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1. Additive Manufacturing of Tailored Macroporous Ceramic Structures for High‐Temperature Applications

   https://doi.org/10.1002/adem.202000158  

   Sobhani, Sadaf; Allan, Shawn; Muhunthan, Priyanka; Boigne, Emeric; Ihme, Matthias (May 2020, Advanced Engineering Materials)

   Macroporous ceramic materials are ubiquitous in numerous energy‐conversion and thermal‐management systems. The morphology and material composition influence the effective thermophysical properties of macroporous ceramic structures and interphase transport in interactions with the working fluid. Therefore, tailoring these properties can enable significant performance enhancements by modulating thermal transport, reactivity, and stability. However, conventional ceramic‐matrix fabrication techniques limit the ability for tailoring the porous structure and optimizing the performance of these systems, such as by introducing anisotropic morphologies, pore‐size gradations, and variations in pore connectivity and material properties. Herein, an integrated framework is proposed for enabling the design, optimization, and fabrication of tailored ceramic porous structures by combining computational modeling, mathematically defined surfaces, and lithography‐based additive manufacturing. The benefits of pore‐structure tailoring are illustrated experimentally for interstitial combustion in a porous‐media burner operating with a smoothly graded matrix structure. In addition, a remarkable range of achievable thermal conductivities for a single material is demonstrated with tuning of the fabrication process, thus providing unique opportunities for modulating thermal transport properties of porous‐ceramic structures. 

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2. Augmenting X-ray micro-CT data with MICP data for high resolution pore-scale simulations of flow properties of carbonate rocks

   https://doi.org/10.1016/j.geoen.2024.212982  

   Ishola, Olubukola; Vilcáez, Javier (August 2024, Geoenergy Science and Engineering)

   Pore-scale modeling is essential in understanding and predicting flow and transport properties of rocks. Generally, pore-scale modeling is dependent on imaging technologies such as Micro Computed Tomography (micro-CT), which provides visual confirmation into the pore microstructures of rocks at a representative scale. However, this technique is limited in the ability to provide high resolution images showing the pore-throats connecting pore bodies. Pore scale simulations of flow and transport properties of rocks are generally done on a single 3D pore microstructure image. As such, the simulated properties are only representative of the simulated pore-scale rock volume. These are the technological and computational limitations which we address here by using a stochastic pore-scale simulation approach. This approach consists of constructing hundreds of 3D pore microstructures of the same pore size distribution and overall porosity but different pore connectivity. The construction of the 3D pore microstructures incorporates the use of Mercury Injection Capillary Pressure (MICP) data to account for pore throat size distribution, and micro-CT images to account for pore body size distribution. The approach requires a small micro-CT image volume (7–19 mm3) to reveal key pore microstructural features that control flow and transport properties of highly heterogeneous rocks at the core-scale. Four carbonate rock samples were used to test the proposed approach. Permeability calculations from the introduced approach were validated by comparing laboratory measured permeability of rock cores and permeability estimated using five well-known core-scale empirical model equations. The results show that accounting for the stochastic connectivity of pores results in a probabilistic distribution of flow properties which can be used to upscale pore-scale simulated flow properties to the core-scale. The use of the introduced stochastic pore-scale simulation approach is more beneficial when there is a higher degree of heterogeneity in pore size distribution. This is shown to be the case with permeability and hydraulic tortuosity which are key controls of flow and transport processes in rocks. 

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3. Continuum to rarefied diffusive tortuosity factors in porous media from X-ray microtomography

   https://doi.org/10.1016/j.commatsci.2021.111030  

   Ferguson, Joseph C; Borner, Arnaud; Panerai, Francesco; Close, Sigrid; Mansour, Nagi N (February 2022, Computational Materials Science)

