Mass Transport Properties Research Articles

Hierarchical 3D Percolation Network of Ag-Au Core-Shell Nanowire-Hydrogel Composite for Efficient Biohybride Electrodes.

Metal nanomaterials are highly valued for their enhanced surface area and electrochemical properties, which are crucial for energy devices and bioelectronics. However, their practical applications are often limited by challenges, such as scalability and dimensional constraints. In this study, we developed a synthesis method for highly porous Ag-Au core-shell nanowire foam (AACNF) using a one-pot process based on a simultaneous nanowelding synthesis method. The unique characteristics of AACNF as metal-based electrodes show the lowest density among metal-based electrodes while demonstrating high electrical conductivity (99.33-753.04 S/m) and mechanical stability. The AACNF's excellent mass transport properties enable multiscale hierarchical incorporation with functional materials including polymeric precursors and living cells. The enhanced mechanical stability at the nanowelded junctions allows AACNF-hydrogel composites to exhibit large stretching (∼700%) and 10,000 times higher electrical conductivity than hydrogel-nanowire composites without the junction. Large particles in the 1-10 μm scale, including fibroblast cells and exoelectrogenic microbes, are also successfully incorporated with AACNF. AACNF-based microbial fuel cells show high power density (∼330.1 W/m3) within the optimal density range. AACNF's distinctive ability to form a hierarchical structure with substances in various scales showcases its potential for advanced energy devices and biohybrid electrodes in the future.

Heat and Mass transport analysis for Williamson MHD nanofluid flow over a stretched sheet

This study focuses on analyzing the behavior of a time-varying magnetohydrodynamic (MHD) Williamson nanofluid (WNF) flowing over a stretched plate. The main objective is to understand the heat and mass transport properties of the nanofluid in this scenario. The mathematical model involves a system of partial differential equations (PDEs) that are transformed into a set of ordinary differential equations (ODEs) using a similarity transformation. These ODEs are then solved using the well-established MATLAB BVP4C technique; a part of the finite difference method. To ensure the reliability and accuracy of the approach, the obtained results are compared with previously published literature, serving as a validation step. The numerical findings are presented graphically and in tabular form. The study focuses on examining the impact of various external factors on the friction factor, Nusselt number, and Sherwood number, providing a comprehensive evaluation of heat transfer and mass transport characteristics. Specifically, the study investigates the flow and heat transfer properties near a stretched plate with a permeable layer. Also, takes into account the transverse dispersion, and heat generation effects in MHD WNF moreover with magnetic field and slip boundary conditions. The results of the study indicate that increasing the Brownian motion parameter (Nb) and Thermophoresis parameter (Nt) leads to higher local Nusselt numbers, reflecting the increased rates of transferring the heat. Similarly, an increase in the Nt is associated with higher local Sherwood numbers, indicating enhanced mass transport. Conversely, higher values of the Brownian motion parameter (Nb) result in lower local Sherwood numbers. By analyzing the influence of various external factors, such as nanofluid properties and magnetic fields, a better understanding of heat transfer and mass transport characteristics can be obtained.

Metallic meta-biomaterials: A critical review of fatigue behaviors

As an important subset of metamaterials with unprecedented combinations of favorable mechanical, mass transport and biological properties, meta-biomaterials have attracted much research interest recently because of their great potential in biomedical applications, especially in orthopedic tissue repair and replacement. Meta-biomaterials must withstand cyclic musculoskeletal loads after implantation when used in the bone repair or replacement; therefore, fatigue resistance is critical to ensure their long-term reliability. The topology-fatigue behavior relationship of meta-biomaterials needs to be investigated before their clinical application. This paper focuses on the fatigue behaviors of metallic meta-biomaterials for their potential application as bone substitutes and orthopedic implants and reviews the currently available results in this field. Technologies of meta-biomaterial fatigue behavior analysis and their features are initially introduced. Risk factors, including topological structures, base material types, manufacturing and posttreatment processes, loading profiles, tissue regeneration, and biodegradation, and their effects on the fatigue behaviors of metallic meta-biomaterials are systematically analyzed and summarized. Moreover, crack propagation and fatigue life prediction models, which characterize the fatigue behaviors of meta-biomaterials, are introduced to describe topology-fatigue behavior relationships. Research progress and limitations are discussed to provide a better understanding of the state-of-the-art trend and direction for future meta-biomaterial research.

