Porous Layer Research Articles

Enhancement of electrochromic efficiency of TiO2 nanorods

In this study, the rutile TiO2 nanorods thin films were deposited via hydrothermal method on fluorine-doped tin oxide (FTO) substrate. To form a porous morphology layer, a thin film of amorphous titanium oxide (TiOx) was deposited on the TiO2 nanorods through sputtering at high pressure. The samples were annelid at 450ᵒC to transform the amorphous surface to anatase phase. Structural, optical, morphology and electrochemical properties of the samples were examined via X-ray diffraction (XRD), Raman scattering, UV–Vis NIR and photoluminescence (PL) spectroscopies, field-emission scanning electron microscopy (FE-SEM) and Potentiostat device respectively. The samples exhibited a large optical bandgap of 3.35–3.40 eV and high transparency of over 77 % at a wavelength of 555 nm. Raman analysis confirmed the formation of anatase phase on the rutile nanorods under thermal treatment. PL analysis indicated that the oxygen vacancies reached their maximum after sputtering, while the intensity of PL emission significantly increased after annealing. Investigation of the electrochromic properties revealed an increase in coloration efficiency from 2.6 C−1cm2 for bare nanorods to 10.0 C−1cm2 for nanorods after sputtering deposition, which decreased to 5.4 C−1cm2 after thermal treatment.

Attaining Substantially Enhanced Oxygen Evolution Reaction Rates on Ni Foam Catalysts in a Gas Diffusion Electrode Setup

Water electrolysis plays a central role in the transition to a fossil‐free society, but there are significant challenges to overcome in order to increase its availability on a large scale. Alkaline water electrolysis is a mature and scalable technology, although it has several disadvantages compared to electrolyzers working in acidic environments. In particular, the use of highly alkaline aqueous electrolytes can lead to corrosion, and the achieved current densities are relatively low. This study addresses the latter limitation by introducing a gas diffusion electrode (GDE) setup as a novel development tool that bridges the gap between research and practical applications in commercial devices such as fuel cells and electrolyzers. A high surface area Ni foam catalyst that can sustain exceptional oxygen evolution reaction (OER) current densities of up to 4 A cm−2 in a quasi‐steady‐state within our GDE setup operating in an alkaline environment is presented. The high performance of this Ni‐based benchmark catalyst is attributed to its deposition onto a mesh‐like porous transport layer (PTL) via hydrogen‐templated electrodeposition. This forms a porous foam‐like structure that augments the mass transport of the gaseous reactants at the GDE.

Stabilizing the Bulk-Phase and Solid Electrolyte Interphase of Silicon Microparticle Anode by Constructing Gradient-Hierarchically Ordered Conductive Networks.

The poor bulk-phase and interphase stability, attributable to adverse internal stress, impede the cycling performance of silicon microparticles (µSi) anodes and the commercial application for high-energy-density lithium-ion batteries. In this work, a groundbreaking gradient-hierarchically ordered conductive (GHOC) network structure, ingeniously engineered to enhance the stability of both bulk-phase and the solid electrolyte interphase (SEI) configurations of µSi, is proposed. Within the GHOC network architecture, two-dimensional (2D) transition metal carbides (Ti3C2Tx) act as a conductive "brick", establishing a highly conductive inner layer on µSi, while the porous outer layer, composed of one-dimensional (1D) Tempo-oxidized cellulose nanofibers (TCNF) and polyacrylic acid (PAA) macromolecule, functions akin to structural "rebar" and "concrete", effectively preserves the tightly interconnected conductive framework through multiple bonding mechanisms, including covalent and hydrogen bonds. Additionally, Ti3C2Tx enhances the development of a LiF-enriched SEI. Consequently, the µSi-MTCNF-PAA anode presents a high discharge capacity of 1413.7 mAh g-1 even after 500 cycles at 1.0 C. Moreover, a full cell, integrating LiNi0.8Mn0.1Co0.1O2 with µSi-MTCNF-PAA, exhibits a capacity retention rate of 92.0% following 50 cycles. This GHOC network structure can offer an efficacious pathway for stabilizing both the bulk-phase and interphase structure of anode materials with high volumetric strain.

