Dead Pores Research Articles

Modulating the electrode pore structure using the magnetic field for reduced local-oxygen transport resistance in polymer electrolyte membrane fuel cell

We utilize a magnetic field to align the pore structure of the PEMFC cathode catalyst layer in the direction of O2 infiltration. This alignment reduces the oxygen diffusion resistance within the catalyst layer, thereby augmenting the performance of the PEMFC. Membrane Electrode Assemblies (MEAs) with magnetically aligned cathodes demonstrate a 50% reduction in O2 transfer resistance compared to conventional MEAs, as verified through electrochemical experiments and it makes a performance enhancement in the I-V curve. Beyond electrochemical experimentation, electrode pore analysis utilizing 3D reconstruction and Lattice Boltzmann Direct Numerical simulation (LB-DNS) for internal flow field analysis within pores, reveals that alignment of the electrode structure in the through-plane direction enhanced pore continuity. This continuity and the resultant minimized proportion of dead pores are identified as the causative factors for the observed performance improvements.

Probing multiphase reactive transport interactions in the polymer electrolyte fuel cell catalyst layer degradation

The multiphase, multicomponent reactive transport plays a critical role in the degradation of the cathode catalyst layer in Polymer Electrolyte Fuel Cells. This warrants a fundamental understanding of the pore-scale, mechanistic interactions in the catalyst layer. Herein, the interfacial and transport interactions due to the flooding dynamics in the presence of carbon support corrosion, which is a primary degradation mode in the cathode catalyst layer, are delineated based on a comprehensive mesoscale model. The mechanistic interrogation of the degradation-transport interactions reveals the spatio-temporal heterogeneity of the pristine and aged microstructures. An electrode-averaged saturation front of 80 % unveils a critical limit of percolation which results in an onset of limiting current density. Further, it is observed that the reactant severity is amplified at progressively higher stages of corrosion owing to the appearance of dead pores and a thicker ionomer film. We also shed light on the fluid displacement patterns which reveal the existence of a capillary fingering regime. The interplay of the operating current density and carbon corrosion in governing the substrate-ionomer interaction is described through an electrochemical Damköhler number.

Numerical study on the impact of carbon deposition on methane/steam mass transport in solid oxide fuel cell porous anode using lattice Boltzmann modeling

Solid Oxide Fuel Cell (SOFC) is an energy conversion device with high efficiency and cleanliness. However, anode carbon deposition severely affects SOFC performance during reforming with hydrocarbon fuels. In this paper, numerical simulations based on the Lattice Boltzmann (LB) method are used to construct the porous anode structure after carbon deposition by means of the binary dilation method, and the effects of different carbon deposition behaviors on the methane/steam flow behaviors and mass transport in the porous medium of SOFC anode are investigated. The results show that anode carbon deposition decreases the methane/steam mass transfer efficiency, and as the degree of carbon deposition increases, dead pores are formed and gas passage is impeded. This paper investigates the effect of different degrees of carbon deposition behavior on anode gas transport, which can further understand the importance of carbon removal in SOFC anode during the methane reforming reaction.

Numerical study of the impact of geometrical parameters on the rarefied gas transport in porous media

To understand the transport mechanism of rarefied gas in the shale rock, the geometry of the porous media is generated based on the Voronoi tessellation, and the gas flows in continuum and rarefied flow regimes are simulated by using the Multiple-Relaxation-Time Lattice Boltzmann Method and Linearized Discrete Velocity Method, respectively. Based on explicit topological relations, porous media with diverse geometries are constructed to investigate the effect of pore-to-throat radius ratio, dead pore number and low-tortuosity throat on the rarefied flow in porous media. The relationships of the mass flow rate, apparent permeability and tortuosity versus the Knudsen number are obtained for varying pore-to-throat radius ratios. Results show that the intrinsic and apparent permeabilities of the porous media decrease as the blockage rate increases, while the reduction in intrinsic permeability is more significant than that in apparent permeability. Moreover, the phenomenon of Knudsen minimum reappears after the addition of low-tortuosity throats to porous media, in which the contribution to mass flow rate increases significantly in rarefied regimes relative to continuum regime, and it is supported by the observation that the tortuosity decreases with increasing Knudsen number. The increase in flow rate with increasing rarefaction effect in the low tortuous regions not only reveals the critical impact of fractures created by hydraulic fracturing on exploitation but also can identify the potential causes for the rapid production decay of shale gas reservoirs.