Cell encapsulation in gelatin methacryloyl bioinks impairs microscale diffusion properties.

Light-assisted bioprinted gelatin methacryloyl (GelMA) constructs have been used for cell-laden microtissues and organoids. GelMA can be loaded by desired cells, which can regulate the biophysical properties of bioprinted constructs. We study how the degree of methacrylation (MA degree), GelMA mass concentration, and cell density change mass transport properties. We introduce a fluorescent-microscopy-based method of biotransport testing with improved sensitivity compared to the traditional particle tracking methods. The diffusion capacity of GelMA with a higher MA significantly decreased compared to a lower MA. Opposed to a steady range of linear elastic moduli, the diffusion coefficient in GelMA varied when cell densities ranged from 0 to 10 × 106 cells/ml. A comparative study of different cell sizes showed a higher diffusivity coefficient for the case of larger cells. The results of this study can help bioengineers and scientists to better control the biotransport characteristics in light-assisted bioprinted microtissues and organoids.

In-Situ Electrolyzer Monitoring Using Electrochemical Impedance Spectroscopy (EIS)

The development of technologies that improve the efficiency and reliability of green hydrogen production and distribution systems is key to lowering the cost and spurring widespread adoption of hydrogen. Electrolyzer reliability is affected by factors such as degradation of catalytic materials and development of anomalies in the membrane electrode assembly, which can in turn lead to hazardous mixing of Hydrogen and Oxygen. Most methods to lower the manufacturing cost further negatively affect the reliability. The effect of such degradation can be alleviated with improved cell monitoring technology [i]—for instance, the ability to predict failures in advance enables predictive maintenance to improve system utilization and minimize impact to the amount of hydrogen produced.Electrochemical Impedance Spectroscopy (EIS) is a widely used tool in lab settings to understand the properties of electrochemical cells. However, due to a combination of cost and technological barriers, scaling EIS technology to in-situ, in-operando monitoring of megawatt scale electrolyzer stacks has proven challenging. In this talk, Analog Devices presents Andromeda (Fig. 1) – a system that can monitor small electrolyzer stacks (up to 4 cells, 100cm2 at current densities up to 3A/cm2) in-situ. In a lab environment, Andromeda enables the use of EIS during long degradation studies with arbitrary power supplies without interrupting the study. We will show that, with appropriate modifications to the hardware, the architecture of the Andromeda system can be scaled to monitor Megawatt-scale electrolyzer stacks.We will additionally show data gathered on small cells that indicates that EIS can be a good indicator of failure mechanisms in an electrolytic cell [ii, iii], which further indicates that in-situ monitoring using EIS can be a powerful tool to monitor electrolyzer state-of-health. As an example, Figure 2 shows that corresponding I/V curves show no discernible difference between a baseline cell and cells with pinholes, indicating that small pinholes, which can be safety hazards, can be challenging to detect during operation. Examination of EIS data (Figure 3a), on the other hand, reveals a widening and depression of the semicircle in the curve from the cell with the pinhole. Detectability has also been demonstrated for defects such as catalyst degradation, membrane poisoning, and drifts in mass transport properties within the cell, proving that an in-situ monitoring system, when combined with modeling and AI, has the potential to give asset owners visibility into their operations that will improve utilization, decrease cost and enable safer production of hydrogen at scale.Future work on the integration of semiconductor technology into hydrogen equipment has focused on bypassing failing cells in the stack [iv] (Figure 4) and designing power systems that enable electrolyzers to exploit existing economies of scale.

A Sensitivity Study of Key Parameters on the Efficiencies and Energy Losses of Organic Redox Flow Batteries

