In situ ellipsometric characterization of films formed by cathodic reduction of chromate

Tidblad, Annika Ahlberg; Mårtensson, Jan

doi:10.1016/s0013-4686(96)00229-0

Cited by 27 publications

(19 citation statements)

References 9 publications

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“…The reduction of chromate on gold is reported to result in very thin films, monolayers, of Cr(III) ,,. The deposition is dependent on potential and the electrolyte composition, in particular the anion and the availability of protons ,.…”

Section: Resultsmentioning

confidence: 99%

Understanding Selectivity in the Chlorate Process: A Step towards Efficient Hydrogen Production

Gomes

Busch²,

Wildlock

et al. 2018

ChemistrySelect

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Chlorate production is a highly energy demanding industrial process, where chlorate formation is accompanied with hydrogen formation on the cathode. To ensure a high cathodic current efficiency, sodium dichromate is added to the chlorate electrolyte to avoid reduction of hypochlorite formed as a reaction intermediate in the process. However, chromate is highly toxic to humans and environment, and therefore a replacement is desired. A model system with ex situ formed chromium oxide/hydroxide films were used to study hypochlorite reduction and hydrogen evolution. The experimental results demonstrate that the hypochlorite reduction is fully blocked while hydrogen evolution readily occurs. However, in the presence of hypochlorite the hydrogen evolution reaction is inhibited. By combining experimental findings with density functional theory (DFT) calculations, the mechanism of hypochlorite reduction was revealed and the reason for inhibition by the deposited chromium(III) film was demonstrated. Based on these results possible replacements for chromate are suggested.

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Section: Resultsmentioning

confidence: 99%

Understanding Selectivity in the Chlorate Process: A Step towards Efficient Hydrogen Production

Gomes

Busch²,

Wildlock

et al. 2018

ChemistrySelect

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“…1,2,6,7,[16][17][18][19][20][21][22] Sodium dichromate plays multiple roles: a) it develops a thin layer of chromium oxide and hydroxide on the cathode surface, thus completely preventing the cathodic reduction of active chlorine and chlorite, b) it inhibits the corrosion of the steel cathode, 23 c) its buffering effect ensures an optimal pH for the chemical conversion of active chlorine into chlorate and d) it has a catalytic effect on the chemical conversion. 1,2,6,7,[16][17][18][19][20][21][22] Sodium dichromate plays multiple roles: a) it develops a thin layer of chromium oxide and hydroxide on the cathode surface, thus completely preventing the cathodic reduction of active chlorine and chlorite, b) it inhibits the corrosion of the steel cathode, 23 c) its buffering effect ensures an optimal pH for the chemical conversion of active chlorine into chlorate and d) it has a catalytic effect on the chemical conversion.…”

Section: Introductionmentioning

confidence: 99%

Current efficiency in the chlorate cell process

Spasojevic

Ribic-Zelenovic

Spasojević³

et al. 2014

JSCS

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A mathematical model has been set up for current efficiency in a chlorate cell acting as an ideal electrochemical tubular reactor with a linear increase in hypochlorite concentration from the entrance to the exit. Good agreement was found between the results on current efficiency experimentally obtained under simulated industrial chlorate production conditions and the theoretical values provided by the mathematical model.

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“…− − − − + + → + 3 2 ClO 3H O 6e Cl 6OH ( 8 ) DSA  anode or platinum-iridium-coated titanium are currently used as anodes and their high electrocatalytic activity for chloride oxidation ensures that, apart from the Foerster reaction of electrochemical chlorate formation (Eq. (6)), the current losses due to anodic water oxidation can be completely neglected because of the much more positive potential for this reaction.…”

mentioning

confidence: 99%

“…This film hinders the unwanted side reactions (7) and (8), while hydrogen evolution can still take place, though with changed kinetics [7]. The thickness and growth rate of the chromium(III) hydroxide film depends on factors such as: the cathode material, the electrode potential and the chromate concentration [8]. Although low chromate concentration as 0.1 g dm -3 Cr 2 O 7 2has been shown to efficiently hinder reduction of Fe(CN) 6 3on smooth platinum electrode [9], in the chlorate production the concentration of dichromate should be much higher (3-8 g dm -3 ) [10].…”

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confidence: 99%

Fe-Mo alloy coatings as cathodes in chlorate production process

Gajić-Krstajić

Elezović

Jović

et al. 2016

Hem Ind

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The aim of this study was to gain a better understanding of the feasibility of partial replacement of dichromate, Cr(VI), with phosphate buffer, focusing on the cathode reaction selectivity for hydrogen evolution on mild steel and Fe-Mo cathodes in undivided cell for chlorate production. To evaluate the ability of phosphate and Cr(VI) additions to hinder hypochlorite and chlorate reduction, overall current efficiency (CE) measurements in laboratory cell for chlorate production on stationary electrodes were performed. The concentration of hypochlorite was determined by a conventional potentiometric titration method using 0.01 mol dm -3 As 2 O 3 solution as a titrant. The chlorate concentration was determined by excess of 1.0 mol dm -3 As 2 O 3 solution and excess of arsenic oxide was titrated with 0.1 mol dm -3 KBrO 3 solution in a strong acidic solution. Cathodic hypochlorite and chlorate reduction were suppressed efficiently by addition of 3 g dm -3 dichromate at both cathodes, except that Fe-Mo cathode exhibited higher catalytic activity for hydrogen evolution reaction (HER). The overvoltage for the HER was around 0.17 V lower on Fe-Mo cathode than on mild steel at the current density of 3 kA m -2 . It was found that a dichromate content as low as 0.1 g dm -3 is sufficient for complete suppression of cathodic hypochlorite and chlorate reduction onto Fe-Mo catalyst in phosphate buffering system (3 g dm -3 Na 2 HPO 4 + NaH 2 PO 4 ). The overall current efficiency was practically the same as in the case of the presence of 3 g dm -3 dichromate buffer (98%). However, for the mild steel cathode, the overall current efficiency for the chlorate production was somewhat lower in the above mentioned mixed phosphate + dichromate buffering system (95%) than in the pure dichromate buffering solution (97.5%).

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In situ ellipsometric characterization of films formed by cathodic reduction of chromate

Cited by 27 publications

References 9 publications

Understanding Selectivity in the Chlorate Process: A Step towards Efficient Hydrogen Production

Understanding Selectivity in the Chlorate Process: A Step towards Efficient Hydrogen Production

Current efficiency in the chlorate cell process

Fe-Mo alloy coatings as cathodes in chlorate production process

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