Microstructure Reconstruction and Multiphysics Dynamic Distribution Simulation of the Catalyst Layer in PEMFC.

Due to the complexity of both material composition and the structure of the catalyst layer (CL) used in the proton-exchange membrane fuel cell (PEMFC), conjugated heat and mass transfer as well as electrochemical processes simultaneously occur through the CL. In this study, a microstructure model of CL was first reconstructed using images acquired by Nano-computed tomography (Nano-CT) of a real sample of CL. Then, the multiphysics dynamic distribution (MPDD) simulation, which is inherently a multiscale approach made of a combination of pore-scale and homogeneous models, was conducted on the reconstructed microstructure model to compute the corresponded heat and mass transport, electrochemical reactions, and water phase-change processes. Considering a computational domain with the size of 4 um and cube shape, this model consisting of mass and heat transport as well as electrochemical reactions reached a stable solution within 3 s as the convergence time. In the presence of sufficient oxygen, proton conduction was identified as the dominant factor determining the strength of the electrochemical reaction. Additionally, it was concluded that current density, temperature, and the distribution of water all exhibit similar distribution trends, which decrease from the interface between CL and the proton-exchange membrane to the interface between CL and the gas-diffusion layer. The present study not only provides an in-depth understanding of the mass and heat transport and electrochemical reaction in the CL microstructure, but it also guides the optimal design and fabrication of CL components and structures, such as improving the local structure to reduce the number of dead pores and large agglomerates, etc.

Numerical simulation of moisture extraction under the influence of an acousto-convective flow from a thin cavern

With using the mechanics of multiphase media, the process of extraction of moisture from a dead pore is considered. The study was carried out by numerical simulation. Two-dimensional approach of interaction of the air flow with droplets without taking into account the processes of heat and mass transfer was considered.

BIMETAL/CARBON NANOCOMPOSITES CuCo@C BASED ON SYNTHETIC HUMIC ACIDS

The new original method for the synthesis of bimetal-carbon nanocomposites of copper and cobalt (CuCo@C) of various compositions using synthetic humic acid as a carbon source has been developed. The technique includes the synthesis of humates of copper and cobalt, preparation of their mixture and its pyrolysis in a hydrogen atmosphere. For characterize the final product, the methods of diffraction, cyclic voltammetry, and scanning electron microscopy were used. Comparison of diffractograms of bimetal nanocomposites shown two systems of reflexes from fcc structures, which correspond to metallic copper and cobalt. Diffractometric measurements also indicate the amorphous nature of the carbon matrix. Carrying out the pyrolysis of the metal humates in the reducing atmosphere afford remove almost completely the contained oxygen from the final product, partly in the form of CO2, partly in the form of water. Ions of the transition metal in these conditions are reduced to the metal atoms, forming nanoparticles surrounded by carbon. The formation of a carbon matrix metal around nanoparticles, on the one hand, can ensure their high thermal stability, and on the other hand, contributes to the stabilization of metal nanoparticles and prevents their aggregation. The size of cobalt nanoparticles in nanocomposites varies from 35 to 54 nm, and copper nanoparticles - from 56 to 88 nm, depending on the ratio used in the synthesis of metal humates. It was found that nanoparticles of an alloy of these metals (alpha-cobalt phase) are formed in nanocomposites containing 20% ​​copper and 80% cobalt. Cyclic voltammogrames of bimetallic nanocomposites indicate the presence of dead pores in their composition. It has been established by scanning electron microscopy that in the case of an excess amount of copper in the nanocomposites, spherical formations about 1000 nm in size with faceting signs are formed. As part of the «bottom up» concept proposed a three-stage model of formation.

