Measurement of Contact Angles at Carbon Fiber–Water–Air Triple-Phase Boundaries Inside Gas Diffusion Layers Using X-ray Computed Tomography

Liu, Christopher P.; Saha, Prantik; Ying, Hai; Shimpalee, Sirivatch; Satjaritanun, Pongsarun; Zenyuk, Iryna V.

doi:10.1021/acsami.1c00849

Cited by 36 publications

(30 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Consistent with previous work, 48 we find that the contact angles measured inside the GDL are, in most cases, lower (more hydrophilic) than those determined for a droplet on the external surface, as shown in Figure 6. Here for a coating percentage of more than 20%, the external contact angle values are high and appear insensitive to the degree of coating− essentially, we are simply measuring the contact angle on PTFE alone.…”

Section: ■ Resultssupporting

confidence: 92%

“…The mode value increases with the degree of coating with noticeably higher values−indicating more strongly hydrophobic conditions−for 60% coating. The mode values and standard deviations of the distributions are in the range observed for different types of GDLs by Liu et al; 48 however they studied systems with only a 5% coating and found average contact angles above 90°, whereas for 5% coating we find an average that is around 74°.…”

Section: ■ Resultssupporting

confidence: 55%

See 1 more Smart Citation

Minimal Surfaces in Porous Materials: X-Ray Image-Based Measurement of the Contact Angle and Curvature in Gas Diffusion Layers to Design Optimal Performance of Fuel Cells

Shojaei

Bijeljic

Zhang

et al. 2022

ACS Appl. Energy Mater.

View full text Add to dashboard Cite

We inject water at a low flow rate through gas diffusion layers containing different percentages of polytetrafluoroethylene (PTFE) coating: 5, 20, 40, and 60%. We use high-resolution three-dimensional X-ray imaging to identify the arrangement of fibers, water, and air in the pore space. We also quantify the contact angle and meniscus curvature once the water has spanned the layer, flow has ceased, and water has reached a position of equilibrium. The average contact angle and water pressure at breakthrough increase with the amount of coating, although we see a wide range of contact angles with values both above and below 90°, indicating a mixed-wet state. We identify that the menisci form minimal surfaces (interfaces of zero curvature) consistent with pinned gas-water-solid contacts. Scanning electron microscopy images of the fibers show that the coated fibers have a rough surface. Between 93 and 100% of the contacts identified were found on the rough, hydrophobic, coated fibers or at the boundary between uncoated (hydrophilic) and coated (hydrophobic) regions; we hypothesize that these contacts are pinned. The one exception is the 60% PTFE layer, which shows distinctly hydrophobic properties and a negative capillary pressure (the water pressure is higher than that of air). The presence of minimal surfaces suggests that the water and gas pressures are equal, allowing water to flow readily without pressure build-up. From topological principles, the negative Gaussian curvature of the menisci implies that the fluid phases are well connected. The implication of these results is explored for the design of porous materials where the simultaneous flow of two phases occurs over a wide saturation range.

show abstract

Section: ■ Resultssupporting

confidence: 92%

Section: ■ Resultssupporting

confidence: 55%

Minimal Surfaces in Porous Materials: X-Ray Image-Based Measurement of the Contact Angle and Curvature in Gas Diffusion Layers to Design Optimal Performance of Fuel Cells

Shojaei

Bijeljic

Zhang

et al. 2022

ACS Appl. Energy Mater.

View full text Add to dashboard Cite

show abstract

Section: Introductionmentioning

confidence: 99%

Continuum Modeling of Porous Electrodes for Electrochemical Synthesis

et al. 2022

Self Cite

View full text Add to dashboard Cite

Electrochemical synthesis possesses substantial promise to utilize renewable energy sources to power the conversion of abundant feedstocks to value-added commodity chemicals and fuels. Of the potential system architectures for these processes, only systems employing 3-D structured porous electrodes have the capacity to achieve the high rates of conversion necessary for industrial scale. However, the phenomena and environments in these systems are not well understood and are challenging to probe experimentally. Fortunately, continuum modeling is well-suited to rationalize the observed behavior in electrochemical synthesis, as well as to ultimately provide recommendations for guiding the design of next-generation devices and components. In this review, we begin by presenting an historical review of modeling of porous electrode systems, with the aim of showing how past knowledge of macroscale modeling can contribute to the rising challenge of electrochemical synthesis. We then present a detailed overview of the governing physics and assumptions required to simulate porous electrode systems for electrochemical synthesis. Leveraging the developed understanding of porous-electrode theory, we survey and discuss the present literature reports on simulating multiscale phenomena in porous electrodes in order to demonstrate their relevance to understanding and improving the performance of devices for electrochemical synthesis. Lastly, we provide our perspectives regarding future directions in the development of models that can most accurately describe and predict the performance of such devices and discuss the best potential applications of future models.

