Effect of Co loading on the hydrogen storage characteristics of hollow glass microspheres (HGMs)

The use of hydrogen as a fuel either direct combustion in an IC engine or for power generation in fuel cells continues to be a topic of significant interest. Developing and popularizing fuel cells for vehicular or other stationary applications depends upon the availability of safe and reliable hydrogen storage method. The greatest challenge as of now in this regard is the production of a light weight, nontoxic and easily transportable material which can store hydrogen. World-wide research is being conducted on developing newer materials for hydrogen storage. Hollow glass microspheres (HGMs) can be considered to be a potential hydrogen carrier which can store and deliver hydrogen for energy release applications. In this paper, we are reporting the preparation and characterization of cobalt loaded HGMs from amber glass powder for hydrogen storage applications. The feed glass powder with different percentage of cobalt loading was prepared by soaking and drying the feed glass powder in required amount of cobalt nitrate hexahydrate solution. Further, the dried feed glass powder was flame spheroidised to get cobalt loaded HGMs. Characterizations of all the HGMs samples were done using SEM, FTIR and XRD techniques. Hydrogen adsorptions on all the samples were done for 10 bar pressure at room temperature and 200 °C for 5 h. The results showed that the hydrogen adsorption capacity on these samples increased with increase in cobalt wt% from 0.2 to 2.0%. The hydrogen storage capacity of HACo2 was found to 2.32 wt% for 10 bar pressure at 200 °C.     

Facile production of optically active hollow glass microspheres for photo-induced outgassing of stored hydrogen

Illumination of engineered hollow glass microspheres with near-infrared light is used to rapidly release stored gases, in particular hydrogen. Photo-induced outgassing of hydrogen is made possible by introducing optically active dopants into the glass such as cobalt. Recycled amber glass frit coated with polypropylene glycol and cobalt sulfate is converted into hollow glass microspheres with a simple, low-cost flame spraying method. Hollow glass microspheres made by this process release hydrogen more quickly when illuminated versus traditional outgassing with a heated oven. A simple model is proposed for engineering the geometry of the hollow glass microspheres.     

Production and characterization of hollow glass microspheres with high diffusivity for hydrogen storage

A process is developed to produce high diffusivity hollow glass microspheres (HGMs) with high concentration of silica for applications in hydrogen storage by volatilizing alkali and boron oxides in shell-forming process. We investigate the effects of the initial glass compositions of gel particles, the pressure and composition of furnace atmosphere, the temperature and length of refining zone on the diffusivity, quality and yield of the resulting HGMs. The results show that with the preferred total contents of alkali oxides and the ratios of potassium to sodium in the initial glass compositions, the ultimate concentrations of SiO₂ in the resulting HGMs can be up to 95%, with most alkali and boron oxides being volatilized in the refining process. The quality and yield of the high silica HGMs change significantly with the initial glass compositions of the gel particles. The total alkali oxide concentrations ranging from 15% to 20% in the initial glass compositions are preferred to obtain high silica HGMs with high quality and yield. The permeability coefficients of the resulting HGMs can be improved remarkably by increasing the temperature and length of the refining zone. The permeability coefficients of the high silica HGMs to hydrogen gas at ambient temperature are between 3 and 4 × 10⁻²⁰ (mol·m)/(m²·s·Pa).     

Floating microparticles of ZnIn2S4 @hollow glass microsphere for enhanced photocatalytic activity

The irreconcilable contradiction between high performance of photocatalysis and reclamation difficulty of micro/nano photocatalysts is still a barrier for the wide application of photocatalytic technology. In order to increase the efficiency of light utilization and facilitate recycling, visible-light photocatalysts ZnIn₂S₄ (ZIS) grafted on floating hollow glass microspheres (HGMs) were prepared through a controllable hydrothermal method. The hollow structural composite microspheres were prepared by depositing a layer of ZIS nano-film onto the surface of the coarsening hydroxyl/amino-functionalized HGMs via a chemical self-assembly process. The different pretreatment methods of HGMs resulted in the change in the structure pattern, morphology and photocatalytic activities of the as-prepared ZIS@HGMs composite microspheres. In addition, the possible growth mechanism of the formation process of ZIS@HGMs composite microspheres was proposed. Finally, the as-prepared ZIS@HGMs composite microspheres exhibited an enhanced degradation efficiency of Rhodamine B (RhB) versus ZIS powder under visible light irradiation. The as prepared floating photocatalysts have good dispersibility and could be recycled by simple filtration. The present study provided a promising approach to keep the high performance of photocatalysis as well as efficient recycling of micro/nano photocatalysts.     