Pressure evaluation in highly porous medium hydrodynamic bearings

This paper presents an experimental investigation into lift generation during the tangential motion of an inclined surface over a compressible porous layer, focusing on an exceptionally slow sliding speed, a condition that has not been considered in previous studies. Specifically, we validated Pascovici's one-dimensional lubrication model for an inclined slider under the above condition. Additionally, we explore the use of woven fibrous material for soft porous lubrication, broadening the range of media for future studies.

Optimizing of a metal foam-assisted solar air heater performance: a thermo-hydraulic analysis of porous insert placement.

A numerical assessment of the heat transfer efficacy of a solar air heater (SAH) was carried out. The SAH is supplied with a porous metal foam layer to improve thermal mixing. Both the local thermal non-equilibrium (LTNE) and Darcy-extended Forchheimer (DEF) models were employed to forecast fluid and thermal transport within the partly filled SAH channel. The analysis was performed for various values of dimensionless foam layer lengths ( ), pore densities ( ), and Reynolds numbers ( ) at a fixed value of layer thickness ( ). Based on the position of the porous layer, three distinct arrangements, marked as Case 1, Case 2, and Case 3, were explored. Regarding the parameters examined, the findings indicate a definite improvement in the average Nusselt number ( ), but unfortunately, the friction factor also increases unfavorably. By reducing the length of the porous layer, a reasonable reduction in heat transfer rate and a significant decrease in pressure drop were noticed. The results showed about 26.64%, 48.73%, and 70.74% reductions in pressure drop by reducing the dimensionless foam length from 1 to 0.25, 0.5, and 0.75 respectively for at . On the other side, there are only about 11.05%, 23.11%, and 40.78% reductions in . The exhaustive analysis of the thermal performance of SAH was conducted using the thermal performance factor (TPF), which considers the trade-off between the SAH channel's potential for improved heat transmission and its cost for pressure loss. The TPF may reach a maximum of 2.82 compared to the empty channel when the metal foam layer is inserted with , for , and .

Self-Ordered Anodic Porous Oxide Layers as a High Performance Electrocatalyst for Water Oxidation

Self-Ordered Anodic Porous Oxide Layers as a High Performance Electrocatalyst for Water Oxidation

MICROPOLAR FLUID FLOWS RELATIVE TO A SWARM OF SPHERICAL POROUS SHELLS

This article investigates the creeping axisymmetric flow of an incompressible micropolar fluid past a swarm of porous shells. Employing the Darcy and a transition Brinkman porous layer, the study presents an analytical model that captures the flow behavior by integrating continuity conditions for velocity, normal and tangential stresses, and microrotations at fluid-porous interface regions.Distinct unit cell techniques, including those proposed by Happel, Kuwabara, Kvashnin, and Mehta and Morse, are analyzed to observe the effects of hydraulic resistivity, porous layer thickness, and porosity on the dimensionless drag for a bounded micropolar fluid system. The results, graphically represented in a series of plots, reveal a complex interplay between these parameters, significantly impacting drag forces and providing insight into the hydrodynamics of a swarm of porous particles, akin to that encountered in oral drug delivery systems.The study identifies a general inverse relationship between hydraulic resistivity and drag and highlights the nuanced effects of porous layer thickness and porosity on fluid resistance, with stark contrasts observed among different unit cell models. These findings underscore the importance of the chosen unit cell technique in predicting and optimizing the flow behavior in micropolar fluid systems.

