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| 2. |
- Cornell, Ann, et al.
(författare)
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Ruthenium Dioxide as Cathode Material for Hydrogen Evolution in Hydroxide and Chlorate Solutions
- 1993
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Ingår i: Journal of The Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 140:11, s. 3123-3129
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Tidskriftsartikel (refereegranskat)abstract
- Ruthenium dioxide as electrocatalyst on an activated cathode for chlorate production was investigated with respect toits activity towards hydrogen evolution, hypochlorite reduction, and chlorate reduction, respectively. Investigations weremade in the presence, as well as in the absence, of a chromium hydroxide film in 1M NaOH and in typical chlorateelectrolyte. Low overvoltages for hydrogen evolution were found and, at technical current densities, an effect of catalystcoating thickness. Commercial DSA® electrodes with RuO2 as the active compound were tested as cathodes and were lessactive but more stable than the coatings produced by us. Hypochlorite and chlorate were reduced in the absence ofchromate, chlorate reduction being fast on ruthenium dioxide compared to the other electrode materials and by far thedominating cathodic reaction in chlorate electrolyte without chromate and hypochlorite at 70°C, 3 kA/m2
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| 3. |
- Cornell, Ann, et al.
(författare)
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The effect of addition of chromate on the hydrogen evolution reaction and on iron oxidation in hydroxide and chlorate solutions
- 1992
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Ingår i: Electrochimica Acta. - 0013-4686 .- 1873-3859. ; 37:10, s. 1873-1881
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Tidskriftsartikel (refereegranskat)abstract
- The addition of chromate to the electrolyte has been shown in previous papers to hinder almost completely the electroreduction of hypochlorite, while the hydrogen evolution reaction can still proceed on the cathode surface. The effect of chromate on the latter reaction has been studied with cyclic voltammetry and by measuring polarization curves for iron electrodes in both chlorate and hydroxide electrolyte. For the sake of comparison, the investigations have also included the effects on the gold electrode in hydroxide solution. The results showed that the kinetics is changed in a way that decreases the differences in electrocatalytic activity between different electrode materials. Also, the innermost layer of the chromium hydroxide film seems to be the most active part in the HER. The chromate also affects the oxidation of the iron surface. A practical result of this is that the activity for the HER on corroded iron in chlorate electrolyte depends on whether the electrolyte contained chromate during the period of corrosion. The activation becomes much smaller if chromate is present.
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| 5. |
- Lindbergh, Göran, et al.
(författare)
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Effect of chromate addition on cathodic reduction of hypochlorite in hydroxide and chlorate solutions
- 1990
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Ingår i: Journal of the Electrochemical Society. ; 137:10, s. 3094-3099
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Tidskriftsartikel (refereegranskat)abstract
- The cathodic reduction of chromate and its effect on the reduction of hypochlorite have been studied by cyclic voltammetry, using a rotating disk electrode of platinum in IM NaOH solution as well as in an electrolyte with a composition and temperature which were typical for industrial chlorate synthesis. It was found that in both electrolytes a thin film of presumably Cr(OH)3, with a thickness of only one or two molecular layers, is formed. After formation of this film in a cathodic sweep of the potential, the hypochlorite reduction reaction is almost completely inhibited in the reversed sweep, up to the potential region for dissolution of the formed film. From the experimental results and a theoretical analysis of the mass transfer rate of hypochlorite ions to the cathode surface, it is concluded that the addition of chromate to the electrolyte in the industrial chlorate process leads to the formation of a thin film on the cathode surface, which hinders electron transfer at the reduction of hypochlorite.
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- Lindbergh, Göran, et al.
(författare)
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Inhibition of cathode reactions in sodium hydroxide solution containing chromate
- 1991
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Ingår i: Electrochimica Acta. ; 36:13, s. 1985-1994
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Tidskriftsartikel (refereegranskat)abstract
- The formation of a film on the cathode surface due to electroreduction of chromate and its effect on other cathode reactions have been studied by cyclic voltammetry using rotating disc electrodes of platinum and gold in 1 M NaOH solution. It was found that the film formed hinders very effectively the cathodic reduction of ClO-, Fe(CN)3-6 and O2(aq) as well as further reduction of chromate, while the hydrogen evolution reaction and the oxidation of the electrode surface can still proceed. The suppression of the cathodic reaction is achieved at a smaller amount of deposit and is more efficient when adsorbed intermediates are involved [reduction of ClO- and O2(aq)] than for simple outer sphere reactions (reduction of Fe(CN)3-6). The largely unhindered adsorption and desorption of hydrogen on platinum as well as the oxidation of the metal surface beneath the film show that it is permeable to hydroxide and/or hydrogen ions, whereas it is impermeable to the larger species used. This also explains the effect of the addition of chromate to the electrolyte in the chlorate process, where the film formed on the cathode effectively hinders the undesired hypochlorite reduction, while it still allows the desired hydrogen evolution reaction to occur. © 1991.
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