Magnesium and iron loaded hollow glass microspheres (HGMs) for hydrogen storage

The development of a safe and efficient method for hydrogen storage is essential for the use of hydrogen with fuel cells for vehicular applications. Hollow glass microspheres (HGMs) have characteristics suitable for hydrogen storage and are expected to be a potential hydrogen carrier to be used for energy release applications. The HGMs with 10–100 μm diameters, 100–1000 Å pore width and 3–8 μm wall thicknesses are expected to be useful for hydrogen storage. In our research we have prepared HGMs from amber glass powder of particle size 63–75 μm using flame spheroidisation method. The HGMs samples with magnesium and iron loading were also prepared to improve the heat transfer property and thereby increase the hydrogen storage capacity of the product. The feed glass powder was impregnated with calculated amount of magnesium nitrate hexahydrate salt solution to get 0.2–3.0 wt% Mg loading on HGMs. Required amount of ferrous chloride tetrahydrate solution was mixed thoroughly with the glass feed powder to prepare 0.2–2 wt% Fe loaded HGMs. Characterizations of all the HGMs samples were done using FEG-SEM, ESEM and FTIR techniques. Adsorption of hydrogen on all the Fe and Mg loaded HGMs at 10 bar pressure was conducted at room temperature and at 200 °C, for 5 h. The hydrogen adsorption capacity of Fe loaded sample was about 0.56 and 0.21 weight percent for Fe loading 0.5 and 2.0 weight percentage respectively. The magnesium loaded samples showed an increase of hydrogen adsorption from 1.23 to 2.0 weight percentage when the magnesium loading percentage was increased from 0 to 2.0. When the magnesium loading on HGMs was increased beyond 2%, formation of nano-crystals of MgO and Mg was seen on the HGMs leading to pore closure and thereby reduction in hydrogen storage capacity.     

Fabrication of monodisperse precursor gel microspheres for hollow glass microspheres by combining the sol-microemulsion-gel process with a T-shaped microfluidic device

To fabricate uniform hollow glass microspheres (HGMs) for application in hydrogen storage, a sol-microemulsion-gel process combined with a T-shaped junction microfluidic technology was developed to fabricate monosized precursor gel microspheres. Precursor gel microspheres with monodispersity index less than 4% can be obtained based on the uniform reactions in the monosized sol droplets as micro-reactors, with monodispersity index less than 3%, generated by the microfluidic device. The results show that the precursor gel microspheres have uniform diameter, density, microstructure, composition and high sphericity. The monosized dried gel microspheres can be transformed into uniform HGMs, with high yield and quality for hydrogen storage, in a high temperature vertical furnace under the optimized operating condition.     

Experimental analysis of a metal hydride hydrogen storage system with hexagonal honeycomb-based heat transfer enhancements-part B

This study is a continuation of the computational analysis of the reactor equipped with hexagonal honeycomb based heat transfer enhancements, performed in Part A of the study. In the present study, the performance of the metal alloy and the reactor is investigated experimentally. The gravimetric capacity and reaction kinetics of the alloy La_0.9Ce_0.1Ni₅ are determined. The performance of the reactor under different external environments is noted. The influence of operating conditions such as supply pressure, heat transfer fluid, heat transfer fluid temperature on the reactor performance is investigated. Evaporative cooling as a heat removal technique for metal hydride based hydrogen storage reactors is tested for the first time and compared to conventional heat removal methods. It is found to improve the heat transfer from the alloy bed significantly.     

Storage of cryo-compressed hydrogen in flexible glass capillaries

We present the results of the theoretical calculations and the corresponding experiments with compressed hydrogen storage in flexible glass capillaries both at room and liquid nitrogen temperatures. It was demonstrated that the strength of produced quartz capillaries can be high enough to withstand the internal hydrogen pressure up to 233 MPa and capillary vessels can have relatively high volumetric and gravimetric capacity.     

Fabrication of zinc‐loaded hollow glass microspheres (HGMs) for hydrogen storage

The greatest challenge for a feasible hydrogen economy lies on the production of pure hydrogen and the materials for its storage with controlled release at ambient conditions. Hydrogen with its great abundance, high energy density and clean exhaust is a promising candidate to meet the current global challenges of fossil fuel depletion and green house gases emissions. Extensive research on hollow glass microspheres (HGMs) for hydrogen storage is being carried out world‐wide, but the right material for hydrogen storage is yet underway. But many other characteristics, such as the poor thermal conductivity etc. of the HGMs, restrict the hydrogen storage capacity. In this work, we have attempted to increase the thermal conductivity of HGMs by ZnO doping. The HGMs with Zn weight percentage from 0 to 10 were prepared by flame spheroidization of amber‐colored glass powder impregnated with the required amount of zinc acetate. The prepared HGMs samples were characterized using field emission‐scanning electron microscope (FE‐SEM), environmental SEM (ESEM), high‐resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy and X‐ray diffraction (XRD) techniques. The deposition of ZnO on the microsphere walls was observed using FE‐SEM, ESEM and HRTEM which was further confirmed using the XRD and ultraviolet–visible absorption data. The hydrogen storage studies done on these samples at 200 °C and 10‐bar pressure for 5 h showed that the hydrogen storage increased when the Zn percentage in the sample increased from 0 to 2%. The percentage of zinc beyond 2, in the microspheres, showed a decline in the hydrogen storage capacity. The closure of the nanopores due to the ZnO nanocrystal deposition on the microsphere surface reduced the hydrogen storage capacity. The hydrogen storage capacity of HAZn2 was found 3.26 wt% for 10‐bar pressure at 200 °C. Copyright © 2015 John Wiley & Sons, Ltd.     

