Thin Porous Layer Research Articles

Ru/Ce/Ni Metal Foams as Structured Catalysts for the Methanation of CO2

The development of highly conductive structured catalysts with enhanced mass- and heat-transfer features is required for the intensification of the strongly exothermic catalytic hydrogenation of CO2 in which large temperature gradients should be avoided to prevent catalyst deactivation and to control selectivity. Therefore, in this work we set out to investigate the preparation of novel structured catalysts obtained from a commercial open cell Ni foam with high pore density (75 ppi) onto which a CeO2 layer was deposited via electroprecipitation, and, eventually, Ru was added by impregnation. Composite Ru/Ce/Ni foam catalysts, as well as simpler binary Ru/Ni and Ce/Ni catalysts were characterized by SEM-EDX, XRD, cyclic voltammetry, N2 physisorption, H2-temperature programmed reduction (TPR), and their CO2 methanation activity was assessed at atmospheric pressure in a fixed bed flow reactor via temperature programmed tests in the range from 200 to 450 °C. Thin porous CeO2 layers, uniformly deposited on the struts of the Ni foams, produced active catalytic sites for the hydrogenation of CO2 at the interface between the metal and the oxide. The methanation activity was further boosted by the dispersion of Ru within the pores of the CeO2 layer, whereas the direct deposition of Ru on Ni, by either impregnation or pulsed electrodeposition methods, was much less effective.

Engineering iron phosphide-on-plasmonic Ag/Au-nanoshells as an efficient cathode catalyst in water splitting for hydrogen production

Constructing highly active electrocatalysts for hydrogen evolution reaction (HER) have drawn considerable attention recently. However, how to design nanostructured electrocatalysts with enhanced catalytic performances is still a challenge. Herein, plasmonic Ag/Au hollow porous nanoshells decorated with porous Fe2P thin layers (denoted as Ag/Au-HPNSs@PFP) are fabricated, in which porous Fe2P (PFP) thin layers are derived from pyrolysis and phosphidation of MIL-100(Fe) coated on plasmonic Ag/Au hollow porous nanoshells (Ag/Au-HPNSs) and the high porosity of the HER-active Fe2P, along with plasmonic enhancement of the Ag/Au hollow porous nanoshells, facilitates hydrogen evolution and electron transport, and accordingly boosts the electrocatalytic HER performance. When applied as a HER electrode, the hybrid electrocatalyst displays an onset overpotential of only 108 mV, satisfactory stability, and enhanced performance for hydrogen evolution under visible light, ascribing to electron interactions between Fe and P and synergistic effects of porous Fe2P and plasmonic Au/Ag hollow porous nanoshells.