Laws of gas and water flow and mechanism of reservoir drying in tight sandstone gas reservoirs

The reservoir permeability of tight sandstone gas reservoirs is low, which makes it difficult to carry out displacement flow experiments on real cores underground conditions, so the microscopic flow mechanism can be hardly studied. Based on the lattice Boltzmann method (LBM), this paper simulated the flow process of formation water displaced by tight gas under the simulated reservoir conditions of high temperature and high pressure to clarify the distribution of bound water in the reservoir. Then, reservoir drying was experimentally studied using the laser etching model, and numerical simulation of reservoir drying was simplified by referring to the visualization results of the experiment. Finally, the influence of reservoir drying on the seepage capacity of tight gas was studied by means of numerical simulation. And the following research results were obtained. First, when the lattice Boltzmann model is used for high temperature and high pressure reservoirs, it satisfies the Laplace law and its numerical solution of two-phase Poiseuille flow rate is basically consistent with the analytical solution, which indicates that this model can be used to simulate gas–water immiscible displacement under reservoir conditions. Second, tight gas preferentially breaks through in large porous media connected channels, and after the breakthrough, the displacement rate of formation water decreases significantly. Third, the contact angle between formation water and rock wall has a significant influence on gas–water two-phase flow. The stronger the water wettability of the rock is, the lower the displacement rate is. Fourth, the bound water in tight sandstone gas reservoirs can be classified into four types, including adsorbed water film, blind end pore water, dead pore water and trapped water. In porous media, a large number of connected micro-channels are occupied by trapped water and adsorbed water film and the phenomenon of “water lock” is obvious, which seriously influences the seepage capacity of tight gas in the porous media of reservoir. Fifth, drying agent can react with bound water to produce a large number of bubbles, which will consume adsorbed water film, trapped water and blind end pore water, so as to improve the gas seepage capacity. Sixth, in the “water lock” regions formed by trapped water, the gas seepage capacity can be effectively improved by increasing the drying strength. On the whole, the tight gas permeability increases with the increase of drying strength, but its increase amplitude decreases gradually when the drying strength exceeds a certain degree.

In situ activation graphitization to fabricate hierarchical porous graphitic carbon for supercapacitor

In situ activation–graphitization method based on the atomically dispersed K and Fe in organic salts is developed to synthesize hierarchical porous graphitic carbon by directly pyrolysis potassium citrate and iron citrate. Moreover, (NH4)2C2O4 is also employed as both N dopant and porogen to open up internal structure and regulate pore structure. The inside-out activation leads to the homogeneous reaction and interconnected hierarchical porous structure with few dead pores. Accompanied by high specific surface area, appropriate pore distribution, good conductivity, and N/O functional groups, the sample exhibits high capacitance of 322.6 F g−1 at 0.5 A g−1, good rate capability, and excellent cycling stability with 101.5% capacitance retention after 15,000 cycles. The supercapacitor shows an energy density of 21.3 W h kg−1 at 456.7 W kg−1 in 1 M Na2SO4. Easy synthesis, cost-effective, and environmentally benign, the work provides a promising strategy to produce hierarchical porous graphitic carbon applied in energy storage.

Three-dimensional porous electrodes for direct formate fuel cells

The dual-layer electrode for fuel cells is typically prepared by binding discrete catalyst nanoparticles onto a diffusion layer. Such a random packing forms a dense catalyst layer and thus creates a barrier for mass/ion transport, particularly for direct liquid fuel cells. Three-dimensional porous electrodes, a thin nano-porous catalyst layer uniformly distributed on the matrix surface of a foam-like structure, are typically employed to improve the mass/ion transport. Such a three-dimensional porous structure brings two critical advantages: (i) reduced mass/ion transport resistance for the delivery of the reactants via shortening the transport distance and (ii) enlarged electrochemical surface area, via reducing the dead pores, isolated particles and severe aggregations, for interfacial reactions. Moreover, the three-dimensional design is capable of fabricating binder-free electrodes, thereby eliminating the use of ionomers/binders and simplifying the fabrication process. In this work, three types of three-dimensional porous electrode are fabricated, via different preparation methods, for direct formate fuel cells: (i) Pd/C nanoparticles coating on the nickel foam matrix surface (Pd-C/NF) via a dip-coating method, (ii) Pd nanoparticles depositing on the nickel foam matrix surface (Pd/NF) via reduction reaction deposition, and (iii) Pd nanoparticles embedding in the nickel foam matrix (Pd/(in)NF) via replacement reaction deposition. The latter two are binder-free three-dimensional porous electrodes. As a comparison, a conventional dual-layer design, Pd/C nanoparticles painting on the nickel foam layer (Pd-C//NF), is also prepared via direct painting method. It is shown that the use of the three-dimensional Pd-C/NF electrode as the anode in a direct formate fuel cell results in a peak power density of 45.0 mW cm−2 at 60°C, which is two times of that achieved by using a conventional dual-layer design (19.5 mW cm−2). This performance improvement is mainly attributed to the unique three-dimensional structure design, which effectively enhances the mass/ion transport through the porous electrode and enlarges the electrochemical surface area (accessible active area) for interfacial reactions. In addition, the delivery of the fuel solution is still sufficient even when the flow rate is as low as 2.0 mL min−1. It is also demonstrated that direct formate fuel cells using two binder-free electrodes yield the peak power densities of 13.5 mW cm−2 (Pd/(in)NF) and 14.0 mW cm−2 (Pd/NF) at 60°C, respectively, both of which are much lower than the power density achieved by using the Pd C/NF electrode. This is because the electrochemical surface areas of two binder free electrodes are much smaller than the Pd/C based electrodes, since the specific area of Pd/C nanoparticles is much larger.

