Search NASA⌕ Search

SEARCH · Search NASA

Results for “Porous”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Nonequilibrium Physics of Multiphase Flow in Porous Media: Wettability and Disorder

Carbon capture and geologic storage, dissociation of methane hydrates in permafrost, enhanced oil recovery, and water dropout in low-temperature fuel cells, all have something in common: two or more fluids flow simultaneously through a porous medium; and the displacement of one fluid by another is often unstable (either due to gravity or viscous forces). Yet, our ability to model multiphase flow in porous media has remained a challenge. The traditional equations are unable to predict, explain, or even reproduce, the formation of the complex patterns observed in experiments. The overarching goal of the project is to develop new physical understanding of the role of wettability and disorder in multiphase flow through permeable media, and to develop new mathematical and computational models at the pore scale and at the continuum scale.

58 GEOSCIENCES↗
DOE OSTI2022

MXene-Based Porous Monoliths

In the past decade, a thriving family of 2D nanomaterials, transition-metal carbides/nitrides (MXenes), have garnered tremendous interest due to its intriguing physical/chemical properties, structural features, and versatile functionality. Integrating these 2D nanosheets into 3D monoliths offers an exciting and powerful platform for translating their fundamental advantages into practical applications. Introducing internal pores, such as isotropic pores and aligned channels, within the monoliths can not only address the restacking of MXenes, but also afford a series of novel and, in some cases, unique structural merits to advance the utility of the MXene-based materials. Here, a brief overview of the development of MXene-based porous monoliths, in terms of the types of microstructures, is provided, focusing on the pore design and how the porous microstructure affects the application performance.

2D nanomaterials↗
DOE OSTI2024

Self-Cleaning Highly Porous TiO 2 Coating Designed by Swelling-Assisted Sequential Infiltration Synthesis (SIS) of a Block Copolymer Template

Photocatalytic self-cleaning coatings with a high surface area are important for a wide range of applications, including optical coatings, solar panels, mirrors, etc. Here, we designed a highly porous TiO 2 coating with photoinduced self-cleaning characteristics and very high hydrophilicity. This was achieved using the swelling-assisted sequential infiltration synthesis (SIS) of a block copolymer (BCP) template, which was followed by polymer removal via oxidative thermal annealing. The quartz crystal microbalance (QCM) was employed to optimize the infiltration process by estimating the mass of material infiltrated into the polymer template as a function of the number of SIS cycles. This adopted swelling-assisted SIS approach resulted in a smooth uniform TiO 2 film with an interconnected network of pores. The synthesized film exhibited good crystallinity in the anatase phase. The resulting nanoporous TiO 2 coatings were tested for their functional characteristics. Exposure to UV irradiation for 1 h induced an improvement in the hydrophilicity of coatings with wetting angle reducing to unmeasurable values upon contact with water droplets. Furthermore, their self-cleaning characteristics were tested by measuring the photocatalytic degradation of methylene blue (MB). The synthesized porous TiO 2 nanostructures displayed promising photocatalytic activity, demonstrating the degradation of approximately 92% of MB after 180 min under ultraviolet (UV) light irradiation. Thus, the level of performance was comparable to the photoactivity of commercial anatase TiO 2 nanoparticles of the same quantity. Our results highlight a new robust approach for designing hydrophilic self-cleaning coatings with controlled porosity and composition.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Facile Synthesis of Micrometer-sized Hierarchical Porous Si@C Anodes for High-Performance Lithium-Ion Batteries

Extensive studies have been conducted to determine if replacing graphite anodes with silicon is feasible since silicon possesses a high capacity and is an abundant resource; however, Si anodes suffer significant volume changes during cycling, which pulverizes its structure and subsequently causes rapid capacity fading. We used SiO2 nanoparticles (nSiO2) and low-cost coal-derived humic acid as a feedstock to synthesize high performance Si-C anodes for Li-ion Batteries through spray drying, calcination, and magnesiothermic reductions. Our Si-C anodes features micrometer-sized porous Si coated with a graphitized carbon shell (mpSi@C). The hierarchical graphitized carbon shell and porous silicon structure relieve the mechanical stress of the Si phase upon cycling, which stabilizes the structure. This mpSi@C composite design allows for a high initial discharge capacity of 2199.9 mAh g-1 at 0.1 A g-1 and a cycling performance of 68% capacity retention after 100 cycles at 1.0 A g-1. The multipoint contact between the Si anode and C structure allows for a remarkable performance rate of 566.3 mAh g-1 at 5.0 A g-1.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2020

