X-ray micro-tomography as a diagnostic tool for the electrode degradation in vanadium redox flow batteries

Trogadas, Panagiotis; Taiwo, Oluwadamilola O.; Tjaden, Bernhard; Neville, Tobias P.; Yun, Sukhwan; Parrondo, Javier; Ramani, Vijay; Coppens, MO; Brett, Dan J. L.; Shearing, Paul R.

doi:10.1016/j.elecom.2014.09.010

Cited by 76 publications

(54 citation statements)

References 31 publications

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“…(19), where Jeff is the effective diffusion flux, c is the molar concentration, ̇ is the effective heat flux, λ bulk is the bulk thermal conductivity. 84,102,146,147 By rearranging the temperature gradient, the heat flux and thus, the tortuosity can be calculated along each axis of a sample. Cooper et al 62 scanned a commercially available LiFePO4 battery cathode using X-ray synchrotron nano CT and investigated the tortuosity of the pore phase using heat flux simulation.…”

Section: Mesh Based Calculation Methodsmentioning

confidence: 99%

Tortuosity in electrochemical devices: a review of calculation approaches

Tjaden

Brett

Shearing

2016

International Materials Reviews

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202

188

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The tortuosity of a structure plays a vital role in the transport of mass and charge in electrochemical devices. Concentration polarisation losses at high current densities are caused by mass transport limitations and are thus a function of microstructural characteristics. As tortuosity is notoriously difficult to ascertain, a wide and diverse range of methods has been developed to extract the tortuosity of a structure. These methods differ significantly in terms of calculation approach and data preparation techniques. Here, we review tortuosity calculation procedures applied in the field of electrochemical devices to better understand the resulting values presented in the literature. Visible differences between calculation methods are observed, especially when using porosity-tortuosity relationships and when comparing geometric and flux based tortuosity calculation approaches.

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Section: Mesh Based Calculation Methodsmentioning

confidence: 99%

Tortuosity in electrochemical devices: a review of calculation approaches

Tjaden

Brett

Shearing

2016

International Materials Reviews

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202

188

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“…A preferred approach would be to use X-ray tomography to visualize the interior of the mat. 37 Porosity measurement.-Porosity, ε, of the electrospun PAN mat was calculated by measuring the mass and volume of a sample cut by a hole punch with 3/8 in. diameter.…”

Section: A2040mentioning

confidence: 99%

Evaluation of Electrospun Fibrous Mats Targeted for Use as Flow Battery Electrodes

Liu

Kok

Kim

et al. 2017

J. Electrochem. Soc.

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Electrospinning was used to create custom-made fibrous electrode materials for redox flow batteries with targeted structural properties. The aim was to increase the available surface area for electrochemical reaction without diminishing the transport properties of the electrode. Electrospinning conditions were identified that could produce fibers several times larger than those typically yielded by the technique, yet much smaller than in commercially available electrodes. These materials were subsequently carbonized using widely reported protocols. The resultant materials were subjected to a range of characterization tests to confirm that the feasibility of the target material, including surface area, pore and fiber sizes, porosity, conductivity, and permeability. The most promising material to emerge from this selection processes was then tested for electrochemical performance in a flow cell. The produced material performed markedly better than a commercially available material. Further optimizations such as improved consistency in the production and some surface activation treatments could provide significant advancements.

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“…The tortuosity is achieved by relating the heat flux through the porous phase of the sample to the heat flux through a dense sample volume of equal dimensions (Cooper et al, 2014;Trogadas et al, 2014;Brown et al, 2016a;Tjaden et al, 2016b). 2) The MATLAB application TauFactor uses an iterative over-relaxation method to solve the diffusion equation and, again, compares the flux through the porous phase to the flux through the dense volume of equal dimensions Brown et al, 2016b;Finegan et al, 2016).…”

Section: Image-based Tortuosity Calculation Approachesmentioning

confidence: 99%

Contradictory concepts in tortuosity determination in porous media in electrochemical devices

Tjaden

Finegan

Lane³

et al. 2017

Chemical Engineering Science

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Porous media are a vital component in almost every electrochemical device in the form of electrode, support or gas diffusion layers. Microstructural parameters of porous layers such as tortuosity, porosity and pore size diameter are of high importance and crucial for diffusive mass transport calculations. Among these parameters, the tortuosity remains ill-defined in the field of electrochemistry, resulting in a wide range of different calculation approaches. Here, we present a systematic approach of calculating the tortuosity of different porous samples using image and diffusion cell experimental-based methods. Image-based analyses include a selection of geometric and flux-based tortuosity calculation algorithms. Differences between the image and diffusion cell-based results are encountered and attributed to the small pore diameters and thereby induced Knudsen effects within the samples which govern the diffusion flux. Highlights Microstructural analysis of oxygen transport membrane porous supports.  Correlative tortuosity determinations via X-ray tomography and diffusion cell experiments.  Evaluation of the effect of tortuosity, porosity and sample thickness on diffusion resistance.  Visible differences between different tortuosity calculation approaches are encountered.  Diffusion cell experiments yield the highest and geometric-based image quantification algorithms result in the lowest tortuosity values.

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X-ray micro-tomography as a diagnostic tool for the electrode degradation in vanadium redox flow batteries

Cited by 76 publications

References 31 publications

Tortuosity in electrochemical devices: a review of calculation approaches

Tortuosity in electrochemical devices: a review of calculation approaches

Evaluation of Electrospun Fibrous Mats Targeted for Use as Flow Battery Electrodes

Contradictory concepts in tortuosity determination in porous media in electrochemical devices

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