Displacement mechanism of polymeric surfactant in chemical cold flooding for heavy oil based on microscopic visualization experiments

In order to study the microscopic oil displacement mechanism of polymeric surfactant in chemical cold flooding for heavy oil, the indoor microscopic visualization displacement experiments were carried out. The flooding experiment of heavy oil was conducted by using water, osmotic modified oil displacing agent (a kind of polymeric surfactant) and water-in-oil emulsion (obtained by mixing polymeric surfactant and heavy oil) as displacing phases to study the mechanism of polymeric surfactant to enhance oil recovery in heavy oil reservoir. The experimental results show that the polymeric surfactant can increase the viscosity of the water phase, reduce the water-oil mobility ratio, expand the swept area, and there is no obvious fingering phenomenon which occurs during water flooding. The polymeric surfactant has the surfactant characteristics which can reduce the interfacial tension between oil and water to promote the formation of oil droplets with smaller droplet diameter. And the interfacial film composed of polymeric surfactant molecules will be formed on the surface of oil droplets to prevent the coalescence of oil droplets and improve the flow ability of oil phase. The water-in-oil emulsion can be miscible with the oil in heavy oil displacement process, and thus sweeps the areas such as the dead pores which cannot be swept by water and polymeric surfactant flooding, which increases the sweep efficiency to a certain extent. Cited as : Xu, F., Chen, Q., Ma, M., Wang, Y., Yu, F., Li, J. Displacement mechanism of polymeric surfactant in chemical cold flooding for heavy oil based on microscopic visualization experiments. Advances in Geo-Energy Research, 2020, 4(1): 77-85, doi: 10.26804/ager.2020.01.07

Investigation of porous materials with large surface heterogeneity using the generalized Porod's scattering law method.

Surface heterogeneity is ubiquitous in both natural and man-made materials, and can significantly influences material properties. However, it is very challenging to noninvasively probe the variation of surface properties in porous materials. Recently, we have proposed a method, i.e., the generalized Porod's scattering law method (GPSLM), to obtain the surface heterogeneity information in bulk porous materials by extending the classic Porod's scattering method. However, it was not clear if the GPSLM can be applied to other more complex materials, such as porous materials with dead pores, i.e., pores that guest fluid molecules cannot access or porous materials whose solid matrix can adsorb small guest molecules. In this paper, we theoretically extend the GPSLM to study those more complex situations. For all five cases with different levels of complexity discussed in this work, the scattering intensity at the Porod's law region always follows a parabolic function of scattering length density (SLD) of the guest fluid. Moreover, the minimum value of the scattering intensity is all related to the surface heterogeneity of the porous materials. The SLD of the guest fluid at which the minimum intensity is reached is always related to the surface-averaged SLD of materials. We also discuss the potential limitations and possible future applications of the GPSLM. As the GPSLM is based on the contrast variation method commonly used for a wide range of materials, such as geological materials, biomaterials, and colloidal suspensions, the theoretical development here is potentially useful for researchers who would like to apply the GPSLM to more complicated materials besides porous materials.