Organic redox flow batteries (ORFB) are promising cost-competitive technologies for large-scale energy storage. At the unit cell scale, the battery performance is controlled by the combined effects of key parameters of microstructure design, physicochemical properties of organic molecules, mass transport, operating conditions, and membrane properties. However, a comprehensive study of how these parameters could affect the overall performance of ORFB has not been done. To address this gap, this work presents a sensitivity study of 12 key parameters on the battery efficiencies and energy losses of ORFB by using a validated numerical model for the Dihydroxyphenazine (DHP) family. The 12 key parameters include the specific area of microstructure; mass transfer rate; diffusivity, viscosity, reaction transfer coefficient, the reaction rate constant, standard potential, and electronic conductivity of DHP anolyte; operation conditions such as initial concentration of active species, pump rate, and applied current; and membrane electronic conductivity. In total, we generated 15,360 combinations of the 12 key parameters. These data are split into 15 groups with each having a fixed current density and flow rate and 1024 random parameter combinations of the remaining 10 parameters. All these parameters are then sent to the validated ORFB model developed in Comsol to predict the coupled flow, reaction, and transport processes at 38 pre-defined SOC between 0.025 and 0.85. We then output the total potential, equilibrium potential, activation potential, and concentration potential for charge (19 SOC) and discharge (19 SOC) from the model to further calculate the Coulombic Efficiency, Energy Efficiency, Voltage Efficiency, and System Efficiency as well as the energy losses contributed by equilibrium, activation, concentration, and ohmic losses. With these calculated efficiencies and the relative importance of energy losses, we used a deep neural network (DNN) to fit the relationship between the input 12 parameters (15,360 combinations), and the model calculated 4 efficiencies/relative ratios of energy losses. A sensitivity score is then calculated based on the DNN model and key factors controlling the ORFB performance are determined.

Modification of Conductive Carbon with N‐Coordinated Fe−Co Dual‐Metal Sites for Oxygen Reduction Reaction

AbstractEarth‐abundant commercial conductive carbon materials are ideal electrocatalyst supports but cannot be directly utilized for single‐atom catalysts owing to the lack of anchoring sites. Therefore, we employed crosslink polymerization to modify the conductive carbon surface with Fe−Co dual‐site electrocatalysts for oxygen reduction reaction (ORR). First, metal‐coordinated polyurea (PU) aerogels were prepared using via crosslinked polymerization at ambient temperature. Then, carbon‐supported, atomically dispersed Fe−Co dual‐atom sites (FeCoNC/BP) were formed by high‐temperatures pyrolysis with a nitrogen source. FTIR and 13C NMR measurements showed PU linkages, while 15N NMR revealed metal–nitrogen coordination in the PU gels. Asymmetric, N‐coordinated, and isolated Fe−Co active structures were found after pyrolysis using XAS and STEM. In alkaline media, FeCoNC/BP exhibited excellent ORR activity, with a E1/2 of 0.93 V vs. RHE, higher than that of Pt/C (20 %) (0.90 V), FeNC/BP (0.88 V), and CoNC/BP (0.85 V). An accelerated durability test (ADT) on FeCoNC/BP indicated good durability over 35000 cycles. FeCoNC/BP also showed moderate ORR and ADT performance in acidic media. The macro/mesoporous N‐doped carbon structures enhanced the mass transport properties of the dual Fe−Co active‐sites. Therefore, modifying carbon supports with nonprecious metal catalysts may be a cost‐effective‐strategy for sustained electrochemical energy conversion.