Progress in bio-inspired porous membranes

Porous membranes are one of the research hotspots in the domain of separation materials and have been widely utilized in various fields (such as water treatment, energy, biological medicine) due to their high separation efficiency, low cost, and non-secondary pollution, etc. However, there still exist many challenges in their application process, such as low selectivity, poor anti-fouling, poor responsive, critically limiting its development. Recently, bio-inspired porous membranes offer a brand-new idea for solving those problems and are becoming one of the most exciting research areas in porous membranes field. Compared with traditional porous membranes, bio-inspired porous membranes, designed by imitating the unique pore structure and separation performance of biological membranes, display distinct advantages in selectivity performance, antifouling property, intelligent gating property, and intelligent response property. This critical review detailedly presents the recent developments of bio-inspired porous membranes with multi-scale pore structure. In this paper, the first section mainly gives a brief introduction to the pore structure, separation selectivity, and response property of both nano-scale biological membranes and micro-scale biological membranes. Among numerous nano-scale biological membranes, the most concerning to date include cell membrane with ion channel, cell membrane with aquaporin, and glomerular filtration membrane. Ion channel embedded within cell membrane provides ion selectivity, ion current rectification, and ion gating characteristics to cell membrane. Inspired by this, novel porous membranes with excellent ion selectivity are developed for regulating ion permeation. Meanwhile, aquaporin can let the passive transport of water across cell membrane while simultaneously excluding ions, offering a new strategy for designing bio-inspired porous membrane for high efficiency desalination. Glomerular filtration membrane with the nano-scale pore can prevent the filtration of blood cells and platelets, and removes most of nano-scale molecules from the blood. Inspired by its unique filtration property, various bio-inspired porous membranes have been designed for clinical kidney replacement treatment. Additionally, the micro-scale porous membranes in nature mainly contain alveolar membrane with intelligent gating property and leaf stomata membrane with intelligent response property. By imitating the alveolar membrane, liquid gating porous membranes with intelligent gating property are developed, achieving for controlling the movement of fluids, vapours, and solids. Learning from leaf stomata membrane, intelligent responsive porous membranes are also designed, and can be applied in controllable transmission. For preparing the high performance of bio-inspired porous membranes, the designed strategies are also introduced in detail. The second section has further outlined the applications of bio-inspired porous membranes in water treatment, energy, biological medicine, and substance detection. In water treatment field, aquaporin-based bio-inspired porous membrane possesses better desalination performance than traditional porous membrane. In energy field, bio-inspired porous membranes offer unique ions selectivity and ions transport, thus enhancing energy conversion efficiency in salinity gradient energy capture. In biological medicine field, alveolar-like liquid gating composite membranes can be utilized for fabricating artificial blood vessel with anticoagulation and drug release properties. Moreover, bio-inspired porous membranes with porous support and thin separation layer are demonstrated as hemodialysis membranes for the treatment of kidney disease. In substance detection, visual and low power consuming chemical detection of specific analytes can be achieved by liquid gating composite membrane. In the last section, future challenges in theory, preparation technology, and application of bio-inspired porous membrane are presented, providing an overview of the various solutions. Ultimately, continued efforts to relative research and materials development will promote the rapid development of bio-inspired porous membrane.

Silica deposition treatment of 2024 aluminum alloy for improved coating adhesion

Silica deposition treatment (trade name: ITRO treatment) is a flame treatment process to form silica deposition on treated surfaces, and could be an innovative, rapid, automated, and clean alternative to reduce costs and hazardous chemicals for aircraft coatings. In this study, the bonding state and adhesion strength of aircraft coatings on an aluminum alloy following silica deposition treatment were evaluated. The chemical structure of the treated surface was examined using scanning electron microscopy and Fourier-transform infrared spectroscopy. The silica deposit consisted of aggregated nanoparticles and contained silica, silanol groups, and water. The amount of silica and silanol groups increased linearly with the number of treatments. The adhesion performance of the coating following the silica deposition treatment using pull-off testing revealed that one-time silica deposition treatment resulted in a high strength comparable to that achieved by anodizing treatments. Flame treatment without organosilicon compounds resulted in low adhesion strength, indicating that the presence of the silica deposit contributes to improving the adhesion strength. Cross-sectional observation of the coated substrate interface revealed that the aggregated nanoparticles formed a thin porous layer of several micrometers. The coating resin completely penetrated this layer, and mechanical interlocking between the silica deposit layer and coating resin was presumed to arise. The fracture surfaces from the pull-off tests revealed that fracture propagated within the silica deposit layer and that part of the silica deposit and coating resin adhered to the silica deposit remained on the substrates. It could thus be concluded that the silica deposit layer was the weakest link in the coated test pieces.

Plasma Nitriding of Hard Chromium Electroplated Low Alloy AISI 4340 Steel in Pure Nitrogen Gas Atmosphere

Duplex treatments are surface modification techniques used to enhance the surface properties of steels. In this study, hard chromium electroplated AISI 4340 steel was plasma nitrided in pure nitrogen gas at 600°C for 90 min. The structural and morphological properties were analysed by an X-ray diffractometer and a scanning electron microscope (SEM), respectively. The hardness profile was obtained by a multicycle nanoindentation test and the tribological properties by a ball-on-disk test at room temperature. The results showed that the duplex layer was composed mainly of Cr2N and it had a rough surface morphology with a network of micro-cracks. The highest values of hardness were registered in the nitrogen diffusion layer beneath the outer porous thin layer. The friction coefficient and the specific wear rate after plasma nitriding were reduced by 3 and 5 factors, respectively.