Calculation of Hydraulic Conductivity for a Porous Medium with Staggered Array of Solid Grains - 20087

For a porous medium with periodic array of solid grains. the flow of an incompressible viscous fluid in the pore space is considered with an aim of calculating the permeability of the medium. The solid grains are of ellipsoidal shape. For this purpose, a unit-cell boundary-value problem (Stokes problem) is solved numerically. With the assumption of periodicity of the medium structure and the fluid properties (in fact constant), the flow field and pressure distributions are determined numerically with inertial effects ignored. By applying the theory of homogenization to the viscous flow through pore space, a microscale boundary-value problem is defined. After solving the problem, the permeability is determined by taking the micro-cell average of the velocity components, Various porous structures are chosen to allow a wide range of porosity values. The permeability increases mildly for porosity values in the lower range. But it increases sharply for porosity values in the upper range of the porosity. The permeability of the present study agrees with the Kozeny-Carman relation excellently for smaller porosity. Certain discrepancy between the calculated permeability in this study and the Kozeny-Carman relation appears and increases with porosity for larger porosity. It is believed that the discrepancy is due to the replacement of the pores by a bundle of capillaries, which is unrealistic, in the Kozeny-Carman relation. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Direct Chemical Vapor Deposition Synthesis of Porous Single-Layer Graphene Membranes with High Gas Permeances and Selectivities

Single-layer graphene containing molecular-sized in-plane pores is regarded as a promising membrane material for high-performance gas separations due to its atomic thickness and low gas transport resistance. However, typical etching-based pore generation methods cannot decouple pore nucleation and pore growth, resulting in a trade-off between high areal pore density and high selectivity. In contrast, intrinsic pores in graphene formed during chemical vapor deposition are not created by etching. Therefore, intrinsically porous graphene can exhibit high pore density while maintaining its gas selectivity. Here in this work, the density of intrinsic graphene pores is systematically controlled for the first time, while appropriate pore sizes for gas sieving are precisely maintained. As a result, single-layer graphene membranes with the highest H 2 /CH 4 separation performances recorded to date (H 2 permeance > 4000 GPU and H 2 /CH 4 selectivity > 2000) are fabricated by manipulating growth temperature, precursor concentration, and non-covalent decoration of the graphene surface. Moreover, it is identified that nanoscale molecular fouling of the graphene surface during gas separation where graphene pores are partially blocked by hydrocarbon contaminants under experimental conditions, controls both selectivity and temperature dependent permeance. Overall, the direct synthesis of porous single-layer graphene exploits its tremendous potential as high-performance gas-sieving membranes.

chemical vapor deposition↗
DOE OSTI2025

High‐Performance Rechargeable Lithium‐Chlorine Batteries with ALD Conformal Starburst Porous Graphene Positive Electrodes

Abstract Rechargeable alkali metal‐chlorine batteries are emerging as a promising high‐energy‐density solution. However, they confront significant challenges, including the primary issue stemming from the weak binding affinity of cathode materials for Cl 2 , which leads to a sluggish and inadequate supply of Cl 2 during the redox reactions, resulting in a shortened cycle life and low Coulombic efficiency (CE), particularly when operating at ultrahigh specific capacity outputs. Herein, an Al 2 O 3 ‐skinned heterostructured starburst porous graphene with conformal metasurfaces (Al 2 O 3 @rGO) is reported, crafted from a hierarchical porous starburst graphene arranged in a unique layered structure by the PTFE microemulsion skin effect, leveraging subsequent fluidized bed atomic layer deposition (FBALD) of Al 2 O 3 groups. Al 2 O 3 @rGO features superhydrophilicity, effective adsorption, fast kinetics from stable dynamic respiratory interface, high electrical and thermal conductivity anisotropy, intelligent thermal management and safe operation over a wide temperature range. Consequently, the Li‐Cl 2 @Al 2 O 3 @rGO battery achieves an ultrahigh discharge specific capacity of 5000 mAh g −1 at ≈100% CE, and even delivers stable cycling over 200 cycles with 2000 mAh g −1 at an average CE of 99.8% under low temperature environment of ‐40 °C. The scalable heterostructure approach offers a sustainable perspective of the development of functionalized metamaterials and metasurfaces for next‐generation safe and energy‐dense batteries and broader applications.

