Metal Anodes and Hydrogen Cathodes: Their Activity Towards  O 2 Evolution and ClO3  −  Reduction Reactions

Tilak, B. V.; Tari, Kamran; Hoover, C. L.

doi:10.1149/1.2095999

Cited by 47 publications

(51 citation statements)

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“…The apparent increase in activity for hydrogen evolution at the corroded electrodes could be due to a catalysing effect of oxides or an increase in surface area, but in the light of later results [22], the apparent activation effect [1] may also be due to reduction of chlorate. The activity for this side reaction is favoured by the presence of oxides on iron electrodes [1,2] and the chromate film has to be built up properly to avoid confusion between increased activity for hydrogen evolution and an increased current due to side reactions. On corroded steel electrodes a high current efficiency for hydrogen evolution was not achieved immediately, but needed around 1 hour of cathodic polarisation in chlorate electrolyte with 3 g dm -3 Na 2 Cr 2 O 7 at 3 k Am -2 to reach a constant level of around 95% [22].…”

Section: Steel Electrodesmentioning

confidence: 99%

“…Reduction of chlorate is highly dependent on electrode material and does not take place to any major extent on Co, Ni, Mo, Ti, Hg and C, whereas iron oxides [2] and ruthenium dioxide [3] are active for chlorate reduction. In a previous study [1] the current efficiency for hydrogen evolution was determined for an iron cathode at 3 kA m -2 in a chromate-free electrolyte containing 550 g dm -3 NaClO 3 and 110 g dm -3 NaCl at 70°C.…”

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confidence: 99%

“…Ref. [2,[18][19][20][21][22][23][24], and a few focus on the DSA-anode potential [15,16,[25][26][27]. For the steel and iron cathodes, polarisation curves at chlorate-like conditions are scarcely presented [1,28,29].…”

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confidence: 99%

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Effects of electrolyte parameters on the iron/steel cathode potential in the chlorate process

Nylén

Cornell

2008

J Appl Electrochem

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This study focuses on how different electrolyte parameters of the chlorate process affect the cathode potential for hydrogen evolution on iron in a wide currentdensity range. The varied parameters were pH, temperature, mass transport conditions and the ionic concentrations of chloride, chlorate, chromate and hypochlorite. At lower current densities, where cathodic protection of the electrode material is important, the pH buffering capacity of the electrolyte influenced the potential to a large extent. It could be concluded that none of the electrolyte parameters had any major effects (\50 mV) on the chlorate-cathode potential at industrially relevant current densities (around 3 kA m -2 ). Certainly, there is more voltage to gain from changing the cathode material than from modifying the electrolyte composition. This is exemplified by experiments on steel corroded from operation in a chlorate plant, which exhibits significantly higher activity for hydrogen evolution than polished steel or iron.Keywords Chlorate cathode Á Chlorate process Á Hydrogen evolution Á Iron Á Steel List of symbolsCathode potential vs reference electrode (Ag/AgCl) (V) F Faraday constant (As mol -1 ) j k Current density for reaction k (A m -2 ) k 0 2 Coefficient in the Tafel expression of Eq. 2, which is given in Eq. 15 (mol m -2 s -1 ) k 14 Coefficient in the Tafel expression of Eq. 14, which is given in equation 16 (m s -1 ) N i Molar flux of species i (mol m -2 s -1 ) R Universal gas constant (J mol -1 K -1 ) R i Homogeneous production rate of species i (mol m -3 s -1 ) T Temperature (K) u z Convective velocity perpendicular to the electrode surface, i.e. in the direction of the z-axis (m s -1 ) zAxial coordinate (m) aTransfer coefficient d D Diffusion layer (m) d R Reaction layer (m)

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Section: Steel Electrodesmentioning

confidence: 99%

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confidence: 99%

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Effects of electrolyte parameters on the iron/steel cathode potential in the chlorate process

Nylén

Cornell

2008

J Appl Electrochem

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“…The thickness and growth rate of the film depends on factors such as the cathode material, the electrode potential and the chromate concentration, [6]. As low chromate concentrations as 0.1 g l )1 Cr 2 O 7 2) has been shown to efficiently hinder reduction of Fe(CN) 6 3) on smooth platinum [2], however the concentration in chlorate electrolyte is generally 3-8 g l )1 Na 2 Cr 2 O 7 , [7]. A parasitic reaction that can have some importance during start-up of the electrolysis process is reduction of iron oxides on steel cathodes.…”

Section: Introductionmentioning

confidence: 99%

Cathodic current efficiency in the chlorate process

Wulff

Cornell

2006

J Appl Electrochem

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Sodium chlorate is produced in undivided electrolysis cells. Hydrogen is evolved on the cathodes, usually made of steel, while chloride ions are oxidised to chlorine on the anodes, usually DSA Ò s. Parasitic cathodic reactions, lowering the cathodic current efficiency (CE), are the reduction of hypochlorite and chlorate ions. These reactions are suppressed by the addition of Cr(VI) to the electrolyte. In this work the effects that time of the electrolysis, chromate concentration and interruption of the electrolysis process have on CE has been investigated. New steel, as well as steel samples cut from cathodes used in a chlorate plant, were used as cathode material. Laboratory experiments in a divided cell were made to determine the rate of hydrogen production, and thereby indirectly CE, at varying operating conditions. It was found that the chromate concentration is important for the CE in the range 0.5-6 g l )1 Na 2 Cr 2 O 7 . The CE was higher on new steel than on the used steel, which had a more corroded and inhomogeneous surface. When starting the electrolysis the CE was initially low, at a value depending on the operating conditions, but increased with time of polarisation. The time to reach an approximate steady CE was generally in the order of hours. Electrolysis shut downs in the presence of hypochlorite ( £ 3 g l )1 NaClO) resulted in corrosion of iron and a low CE when restarting the process. After one such corrosion shut down the new steel showed as low CE as the used steel. When restarting the electrolysis after a shut down without hypochlorite the CE was higher than before the shut down. Current densities of a simulated bipolar plate during a shut down were measured to 50-150 A m )2 , resulting from oxidation of steel and reduction of oxy chlorides on the catalytic DSA Ò electrode.

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“…More recently, for instance, ion implantation has been used to modify and characterize the properties of mixed ruthenium-titanium oxide films.9 Tilak et a1. 10 presented a more fundamental analysis of the factors influencing the kinetics of oxygen versus chlorine evolution on ruthenium oxide-based anodes. They suppressed oxygen evolution by operating with low surface areas and by adding dopants.…”

Section: March • Jommentioning

confidence: 99%

The history of progress in dimensionally stable anodes

Duby¹

1993

JOM

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This article provides a brief history of dimensionally stable anodes by reviewing innovations in the chlor-alkali industry, electroplating and electrogalvanizing, and electrowinning. These anodes are attractive for numerous reasons (e.g., long life and reduced energy consumption), but they must still overcome the hurdle of cost to gain wider acceptance for applications in the metallurgical process industries.

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Metal Anodes and Hydrogen Cathodes: Their Activity Towards O 2 Evolution and ClO3 − Reduction Reactions

Cited by 47 publications

References 1 publication

Effects of electrolyte parameters on the iron/steel cathode potential in the chlorate process

Effects of electrolyte parameters on the iron/steel cathode potential in the chlorate process

Cathodic current efficiency in the chlorate process

The history of progress in dimensionally stable anodes

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