Ni- and Ni-Sn Anode Porous Layers for SOFCs Operating with Carbonaceous Fuels

Nickel metal layers with various morphologies have been investigated as electrical contact, electrocatalyst, and catalyst layer for high temperature hydrogen electro-oxidation reactions and heterogeneous reactions, such as steam methane reforming and water gas shift, in high temperature fuel cells supplied by carbonaceous fuels of various nature. From a heterogeneous catalysis perspective Ni metal alloy, with various dopant concentrations, have been studied to increase metal Nickel tolerance to carbon deposition, which is thermodynamically favoured in SOFC fed with a steam/methane molar ratio <2.0. Metallic nickel electric and thermal conductivity are typically of the order of 107 S/m and 102 W/m.K, respectively, while its coefficient of thermal expansion measures 12x106 m/m.C , making it a good and relatively cheap candidate for electric contact layers and current collectors. The optimization of its morphology is fundamental to improve the nickel layer mass transport properties in conjunction with its catalytic and electrocatalytic performance. Others have proposed and optimized Ni-based porous layers: Smorygo et al. investigated nickel metallic foam supports to promote steam methane reforming and found good corrosive resistance and stability1. Fu et al. studied the effects of modifying nickel foam with copper; they found that copper modification significantly reduced the amount of carbon deposition found in the foam after operation2. Enhanced stability of the foam was reported alongside the resistance to coking. Kan and Lee fabricated a tin-doped Nickel/YSZ anode catalyst which was proven to drastically improve cell stability at a comparable performance3. The cell performance and deposition rates were reported as highly dependent on the tin concentration.Our goal is to compare the electrochemical performance, the catalytic activity towards steam methane reforming reaction yield, and the resistance towards the Boudouard reaction for solid carbon formation of a Ni-based SOFC: i) without Ni porous layer; ii) with a 200 μm thick Ni porous mesh; iii) with a 200 μm thick NiSn porous mesh (porous nickel and nickel-tin mesh ‘Celmet’ are supplied by Sumitomo Electric Toyama Co., Ltd.). We investigate the electrocatalytic performance of the two Nickel-based porous layers on a Ni-YSZ/Ni-GDC|SSZ|LSC-YSZ button cell with 20mm diameter (active area 1.23 cm2). The porous meshes are characterized by a pore size of 230-250 μm (as depicted in Figure 1(v)). The cell assembly is depicted in Figure 1 (iv), where we show how the Ni porous mesh works both as a catalyst layer and a mass transport layer between the gas bulk phase and the triple phase boundary.The cells are operated between 700°C and 850°C with inlet feed compositions comprising CH4, H2, H2O, and N2 with varying S/C ratios from 2.5 to 0 (i.e., dry methane feed). The performance of the three configurations is expressed in terms of electrochemical impedance spectroscopy (EIS) and chronoamperometry measurements within the temperature and composition experimental matrix. X-ray diffraction (XRD) and fluorescence (XRF) are used to analyze the cells and meshes at beginning of life and post-mortem to identify any carbon phases forming on either surface. Scanning Electron Microscopy Energy Dispersion Spectroscopy (SEM-EDS) is used to identify carbon composition and map both the cell and mesh surfaces.The electrochemical performance between case i) and case ii) is reported in Figure 1(i), where polarization curves are summarized for a cell operating with a 1:1 mixture of H2/H2O at 750°C. The increased polarization of case ii) is associated to the additional series resistance of the Ni mesh on the anode layer. Preliminary operation with mixtures of CH4/H2O with S/C as low as 1.5 display performances in-line with expectations, while long-term degradation effects due to carbon deposition remain to be studied. XRD measurements report the formation of solid carbon on a Ni mesh operating with S/C=1.5 (see Figure 1(ii)) for a cell working at 750°C for less than 50 hours. From our preliminary results, we show that the addition of a porous nickel mesh results in methane reformation prior to reaching the cell anode. The deposition is characterized by XRD and SEM and reported along with the polarization curves and electrochemical impedance spectroscopy which define the performance of the cells. O. Smorygo et al., Int J Hydrogen Energy, 34 (2009).X. Z. Fu et al., Int J Hydrogen Energy, 35 (2010).H. Kan and H. Lee, Appl Catal B, 97 (2010). Figure 1

Hydrodynamic voltammetry of Fe2+/3+ in aqueous deep eutectic solvents towards redox flow batteries

Deep eutectic solvents (DESs) have recently attracted much attention as potential green electrolyte solvents for redox flow batteries. DESs are considered not only as environmentally sustainable but also economically attractive electrolytes because they can be resourced from biological feedstock (alcohols, urea, choline) and are earth-abundant and of low toxicity. Despite these advantages, DESs still have limitations in important aspects such as reactant and ion transport, which is inhibited due to hydrogen-bonding-induced viscosity. Thus, improving the transport properties of redox species in DESs is essential. In addition, we explore the quantitative addition of water to ethaline (a 1:2 choline chloride: ethylene glycol mixture) in order to understand its influence on the kinetics and mass transport properties of DESs. In this work, we show that DESs can be made more fluid and less dense, while avoiding most of the electrochemical instabilities of water. Herein, we investigate the effects of gradually increasing amounts of water to the redox system of Fe2+/3+in ethaline. Our study shows that systematic addition of water leads to a three-fold increase in ionic conductivity and decrease in viscosity that enhances the mass transport and kinetics of DES-based electrolytes while still maintaining an electrochemical window of approximately 1.90 V. The use of environmentally benign electrolyte components together with the observed increase in conductivity will result in a more efficient redox flow battery (RFB) that operates at higher power density without relying on harmful solvents and fossil fuel-based processes.