Modeling tracer flowback in tight oil reservoirs with complex fracture networks

Tight oil reservoirs are commonly developed by a combination of horizontal wells and multistage hydraulic fracturing techniques. The characterization of complex fracture networks after fracturing treatments is a common challenge for unconventional reservoirs. Tracer flowback profiles can reveal a fracture network at an individual stage. However, the numerical simulation of tracer transport in fractured reservoirs usually employs a dual-porosity continuum medium model or describes fractures by an enlarged fracture aperture in a regular grid system that is not capable of modeling a complex fracture network. Especially, the influences of the properties of fracturing fluid and variations in fracture permeability caused by pressure changes on tracer flowback profiles are not investigated.In this paper, a two-phase (water and oil), four-component (oil, water, fracturing fluid and tracer) numerical simulator is developed based on a discrete fracture model for modeling tracer injection and flowback in tight oil reservoirs. With respect to fracture network modeling, the simulator is capable of explicitly modeling an arbitrary distribution of fracture networks with a real fracture aperture by triangular grids. With respect to mechanism consideration, the simulator considers the influences of fracturing fluid and pressure-dependent fracture permeability on tracer flowback profiles. The properties of tracer dispersion and adsorption are also considered in both fractures and matrix. To validate the proposed model, a comparison is performed with the commercial software Eclipse. Sensitivity studies are performed to investigate the influences of parameters on tracer flowback profiles. The presented simulator is applied in the Changji oilfield to characterize individual stages using a stochastic method.Results show that the developed simulator is accurate as with Eclipse. The filed application indicates that the presented simulator can model tracer flowback and production performance. Sensitivity studies show that an increase in permeability modulus and the viscosity of fracturing fluid delays the peak arrival time. An increase in permeability modulus decreases the peak amplitude while an increase in the viscosity of the fracturing fluid increases the peak amplitude. An increase in a dead pore volume and a residual resistance factor has little impact on the peak position and lowers the tails of tracer flowback profiles. The sensitivity studies provide valuable information in characterization of a fracture network using tracer flowback data.

Fully implicit higher-order schemes applied to polymer flooding

In water-based EOR methods, active chemical or biological substances are added to modify the physical properties of the fluids or/and the porous media at the interface between oil and water. The resulting displacement processes are governed by complex interplays between the transport of chemical substances, which is largely linear and highly affected by numerical diffusion, and how these substances affect the flow by changing the properties of the fluids and the surrounding rock. These effects are highly nonlinear and highly sensitive to threshold parameters that determine sharp transitions between regions of very different behavior. Unresolved simulation can therefore lead to misleading predictions of injectivity and recovery profiles. Use of higher-order spatial discretization schemes have been proposed by many authors as a means to reduce numerical diffusion and grid-orientation effects. Most higher-order simulators reported in the literature are based on explicit time stepping, and only a few are implicit. One reason that fully implicit formulations are not widely used might be that it becomes quite involved to compute the necessary linearizations for modern high-resolution discretizations of TVD and WENO type. Herein, we solve this problem by using automatic differentiation. We also demonstrate that using lagged evaluation of slope limiters and WENO weights alleviates the nonlinearity of the discrete systems and improves the computational efficiency, without having an adverse effect on the stability and accuracy of the higher-resolution schemes. As an example of EOR, we consider polymer flooding, which involves complex and adverse phenomena like adsorption in the rock, degradation and in-situ chemical reactions, shear thinning/thickening, dead pore space, etc. Using a few idealized test cases, we compare and contrast explicit and fully implicit time stepping for a variety of high and low-resolution spatial discretizations.

GluD1, linked to schizophrenia, controls the burst firing of dopamine neurons

Human mutations of the GRID1 gene encoding the orphan delta1 glutamate receptor-channel (GluD1) are associated with schizophrenia but the explicit role of GluD1 in brain circuits is unknown. Based on the known function of its paralog GluD2 in cerebellum, we searched for a role of GluD1 in slow glutamatergic transmission mediated by metabotropic receptor mGlu1 in midbrain dopamine neurons, whose dysfunction is a hallmark of schizophrenia. We found that an mGlu1 agonist elicits a slow depolarizing current in HEK cells co-expressing mGlu1 and GluD1, but not in cells expressing mGlu1 or GluD1 alone. This current is abolished by additional co-expression of a dominant-negative GluD1 dead pore mutant. We then characterized mGlu1-dependent currents in dopamine neurons from midbrain slices. Both the agonist-evoked and the slow postsynaptic currents are abolished by expression of the dominant-negative GluD1 mutant, pointing to the involvement of native GluD1 channels in these currents. Likewise, both mGlu1-dependent currents are suppressed in GRID1 knockout mice, which reportedly display endophenotypes relevant for schizophrenia. It is known that mGlu1 activation triggers the transition from tonic to burst firing of dopamine neurons, which signals salient stimuli and encodes reward prediction. In vivo recordings of dopamine neurons showed that their spontaneous burst firing is abolished in GRID1 knockout mice or upon targeted expression of the dominant-negative GluD1 mutant in wild-type mice. Our results de-orphanize GluD1, unravel its key role in slow glutamatergic transmission and provide insights into how GRID1 gene alterations can lead to dopaminergic dysfunctions in schizophrenia.