Modeling Single and Two-Phase Transport in Thin Porous Layers Using a Composite Continuum-Pore Network Formulation

In this work, a composite continuum-pore network formulation is presented to model single and two-phase transport thin porous layers, such as gas diffusion layers in polymer electrolyte fuel cells (PEFCs) and active electrodes in redox flow batteries (RFBs). The formulation can be integrated into CFD codes, thus combining the ease of implementation of continuum-based modeling and the computational power of pore-network modeling. The composite model includes a control volume (CV) mesh at the layer scale, which embeds a cubic pore network [1,2]. The pore-network model is used to determine analytically local anisotropic effective transport properties (local effective diffusivity and permeability), which are mapped onto the CV mesh to simulate transport in the porous transport layer [3,4]. Good agreement is found between the predicted global effective transport properties (global effective diffusivity and permeability) under dry and wet conditions and previous experimental data reported in the literature for Toray TGP-H series carbon paper. Water saturation distributions are also compared with results obtained using X-ray computed tomography [4].[1] P.A. García-Salaberri, I.V. Zenyuk, J.T. Gostick, A.Z. Weber, Modeling Gas Diffusion Layer in Polymer Electrolyte Fuel Cells Using a Continuum-Based Pore-Network Formulation, ECS Trans. 97 (2020) 615.[2] P.A. García-Salaberri, Modeling diffusion and convection in thin porous transport layers using a composite continuum-network model: Application to gas diffusion layers in polymer electrolyte fuel cells, Int J. Heat Mass Transf. (2020), submitted.[3] P.A. García-Salaberri, J.T. Gostick, G. Hwang, A.Z. Weber, M. Vera, Effective diffusivity in partially-saturated carbon-fiber gas diffusion layers: Effect of local saturation and application to macroscopic continuum models, J. Power Sources 296 (2015) 440–453.[4] P.A. García-Salaberri, G. Hwang, M. Vera, A.Z. Weber, J.T. Gostick, Effective diffusivity in partially-saturated carbon-fiber gas diffusion layers: Effect of through-plane saturation distribution, Int. J. Heat Mass Transf. 86 (2015) 319–333.

(Invited) Promising Methods for Overcoming Trade-Offs Among Catalytic Activity, Durability, and Power Density By Controlling Pt/Ionomer Interfaces

For improving the efficiency and reducing Pt use in polymer electrolyte fuel cells, it is essential to improve the catalytic activity per Pt mass for oxygen reduction reaction (ORR) in the cathode. In addition, recent studies have demonstrated that a high surface area of the catalyst per Pt mass is necessary for reducing the oxygen transport resistance in the catalyst layer. Alloying inner cores of nanoparticles by introducing base metals and reducing particle sizes are established methods to increase the mass activity and the surface area, respectively. Both the methods are, however, disadvantageous for the catalyst durability. Thus, the activity, durability, and power density are generally in trade-off relations. A promising method for solving this problem is to change the properties of the surrounding rather than the catalyst itself. Ionomers adsorbed on Pt catalyst have been confirmed to inhibit ORR and oxygen permeation to the interface [1, 2]. In other words, both the reaction and permeation can be promoted without deteriorating the catalyst durability by mitigating the ionomer adsorption. We have indeed shown that the ionomer adsorption can be suppressed by modifying the molecular structure of ionomer [3]. The ionomer adsorption can be suppressed also by inserting a sub-nanometer thin porous carbon layer between the Pt surface and ionomer. The inserted carbon layer has been also shown to suppress the catalyst degradation during potential cycles [4]. In this talk, we first summarize our analytical works on Pt/ionomer interfaces, focusing on the mechanisms of the adsorption of anionic moieties in ionomers and its effect on ORR. Then, we discuss the effectiveness of various approaches for mitigating ionomer adsorption, as well as their limitations. The future direction of cathode catalyst developments is also discussed.[1] Subbaraman et al., ChemPhysChem 11, 2825 (2010).[2] Jinnouchi et al., Electrochim. Acta, 188, 767 (2016)[3] Kodama et al., ACS Catal. 8 694 (2018).[4] Yamada et al., J. Electrochem. Soc., in press.