   The diffusive tortuosity factor of a porous media quantifies the material’s resistance to diffusion, an important component of modeling flows in porous structures at the macroscale. Advances in X-ray micro-computed tomography (-CT) imaging provide the geometry of the material at the microscale (microstructure) thus enabling direct numerical simulation (DNS) of transport at the microscale. The data from these DNS are then used to close material’s macroscale transport models, which rely on effective material properties. In this work, we present numerical methods suitable for large scale simulations of diffusive transport through complex microstructures for the full range of Knudsen regimes. These numerical methods include a finite-volume method for continuum conditions, a random walk method for all regimes from continuum to rarefied, and the direct simulation Monte Carlo method. We show that for particle methods, the surface representation significantly affects the accuracy of the simulation for high Knudsen numbers, but not for continuum conditions. We discuss the upscaling of pore-resolved simulations to single species and multi-species volume-averaged models. Finally, diffusive tortuosities of a fibrous material are computed by applying the discussed numerical methods to 3D images of the actual microstructure obtained from X-ray computed micro-tomography. 

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4. A comparative study of porous and hollow carbon nanofibrous structures from electrospinning for supercapacitor electrode material development

   https://doi.org/10.1016/j.surfin.2021.101386  

   K Asare, MF Hasan (August 2021, Surfaces and interfaces)

   Co-axial electrospinning is an efficient technique to develop core-shell or hollow nanofibrous structures. In this study electrospun carbon nanofibers with three different morphologies, i.e. solid nanofibers with porous structure (P-ECNF), hollow nanofibers with solid wall (H-ECNF), and hollow nanofibers with porous wall (HP-ECNF) were developed through bicomponent electrospinning and co-axial electrospinning of polyacrylonitrile (PAN) and poly (methyl methacrylate) (PMMA) by varying proportion of the sacrificial PMMA. Through comparative electrochemical analyses, it is revealed that the primary factors for electrochemical performance, i.e. specific capacitance, of the electrospun carbon nanofibrous materials are mesopore volume and total pore volume. The hollow structure as well as ordered carbon structure and intact fiber structure also benefits electrolyte transfer and subsequent electrochemical performance but is secondary. Overall the porous carbon nanofibrous electrode material from electrospinning PAN/PMMA (50/50) solution (P-ECNF-50-50) outperformed those hollow and hollow-porous counterparts from co-axial electrospinning and demonstrated the largest specific capacitance due to the largest mesopore volume as well as the largest total pore volume. This electrode material also showed excellent cycling stability (without any loss of specific capacitance) after 3,000 cycles of charging and discharging. It even showed some increase of specific capacitance with cycling test due to its relatively large amount of micropores. 

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5. Ultrahigh capacity 2D anode materials for lithium/sodium-ion batteries: an entirely planar B ₇ P ₂ monolayer with suitable pore size and distribution

   https://doi.org/10.1039/D0TA02767G  

   Zhu, Changyan; Lin, Shiru; Zhang, Min; Li, Quan; Su, Zhongmin; Chen, Zhongfang (May 2020, Journal of Materials Chemistry A)

   Lithium-ion batteries (LIBs) are widely used energy storage devices, and sodium-ion batteries (SIBs) are promising alternatives to LIBs because sodium is of high abundance and low toxicity. However, a dominant obstacle for the advancement of LIBs and SIBs is the lack of high capacity anode materials, especially for SIBs. Here, we propose that three characteristics, namely appropriate pore size, suitable pore distribution, and an entirely planar topology, can help achieve ultrahigh capacity 2D anode materials. Under such guidelines, we constructed a B 7 P 2 monolayer, and investigated its potential as a LIB/SIB anode material by means of density functional theory (DFT) computations. Encouragingly, the B 7 P 2 monolayer possesses all the essential properties of a high-capacity LIB/SIB anode: its high stability ensures the experimental feasibility of synthesis, its metallicity does not change upon Li/Na adsorption and desorption, the Li/Na can well diffuse on the surface, and the open-circuit voltage is in a good range. Most importantly, the B 7 P 2 monolayer has a high storage capacity of 3117 mA h g −1 for both LIBs and SIBs, and this capacity value ranks among the highest for 2D SIB anode materials. This study offers us some good clues to design/discover other anode materials with ultrahigh capacities, and serves us another vivid example that (implicit and hidden) trends/rules in the literature can guide us in the design of functional materials more efficiently. 

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