TiO2 nanotubes and mesoporous silica as containers in self-healing epoxy coatings.

The potential of inorganic nanomaterials as reservoirs for healing agents is presented here. Mesoporous silica (SBA-15) and TiO2 nanotubes (TNTs) were synthesized. Both epoxy-encapsulated TiO2 nanotubes and amine-immobilized mesoporous silica were incorporated into epoxy and subsequently coated on a carbon steel substrate. The encapsulated TiO2 nanotubes was quantitatively estimated using a ‘dead pore ratio’ calculation. The morphology of the composite coating was studied in detail using transmission electron microscopic (TEM) analysis. The self-healing ability of the coating was monitored using electrochemical impedance spectroscopy (EIS); the coating recovered 57% of its anticorrosive property in 5 days. The self-healing of the scratch on the coating was monitored using Scanning Electron Microscopy (SEM). The results confirmed that the epoxy pre-polymer was slowly released into the crack. The released epoxy pre-polymer came into contact with the amine immobilized in mesoporous silica and cross-linked to heal the scratch.

Study of the Well-Posedness of Models for the Inaccessible Pore Volume in Polymer Flooding

Inaccessible pore volume, also known as dead pore space, is used when simulating enhanced oil recovery by polymer injection. We show that a widely used model for inaccessible pore volume can lead to an ill-posed problem, resulting in unphysical results. By considering shock solutions of the one-dimensional problem, we derive a necessary condition that an inaccessible pore volume model must fulfill in order to obtain well-posed equations. In this derivation, we use the Rankine–Hugoniot jump condition as a selection criterion for acceptable solutions. There are other possible criteria for the one-dimensional problem, in particular $$\delta $$ -shock solutions, which we also briefly describe, but these are challenging and impractical to use. Based on a heuristic understanding of relative permeability, we subsequently derive two modified models for inaccessible pore volume. The first model follows directly from the modeling assumptions, but it has limited applicability. If the inaccessible pore volume is larger than the irreducible water saturation, then the equations are ill-posed for convex relative permeabilities. A second model is derived by relaxing the assumption of inaccessibility, allowing a limited fraction of the polymer to enter the smallest pores. This second model fulfills our necessary condition for well-posedness for all values of the inaccessible pore volume and any choice of relative permeabilities. Through one- and two-dimensional numerical examples, the different models for inaccessible pore volume are compared. For our second suggested model, the polymer concentration is observed to stay below the maximum injected value, which is not the case for the conventional model. This enables a more stable implementation of the highly nonlinear system, and a reduction in the number of nonlinear iterations is also observed in some cases. As this suggested model is straightforward to implement into existing reservoir simulators and can be used for a wide range of polymer models, it serves as a possible alternative to the conventional model.

Hollow/porous nanostructures derived from nanoscale metal–organic frameworks towards high performance anodes for lithium-ion batteries