Performance evaluation of proton exchange membrane fuel cells adopting rectangular-baffle and tapered flow channels with an equivalent average depth

ABSTRACT Optimizing the flow channel structures can improve the efficiency of proton exchange membrane fuel cells and promote the efficient utilization of clean energy. This study investigates the impacts of rectangular-baffle and tapered flow channels on electrical performance, temperature distribution and mass transfer of proton exchange membrane fuel cells, based on a 3D, multi-physical model. The equivalent average depth is adopted as the reference benchmark to mitigate the influence of channel depth. Results indicate that adopting variable-depth channels enhances convective mass transfer on the porous layer surface under higher voltage. The convective mass transfer of oxygen is dominant in the activation polarization region, while diffusion is dominant in the concentration polarization region. Variable-depth channels enhance heat and mass transfer in comparison to the straight channel. The tapered channel can improve the mass transfer flux in oxygen starvation region, and the drainage ability of the rectangular baffle channel is inferior to the tapered channel. The rectangular baffle channel demonstrates better convective heat transfer performance and temperature uniformity. A rectangular-baffle channel can increase net power by 4.31%, while a tapered channel can achieve a maximum increase of 9.27% when the pumping power is considered. Therefore, incorporating a tapered channel is an optimal strategy to boost cell efficiency.

Flexible SERS substrates with gradient porous Cu structure dealloying from the thermal diffusion couples of Al/Cu stacking foils

Accurate and sensitive surface-enhanced Raman scattering (SERS) substrates are urgently demanded for the various analytic techniques. The SERS substrates with multimodal and gradient porous structure, utilized for the Rhodamine 6G (R6G) detection, have been designed and successfully fabricated from the thermal diffusion couples of Al and Cu foils via chemical dealloying. The structural inheritance of the initial microstructure of thermal diffusion couple precursors governs the formation of the final layer-by-layer gradient porous Cu with different characteristic pore sizes and morphology. An outmost surface layer of disordered lipstick-like porous structure on the SERS substrates enhances SERS effects as has been expected. The SERS activity of R6G Raman probes on gradient porous Cu is evaluated as a SERS enhancement factor of 6.63 × 1012 and limit of detection of 2.10 × 10−17 mol/L, higher than other porous SERS substrates. Meanwhile, the present SERS substrates are flexible and exhibit good bending properties due to the unreacted Cu layer as a supporting skeleton and other gradient porous Cu layers. The superior SERS performances are considered to result from the synergetic effects of the surface scattering of porous Cu rods and enhancements of the high electromagnetic fields between the small gaps between the nanopores.

Optimizing Ionomer Distribution in Anode Catalyst Layer for Stable Proton Exchange Membrane Water Electrolysis.

The high cost of proton exchange membrane water electrolysis (PEMWE) originates from the usage of precious materials, insufficient efficiency, and lifetime. In this work, an important degradation mechanism of PEMWE caused by dynamics of ionomers over time in anode catalyst layer (ACL), which is a purely mechanical degradation of microstructure, is identified. Contrary to conventional understanding that the microstructure of ACL is static, the micropores are inclined to be occupied by ionomers due to the localized swelling/creep/migration, especially near the ACL/PTL (porous transport layer) interface, where they form transport channels of reactant/product couples. Consequently, the ACL with increased ionomers at PTL/ACL interface exhibit rapid and continuous degradation. In addition, a close correlation between the microstructure of ACL and the catalyst ink is discovered. Specifically, if more ionomers migrate to the top layer of the ink, more ionomers accumulate at the ACL/PEM interface, leaving fewer ionomers at the ACL/PTL interface. Therefore, the ionomer distribution in ACL is successfully optimized, which exhibits reduced ionomers at the ACL/PTL interface and enriches ionomers at the ACL/PEM interface, reducing the decay rate by a factor of three when operated at 2.0 A cm-2 and 80°C. The findings provide a general way to achieve low-cost hydrogen production.

