Abstract
Gas evolution during electrode reactions has several effects on the electrode behaviour. One of these effects is the nonuniform increase of the resistivity of the electrolyte with the resultant increase of IR drop through the solution and the distortion of current distribution. Calculations of these effects are presented for an electrode built of vertical blades. This geometry has the peculiarity that it allows the inclusion of linear polarization and gas effects in the treatment, without the necessity to use numerical or approximate solutions of the differential equations. It is shown that the system parameters can be combined into a single dimensionless parameter to describe those aspects of the electrode behaviour which depend on the gas evolution. The parameters examined include the geometry of the electrode, the polarization resistance, gas bubble rise velocity, and solution resistivity. Expressions are given for optimization of the electrode geometry to achieve minimum overpotential.
Similar content being viewed by others
Abbreviations
- b :
-
Polarization resistance (Ω cm2)
- C :
-
Constant, =RT(δ + t)/δlPtFs (A−1cm)
- E(x) :
-
Potential of the solution at pointx (V)
- f av :
-
Average volume fraction of gas (dimensionless)
- (fy):
-
Volume fraction of gas at heighty (dimensionless)
- f(Y) :
-
Volume fraction of gas at reduced heightY (dimensionless)
- F :
-
Faraday number (coulomb mol−1)
- h :
-
Height of the electrode (cm)
- i :
-
Nominal current density of the electrode =I T/hw (A cm−2)
- i(y) :
-
Local electrode current density at heighty (A cm−2)
- i(Y) :
-
Local electrode current density at reduced heightY (A cm−2)
- i f(x):
-
Faradaic current density at pointx (A cm−2)
- i f(X):
-
Faradaic current density at reduced lengthX (A cm−2)
- i f,av :
-
Average faradaic current density in the slot=I s/2hl(Acm−2)
- I s :
-
Total current entering one slot (A)
- I T :
-
Total current flowing to the electrode (A)
- I(x) :
-
Current flowing in the solution phase of one slot at pointx (A)
- k :
-
Constant, = (2ρ/bδ)1/2 (cm−1)
- K :
-
Dimensionless parameter =ηhRT(2δ/bρ)1/2/4δlPzFs, or = 1−(1−iCh)1/4
- l :
-
Horizontal length of the slot (cm)
- n :
-
Number of slots on the electrode (dimensionless)
- p :
-
Pressure of gas liberated on the electrode (assumed to be independent of height) (atm)
- R :
-
Universal gas constant (cm3 atm K−1 mol−1)
- s :
-
Bubble rise velocity (cm s−1)
- t :
-
Thickness of the blades (cm)
- T :
-
Temperature of the gas (K)
- dV(y) :
-
Volume of gas present in a volume element of the slot (cm3)
- w :
-
Width of the electrode (cm)
- x :
-
Horizontal distance from the back plate (cm)
- X :
-
Reduced horizontal distance =x/l (dimensionless)
- y :
-
Vertical distance from the bottom of the electrode (cm)
- Y :
-
Reduced vertical distance =y/h (dimensionless)
- z :
-
Number of Faradays needed to produce one mole of gas (mol−1)
- δ :
-
Width of a slot (blade spacing) (cm)
- η :
-
Measured overpotential of the electrode =η(l)(V)
- η(x) :
-
Overpotential at pointx (V)
- ρ :
-
Resistivity of gas free electrolyte (Ω cm)
- ρ(y) :
-
Resistivity of gas filled electrolyte at, heighty (Ω cm).
References
F. Hine, S. Yoshizawa and S. Okada,Denki Kagaku,24 (1956) 370.
S. Okada, S. Yoshizawa, F. Hine and Z. Takehara,J. Electrochem. Soc. Japan 26 (1958) E55.
S. Okada, S. Yoshizawa, F. Hine and Z. Takehara,ibid 26 (1958) E66.
S. Yoshizawa, F. Hine, Z. Takehara and M. Yamashita,ibid 28 (1960) E88.
K. Takata, H. Morishita and Y. Kihara,Denki Kagaku 32 (1964) 378.
T. Matsuno,Bull. Fac. Eng., Yokohama Nat'l Univ. 8 (1959) 155. (CA53:16760g).
C. W. Tobias,J. Electrochem. Soc. 106 (1959) 833.
J. E. Funk and J. F. Thorpe,ibid 116 (1969) 48.
J. F. Thorpe, J. E. Funk and T. Y. Bong,J. Basic Eng. 92 (1970) 173.
F. A. Posey,J. Electrochem. Soc. 111 (1964) 1173.
D. A. G. Bruggema,Ann. Physik. 24 (1935) 636.
R. E. De La Rue and C. W. Tobias,J. Electrochem. Soc. 106 (1959) 827.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Nagy, Z. Calculations on the effect of gas evolution on the current-overpotential relation and current distribution in electrolytic cells. J Appl Electrochem 6, 171–181 (1976). https://doi.org/10.1007/BF00615384
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00615384