Local Measurement of Anode Current Collector Potential in a PEM Water Electrolyzer

The current collector (CC) components (bipolar plate and porous transport layer) of a polymer electrolyte membrane water electrolyser (PEMWE) comprise one of the highest proportion of the cost of the stack [1]. It is widely accepted that the PEMWE CC material needs to withstand the relatively high potentials encountered at the anode electrode, with ex situ qualification testing typically carried out at an applied potential of at least 2 V vs the standard hydrogen electrode (SHE). As a result, platinum-coated titanium is the common material of choice. However, we offer a counter hypothesis that it is unlikely that the corrosion potential of the anode CC is equal to that of the anode electrode due to the very low ionic conductivity of the pure water phase separating the two components.In this work, an innovative in situ reference electrode consisting of a Nafion®/H2SO4 salt bridge connected to a reversible hydrogen electrode is used to measure the corrosion potential of the anode CC during PEMWE cell operation. Using this technique, we demonstrate for the first time that the corrosion potential of the anode current collector is effectively decoupled from that of the anode electrode [2]. Furthermore, we demonstrate that carbon paper can be applied as anode CC material without any noticeable corrosion taking place.The implications of this work are that significantly cheaper materials such as carbon or carbon-coated stainless steel can be used for CC components, which could reduce the cost of PEMWE technology substantially. The key advance is the use of a thin porous spacer layer between the anode and the CC. Factors that may influence the implementation of this new concept are discussed, including the influence of spacer layer tortuosity and water conductivity on the corrosion potential of the CC.

Polyvinyl alcohol-based monovalent anion selective membranes with excellent permselectivity in selectrodialysis

Recently, monovalent anion selective membranes (MASMs) with excellent permselectivity for selectrodialysis applications have become both very desirable and competitive. In this study, a series of polyvinyl alcohol-based MASMs were fabricated by depositing a thin electronegative layer with a loose structure on the surface of base membranes through interfacial polymerization. The base membranes were prepared by blending quaternized polyethyleneimine (QPEI) and polyvinyl alcohol (PVA) or modified PVA with hydrophobic alkyl chains of different lengths. Due to the hydration energy effect, the base membrane QPEI/PVA-C10, which had the longest hydrophobic alkyl chain, showed the highest permselectivity, 2.47, for a Cl−/SO42− system. The thin loose porous electronegative layer for as-prepared MASMs inhibited the transfer flux of large SO42− from 4.91 × 10−8 (QPEI/PVA) to 1.96 × 10−8 mol/cm2s (QPEI/PVA-5), but scarcely diminished that of Cl− (4.84–4.56 × 10−8 mol/cm2s for QPEI/PVA series membranes). Because of the hydration energy and Donnan exclusion effects, the membrane QPEI/PVA-C10-5, which used the longest hydrophobic alkyl chain and largest 4D2SA concentration, showed the highest permselectivity, specifically 6.31, higher than that of commercial Neosepta ACS (5.27) as well as an acceptable membrane area resistance of 5.11 ± 0.07 Ω cm2. Moreover, QPEI/PVA-C10-5 and QPEI/PVA-5 both illustrated a reasonable long-term operational stability for commercial selectrodialysis applications. This work suggests an effective approach to guide the fabrication of MASMs in selectrodialysis applications.

Sulfide@hydroxide core–shell nanostructure via a facile heating-electrodeposition method for enhanced electrochemical and photoelectrochemical water oxidation

Designing low-cost, easy-fabricated, highly stable and active electrocatalysts for oxygen evolution reaction (OER) is crucial for electrochemical (EC) and solar-driven photoelectrochemical (PEC) water splitting. By using a facile heating-electrodeposition method, here we fabricated a porous but crystalline Fe-doped Ni3S2. A thin porous surface NiFe hydroxide layer (~10 nm) is then formed through OER-running. By virtue of the core Fe-doped Ni3S2 with good conductivity and the shell NiFe hydroxide surface with good electrocatalytic activity, the core–shell nanostructure on Ni foam exhibits excellent OER activity in 1 M NaOH, needing only 195 and 230 mV to deliver 10 and 100 mA/cm2, respectively, much more superior to those of 216 and 259 mV for the sample deposited under normal temperature. The enhanced photo-response of the [email protected] core–shell structure was also demonstrated, due to the efficient transfer of photo-generated carriers on the core/shell interface. More interestingly, it shows a good compatibility with Si based photoanode, which exhibits an excellent PEC performance with an onset potential of 0.86 V vs. reversible hydrogen electrode, an applied bias photon-to-current efficiency of 5.5% and a durability for over 120 h under AM 1.5 G 1 sun illumination, outperforming the state-of-the-art Si based photoanodes.