In-plane measurements and computational fluid dynamics prediction of permeability for biocompatible NiTi gyroid scaffolds fabricated via laser powder bed fusion

Laser powder bed fusion (LPBF) is considered a promising technology for manufacturing porous, biomimetic, and patient-specific scaffolds for bone repair. Scaffold permeability is one of the key factors to be considered for acquiring the required mass-transport properties in bone tissue engineering. This study aims to reveal the relationship between the design parameters of gyroid-based porous structure and scaffold permeability. A set of gyroid samples was manufactured from intermetallic NiTi alloy. Nine configurations of porous structures were obtained by varying the main design parameters, namely wall thickness and unit cell size. The in-plane method was employed to measure the permeability coefficient for the gyroid structures. Computational fluid dynamics simulations of the porous structures were performed to predict the targeted properties in an implant at the design stage before LPBF manufacturing. The results of the simulations were validated with the obtained experimental results. Geometrical accuracy and surface morphology of the as-built samples were investigated with various techniques. Biocompatibility assessment of the gyroid scaffolds was performed with human cell culture experiments.&amp;nbsp;

Elucidating the Mass Transportation Behavior of Gas Diffusion Layers via a H2 Limiting Current Test.

The gas diffusion layer (GDL), as a key component of proton exchange membrane fuel cells (PEMFCs), plays a crucial role in PEMFC's polarization performance, particularly in mass transport properties at high current densities. To elucidate the correlation between GDLs' structure and their mass transport properties, a limiting current test with the H2 molecular probe was established and employed to investigate three representative GDLs with and without the microporous layer (MPL). By varying humidity and back pressure, the mass transport resistance of three GDLs was measured in an operating fuel cell, and an elaborate analysis of H2 transport was conducted. The results showed that the transport resistance (RDM) of GDLs was affected by the thickness and pore size distribution of the macroporous substrate (MPS) and the MPL. In the process of gas transport, the smaller pore size and thicker MPL increase the force of gas on the pore wall, resulting in an increase in transmission resistance. Through further calculation and analysis, the total transport resistance can be divided into pressure-related resistance (RP) and pressure-independent resistance (RNP). RP mainly originates from the transport resistance in both MPLs and the substrate layers of GDLs, exhibiting a linear relationship to the pressure; RNP mainly originates from the transport resistance in the MPLs. 29BC with thick MPL shows the largest RNP, and T060 without MPL shows the RNP = 0. This methodology enables in situ measurements of mass transport resistances for gas diffusion media, which can be easily applied for developing and deploying PEMFCs.

Tortuosity quantification of fly ash concrete considering interfacial transition zone

For concrete materials, durability is closely related to the mass transport property. The tortuosity of concrete material is an important factor accounting for the transport property. In this paper, the tortuosity of concrete is studied by mercury intrusion porosimetry and permeation tests in order to consider the existence of aggregate induced in the interfacial transition zone (ITZ). Tortuosity gained through the corrugated pore structure model and the Katz–Thompson model are compared and analysed to quantify the tortuosity of fly ash concrete. The ITZ was observed by scanning electron microscopy. The results show that the effect of aggregate should be considered when studying the tortuosity of concrete materials. With an aggregate value fraction of 43.8%, when considering the ITZ around coarse aggregate, concrete tortuosity is 1.29–16.18 times higher than that of the mortar matrix.

Heat transfer behaviour of mixing nano-non-Newtonian fluid in a chaotic micromixer

The hydrodynamic and thermal behaviors of Nano-Non-Newtonian fluids were examined using three-dimensional numerical simulations of a unique passive micromixer. To comprehend the quantitative and qualitative fluid fraction distributions with temperature homogenization, mass and heat transport properties of two heated fluids have been examined. For varied Reynolds numbers, the influence of fluid behavior and various Al2O3 nanoparticle concentrations on the pressure drop and thermal mixing capabilities were examined. Using CFD, the simulation of performance enhancement was run in intervals of varying Nanoparticle concentrations with Power-law index (n). In terms of fluid homogenization, the proposed micromixer demonstrated a mixing energy cost of 60% comparable to that realized for a recent micromixer (2021y). According to the analysis, for high nanofluid.

