Mixed Chromate and Molybdate Additives for Cathodic Enhancement in the Chlorate Process

Smulders, Vera; Gomes, Adriano S. O.; Simic, Nina; Mei, Bastian; Mul, Guido

doi:10.1007/s12678-021-00666-7

Cited by 6 publications

(15 citation statements)

References 31 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…66 As previously seen for dichromate, 31 these oligomers are likely to possess very different catalytic which in turn may render them inert. Furthermore, molybdate was found to adversely affect the selectivity toward Cl 2 generation at the anode 27 as well as increasing the hypochlorite decomposition to oxygen in the electrolyte, 24 which renders it unsuitable as an additive. Similarly, also, arsenates are, despite their potential activity for chlorate formation, unsuitable due to their high toxicity.…”

Section: ■ Computational Detailsmentioning

confidence: 99%

“…Most of the research has been focused on the selectivity of the cathode reactions, ,− but comparably, little efforts have been made to find a suitable replacement for its role as a homogeneous catalyst for chlorate formation. Indeed, most evidence for this important function is quite recent, ,− even though it has been discussed earlier in more general terms. − , …”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Can We Replace Cr(VI) as a Homogeneous Catalyst in the Chlorate Process?

Busch

Wildlock²,

Simic³

et al. 2022

J. Phys. Chem. C

Self Cite

View full text Add to dashboard Cite

The chemistry of hypochlorous acid in the presence of metal impurities is of high importance for many areas of chemistry ranging from water purification and disinfection to sea water splitting and the electrosynthesis of chlorate. The production of chlorate comprises one of the most important electrochemical processes and relies on the Cr(VI) catalyzed transformation of HOCl to chlorate. Since the use of Cr(VI) has been restricted in the European Union due to its toxicity, mutagenicity, and carcinogenicity, alternative catalysts need to be developed. Building on the recently identified mechanism for the chromate catalyzed oxidation of HOCl to chlorate, we performed a screening for potential alternative catalysts using density functional theory modeling. Based on these results, a volcano plot, which combines all previously reported reaction paths, was constructed and the thermodynamic limitations were identified. Our results indicate that, in principle, many materials are able to catalyze the chlorate formation at much higher rates. However, in practice, the reaction is limited by the strong correlation between the pKa of the active site and the activity and the limitation to pH neutral conditions. This renders chromate, despite its overall poor performance, effectively the most active material. Furthermore, we show that none of the remaining considered molecules is able to replace Cr(VI) as the homogeneous catalyst due to side reactions or process limitations. Thus, these results will have a significant impact in the political decision of banning Cr(VI) in the chlorate process and also clearly show that alternative approaches for chlorate synthesis need to be developed if Cr(VI) is to be removed from the process.

show abstract

Section: ■ Computational Detailsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Can We Replace Cr(VI) as a Homogeneous Catalyst in the Chlorate Process?

Busch

Wildlock²,

Simic³

et al. 2022

J. Phys. Chem. C

Self Cite

View full text Add to dashboard Cite

show abstract

“…The limiting current corresponding to hypochlorite electroreduction shifts to lower current densities when 10 mmol L −1 Na 2 MoO 4 is added to the electrolyte, depicting a small retarding effect of the MoO x H y film on the hypochlorite electroreduction. An increase in cathodic current efficiency at small chromate concentrations in the presence of molybdate was recently reported 18 . The cathode potential shifts to less negative potentials in the presence of the molybdate additive: when the Cr VI concentration amounts to 13.5 μmol L −1 , the cathode potential shifts 260 mV to less negative values at 300 mA cm −2 compared to the values obtained in molybdate‐free electrolytes.…”

Section: Resultsmentioning

confidence: 69%

“…An increase in cathodic current efficiency at small chromate concentrations in the presence of molybdate was recently reported. 18 The cathode potential shifts to less negative potentials in the presence of the molybdate additive: when the Cr VI concentration amounts to 13.5 μmol L −1 , the cathode potential shifts 260 mV to less negative values at 300 mA cm −2 compared to the values obtained in molybdate-free electrolytes. Also, the inhibiting effect of molybdate on the hypochlorite reduction could be further enhanced by adding low amounts of chromate to the electrolyte (see polarization curves in green in Fig.…”

Section: Resultsmentioning

confidence: 87%

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

Self Cite

View full text Add to dashboard Cite

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.

show abstract

“…The principal argument is the formation of a chromium hydroxide (Cr(OH) 3 )/chromium oxide (Cr 2 O 3 ) layer on the electrode surface that is considered to hinder the hypochlorite reduction acting as a diaphragm. A similar argument has been promulgated during the formation of lepidocrocite (γ-FeOOH) and some other alkaline hydroxides for different types of chlorate productions. − Cerium oxide can quickly form a layer composed of cerium oxide and cerium hydroxide when immersed in an aqueous media that is favorable in an alkaline medium due to the presence of Ce 4+ and Ce 3+ . In the presence of this layer, the electrode selectivity toward hypochlorite reduction decreases in favor of hydrogen evolution due to hydroxylation of the metal site blocking the active site for hypochlorite reduction …”

Section: Resultsmentioning

confidence: 71%

Cerium Oxide on a Fluorinated Carbon-Based Electrode as a Promising Catalyst for Hypochlorite Production

2022

View full text Add to dashboard Cite

Sodium hypochlorite (NaOCl) is widely used as a disinfectant agent for water treatment and surface cleaning. A straightforward way to produce NaOCl is by the electrolysis of an aqueous sodium chloride (NaCl) solution. This process presents several side reactions decreasing its efficiency with hypochlorite reduction on the cathode surface being one of the main detrimental reactions. In this work, we have studied carbon-based electrodes modified with cerium oxide (CeO2), fluorine, and platinum nanoparticles as cathodes for hypochlorite production. Fluorination was carried out electrochemically; the polyol method was used to synthesize platinum nanoparticles; and the hydrothermal process was applied to form a CeO2 layer. Scanning electron microscopy, FTIR, and inductively coupled plasma (ICP) indicated the presence of cerium oxide as a film, fluorine groups on the substrate, and a load of 3.2 mg/cm2 of platinum nanoparticles and 2.7 mg/cm2 of CeO2. From electrochemical impedance spectroscopy, it was possible to demonstrate that incorporating platinum and fluorine decreases the charge transfer resistance by 16% and 28%, respectively. Linear sweep voltammetry showed a significant decrease in hypochlorite reduction when the substrate was doped with fluorine from −16.6 mA/cm2 at −0.6 V to −9.64 mA/cm2 that further reduced to −8.78 mA/cm2 with cerium oxide covered fluorinated electrodes. The performance of the cathode materials during hypochlorite production improved by 80% compared with pristine activated carbon cloth (ACC) electrodes. The improvement toward hindering NaOCl reduction is probably caused by the incorporation of a partial negative charge upon doping with fluorine.

show abstract

Mixed Chromate and Molybdate Additives for Cathodic Enhancement in the Chlorate Process

Cited by 6 publications

References 31 publications

Can We Replace Cr(VI) as a Homogeneous Catalyst in the Chlorate Process?

Can We Replace Cr(VI) as a Homogeneous Catalyst in the Chlorate Process?

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

Cerium Oxide on a Fluorinated Carbon-Based Electrode as a Promising Catalyst for Hypochlorite Production

Contact Info

Product

Resources

About