Characterization of a carbon felt electrode: structural and physical properties

González-Garcı́a, José; Bonete, Pedro; Expósito, Eduardo; Montiel, Vicente; Aldaz, A.; Torregrosa-Maciá, Rosa

doi:10.1039/a805823g

Cited by 132 publications

(69 citation statements)

References 22 publications

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“…10 À9 m 2 [23]. Choosing a porous separator (insulator) with similar structure as the porous anode can minimise the electrolyte by-passing the porous anode.…”

Section: Reactor With Porous Anode and Plate Cathodementioning

confidence: 99%

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Models of Hypochlorite production in electrochemical reactors with plate and porous anodes

Cheng

Kelsall

2007

J Appl Electrochem

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Pseudo two-dimensional finite element models were developed to predict the hypochlorite (chloric(I)) (HOCl + OCl À ) production by electrolysis of near-neutral aqueous sodium chloride solution, in reactors with (a) an anode and cathode in the form of plates, and (b) a lead dioxide-coated graphite felt anode and titanium plate cathode. The model was used to investigate the feasibility of using a porous anode to achieve high single pass conversions in oxidising chloride ions. For the model reactor with planar anode, the effects of diffusion, migration and convection on the mass transport of the reacting species were considered, whereas with the porous anode, a supporting electrolyte (Na 2 SO 4 ) was notionally present to eliminate the migrational contribution to reactant transport. For an electrolyte flow rate of 10 À6 m 3 s À1 (Re = 10 for plate electrodes, Re porous = 0.76 for porous anode), a cell voltage of 3.0 V and an inlet NaCl of 100 mol m À3 , the single-pass conversion of Cl À was predicted to increase from 0.45 for the reactor with a planar anode to 0.81 for the reactor with a porous anode. For the same operating conditions, the overall current efficiency was also predicted to increase from 0.71 to 0.77 by replacing the plate with the porous anode. Keywords Hypochlorite Á Chloric(I) Á Chloride Á Modelling Á Porous electrode Notation A Specific surface area of porous electrode (m 2 m À3 ) C i Concentration of species i (mol m À3 ) C i,in Inlet concentration of species i (mol m À3 ) D i Diffusion coefficient of species i (m 2 s À1 ) d Distance between the planar anode and cathode (m) d f Fibre diameter (m) d h Hydraulic diameter of felt fibre (m) E k Equilibrium electrode potential of reaction k versus reference electrode (SHE) (V) F Faraday constant (C mol À1 ) j k Current density of reaction k (A m À2 ) j L Limiting current density (A m À2 ) j 0 Exchange current density (A m À2 ) k Standard heterogeneous rate constant coefficient (m s À1 ) k m Mass transport rate coefficient (m s À1 ) K Equilibrium constant (mol À1 dm 3 ) N i Superficial flux of species i (mol m À2 s À1 ) n Number of electrons involved in a reaction (-) R Universal gas constant (J mol À1 K À1 ) Re Reynolds number for reactor with planar electrodes (vd/m) (-) Re porous Reynolds number for porous electrode (v eff d h /m) r k Rate of homogeneous reaction k (mol m 3Linear electrolyte velocity (m s À1 ) v eff Solution velocity in the empty cross-section area (m s À1 ) z i Number of charge on species i (-) iSubscript i refers to reacting species (-) kSubscript k refers to reactions (-)

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“…10 À9 m 2 [23]. Choosing a porous separator (insulator) with similar structure as the porous anode can minimise the electrolyte by-passing the porous anode.…”

Section: Reactor With Porous Anode and Plate Cathodementioning

confidence: 99%

“…j Cl 2 þ j O 2 , a is the specific surface area of the graphite felt, which was assumed to be 10 4 m 2 m À3 [23] and j s is the effective solid phase conductivity, calculated from Bruggeman's equation:…”

Section: Reactor With Porous Anode and Plate Cathodementioning

confidence: 99%

Models of Hypochlorite production in electrochemical reactors with plate and porous anodes

Cheng

Kelsall

2007

J Appl Electrochem

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“…Carbon felt provides a high specific surface area (app. 22000 m 2 m )3 [19]). High porosity enhances the convection of electroactive species to the electrode surface resulting in high conversion rates and extremely low outlet concentrations even for very dilute solutions.…”

Section: Introductionmentioning

confidence: 99%

Electrochemical reduction of dilute chromate solutions on carbon felt electrodes

Frenzel¹,

Holdik²,

Barmashenko³

et al. 2005

J Appl Electrochem

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Carbon felt is a potential material for electrochemical reduction of chromates. Very dilute solutions may be efficiently treated due to its large specific surface area and high porosity. In this work, the up-scaling of this technology is investigated using a new type of separated cell and once-through flow of industrial rinse water. A significant enhancement of the process is obtained due to copper deposition during long-term operation. The co-deposition and re-solution of copper occurs depending on the inlet chromate concentration. When previously deposited copper is present a current-free reduction of chromate takes place resulting in current efficiencies apparently above 100%. Very high space time yields are obtained even for effluents at low concentration and optimised conditions (high flow rates and pH 2). The economic feasibility of the technology is also considered. Continuous, single-pass operation results in lower energy requirements than batch processing. The economic potential of the process is also evaluated in comparison with chemical detoxification of chromate. The operating costs for the electrochemical treatment of very dilute effluents on a carbon felt electrode are 30% lower than for the chemical method.

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“…The average pore diameter of the porous carbon foam or felt electrodes is typically in the range 100-800 m [30], with a value of around 150 m [31,32] for Sigratherm electrodes. The bubble diameter depends on various factors, including the electrolyte composition, current density and flow rate.…”

Section: Numerical Details and Parametersmentioning

confidence: 99%

Modelling the effects of oxygen evolution in the all-vanadium redox flow battery

Al-Fetlawi

Shah

Walsh

2010

Electrochimica Acta

209

132

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a b s t r a c tThe impact of oxygen evolution and bubble formation on the performance of an all-vanadium redox flow battery is investigated using a two-dimensional, non-isothermal model. The model is based on mass, charge, energy and momentum conservation, together with a kinetic model for the redox and gas-evolving reactions. The multi-phase mixture model is used to describe the transport of oxygen in the form of gas bubbles. Numerical simulations are compared to experimental data, demonstrating good agreement. Parametric studies are performed to investigate the effects of changes in the operating temperature, electrolyte flow rate and bubble diameter on the extent of oxygen evolution. Increasing the electrolyte flow rate is found to reduce the volume of the oxygen gas evolved in the positive electrode. A larger bubble diameter is demonstrated to increase the buoyancy force exerted on the bubbles, leading to a faster slip velocity and a lower gas volume fraction. Substantial changes are observed over the range of reported bubble diameters. Increasing the operating temperature was found to increase the gas volume as a result of the enhanced rate of O 2 evolution. The charge efficiency of the cell drops markedly as a consequence.

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Characterization of a carbon felt electrode: structural and physical properties

Cited by 132 publications

References 22 publications

Models of Hypochlorite production in electrochemical reactors with plate and porous anodes

Models of Hypochlorite production in electrochemical reactors with plate and porous anodes

Electrochemical reduction of dilute chromate solutions on carbon felt electrodes

Modelling the effects of oxygen evolution in the all-vanadium redox flow battery

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