CoNiFe‐layered double hydroxide decorated Co‐N‐C network as a robust bi‐functional oxygen electrocatalyst for zinc‐air batteries

AbstractRechargeable zinc‐air batteries (ZABs) are cost‐effective energy storage devices and display high‐energy density. To realize high round‐trip energy efficiency, it is critical to develop durable bi‐functional air electrodes, presenting high catalytic activity towards oxygen evolution/reduction reactions together. Herein, we report a nanocomposite based on ternary CoNiFe‐layered double hydroxides (LDH) and cobalt coordinated and N‐doped porous carbon (Co‐N‐C) network, obtained by the in‐situ growth of LDH over the surface of ZIF‐67‐derived 3D porous network. Co‐N‐C network contributes to the oxygen reduction reaction activity, while CoNiFe‐LDH imparts to the oxygen evolution reaction activity. The rich active sites and enhanced electronic and mass transport properties stemmed from their unique architecture, culminated into outstanding bi‐functional catalytic activity towards oxygen evolution/reduction in alkaline media. In ZABs, it displays a high peak power density of 228 mW cm−2 and a low voltage gap of 0.77 V over an ultra‐long lifespan of 950 h.image

Effect of high aspect ratio additives on microstructural and mass transport properties of the microporous layer in a proton exchange membrane fuel cell

Tuning up transport properties of the microporous layer is an effective way to enhance mass transport in a proton exchange membrane fuel cell. The incorporation of non-spherical conductive additives in the conventional microporous layer can modify its pore structure. In this study, 5, 20, and 50 wt.% of two high aspect ratio additives, multiwall carbon nanotube and graphene nanoplatelet, are mixed with the acetylene-black carbon to systematically study their impact on ink and the final diffusion media properties. Using a bottom-up approach, the rheological properties of the ink are correlated to the mass transport resistance in the diffusion media. The ink with additives exhibits rheological properties of a less compact microstructure with large agglomerates. Whereas, a more compact agglomerated network is observed from the ink with pure acetylene black carbon nanoparticles. Graphene nanoplatelet has a dominating effect on the surface quality of the microporous layers due to its two-dimensional structure. The test results show that the microstructure formed by the synergy of acetylene black and additives can enhance ohmic and mass transport performance. 20 wt.% of the additive loading is found to be optimal and multiwall carbon nanotube shows the best fuel cell performance.

Isotope Exchange Raman Spectroscopy (IERS): A Novel Technique to Probe Physicochemical Processes in situ.

Wehave developed a novel in situ methodology for the direct study of mass transport properties in oxides with spatial and unprecedented time resolution, based on Raman spectroscopy coupled to isothermal isotope exchanges. Changes in the isotope concentration, resulting in a Raman frequency shift, can be followed in real time, not accessible by conventional methods, enabling complementary insights for the study of ion transport properties of electrode and electrolyte materials for advanced solid-state electrochemical devices. The proof of concept and strengths of isotope exchange Raman spectroscopy (IERS) are demonstrated by studying the oxygen isotope back-exchange in gadolinium-doped ceria (CGO) thin films. Resulting oxygen self-diffusion and surface exchange coefficients are compared to conventional time-of-flight secondary ion mass spectrometry (ToF-SIMS) characterisation and literature values, showing good agreement, while at the same time providing additional insight, challenging established assumptions. IERS captivates through its rapidity, simple setup, non-destructive nature, cost effectiveness and versatile fields of application and thus can readily be integrated as new standard tool for in situ and operando characterization in many laboratories worldwide. The applicability of this method is expected to consolidate ourunderstanding of elementary physicochemical processes and impact various emerging fields including solid oxide cells, battery research andbeyond. This article is protected by copyright. All rights reserved.