A nonlinear asymptotic model for the inertial flow at a fluid-porous interface

An original nonlinear multi-dimensional model for the inertial fluid flow through a fluid-porous interface is derived by asymptotic theory for arbitrary flow directions. The interfacial region between the pure fluid and the homogeneous porous region is viewed as a thin transition porous layer characterized by smoothly evolving heterogeneities. The asymptotic analysis applied to the homogenized Navier-Stokes equations in this thin heterogeneous porous layer leads to nonlinear momentum jump conditions at the equivalent dividing interface. These jump conditions involve slip and friction coefficients whose dependence on porosity are analyzed. Moreover, we show that the resulting Navier-Stokes/Darcy-Forchheimer macroscale coupled model is globally dissipative in the porosity range 0<ϕp≤0.95,which also contributes to its physical relevance. To our knowledge, this innovative asymptotic model is the first nonlinear multi-dimensional model proposed in the literature for the inertial flow with arbitrary flow directions at a permeable interface. Besides, it clearly opens new perspectives to study turbulent flows at the fluid-porous interface.

Infiltration of impacting droplets into porous substrates

The impact of water droplets on thin porous layers of glass beads held vertically between glass plates was photographed to observe simultaneous spreading and infiltrating of the liquid into the porous medium. Glass beads with diameters of either 100 µm or 500 µm were tested and micro-computed tomography was used to measure the porosities of the layers. The water drop diameter was kept constant at 2 mm while the impact velocity was varied from 0.06, to 1.9 m/s. High-speed videos of the advance of water into the porous structure were studied with image analysis software and the volume flow rate of liquid calculated. Increasing droplet impact velocity decreases droplet infiltration time because higher droplet inertia drives more liquid into the porous material and a larger droplet spreading diameter increases the area in contact with the substrate. Too high of an impact velocity results in droplet cleaving where a portion of the drop remains on the upper surface. A simple model is proposed to determine when inertia driven infiltration will be significant. Once droplet inertia is dissipated capillary forces draw liquid into the substrate and analytical models are compared to predict the rate of capillary driven flow.

Laser micro/nano machining of silicon

This work investigate the formation of micro/nanostrucutred layers of silicon wafers having various conductivity types emphasizing the crucial role of laser in stimulating the etching reaction as well as controlling the silicon surface structures in photochemical and photoelectrochemical etching processes. A CW visible laser beam was used to synthesize silicon nanostructures of various morphologies in this work. It is found in photochemical etching that short laser wavelengths produce a thin porous layer compared to longer laser wavelengths which are appropriate for thicker porous layers. SEM investigation reveals the formation of different nanostructures that were synthesized by photochemical etching. Results show that optimum porosity of 70 %, 80 %, and 90 % are achievable for n, p, and p-n silicon respectively when using a current density of 25 mA/cm2in the photoelectrochemical etching process.AFM images confirm that very small nanostructure features with average size of 80 nm can be obtained for p-n silicon in the photochemical etching process. Energy band diagrams of the three etching processes; Photochemical (PC), Electrochemical (EC) and Photoelectrochemical (PEC) provide good knowledge of the photogenerated/injected holes affecting the nanostructured surface formation. Image analysis software was used to examine the microstructuredsilicon surface produced by pulsed Nd:YAG laser. The thermal distribution profile showed that the surface temperature rises to about 2000 °C when a short laser pulse of 0.6 ms and high laser energy of 1 J were used. The surface and sub-surface temperature were estimated using COMSOL multiphysics software.