Chemistry↗
DOE OSTI2026

Hybrid Ionomer-Free Porous Transport Electrodes With Catalyst Coated Membranes for Enhanced Water Electrolysis

To promote industrial uptake of clean hydrogen production technologies such as polymer electrolyte membrane (PEM) water electrolyzers, advancements in catalyst layer (CL) morphology are required. We demonstrate how improved electrochemical performance can be achieved when using an ionomer free porous transport electrode (PTE) coupled with a traditional catalyst coated membrane (CCM) assembly in PEM water electrolyzers. Notably, we reveal that the superior performance achieved when utilizing a hybrid PTE and CCM assembly is due to enhanced ohmic performance caused by optimal contact with both the porous transport layer (PTL) and PEM interfaces. Using operando neutron radiography, we demonstrate that configurations utilizing a CCM resulted in more rapid water replenishment to reaction sites, indicating enhanced membrane hydration beneficial for performance. This enhanced membrane hydration coupled with improved contact area at the PEM-catalyst layer (CL) and PTL-CL interfaces was revealed through the reduced ohmic overpotentials of the hybrid PTE-CCM design, which achieved the lowest ohmic overpotential of 431 mV at 2000 mA cm−2. While the average in-plane water distributions are generally similar between cell configurations, we reveal that utilizing a PTE configuration promotes a more homogenous water distribution near the CL-membrane interface due to enhanced catalyst utilization.

Seip, Tess [ORNL] (ORCID:0000000232740594)↗
DOE OSTI2020

A Three‐Dimensional Porous Organic Semiconductor Based on Fully sp 2 ‐Hybridized Graphitic Polymer

Abstract Dimensionality plays an important role in the charge transport properties of organic semiconductors. Although three‐dimensional semiconductors, such as Si, are common in inorganic materials, imparting electrical conductivity to covalent three‐dimensional organic polymers is challenging. Now, the synthesis of a three‐dimensional π‐conjugated porous organic polymer (3D p‐POP) using catalyst‐free Diels–Alder cycloaddition polymerization followed by acid‐promoted aromatization is presented. With a surface area of 801 m 2 g −1 , full conjugation throughout the carbon backbone, and an electrical conductivity of 6(2)×10 −4 S cm −1 upon treatment with I 2 vapor, the 3D p‐POP is the first member of a new class of permanently porous 3D organic semiconductors.

Byun, Yearin↗
DOE OSTI2021

Dual‐Ion Intercalation and High Volumetric Capacitance in a Two‐Dimensional Non‐Porous Coordination Polymer

Abstract Intercalation is a promising ion‐sorption mechanism for enhancing the energy density of electrochemical capacitors (ECs) because it offers enhanced access to the electrochemical surface area. It requires a rapid transport of ions in and out of a host material, and it must occur without phase transformations. Materials that fulfil these requirements are rare; those that do intercalate almost exclusively cations. Herein, we show that Ni 3 (benzenehexathiol) (Ni 3 BHT), a non‐porous two‐dimensional (2D) layered coordination polymer (CP), intercalates both cations and anions with a variety of charges. Whereas cation intercalation is pseudocapacitive, anions intercalate in a purely capacitive fashion. The excellent EC performance of Ni 3 BHT provides a general basis for investigating similar dual‐ion intercalation mechanisms in the large family of non‐porous 2D CPs.

Banda, Harish↗
DOE OSTI2023

Porous Materials for Water Purification

Abstract Water pollution is a growing threat to humanity due to the pervasiveness of contaminants in water bodies. Significant efforts have been made to separate these hazardous components to purify polluted water through various methods. However, conventional remediation methods suffer from limitations such as low uptake capacity or selectivity, and current water quality standards cannot be met. Recently, advanced porous materials (APMs) have shown promise in improved segregation of contaminants compared to traditional porous materials in uptake capacity and selectivity. These materials feature merits of high surface area and versatile functionality, rendering them ideal platforms for the design of novel adsorbents. This Review summarizes the development and employment of APMs in a variety of water treatments accompanied by assessments of task‐specific adsorption performance. Finally, we discuss our perspectives on future opportunities for APMs in water purification.