Catalyst Aggregate Size Effect on the Mass Transport Properties of Non-Noble Metal Catalyst Layers for PEMFC Cathodes

Non-noble metal catalysts (NNMCs) are regarded as a promising alternative to the costly Pt-based materials required to catalyze the oxygen reduction reaction (ORR) in proton exchange membrane fuel cell (PEMFC) cathodes. However, the large diversity of NNMC synthesis approaches reported in the literature results in materials featuring a wide variety of particle sizes and morphologies, and the effect of these properties on these catalysts’ PEMFC performance remains poorly understood. To shed light on this matter, in this work we studied the physical and electrochemical properties of NNMC layers prepared from materials featuring broadly different aggregate sizes, whereby this property was tuned by ball milling the precursors used in the NNMCs’ synthesis in the absence vs presence of a solvent. This led to two NNMCs featuring similar Fe-speciations and ORR-activities, but with vastly different aggregate sizes of >5 μm vs ≈100 nm, respectively. Following the extensive characterization of catalyst layers (CLs) prepared with these materials via electron microscopy and X-ray tomography, PEMFC tests at different loadings unveiled that the smaller aggregate size and ≈20% higher porosity of the CL prepared from the wet-milled sample resulted in an improvement of its mass transport properties (as well as a ≈2-fold enhancement of its peak power density under H2/air operation) over the dry-milled material.

3D Printed Biomimetic Metamaterials with Graded Porosity and Tapering Topology for Improved Cell Seeding and Bone Regeneration.

Biomimetic metallic biomaterials prepared for bone scaffolds have drawn more and more attention in recent years. However, the topological design of scaffolds is critical to cater to multi-physical requirements for efficient cell seeding and bone regeneration, yet remains a big scientific challenge owing to the coupling of mechanical and mass-transport properties in conventional scaffolds that lead to poor control towards favorable modulus and permeability combinations. Herein, inspired by the microstructure of natural sea urchin spines, biomimetic scaffolds constructed by pentamode metamaterials (PMs) with hierarchical structural tunability were additively manufactured via selective laser melting. The mechanical and mass-transport properties of scaffolds could be simultaneously tuned by the graded porosity (B/T ratio) and the tapering level (D/d ratio). Compared with traditional metallic biomaterials, our biomimetic PM scaffolds possess graded pore distribution, suitable strength, and significant improvements to cell seeding efficiency, permeability, and impact-tolerant capacity, and they also promote in vivo osteogenesis, indicating promising application for cell proliferation and bone regeneration using a structural innovation.

Magnetic Resonance Velocimetry for porous media: sources and reduction of measurement errors for improved accuracy

Nuclear Magnetic Resonance (NMR) is a powerful tool for noninvasively investigating static and dynamic properties of fluids inside complex and opaque structures. Thus, Magnetic Resonance Velocimetry (MRV) allows for the in situ analysis of the local flow velocity of fluids. Such an analysis characterises mass transport properties and helps to validate or improve numerical predictions for porous media. The benefit of such validations is lowered by several problems worsening the measurement accuracy. This publication addresses systematic errors and the influence of noise, which may reduce the accuracy of MRV measurements. Techniques are described to minimise or correct displacement and phase errors. A new multi-echo MRV-sequence is proposed as a compromise between Velocity-to-Noise Ratio (VNR), total measurement time, spatial resolution and displacement errors. For improved VNR, a dual-VENC encoding scheme was used and repetition time T_{text{R}} was optimised. As an example, the proposed MRV sequence was used to measure the three-directional flow velocity of water in an Open Cell Foam (OCF) with 10 pores per inch with three-dimensional isotropic spatial resolution.

Bio-inspired design, mechanical and mass-transport characterizations of orthotropic TPMS-based scaffold

To obtain porous scaffolds with bionic anisotropic structures similar to human bone, the orthotropic triply periodic minimal surface (TPMS)-based structures were proposed in this study. The orthotropic Schoen’s I-WP (AP) and orthotropic Gyroid (AG) were designed based on isotropic I-WP (IP) and isotropic Gyroid (IG). The four scaffolds with 70% porosity were fabricated by electron beam melting, and then were scanned by microcomputer tomography to evaluate their manufacturability. The anisotropic degrees of elastic properties of the scaffolds were calculated using the homogenization approach. Compression test along the three orthogonal directions was conducted on the scaffolds to analyze their mechanical properties. Computational fluid dynamics was performed to the scaffolds along the three orthotropic directions to characterize their mass transport properties. Results show that AP and AG possess irregular pores and perform well in manufacturability compared with IP and IG. Similar to human bone, AP and AG exhibit orthotropic mechanical properties and mass transport performances. Furthermore, the elastic modulus ratio of AG along the three orthogonal directions is close to the value of cancellous bone. The designed scaffolds are advantageous for their bionic mechanical and mass transport properties of human bone and can be the proper candidates in bone graft surgery.