In situ preparation of LiFePO4/C with unique copolymer carbon resource for superior performance lithium-ion batteries

Olivine-type LiFePO4, taking advantage of structure stability and environmental friendliness, points out a new direction towards development of Li-ion batteries applying in the plug-in hybrid vehicles. However, the inferior electronic conductivity (∼10−9 S cm−1 at 298 K) and lower lithium ion diffusion coefficient (∼1015 cm2 S−1 at 298 K) still hinder the farther application in power battery. To overcome the defects, LiFePO4/C composite with special copolymer carbon resource (polyacrylonitrile block polymethyl methacrylate) is synthesized successfully by in situ carbothermal reduction method. From BET, SEM and TEM, the sample obtained is coated by thin and homogeneous porous carbon layers, which may be induced by the copolymer carbon resource. The porous layers give opportunity to faster diffusion of Li-ion and closely contact between active substance and electrolyte, providing the high active sites. Unquestionably, the modified LiFePO4/C demonstrates such outstanding properties as high initial discharge capacity (165.3 mA h g−1 at 0.2C), superior rate capability (78.9 mA h g−1 at 30C), and excellent cycling performance with 98% cycle retention after 100 cycles at 0.2C. The well-designed LiFePO4/C cathode material becomes an increasingly eye-catching candidate applicable to the fields of rechargeable lithium ion batteries.

Impinging jet into an open trapezoidal cavity partially filled with a porous layer

A confined slot jet impinging into an open trapezoidal cavity containing a porous layer is investigated. To make the study accounts for a practical problem, constant heat flux is applied at the bottom of the cavity which is covered by a thin porous layer subjected to a cold impingement air jet. Darcy-Forchheimer model is used for the porous layer and its porosity range was taken to ensure thermal equilibrium between the fluid and the porous matrix. Finite element method is adopted for the numerical solution. Results show that the best thickness of the porous layer should be as minimal as possible, where increasing the porous layer thickness from 0.1 to 0.3 reduces the average Nusselt number by 17% when Darcy number is 10−3. It is found also that the trapezoidal cavity serves in attaining the fully developed condition early.

Solving Nafion poisoning of ORR catalysts with an accessible layer: designing a nanostructured core‐shell Pt/C catalyst via a one‐step self‐assembly for PEMFC

A core-shell Pt/C@NCL300 catalyst with an accessible layer was designed to recover lost ORR activity and was constructed via a one-step self-assembly process in this paper. A thin porous layer derived from Nafion was first formed on the surface of Pt/C catalyst to create a shell. This first coating successfully separated the Nafion and Pt particles in the catalysts and reducing the negative impact of Nafion on ORR activity and enhancing the fuel cell performance. The newly fabricated Pt/C@NCL300 catalyst exhibited much higher specific activity than the original Pt/C catalyst in RDE tests under the same conditions and were comparable to the activity of Pt/C electrode without Nafion poisoning. Moreover, the fuel cell with Pt/C@NCL300 catalyst exhibited a higher power density without an obvious increase in proton transport and O2 transport resistance compared to that of a Pt/C fuel cell with a low Pt loading. This result indicates that coating the Pt/C catalyst with a layer accessible for oxygen and protons is a promising way to effectively promote Pt-based catalysts that work under normal operating conditions.

The use of microperforated materials as duct liners: Comparison with fibrous linings

The acoustical performance of a microperforated duct liner and a fibrous lining was compared to confirm that a microperforated panel lining can be used to re- place a fibrous liner as a sound attenuator in a duct. Fibrous materials are often used to line ducts in order to attenuate HVAC noise, for example. These treatments are often primarily useful in a limited frequency range owing to the characteristics of non-planar wave propagation in ducts. At the same time, microperforated mate- rials backed by a finite-depth air space are effective in a limited frequency range owing to the nature of the reactive impedance of this combination. Here, it will be shown that microperforated materials may be used to create duct linings that produce attenuation comparable with that of fibrous materials in the latter's high- performance region. The characteristics of the microperforated panel were studied based on the Maa model. To compare the performance of these two linings, theoret- ical, numerical and experimental tools were used. In the various case studies, both extended reaction and locally reacting treatments were considered. For the analyti- cal approach, Morse's theory was applied in the local reaction case. On the other hand, Scott's analysis was used to study the extended reaction case. In the experi- mental work, the transmission losses of various liner configurations were measured in a square impedance tube. To tune the performance of a microperforated sheet to reproduce that of a fibrous material, the hole size, porosity, thickness, density, and air-backing depth were modified. To validate the experimental and analytical data and to handle situations that are not easily modeled using an analytical approach, a finite element model was also used for the calculations. For the finite element model analysis, COMET/VISION and SAFE were used. Since that software does not include explicit microperforated material models, an alternative approach was used. The alternative model was based on the Attala and Sgard model for perforated panels. This alternative approach in which the perforated panel is modeled as a thin porous layer was successfully implemented in finite element form. Finally, it was demonstrated that the microperforated panel can successfully reproduce the acous- tical performance of glass fiber as a duct lining material.

