Abstract
Sodium chloride solutions of concentration 15 and 30 g dm−3 were electrolysed in a flow-through electrolyser with a titanium/TiO)2/RuO2 anode at current densities 1059–4237 A m−2. The current yield for the reduction of hypochlorite on a stainless steel cathode was found to be 13–32% at 7 g dm−3 NaClO, in agreement with that calculated on the basis of the Stephan-Vogt theory. Migration of ions was taken into account, the diameter of hydrogen bubbles was set equal to 0.04 mm and the coverage of the electrode with the bubbles was estimated as ϑ = 0.897. The results of calculations show that the reduction rate of hypochlorite at low NaCl concentrations is lowered by migration. Literature data for the reduction of hypochlorite are in accord with the current yield calculated on the basis of the Stephan-Vogt theory using ϑ = 0.787 and ϑ = 0.949.
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Abbreviations
- C o i :
-
concentration of species i in the bulk (mol m−3)
- C s i :
-
concentration of species i at the cathode surface (mol m−3)
- d B :
-
bubble diameter (m)
- D e :
-
equivalent diameter (characteristic dimension) (m)
- D i :
-
diffusion coefficient of species i (m2 s−1)
- f G :
-
gas evolution efficiency
- F :
-
Faraday constant (96 487 C mol−1)
- j :
-
total current density (Am−2)
- j B :
-
current density for gas evolution (Am−2)
- j c, lim :
-
limiting current density for cathodic reduction of ClO− (A m−2)
- j c, r :
-
critical current density (A m−2)
- L :
-
length of electrode (m)
- M :
-
migration correction factor
- n B :
-
number of electrons exchanged in gas evolution
- n ClO − :
-
number of electrons exchanged in reduction of ClO−
- N i :
-
flux of species i (mol m−2 s−1)
- Q :
-
charge passed (C)
- P t :
-
total gas pressure (Pa)
- Re :
-
Reynolds number (Equation 14)
- Re B :
-
Reynolds number (Equation 17)
- Sc :
-
Schmidt number (Equation 13)
- Sh :
-
Sherwood number (Equation 12)
- Sh B :
-
Sherwood number (Equation 15)
- T :
-
absolute temperature (K)
- u i :
-
mobility of ion i (m2 s−1 V−1)
- νB :
-
fictitions linear velocity of gas formation (ms−1)
- νel :
-
rate of electrolyte flow (ms−1)
- V :
-
volume of the electrolyte in the system (m3)
- V H 2 :
-
content of hydrogen in gas phase (%)
- V O 2 :
-
content of oxygen in gas phase (%)
- y i :
-
current yield (differential) for production of species i (%)
- y r :
-
current yield (differential) for reduction of ClO− and ClO −3 (%)
- Y ClO−,r :
-
current yield (differential) for reduction of CIO− (%)
- Y i :
-
integral current yield for production of species i (%)
- z i :
-
charge number of ion i
- δ:
-
thickness of Nernst diffusion layer (m)
- δc :
-
thickness of convective diffusion layer (m)
- δB :
-
thickness of diffusion layer controlled by gas evolution (m)
- ν:
-
dynamic viscosity (m2 s−1)
- τ:
-
time (s)
- θ:
-
coverage of electrode surface with gas bubbles
- φ:
-
Galvani potential (V)
- Φ:
-
correction function (Equation 11)
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Rudolf, M., Rousar, I. & Krysa, J. Cathodic reduction of hypochlorite during reduction of dilute sodium chloride solution. J Appl Electrochem 25, 155–165 (1995). https://doi.org/10.1007/BF00248173
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DOI: https://doi.org/10.1007/BF00248173