Insights into the Effect of Structural Heterogeneity in Carbonized Electrospun Fibrous Mats for Flow Battery Electrodes by X‐Ray Tomography

Abstract

Electrospun custom made flow battery electrodes are imaged in 3D using X-ray computed tomography. A variety of computational methods and simulations are applied to the images to determine properties including the porosity, fiber size, and pore size distributions as well as the material permeability and flow distributions. The simulations are performed on materials before and after carbonization to determine the effect it has in the internal microstructure and material properties. It is found that the deposited fiber size is constantly changing throughout the electrospinning process. The results also show that the surfaces of the fibrous material are the most severely altered during carbonization and that the rest of the material remained intact. Pressure driven flow is modeled using the lattice Boltzmann method and excellent agreement with experimental results is found. The simulations coupled with the material analysis also demonstrate the highly heterogeneous nature of the flow. Most of the flow is concentrated to regions with high porosity while regions with low porosity shield other pores and starve them of flow. The importance of imaging these materials in 3D is highlighted throughout.

X‐ray Nano Computed Tomography of Electrospun Fibrous Mats as Flow Battery Electrodes

“…The electrospun materials were generated on a custom built electrospinner ,. The spin dope was pumped by a syringe pump through a connecting tube to a grounded needle.…”

“…Recently, the authors demonstrated the successful application of X‐ray micro‐CT to electrospun fibrous materials, producing virtual volumes of the mats for detailed computer modelling and assessment of the structural heterogeneity within the full thickness of the materials ,. The electrodes used in this study were composed of relatively large fiber sizes and displayed inhomogeneity through the thickness of the mat.…”

“…The application of tomographic images in the study of porous media has the benefit of allowing numerical simulations to be conducted directly on the actual structures represented in the images, and therefore allowing prediction of the material's performance based on its microstructural properties. For this reason, there has been a recent surge in the desire to acquire high quality X‐ray CT data of porous media ,…”

“…Nano‐ and micro‐fibers are ‘spun’ from a polymer‐containing solution onto a target with a large potential difference, typically over 10 kV. The technique has been used to generate materials for lithium‐ion battery separators, supercapacitors, fuel cells, and, recently, RFBs ,. The advantage of using electrospun fibers in these devices is that it allows for small fiber diameters, which increase the specific surface area, and with careful variation of various parameters can allow control of porosity, fiber size and alignment.…”

Comparison of Electrospun Carbon−Carbon Composite and Commercial Felt for Their Activity and Electrolyte Utilization in Vanadium Redox Flow Batteries

“…The pore network determines the morphology as a network of pores and throats where the pores act as reservoirs and the connecting throats define the transport pathways. Several groups have worked with pore network models in defining the transport through porous materials, in applications varying from fuel cell diffusion media,, PEM electrolyzers, redox flow battery electrodes, and rock structures . Banerjee et al .…”