Cathodic current efficiency in the chlorate process

Wulff, Josefin; Cornell, Ann

doi:10.1007/s10800-006-9263-3

Cited by 27 publications

(35 citation statements)

References 9 publications

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“…It is generally believed that hypochlorite will oxidise the chromium film formed at the cathode during polarisation [8]. This belief is also supported from a thermodynamic point of view, as the oxidising power of hypochlorite is, by far and even at very low hypochlorite concentrations, enough to oxidise the chromium (III) film and the steel cathode.…”

Section: Surface Characterisationmentioning

confidence: 94%

“…A large drawback of the steel cathode is that it corrodes severely during the shutdown of the process, at which time the cathodic protection is lost. The corrosion process renders the need for a high concentration of chromate in the electrolyte and also a decreased current efficiency after the stop and during the build-up of the Cr(III) film [8].…”

Section: Introductionmentioning

confidence: 99%

“…The influence of different parameters, such as the addition of chromate, changing the temperature, the electrolyte concentration, the pH and the presence of additives, on the performance of the chlorate process has been reported [7][8][9][10][11]. The current efficiency has been studied in some publications, but the most common approach is to study the cell or electrode potential and oxygen production [9,10,[12][13][14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

“…The current efficiency has been studied in some publications, but the most common approach is to study the cell or electrode potential and oxygen production [9,10,[12][13][14][15][16][17]. It has also been reported that the time it takes to reach stable conditions in a chlorate cell or at the surface of a chlorate cathode is significantly long [8]. The growth of the chromium (III) film on chromium and steel substrates was studied by Hamm, Olsson and Landolt [18].…”

Section: Introductionmentioning

confidence: 99%

“…Several studies on the cathodic current efficiency, as related to the chlorate process, clearly show that the performance is time dependent. Directly after startup, a quick and immediate increase in current efficiency is observed, followed by a slow increase in current efficiency until a final steady state far away from the timeline of most experiments is reached [8,20,21]. Hence, to achieve results that are relevant to full-scale conditions, it is of utmost importance to allow the system to reach the steady state in the study of the parameters.…”

Section: Introductionmentioning

confidence: 99%

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Current efficiency of individual electrodes in the sodium chlorate process: a pilot plant study

et al. 2017

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Current efficiency in the sodium chlorate process is a key issue in the evaluation of the power consumption. A pilot cell unit for executing the sodium chlorate process was constructed to study the current efficiency of the anode and cathode separately. The effects of sodium dichromate and sodium sulphate concentrations and the electrolyte temperature on the anode and cathode current efficiencies were studied. Corrosion products formed on the mild steel cathodes after their removal from the cell were characterised using X-ray diffraction and infrared spectroscopy. The results show that the cathodic current efficiency increases with increasing dichromate concentrations in the electrolyte until approximately 5 g dm -3 is reached. At this optimum concentration of dichromate, the presence of sulphate ions decreases the cathodic current efficiency. For moderate increases in temperature, the cathodic current efficiency increases, but oxygen evolution is promoted, and the power consumption also increases. Surface characterisation of the electrodes after their exposure to air shows two primary types of behaviour, depending on the process parameters. At low dichromate concentrations, amorphous corrosion layers are formed, while at higher concentrations, reduced forms of iron hydroxides, i.e., ''green rust'', are identified. Although the electrodes were positioned at the open circuit potential for 40 min before their removal from the cell, chromium remains on the cathode surface. This result might explain the corrosion-inhibiting effect of the addition of chromate to the electrolyte. The results from this study can be used to optimise operating procedures in real plants, decrease the energy consumption and minimise the environmental impact of these processes.Electronic supplementary material The online version of this article

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Section: Surface Characterisationmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Current efficiency of individual electrodes in the sodium chlorate process: a pilot plant study

et al. 2017

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Catalytic effects of molybdate and chromate–molybdate films deposited on platinum for efficient hydrogen evolution

Díaz‐Morales

Lindberg

Smulders

et al. 2023

J of Chemical Tech & Biotech

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BACKGROUND: Sodium chlorate (NaClO 3 ) is extensively used in the paper industry, but its production uses strictly regulated highly toxic Na 2 Cr 2 O 7 to reach high hydrogen evolution reaction (HER) Faradaic efficiencies. It is therefore important to find alternatives either to replace Na 2 Cr 2 O 7 or reduce its concentration. RESULTS: The Na 2 Cr 2 O 7 concentration can be significantly reduced by using Na 2 MoO 4 as an electrolyte co-additive. Na 2 MoO 4 in the millimolar range shifts the platinum cathode potential to less negative values due to an activating effect of cathodically deposited Mo species. It also acts as a stabilizer of the electrodeposited chromium hydroxide but has a minor effect on the HER Faradaic efficiency. X-ray photoelectron spectroscopy (XPS) results show cathodic deposition of molybdenum of different oxidation states, depending on deposition conditions. Once Na 2 Cr 2 O 7 was present, molybdenum was not detected by XPS, as it is likely that only trace levels were deposited. Using electrochemical measurements and mass spectrometry we quantitatively monitored H 2 and O 2 production rates. The results indicate that 3 ∼mol L −1 Na 2 Cr 2 O 7 (contrary to current industrial 10-30 mmol L −1 ) is sufficient to enhance the HER Faradaic efficiency on platinum by 15%, and by co-adding 10 mmol L −1 Na 2 MoO 4 the cathode is activated while avoiding detrimental O 2 generation from chemical and electrochemical reactions. Higher concentrations of Na 2 MoO 4 led to increased oxygen production.CONCLUSION: Careful tuning of the molybdate concentration can enhance performance of the chlorate process using chromate in the micromolar range. These insights could be also exploited in the efficient hydrogen generation by photocatalytic water splitting and in the remediation of industrial wastewater.

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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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Cathodic current efficiency in the chlorate process

Cited by 27 publications

References 9 publications

Current efficiency of individual electrodes in the sodium chlorate process: a pilot plant study

Current efficiency of individual electrodes in the sodium chlorate process: a pilot plant study

Catalytic effects of molybdate and chromate–molybdate films deposited on platinum for efficient hydrogen evolution

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

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