Engineering Robust Porous/Dense Composite Hollow Fiber Membranes for Highly Efficient Hydrogen Separation

BaZr0.7Ce0.2Y0.1O3-δ (BZCY), a perovskite-type mixed protonic and electronic conducting oxide, holds significant potential for H2 separation and purification as a membrane. The introduction of a porous modification layer as an exchange-active component offers a potential solution to enhance H2 permeability. However, achieving the desired porous/dense structure presents a notable challenge for practical implementation. In this study, various methods were developed to address sintering kinetics, encompassing both chemical aspects (e.g., interlayer reactions) and physical factors (e.g., thermal expansion), for fabricating a porous BZCY modification layer on a 4-channel BZCY hollow fiber membrane. The optimal composite hollow fiber membrane, resulting from a combination of readily sintered hollow fiber and powders for constructing the porous layers, exhibits an exceptional H2 permeation flux of 0.48 mL min-1 cm-2 at 900 °C using 50% H2/N2 as the feed gas, which represents a threefold increase compared to the performance of the bare BZCY membrane. The H2 permeation flux stabilized at 0.52 mL min-1 cm-2 for 500 h under water vapor conditions. These findings enabled us to identify the most effective approach, unlocking the full potential of surface-modified hollow fiber membranes and advancing their capabilities in H2 permeation applications.

Influence of porosity properties on natural convection heat transfer in porous square cavity

A numerical investigation was conducted to examine free convection heat transfer within a square cavity containing a fluid-saturated porous layer at the bottom under laminar flow conditions. The enclosure's left and right walls experienced heating and cooling, while the top and bottom walls remained adiabatic. The study explored the influence of the Darcy number, porosity number, and dimensionless thickness of the porous layer on heat transmission. This investigation utilized a FORTRAN computation program alongside the finite volume method, effectively solving the equations governing flow and heat exchange within porous materials through natural convection. The flow pattern is determined by the Navier–Stokes equations in the fluid region and the Darcy–Brinkman–Forchheimer formula in the porous region. The energy equation was employed to compute the thermal field. The increase in the Darcy number results in both an increase in heat transfer rate due to enhanced fluid flow through pores and an intensification of fluid flow patterns. Higher porosity leads to higher heat transfer rates due to greater fluid penetration and an increased surface area for heat exchange. The thicker porous layer reduces heat transfer rate due to increased resistance to fluid flow and decreased contact area.

Asymmetric polyamide nanofilm boosted by protonated dendrimer porous intermediate layer for Li+/Mg2+ separation

Nanofiltration membrane with fine-tuned pore structure and inner charge can achieve the efficient extraction of Li resource from Salt Lake. Herein, we synthesized three water-soluble dendrimers with 128, 256, and 512-aromatic amine groups that enable to be protonated to show positive charge. Protonated dendrimer porous intermediate layer, thus can be designed and fabricated via diazotization-coupling reaction, which imparts polyamide dense layer made by interfacial polymerization with optimized screening pore structure and decreased inner negative charge. Enhanced water/salt permeance was obtained due to the formation of nanostripe structure and thinner thickness of separation layer, as high as 360.87 kg m−2 h−1 MPa−1 for 2000 ppm LiCl. Moreover, the asymmetric polyamide nanofilm with decreased negative charge density provided 11.52 times of Li+/Mg2+ separation selectivity compared to the pristine counterparts. For example, the PSF-160A-PA membrane exhibited a Li+/Mg2+ selectivity of 45.8. Higher cut-off lines between water permeance and Li+/Mg2+ separation selectivity were achieved, while achieving higher Li purity and Li recovery was observed, which was better than some of literature-reported membranes. Such work provides a scalable strategy to fine-tune the structural feature of intermediate layer, then form defect-free polyamide nanofilm for accurate ion sieving.

A Janus, robust, biodegradable bacterial cellulose/Ti3C2Tx MXene bilayer membranes for guided bone regeneration

