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

Gomes, Adriano S. O.; Busch, Michael; Wildlock, Mats; Simic, Nina; Ahlberg, Elisabet

doi:10.1002/slct.201800628

Cited by 15 publications

(31 citation statements)

References 48 publications

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“…Hydration of Cr(OH)3 will add significant volume without causing dramatic changes in film weight. In addition, the finding that 1-3 monolayers of chromium are involved is consistent with previous studies [31], [32], [40], [41]. It should also be mentioned that the mass gain appears to be independent of the concentration of sodium dichromate for concentrations between 10 and 40 mM (see Figure A3.3).…”

Section: Mass Vs Charge Determined By Eqcmsupporting

confidence: 91%

“…An oxidative ring current is observed during reduction of chromate, which extends from +0.4 V to +0.1 V, giving it a distinctive shape that is very similar in appearance to that found on Au electrodes. PtO reduction and HER are not significantly affected by the Cr III Ox film, in agreement with literature [37], [40], [44], suggesting the underlying Pt surface is not much affected by the film.…”

Section: Introductionsupporting

confidence: 91%

“…Finally, we apply density-functional theory (DFT) in order to further evaluate the origin of the selectivity. In line with earlier work [40] we discuss that from a purely thermodynamic perspective hypochlorite reduction is fully inhibited by surface -OH and =O groups, but this blocking may be circumvented by a ligand exchange mechanism.…”

Section: Introductionsupporting

confidence: 85%

“…Exactly how the chromate film accomplishes this selectivity remains an active research topic in the community. Experimental work has focused on several aspects of the film, including its structure [30], [38], thickness [39], the mechanism of selectivity [31], [32], [38], [40], the effect of the underlying electrode [30], [38], [39], [41]- [43], and the improved current efficiency induced by the film [44].…”

Section: Cathode Selectivitymentioning

confidence: 99%

“…Of the alternatives to chromate proposed [40], [45], [46], [55], [74] MnOx containing films seem very promising owing to the fact that they can be deposited in situ from non-toxic permanganate solutions, and have shown very similar selectivity towards H2 production [55], [56]. MnOx is also used as a selectivity-inducing film for the oxygen evolution reaction [75].…”

Section: Permanganatementioning

confidence: 99%

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Understanding selective thin films in the chlorate process

Smulders¹

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This chapter provides context and background information for the work in this thesis. First, chlorate is introduced and its applications are described. Then, an overview of the chlorate production process is provided, describing the reactions involved, the conditions in the industrial process, and a history of its development. 1.1.4 History of chlorate production and research Chlorate is one of the oldest electrochemical processes, with the first confirmed electrosynthesis dating back to 1802 [12]. The process was discovered by Wilhelm von Hisinger and Jöns Jakob Berzelius [12], hobbyist scientists, only two years after Alessandro Volta first invented the pile, a source of electrical current [13]. The first electrochemical plant opened in 1886 in Villers-St. Sépulcre, Switzerland, using a diaphragm setup in a reactor made of wood. It was not very successful due to cathodic losses, and production ended in 1898 [12]. Around the same year, plants opened in Buckingham and Niagara in Quebec, Canada. These had no diaphragm and used bipolar electrodes with a small cell gap (1.5 to 3 mm), already remarkably similar to today's designs [14]. At the turn of century there were also factories in Switzerland, Sweden, and France. Surprisingly, there were no factories in Germany, despite most chlorate research being performed there [12]. Research focused on developing an understanding of the formation of chlorate. Initially it was believed that the formation was a purely chemical process, but within a few years this theory was completely upended several times. The revisions were driven by thorough experiments and reportedly accompanied by "sometimes violent discussions" [12]. Several papers and discussions in rude tones were exchanged between Foerster and Wohlwill [15], [16] in particular. Foerster insisted there was no electrochemical aspect to chlorate formation, while Wohlwill, a student of Nernst, held that there was. The matter was eventually clarified in 1900 when Lorenz and Wehrlin published extensive experimental results that showed chlorate could be formed electrochemically under certain circumstances [17], although Foerster nevertheless maintained his stance [12]. Regardless of the exact mechanism, it was generally agreed that hypochlorite plays an important part in chlorate formation, and that its Finally, Chapter 7 summarizes my findings and provides a perspective on the future of this topic.

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Section: Mass Vs Charge Determined By Eqcmsupporting

confidence: 91%

Section: Introductionsupporting

confidence: 91%

Section: Introductionsupporting

confidence: 85%

Section: Cathode Selectivitymentioning

confidence: 99%

Section: Permanganatementioning

confidence: 99%

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Understanding selective thin films in the chlorate process

Smulders¹

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Exploring the Mechanism of Cr(VI) Catalyzed Hypochlorous Acid Decomposition**

Busch

Simic²,

Ahlberg

2022

ChemCatChem

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Chlorate is produced through electrolysis of a chloride containing electrolyte in an undivided cell. Cr(VI) is added to the electrolyte in order to minimize the amount of oxygen formed through the homogeneous decomposition of hypochlorite. Despite the importance of Cr(VI) for the chlorate process we posses only very limited knowledge regarding the active Cr(VI) species and mechanisms through which it aids chlorate formation and inhibits O 2 evolution. Using density functional theory (DFT) modeling we present for the first time a detailed reaction mechanism for the chromate catalyzed chlorate formation. Our calculations indicate, that the reaction is initialized by the formation of a Cr(VI)-OÀ ClOCl species which forms Cr(VI)-OClO intermediate. This step is found to be rate determining with a rate constant which is comparable to the disproportionation reaction without catalyst. Chlorate is then obtained either through an uncatalyzed oxidation of chlorite to chlorate or the nucleophilic attack of OCl À followed by a second Cl À elimination step. The comparison of the activity of the different Cr(VI) species reveals that only CrO 4 2À is active whereas HCrO 4À and Cr 2 O 7 2À display sluggish kinetics.[a] M.

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Can Telluric Acid Replace Chromate as a Homogeneous Catalyst in the Chlorate Process?

Sellin,

Busch,

Wildlock

et al. 2023

ChemElectroChem

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Finding an alternative to Cr(VI) as catalyst for the conversion of hypochlorite/hypochlorous acid to chlorate is of critical importance to render the industrial chlorate process safe and sustainable. Recently, telluric acid was identified as a potential replacement but its performance under industrial conditions and its interactions with other parts of the process are still unknown. These factors are elucidated by a combination of density functional theory (DFT) modeling and pilot plant studies. Our results indicate, that the addition of telluric acid indeed has a beneficial effect on the decomposition of HOCl to chlorate. The increased performance, shown as a decreased oxygen formation and an increase in anodic current efficiency. It is mostly related to a buffering effect and an increased selectivity for chlorate formation. Unfortunately, a low cathodic current efficiency was achieved due to reduction of telluric acid to solid Te/TeO2 particles in the electrolyte and at the cathode. Despite the benefits of buffering effects and increased selectivity for chlorate formation, telluric acid is unsuitable as replacement for Cr(VI) in the chlorate process due to lack of compatibility with all process conditions.

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

Cited by 15 publications

References 48 publications

Understanding selective thin films in the chlorate process

Understanding selective thin films in the chlorate process

Exploring the Mechanism of Cr(VI) Catalyzed Hypochlorous Acid Decomposition**

Can Telluric Acid Replace Chromate as a Homogeneous Catalyst in the Chlorate Process?

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