Song, Yanpei↗
DOE OSTI2025

Sub‐5 Ångstrom Porosity Tuning in Calixarene‐Derived Porous Liquids via Supramolecular Complexation Construction

Abstract Sub‐Ångstrom‐level porosity engineering, which is appealing in gas separations, has been demonstrated in solid carbon, polymer, and framework materials but rarely achieved in the liquid phase. In this work, a gas molecular sieving effect in the liquid phase at sub‐5 Ångstrom scale is created via sophisticated porosity tuning in calixarene‐derived porous liquids (PLs). Type II PLs are constructed via supramolecular complexation between the sodium salts of calixarene derivatives and crown ether solvents. The chemical structure variation and assembly behavior of the porous host upon PL construction are monitored by spectroscopy‐, X‐ray‐, and neutron‐scattering techniques. The presence of permanent porosity in calixarene‐derived PLs is verified by pressure swing gas uptake, altered CO 2 physisorption behavior, and molecular simulations. Sub‐5 Ångstrom porosity tuning within the PL phase is achieved by introducing bulky substituted groups on the benzene ring of the calixarene host, which then greatly affects the dynamic motion and transport behavior of CO 2 molecules and the Xe uptake performance. The approach being demonstrated in this work represents a promising pathway to tune and leverage the porosity effect for enhanced gas uptake capacity and selectivity in liquid sorbents.

Li, Errui [Department of Chemistry University of T↗
DOE OSTI2021

Dual-Ion Intercalation and High Volumetric Capacitance in a Two-Dimensional Non-Porous Coordination Polymer

Intercalation is a promising ion-sorption mechanism for enhancing the energy density of electrochemical capacitors (ECs) because it offers enhanced access to the electrochemical surface area. It requires a rapid transport of ions in and out of a host material, and it must occur without phase transformations. Materials that fulfil these requirements are rare; those that do intercalate almost exclusively cations. Herein, we show that Ni3(benzenehexathiol) (Ni 3 BHT), a non-porous two-dimensional (2D) layered coordination polymer (CP), intercalates both cations and anions with a variety of charges. Whereas cation intercalation is pseudocapacitive, anions intercalate in a purely capacitive fashion. The excellent EC performance of Ni3BHT provides a general basis for investigating similar dual-ion intercalation mechanisms in the large family of non-porous 2D CPs.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Discretization limits of lattice‐Boltzmann methods for studying immiscible two‐phase flow in porous media

Summary Digital images of porous media often include features approaching the image resolution length scale. The behavior of numerical methods at low resolution is therefore important even for well‐resolved systems. We study the behavior of the Shan‐Chen (SC) and Rothman‐Keller (RK) multicomponent lattice‐Boltzmann models in situations where the fluid‐fluid interfacial radius of curvature and/or the feature size of the medium approaches the discrete unit size of the computational grid. Various simple, small‐scale test geometries are considered, and a drainage test is also performed in a Bentheimer sandstone sample. We find that both RK and SC models show very high ultimate limits: in ideal conditions the models can simulate static fluid configuration with acceptable accuracy in tubes as small as three lattice units across for RK model (six lattice units for SC model) and with an interfacial radius of curvature of two lattice units for RK and SC models. However, the stability of the models is affected when operating in these extreme discrete limits: in certain circumstances the models exhibit behaviors ranging from loss of accuracy to numerical instability. We discuss the circumstances where these behaviors occur and the ramifications for larger‐scale fluid displacement simulations in porous media, along with strategies to mitigate the most severe effects. Overall we find that the RK model, with modern enhancements, exhibits fewer instabilities and is more suitable for systems of low fluid‐fluid miscibility. The shortcomings of the SC model seem to arise predominantly from the high, strongly pressure‐dependent miscibility of the two fluid components.

