Posey and T. Morozumi,J. Electrochem. Soc. 113 (1966) 176.Google Scholar

Copyright information

© Chapman and Hall Ltd 1981

Authors and Affiliations

  • P. S. Fedkiw
    • 1
  1. 1.Department of Chemical EngineeringNorth Carolina State UniversityRaleighUSA

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