Guided bone regeneration (GBR) stands as an essential modality for craniomaxillofacial bone defect repair, yet challenges like mechanical weakness, inappropriate degradability, limited bioactivity, and intricate manufacturing of GBR membranes hindered the clinical efficacy. Herein, we developed a Janus bacterial cellulose(BC)/MXene membrane through a facile vacuum filtration and etching strategy. This Janus membrane displayed an asymmetric bilayer structure with interfacial compatibility, where the dense layer impeded cell invasion and the porous layer maintained stable space for osteogenesis. Incorporating BC with Ti3C2Tx MXene significantly enhanced the mechanical robustness and flexibility of the material, enabling clinical operability and lasting GBR membrane supports. It also contributed to a suitable biodegradation rate, which aligned with the long-term bone repair period. After demonstrating the desirable biocompatibility, barrier role, and osteogenic capability in vitro, the membrane's regenerative potential was also confirmed in a rat cranial defect model. The excellent bone repair performance could be attributed to the osteogenic capability of MXene nanosheets, the morphological cues of the porous layer, as well as the long-lasting, stable regeneration space provided by the GBR membrane. Thus, our work presented a facile, robust, long-lasting, and biodegradable BC/MXene GBR membrane, offering a practical solution to craniomaxillofacial bone defect repair.

Fabrication of free-standing GaN substrates using electrochemically formed porous separation layers

We have developed a pore-assisted separation (PAS) method for the fabrication of free-standing GaN substrates, where bulk GaN crystals were separated from seed GaN templates at electrochemically formed porous layers. The pore size was controlled by the electrochemical process conditions and must be greater than 100 nm to realize separation within whole wafers. A 2 inch free-standing GaN substrate having a low dislocation density of ∼2.7 × 106 cm−2 was realized by growth of an 800 μm thick GaN layer on the porous GaN template. A 3 inch free-standing GaN substrate was also fabricated by the PAS method, indicating its good scalability.

Construction of micro-tubular proton-conducting ceramic electrochemical reactor (MT-PCER) for ammonia production at atmospheric pressure

Micro-tubular ceramic electrochemical reactors have attracted significant interest due to their high packing density, large electrode specific surface area, and long triple phase boundaries (TPBs). In this work, a micro-tubular proton-conducting ceramic electrochemical reactor (MT-PCER) with a unique microstructure is facilely constructed for ammonia synthesis at atmospheric pressure. BaCe0.7Zr0.1Y0.2O3-δ (BCZY as the electrolyte)/Ni-BaCe0.7Zr0.1Y0.2O3-δ (Ni-BCZY as the catalytic cathode) dual-layer hollow fibers with open finger-like pores on the inner surface are first fabricated using a modified co-spinning/co-sintering process to form a basic MT-PCER. Fe-based catalyst was then coated into these open finger-like pores in Ni-BCZY layer as an additional catalytic cathode of the MT-PCER. The unique open finger-like pores structure of the basic MT-PCER decreases the mass transfer resistance and also provides space for loading additional catalysts, contributing towards the higher catalytic performance of the MT-PCER. However, the Faradaic efficiency for ammonia formation remained low, indicating that the cathode catalyst required further improvement. This fabrication technique provides a flexible method to adjust the cathode catalysts to optimize the catalytic performance of the MT-PCERs.

Defect-Rich porous graphitic phase carbon nitride layer grafted MXene as desolvation promoter for efficient sulfur conversion in extremely harsh conditions

Lithium-sulfur (Li-S) batteries exhibit superior theoretical capacity and energy density but are still hindered by the sluggish redox conversion kinetic of lithium polysulfides arising from the significant desolvation barrier, especially under high current density or low-temperature environments. Herein, a two-dimensional (2D) porous graphitic phase carbon nitride/MXene (CN-MX) heterostructure with intrinsic defects was designed via electrostatic adherence and in-situ thermal polycondensation. In the design, the defect-rich CN with abundant catalytic activity and porous structure could efficiently facilitate the lithium polysulfides capture, the dissociation of solvated lithium-ion (Li+), and fast Li+ diffusion. Concurrently, 2D MXene nanosheets with high electronic conductivity could act as charge transport channels and provide electrochemical active sites for sulfur redox reactions. The Li-S cells with CN-MX heterostructure modified separator demonstrated uncommon rate performance (945 mAh/g at 4.0C) and satisfactory areal capacity (5.5 mAh cm−2 at 0.2C). Most remarkably, even at 0 °C, the assembled Li-S batteries performed favorable cycle stability (91.6 % capacity retention after 100cycles at 0.5C) and outstanding rate performance (695 mAh/g at 2.0C), and superior high loading performance (5.1 mAh cm−2 at 0.1C). This work offers exciting new insights to enable Li-S batteries to operate in extreme environments.