Li, Zhe↗
DOE OSTI2026

Machine learning insights into microstructural origins of transport and mechanical properties in porous microstructures

Multifunctional porous materials are increasingly needed across various fields, but their complex microstructures create significant challenges due to the intricate microstructure-property relationships. This complexity, combined with limitations of traditional analysis methods, hinders efforts to understand and optimize microstructure–property relationships. Here, to address this, we integrate physics-based mesoscale modeling with interpretable machine learning (ML) to uncover how microstructural features govern effective diffusivity and elastic modulus. At constant porosity, we show diffusivity varies by over 150 × and modulus by ∼50 ×, highlighting the power of microstructure engineering. Statistical analysis reveals bimodal behavior in diffusivity and unimodal in modulus. ML identifies connectivity as the dominant factor, while modulus is also sensitive to domain size and feature interactions. Controlled simulations further highlight domain shape as a critical feature for modulus. This framework enables efficient exploration of microstructure-property correlations, offering new insights to guide the design of advanced porous materials.

Bicontinuous microstructure↗
DOE OSTI2020

Verification benchmarks for single-phase flow in three-dimensional fractured porous media

Flow in fractured porous media occurs in the earth’s subsurface, in biological tissues, and in man-made materials. Fractures have a dominating influence on flow processes, and the last decade has seen an extensive development of models and numerical methods that explicitly account for their presence. To support these developments, four benchmark cases for single-phase flow in three-dimensional fractured porous media are presented. Furthermore, the cases are specifically designed to test the methods’ capabilities in handling various complexities common to the geometrical structures of fracture networks. Based on an open call for participation, results obtained with 17 numerical methods were collected. This paper presents the underlying mathematical model, an overview of the features of the participating numerical methods, and their performance in solving the benchmark cases.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

Non-intrusive reduced order modeling of natural convection in porous media using convolutional autoencoders: Comparison with linear subspace techniques

Natural convection in porous media is a highly nonlinear multiphysical problem relevant to many engineering applications (e.g., the process of CO 2 sequestration). Here, we extend and present a non-intrusive reduced order model of natural convection in porous media employing deep convolutional autoencoders for the compression and reconstruction and either radial basis function (RBF) interpolation or artificial neural networks (ANNs) for mapping parameters of partial differential equations (PDEs) on the corresponding nonlinear manifolds. To benchmark our approach, we also describe linear compression and reconstruction processes relying on proper orthogonal decomposition (POD) and ANNs. Further, we present comprehensive comparisons among different models through three benchmark problems. The reduced order models, linear and nonlinear approaches, are much faster than the finite element model, obtaining a maximum speed-up of 7 × 10 6 because our framework is not bound by the Courant–Friedrichs–Lewy condition; hence, it could deliver quantities of interest at any given time contrary to the finite element model. Our model’s accuracy still lies within a relative error of 7% in the worst-case scenario. We illustrate that, in specific settings, the nonlinear approach outperforms its linear counterpart and vice versa. We hypothesize that a visual comparison between principal component analysis (PCA) and t-Distributed Stochastic Neighbor Embedding (t-SNE) could indicate which method will perform better prior to employing any specific compression strategy.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Self-grown NiCuO x hybrids on a porous NiCuC substrate as an HER cathode in alkaline solution

Electrocatalysts converted directly from the substrates hold the key to achieve high catalytic activity and durability due to their high bonding strength, intimate electronic contact, and tunable phase composition. Herein, an electrically conductive porous NiCuC substrate was adopted to develop a multi-porous NiCuO x /NiCuC hydrogen evolution reaction (HER) catalyst using a one-step oxidation method in this research. The NiCuO x hybrids were characterized as three typical layers: an outer layer with NiCuO 2 solid solution phase, a partially oxidized intermediate layer, and an inner layer with limited stable oxygen content. Here, the NiCuO x /NiCuC possesses abundant Ni(II)–Cu(II) sites to accelerate the Volmer step via the electrostatic effect with OH – , numerous metallic NiCu sites to facilitate the H adsorption, and highly accessible channels to promote the Heyrovsky step during HER catalysis. As a result, high electrocatalytic performance was obtained with an overpotential of 116 mV at a current density of 10 mA cm –2 in 1.0 M potassium hydroxide, and a stable catalytic performance during the HER process for more than 24 h.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