Gas-diffusion-layer structural properties under compression via X-ray tomography

Obtaining structural information from tomographic images of porous materials is a critical component of porous media research. Extracting pore networks is particularly valuable since it enables pore network modeling simulations which can be useful for a host of tasks from predicting transport properties to simulating performance of entire devices. This work reports an efficient algorithm for extracting networks using only standard image analysis techniques. The algorithm was applied to several standard porous materials ranging from sandstone to fibrous mats, and in all cases agreed very well with established or known values for pore and throat sizes, capillary pressure curves, and permeability. In the case of sandstone, the present algorithm was compared to the network obtained using the current state-of-the-art algorithm, and very good agreement was achieved. Most importantly, the network extracted from an image of fibrous media correctly predicted the anisotropic permeability tensor, demonstrating the critical ability to detect key structural features. The highly efficient algorithm allows extraction on fairly large images of 500 3 voxels in just over 200 s. The ability for one algorithm to match materials as varied as sandstone with 20% porosity and fibrous media with 75% porosity is a significant advancement. The source code for this algorithm is provided.

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“…The size distributions shown in Fig. 13 are in good agreement with accepted values for similar materials [59][60][61][62].…”

Section: Fibrous Mediasupporting

confidence: 84%

Versatile and efficient pore network extraction method using marker-based watershed segmentation

2017

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“…15,17,18,[20][21][22][23][24] While such reports represent excellent engineering efforts to improve RFB power density, increases in mass transfer rates are rarely quantified, arguably due to insufficient knowledge of relevant transport processes within the specific electrode material. 14 The porous electrodes used for RFBs are typically comprised of loose cylindrical fiber beds where the porosity is ∼ 70-90%, 25 but prior electrochemical modeling efforts have described the mass transport rates in RFBs as a function of either mass transfer coefficients for packed bed reactors 18,26 or Bruggemancorrected diffusion coefficients. 27 Additionally, recent reports have suggested that flow rate dependent reactor performance improvements vary for different flow field types.…”

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confidence: 99%

Quantifying Mass Transfer Rates in Redox Flow Batteries

Milshtein

Tenny

Barton

et al. 2017

J. Electrochem. Soc.

151

176

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Engineering the electrochemical reactor of a redox flow battery (RFB) is critical to delivering sufficiently high power densities, as to achieve cost-effective, grid-scale energy storage. Cell-level resistive losses reduce RFB power density and originate from ohmic, kinetic, or mass transfer limitations. Mass transfer losses affect all RFBs and are controlled by the active species concentration, state-of-charge, electrode morphology, flow rate, electrolyte properties, and flow field design. The relationship among flow rate, flow field, and cell performance has been qualitatively investigated in prior experimental studies, but mass transfer coefficients are rarely systematically quantified. To this end, we develop a model describing one-dimensional porous electrode polarization, reducing the mathematical form to just two dimensionless parameters. We then engage a single electrolyte flow cell study, with a model iron chloride electrolyte, to experimentally measure cell polarization as a function of flow field and flow rate. The polarization model is then fit to the experimental data, extracting mass transfer coefficients for four flow fields, three active species concentrations, and five flow rates. The relationships among mass transfer coefficient, flow field, and electrolyte velocity inform engineering design choices for minimizing mass transfer resistance and offer mechanistic insight into transport phenomena in fibrous electrodes. Grid-scale energy storage has been identified as a key technology for improving sustainability in the electricity generation sector 1 by increasing the efficiency of the existing fossil fuel infrastructure, 2 alleviating intermittency of renewables (e.g., wind, solar), 3 and providing regulatory services.2 In particular, redox flow batteries (RFBs) have emerged as attractive devices for grid storage.1 In these rechargeable electrochemical cells, energy is stored and released by reducing or oxidizing electroactive species that are dissolved in liquid-phase electrolyte solutions. [4][5][6][7] The electrolytes are housed in large, inexpensive tanks and pumped through a power-converting electrochemical reactor. Within the reactor, a selective membrane, which permits transport of charge-balancing ions but blocks active species, separates two porous electrodes where the respective reduction and oxidation reactions take place. The decoupling of the electrochemical reactor and the energy storage tanks enables independently scalable power (reactor size) and energy capacity (tank size), as well as simplified manufacturing, easy maintenance, and improved safety.4-7 Designing the electrochemical reactor to deliver sufficiently high power is a critical consideration toward achieving the low battery costs required for economic viability and enabling the efficient delivery of various grid services. [8][9][10] Cell-level resistive losses in RFBs can originate from one of three areas: ohmic, charge transfer, or mass transport losses. Ohmic losses arise from the current collector, the porous electrode...

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“…For comparison the pore sizes in SGL 25AA and Toray 090 are typically greater than 30 microns. 49 Permeability coefficient.-In-plane permeability as a function of compression was measured before and after carbonization. As expected, permeability decreased with increasing compression, since porosity and open space for flow is reduced.…”

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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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Gas-diffusion-layer structural properties under compression via X-ray tomography

Cited by 237 publications

References 71 publications

Versatile and efficient pore network extraction method using marker-based watershed segmentation

Versatile and efficient pore network extraction method using marker-based watershed segmentation

Quantifying Mass Transfer Rates in Redox Flow Batteries

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

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