Magnetic field effects on the thermomechanical vibration behavior of functionally graded biocompatible material sandwich nanobeams

This study focuses on modeling and analyzing the thermomechanical vibration behavior of sandwich nanobeams made from biocompatible zirconia and Ti-6Al-4V materials. The sandwich nanobeam is composed of the materials mentioned earlier, featuring a porous structure in the core layer. The sandwich nanobeam experiences significant thermal load and is subjected to a horizontal external electromagnetic field. The equations of motion for the sandwich nanobeam were derived through the application of the sinusoidal high-order shear stress theorem and the constitutive equation based on nonlocal strain gradient elasticity. The equations were converted into equations of motion using Hamilton’s principle, incorporating the thermal load and the Lorentz force generated in the electromagnetic field, and solved using the Navier method. Analyses were conducted on the thermomechanical vibration behavior of the sandwich nanoplate, taking into consideration the properties of the sandwich layers, the impact of temperature, and the intensity of the applied horizontal magnetic field. The impact of the porous core layer in the sandwich nanoplate on the porosity volume ratio and porosity distribution function in thermomechanical behavior has been established. Research has demonstrated that the application of an external magnetic field can effectively mitigate the adverse impacts of thermal loads caused by high temperatures.

High-efficient N2O decomposition over dual-phase hydrogen/oxygen-transporting membrane reactors

Nitrous oxide (N2O) emissions sourced from agricultural and industrial activities have gained much attention because of their contribution to the global greenhouse effect and ozone layer depletion. Significant efforts have been devoted to developing the cost-effective and highly efficient technologies for N2O removal. The direct N2O decomposition is limited by the thermodynamic equilibrium at high temperatures. Recently, catalytic reduction of N2O with carbon-free hydrogen derived from in situ ammonia decomposition is considered as an ideal approach. Herein, thermal decomposition of N2O is investigated by employing a BaCe0.85Fe0.15O3-δ-BaCe0.15Fe0.85O3-δ (BCF8515-BCF1585) hydrogen-transporting membrane or a Ce0.85Sm0.15O1.925-Sm0.6Sr0.4FeO3-δ (SDC-SSF) oxygen-transporting membrane respectively. It is noted that the membrane catalysis of N2O decomposition by reacting with permeated hydrogen or via in-situ oxygen removal displayed significant advantages over the direct thermal decomposition of N2O under a fixed bed condition. Moreover, the N2O conversion as well as hydrogen/oxygen permeability of such membranes were greatly improved by the introduction of porous Ni-CeO2 or SDC-NCO layers due to the increased catalytic activities and hydrogen/oxygen surface exchange kinetics.

Nonlinear stability of ES-FG porous sandwich cylindrical shells subjected to axial compression in thermal environment

Stability analysis of cylindrical shells subjected to axial compression is a common problem in engineering applications. The phenomenon of instability can easily appear with thin cylindrical shells. Therefore, to increase the load-carrying capacity of this type of structure, the cylinders are increased in thickness by adding a porous core layer and reinforcing orthogonal stiffeners. In this study, the nonlinear buckling and postbuckling behavior of functionally graded (FG) porous sandwich cylindrical shells with orthogonal eccentrically stiffeners (ES) are investigated via analytical approach. The FG porous sandwich cylindrical shells are rested on Pasternak elastic foundations and subjected to axial compression load in a thermal environment. The reinforcement of the shells is achieved through closely spaced stringers and rings, with the material properties of both the shell and stiffeners graded continuously in the thickness direction. The governing equations are derived based on the Donnell’s shell theory with von Karman geometrical nonlinearity and the smeared stiffeners technique. The Galerkin procedure is employed to ascertain the critical load and post-buckling response, employing a three-term deflection solution. The study analyzed the effects of parameters such as porosity coefficient, material, temperature, dimensional parameters, stiffener, and foundation characteristics.