Solute dispersion in two-fluid flowing through tubes with a porous layer near the absorbing wall: Model for dispersion phenomenon in microvessels

Present study concerns the solute dispersion analysis in a two-fluid model of blood flow through tubes with a thin porous layer near the absorbing wall. A thin porous layer near the wall represents an endothelial glycocalyx layer the composition of which may be attributed to the accumulation of carbohydrates, absorbed plasma proteins and macromolecules in a layer at the wall that affects the plasma flow (Secomb et al., 1998. A model for red blood cell motion in glycocalyx-lined capillaries. Am. J. Physiol. 274 (Heart Circ. Physiol. 43), H1016-H1022; Pries et al., 2000. The endothelial surface layer. Eur. J. Physiol. 440, 653–666). Two-fluid model for blood flow is considered in which the central region of the blood vessel is occupied by Herschel-Bulkley fluid with variable viscosity and a peripheral region of plasma surrounded over the central region is occupied by a Newtonian fluid with constant viscosity. Governing equations are solved analytically for all the regions (central, intermediate and porous regions) and the approach of Sankarasubramanian and Gill (Sankarasubramanian, R, Gill, W N, 1973. Unsteady convective diffusion with interphase mass transfer. Proc. R. Soc. London Ser. A 333, 115–132) is followed to solve the diffusion equation by series expansion method. The impact of porous layer (and hence the porous layer parameters), varying viscosity, plasma layer and wall absorption parameters on the diffusion process like convective, dispersion and mean concentration have been analyzed. A comparative investigation of solute dispersion between Newtonian and non-Newtonian fluids has also been discussed. It is perceived that the presence of such a layer reduces the convective and axial dispersion for a highly reactive wall. A remarkable observation is that a reduced porosity near the wall contributes towards reduced average concentration of the solvent. The analysis of the porous layer inside the arterial wall may be used to understand the diffusion process for flow through arteries with a deposition of a porous layer near the absorbing wall.

Optimisation of Gas Access Through a Thin Porous Layer with a Partially Occluded Inlet Surface

The gas access through a thin porous layer is studied in relation to the reactant gas transfer in the gas diffusion layer (GDL) of polymer electrolyte membrane fuel cells. In the considered situation, the surface through which the gas enters into the porous layer is partially occluded. The aim is to design the porous medium microstructure so that the gas flux is uniformly distributed over the gas exit surface. The method combines pore network simulations and an optimisation method based on a genetic algorithm. The optimisation procedure is performed for a dry GDL. Then, various scenarios of wet GDL are considered in order to check whether the optimised GDL still performs better than the non-optimised GDL in the presence of liquid water.

Assessment of the electrochemical behaviour of silicon@carbon nanocomposite anode for lithium-ion batteries

Abstract Silicon nanocomposites have great potential applications in lithium-ion batteries. However, huge mechanical strain, capacity retention and unstable solid electrolyte interface formation weaken their applications in the real world. To overcome the above challenges, a novel facile route was adopted to design nanostructured silicon core carbon shell composites (Si@C), where the carbonization of phenolic resins led to a uniform porous thin interfacial layer of carbon. The phenolic resin precursor endowed mesoporous morphology with the carbon layer due to the carbonization of aromatic carbon, methylene linkages and hydroxyl groups. The mesoporous conductive carbon helped effectively to control the mechanical strain of silicon nanoparticles which maintained the integrity of Si@C nanocomposites and provided effective channels to easy access of electrolyte and short lithium ions transport. This novel Si@C anode offered a stable specific capacity of ∼868 mAh g−1 at 0.1 Ag-1 up to 500 cycles with ≥99% columbic efficiency.