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Journal of Applied Electrochemistry

, Volume 17, Issue 6, pp 1177–1189 | Cite as

Mass transfer at gas-evolving vertical electrodes

  • L. J. J. Janssen
Papers

Abstract

Various models have been proposed to describe the mass transfer of indicator ions to gas-evolving electrodes. For verification of the proposed models, the dependence of the mass transfer coefficient of indicator ions,kj, on the length,Le, of a gas-evolving electrode may be very useful. Experimental relations betweenkj andLe have been determined for oxygen-evolving as well as hydrogen-evolving vertical electrodes in a supporting electrolyte of 1 M KOH. Moreover, a modified hydrodynamic model, where a laminar solution flow is induced by rising bubbles, has been proposed in order to calculatekj. It has been found that this model is not useful for both types of gas-evolving electrodes. The experimental results support the earlier proposed convection-penetration model for the oxygen-evolving electrode. The solution flow near a vertical electrode, induced by rising bubbles, behaves in a turbulent manner.

Keywords

Physical Chemistry Mass Transfer Transfer Coefficient Mass Transfer Coefficient Hydrodynamic Model 
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

Ae

electrode surface area

A1

parameter defined by Equation 13

A2

parameter defined by Equation 14

A3

A1/A2

A4

parameter defined by Equation 34

c

concentration

cs

concentration in bulk of solution

D

diffusion coefficient

de

equivalent diameter of cell compartment at the level of the working electrode

F

Faraday constant

FB

buoyant force

FS

shear force

g

acceleration due to gravity

i

current density

kj

mass transfer coefficient of indicator ion j to an electrode

Lc

length of electrode

m

parameter defined by Equation 13

mj

quantity of speciesj

M

momentum flow

ΔM

change inM

n

parameter defined by Equation 13

p

parameter,x3/4

υ

velocity of solution flow

υs

velocity of bulk solution flow

υ1

υ defined by Equation 2

VB

volume of bubbles

w

width of a volume element

x

coordinate, distance from leading edge of electrode

y

coordinate, distance to the electrode

z

coordinate, width of electrode

δ

boundary layer thickness

δb

bubble layer thickness at the electrode

δn

Nernst diffusion layer thickness

ε

gas voidage

ϱ

density

εav

average density of a mixture of solution and bubbles in a volume element

εs

density of bulk solution

εg

density of gas

μ

viscosity

μw

viscosity of solution-gas bubble mixture at the electrode surface

ν

kinematic viscosity, ν=μ/ϱ

ψ

parameter defined by Equation 26

Subscripts

av

average

b

bubble layer at the surface of electrode

B

bubble-induced convection

e

electrode

F

forced convection

fi

Fe(CN) 6 3−

fo

Fe(CN) 6 4−

FB

combined forced and bubble-induced convection

g

gas

max

maximum

N

natural convection

s

bulk of solution

w

on the electrode surface

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Copyright information

© Chapman and Hall Ltd. 1987

Authors and Affiliations

  • L. J. J. Janssen
    • 1
  1. 1.Laboratory for Electrochemistry, Department of Chemical TechnologyEindhoven University of TechnologyEindhovenThe Netherlands

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