Lithium-ion batteries (LIBs), owing to their high energy density, light weight, and long cycle life, have shown considerable promise for storage devices. The successful utilization of LIBs depends strongly on the preparation of nanomaterials with outstanding lithium storage properties. Recent progress has demonstrated that hollow/porous nanostructured oxides are very attractive candidates for LIBs anodes due to their high storage capacities. Here, we aim to provide an overview of nanoscale metal-organic frameworks (NMOFs)-templated synthesis of hollow/porous nanostructured oxides and their LIBs applications. By choosing some typical NMOFs as examples, we present a comprehensive summary of synthetic procedures for nanostructured oxides, such as binary, ternary and composite oxides. Hollow/porous structures are readily obtained due to volume loss and release of internally generated gas molecules during the calcination of NMOFs in air. Interestingly, the NMOFs-derived hollow/porous structures possess several special features: pores generated from gas molecules release will connect to each other, which are distinct from "dead pores"; pore size often appears to be <10 nm; in terms of surface chemistry, the pore surface is hydrophobic. These structural features are believed to be the most critical factors that determine LIBs' performance. Indeed, it has been shown that these NMOFs-derived hollow/porous oxides exhibit excellent electrochemical performance as anode materials for LIBs, including high storage capacity, good cycle stability, and so on. For example, a high charge capacity of 1465 mA h g(-1) at a rate of 300 mA g(-1) was observed after 50 cycles for NMOFs-derived Co3O4 porous nanocages, which corresponds to 94.09% of the initial capacity (1557 mA h g(-1)), indicating excellent stability. The capacity of NMOFs-derived Co3O4 is higher than that of other Co3O4 nanostructures obtained by a conventional two-step route, including nanosheets (1450 mA h g(-1) at 50 mA g(-1)), nanobelts (1400 mA h g(-1) at 40 mA g(-1)) and nanoflowers (694 mA h g(-1) at 100 mA g(-1)). The capacity is also better than Co3O4 octahedra obtained by a one-step hydrothermal method (946 mA h g(-1) at 100 mA g(-1)). In this review, we will summarize the recent research advances on NMOFs-derived hollow/porous oxides as LIBs anodes. The enhanced lithium storage properties have been discussed in relation to their special structural parameters. Moreover, remarks on the current challenges and perspectives for future NMOFs applications are proposed. Through this systematic review, we aim to stress the importance of NMOFs templates for the fabrication of hollow/porous functional materials that would result in improved physicochemical properties and provide insights to guide future research for LIBs applications.

Low dielectric property of novel mesoporous silica/polymer composites using smart molecular caps: Theoretical calculation of air space encapsulated inside mesopores

Here we demonstrate the fabrication of novel mesoporous silica/polymer composites using smart molecular caps and investigate the low dielectric property. For the preparation of mesoporous silica/polymer composites, the entrance of the mesopores are firstly modified by polysilsesquioxane (POSS) molecules. The large-sized POSS molecules can act as smart caps to prevent a penetration of the polymers into the inside mesopores (to keep the air space in the mesopores). After that, trimethylsilyl (TMS) agents are grafted onto silanol groups at the inner mesopores to reduce the polarity. Then, organically modified mesoporous silicas are mixed with epoxy polymers by mechanical processing. Here, various types organically modified mesoporous silica with different amount of the modified POSS molecules are utilized to prepare the composites. From the specific gravity data, it is proved that 20 wt% POSS modification is the best for effective blocking the penetration of the polymer into the mesopores. In this composite, lots of air space can remain, showing the excellent low dielectric property. On the other hand, when the POSS modification is less, some polymers penetrate the mesopores at the inner parts of the particles, decreasing the air space. In this paper, we propose new parameter “dead pore ratio” and theoretically discuss how much mesopores maintain as air spaces in the composite, which is an important value for understanding for low- k property of mesoporous silica/polymer composites.

3-D Analysis of Pore Structure of Porous Biomaterials Using Micro Focus X-Ray Computed Tomography

Generally, characterizations of pore structures of porous biomaterials are mainly based on 2-dimensional (2-D) analysis using cross sectional micrographs. However, interconnectivity of each pore may be more important factor, when tissue ingrowth into deeper pores is considered. In this paper, using micro-CT imaging with 3-D image processing software, analyses of porous material based on 3-demensional (3-D) geometrical considerations were successfully performed. Plasmasprayed porous titanium implant (PT) and four types of sintered porous titanium implants (ST50- 200, ST50-500, ST70-200, and ST70-500) that possess different porosities (50% and 70%) and pore sizes (200-500+m and 500-1500+m) were analyzed in this study. A micro focus X-ray computed tomography system was employed to acquire microstructural information from the porous implants. Using 3-D image processing software, we performed three types of 3-D analysis including detection of the dead space (% dead pore), analysis of interconnectivity by blocking the narrow pore throat with caliber less than 52 +m (% pore with narrow throat) and analysis of material construct by contracting thin strut with thickness less than 52 +m (% construct with thin strut). ST50S and ST50L possessed interconnected porous structure with thicker strut; however, pore throat was considered to be relatively narrow. On the other hand, PT implant possesses favorable interconnectivity despite its’ low porosity; however, relatively thin strut indicate the structural disadvantage for mechanical property. These results suggest that the 3-D analysis of pore and strut structure using micro focus X-ray computed tomography and 3-D image processing software will provide effective information to develop porous implant.