Mass-transfer study of the carbon felt electrode

Vatistas, Nicolaos; Marconi, Pier Filippo; Bartolozzi, M.

doi:10.1016/0013-4686(91)85259-a

Cited by 39 publications

(17 citation statements)

References 16 publications

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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

211

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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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

211

132

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“…For carbon felt electrodes, although some attention has been paid to the dependence of mass transfer coefficient on the electrolyte velocity, [16][17][18][19] correlations between these two parameters are not consistent. Moreover, it is rarely verified whether the mass transfer correlation obtained by measuring limiting currents is applicable in the condition of supplying adequate reactants.…”

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confidence: 99%

The Dependence of Mass Transfer Coefficient on the Electrolyte Velocity in Carbon Felt Electrodes: Determination and Validation

You

Cheng

2017

J. Electrochem. Soc.

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In a flow battery, the salient impact of the electrolyte velocity on the mass transfer coefficient in carbon felt electrodes is demonstrated and quantified. A lab-scale flow battery, fed with identical electrolyte solutions containing Fe 2+ /Fe 3+ as active substances in both the anode and the cathode, is used to realize stable tests free from side reactions in a broad range of current densities. The electrolyte velocities ranging from 2.5 to 15 mm s −1 are selected in this work, which are typical in flow through electrodes in most flow batteries. By measuring limiting currents at various flow rates, a correlation between the mass transfer coefficient and the velocity in dimensionless form is obtained as Sh = 1.68 Re 0.9 . Meanwhile, a 2-D numerical model incorporating this correlation and the experimentally measured electrolyte conductivity is proposed. Voltage losses of the battery fed with adequate reactants at different velocities are both experimentally measured and numerically simulated. The agreement between simulated results and experimental data verifies the applicability of this correlation under normal operating conditions below limiting currents. Owing to the exclusive advantage of decoupling power generation and energy storage, redox flow batteries (RFBs) have been considered as a critical candidate for large-scale electrical energy storage (EES). [1][2][3][4] Unlike the electrodes of conventional secondary batteries, the electrodes of RFBs do not participate in reactions but only provide electrochemical reaction sites for active ions and support electrons transfer. For numerous kinds of developed RFBs, the porous carbon felts, composed of randomly interlaced carbon fibers, are generally selected as electrodes. [5][6][7] Obtaining high voltage efficiency at high current densities is one of the major challenges in the commercialization of RFBs. Much efforts have been devoted to diminishing the activation loss by modifying the carbon fiber surface. [8][9][10][11][12] In addition, ohmic loss and mass transfer loss also lead to the reduction of the voltage efficiency. It is generally recognized that supplying high flow rate of electrolyte for the RFB is the most feasible method to minimizing mass transfer loss, but more pumping power is inevitably required for increasing flow rates. Tang et al. 6 and Ma et al. 7 carried out special research on optimizing the operating strategy of electrolyte flow rate for kilowatts class allvanadium flow battery (VRFB) systems, in which the significant impact of flow rate on cell voltage was detected during the whole charge/discharge process. In a carbon felt electrode, the mass transfer loss is caused by the species transport between the bulk solution in the pore and the carbon fiber surface, which is usually quantified by the mass transfer coefficient k m . 13 For cells operating under high current densities, the mass transfer loss also contributes a significant proportion to the voltage loss, especially when approaching the end of charge/discharge process. Considerin...

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“…However, we have found few papers dealing with the study of the properties of carbon felts, in spite of its attractive characteristics and applications [8][9][10][11] (i.e. electrosynthesis 12 , metal recovery 13 ), probably due to the fact that the hydrophobic nature and the compressibility of this material restrict its applications.…”

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confidence: 99%

Characterization of a carbon felt electrode: structural and physical properties

González-Garcı́a¹,

Bonete²,

Expósito³

et al. 1999

J. Mater. Chem.

136

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The aim of this paper is the characterization of a carbon felt (Le Carbone Lorraine, RVC 4002) to be used as three-dimensional electrode. A wide group of very different techniques were used in the physical and structural characterization of this material. Both, structural (porosity, mean pore radius, specific surface area, tortuosity) and physical properties (permeability, electrical resistance) were determined by using mercury porosimetry, adsorption isotherm analysis, a filamentary analog procedure and liquid permeametry (pressure drop method). The results obtained from the modelling of the hydrodynamic behaviour, from previous work, were also applied here. The carbon felt studied was found to have a porosity around 0.98, a specific surface area of 22100-22700 m -1 , 2.7 10 -3 Ω m electrical resistivity and a tortuosity between 5 and 6. The comparison of these results with those found in the literature for other similar materials, used as three-dimensional electrodes, highlights the attractions of this

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Mass-transfer study of the carbon felt electrode

Cited by 39 publications

References 16 publications

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

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

The Dependence of Mass Transfer Coefficient on the Electrolyte Velocity in Carbon Felt Electrodes: Determination and Validation

Characterization of a carbon felt electrode: structural and physical properties

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