show abstract

“…We utilized a method originally developed in the geological community to extract the contact angle within the GDLs at the triple-phase boundary for water–fiber–air, as shown in Figure . X-ray CT domains of GDLs and water were utilized to extract these triple-phase boundary contact lines . The externally measured contact angle by the goniometer was shown to be 20–30° higher than the internally measured contact angle with the algorithm applied to the X-ray CT data.…”

Section: Surface Wettability Measurementsmentioning

confidence: 99%

Gas Diffusion Layers: Experimental and Modeling Approach for Morphological and Transport Properties

2022

Self Cite

View full text Add to dashboard Cite

Metrics & MoreArticle Recommendations * sı Supporting Information CONSPECTUS: Electrochemical technologies are key to decarbonizing the energy sector. Electrification of the energy sector is underway with battery technologies dominating the lightduty electric vehicles market. It is more challenging to decarbonize historically difficult to decarbonize sectors, such as heavy-duty transportation, planes, ships, and the chemical manufacturing industry (ammonia, cement, steel). Green hydrogen produced via electrolysis will be used as a fuel and a feedstock in some of these processes. At the heart of the hydrogen economy are polymer electrolyte fuel cells (PEFCs), devices that convert hydrogen into electricity. Gas diffusion layers (GDLs) have an integral role in PEFCs, as they are porous carbon layers that transport reactants and products and also remove heat and conduct electricity. To improve the PEFCs' performance and reduce degradation of materials, an understanding of coupled morphological properties and transport phenomena in the GDLs is needed. In this Account, we emphasize the integration of experimental and modeling approaches to achieve complete understanding of materials and transport properties of the GDLs. Our approach builds in complexity from simpler ex situ experiments to in situ and last to 3-D integrated modeling predictions. GDL morphology is complex, as its fabrication includes several stochastic steps (immersion of GDL in various baths to achieve the desired surface wettability) and only 3-D techniques, such as X-ray computed tomography can capture morphology correctly. Porosity, pore-size distribution, tortuosity, and formation factor are the most important morphological properties of the GDLs. For PEFC applications, water is generated in the catalyst layers and is transported through the GDLs. Therefore, GDL wettability directly impacts water permeability through the GDLs. Using in situ water injection experiments, we directly observe which pores water fill at what liquid pressure. This result provides information about the GDL's affinity to intake water. GDLs are typically of mixed wettabilities, and internal wettability until recently has been unknown. Having images of water inside the GDL enabled us to track the triple-phase boundary at the fiber− water−air interface to obtain local contact angles in the locations where water was present. The percentage of contact angles that were hydrophilic correlated well to the percentage of surface oxides on the GDL surface using X-ray photoelectron spectroscopy (XPS). We envision many other groups using the method of XPS to determine internal surface wettability of the GDLs, as it is relatively fast. Heat transport and evaporation/condensation of water in the GDL is studied using in situ X-ray CT experiments. These provide direct insight into pore-scale water transport under thermal gradients. Three-dimensional geometries of GDLs are exported for transport simulations using the lattice Boltzmann method (LBM). Similarly, we advocate for building the LBM ...

show abstract

Measurement of Contact Angles at Carbon Fiber–Water–Air Triple-Phase Boundaries Inside Gas Diffusion Layers Using X-ray Computed Tomography

Cited by 36 publications

References 39 publications

Minimal Surfaces in Porous Materials: X-Ray Image-Based Measurement of the Contact Angle and Curvature in Gas Diffusion Layers to Design Optimal Performance of Fuel Cells

Minimal Surfaces in Porous Materials: X-Ray Image-Based Measurement of the Contact Angle and Curvature in Gas Diffusion Layers to Design Optimal Performance of Fuel Cells

Continuum Modeling of Porous Electrodes for Electrochemical Synthesis

Gas Diffusion Layers: Experimental and Modeling Approach for Morphological and Transport Properties

Contact Info

Product

Resources

About