Improvement of heat transfer model for adsorptive hydrogen storage system

Hydrogen adsorption on high surface area activated carbon is an effective solution of hydrogen storage. Improvement is necessary for the heat transfer model of adsorptive hydrogen storage system. Distributed and lumped parameter models are implemented by the Comsol software and Matlab/Simulink software respectively. The evolution of pressure and temperature during charge and discharge processes is investigated. We adopted following measures for a further improvement on the model: (1) Wall temperature is improved by varying heat transfer coefficient; (2) A more realistic geometry with insert tube improves near inlet temperature; (3) Lumped parameter model is improved by considering thermal conductivity; (4) Distributed and lumped parameter models are well validated by experiments; (5) Heat transfer is modeled under conditions of air cooling and water cooling. The water cooling condition is better than air cooling condition in decreasing the temperature of the storage tank and improving the storage capacity.     

Design of a large-scale metal hydride based hydrogen storage reactor: Simulation and heat transfer optimization

An optimized design for a 210 kg alloy, TiMn alloy based hydrogen storage system for stationary application is presented. A majority of the studies on metal hydride hydrogen systems reported in literature are based on system scale less than 10 kg, leaving questions on the design and performance of large-scale systems unanswered. On the basis of sensitivity to various design and operating parameters such as thermal conductivity, porosity, heat transfer coefficient etc., a comprehensive design methodology is suggested. Following a series of performance analyses, a multi-tubular shell and tube type storage system is selected for the present application which completes the absorption process in 900 s and the desorption process in 2000 s at a system gravimetric capacity of 0.7% which is a vast improvement over similar studies. The study also indicates that after fifty percent reaction completion, heat transfer ceases to be the major controlling factor in the reaction. This could help prevent over-designing systems on the basis of heat transfer, and ensure optimum system weight.     

Mg-based composites for enhanced hydrogen storage performance

Hydrogen storage in solids of hydrides is advantageous in comparison to gaseous or liquid storage. Magnesium based materials are being studies for solid-state hydrogen storage due to their advantages of high volumetric and gravimetric hydrogen storage capacity. However, unfavorable thermodynamic and kinetic barriers hinder its practical application. In this work, we presented that kinetics of Mg-based composites were significantly improved during high energy ball milling in presence of various types of carbon, including plasma carbon produced by plasma-reforming of hydrocarbons, activated carbon, and carbon nanotubes. The improvement of the kinetics and de-/re-hydrogenation performance of MgH₂ and TiC-catalysed MgH₂ by introduction of carbon are strongly dependent on the milling time, amount of carbon and carbon structure. The lowest dehydrogenation temperature was observed at 180 °C by the plasma carbon–modified MgH₂/TiC. We found that nanoconfinement of carbon structures stabilised Mg-based nanocomposites and hinders the nanoparticles growth and agglomeration. Plasma carbon was found to show better effects than the other two carbon structures because the plasma carbon contained both few layer graphene sheets that served as an active dispersion matrix and amorphous activated carbons that promoted the spill-over effect of TiC catalysed MgH₂. The strategy in enhancing the kinetics and thermodynamics of Mg-based composites is leading to a better design of metal hydride composites for hydrogen storage.     

System simulation modeling and heat transfer in sodium alanate based hydrogen storage systems

In this paper, we examine the feasibility of an on-board hydrogen storage system using sodium alanate as the hydrogen storage material. A two-dimensional model is used for evaluating refueling dynamics as well as heat transfer coefficients for the system level model. A parametric study is conducted to understand the influence of different operating parameters on the refueling time. System level performance of this storage system during driving conditions is evaluated using a simulation model developed in Matlab/Simulink platform.     

Simulation of heat and mass transfer in activated carbon tank for hydrogen storage

The charging process of hydrogen storage tank based on bed of activated carbon in a steel container at room temperature (295 K) and medium storage pressure (10 MPa) is simulated with an axisymmetric geometry model using the finite volume commercial solver Fluent. The mass flux profile at the entrance is established using user-defined functions (UDFs). The heat and mass transfer processes in the cylindrical steel tank packed with activated carbon are discussed considering the influence of viscous resistance and inertial resistance of the porous media. The velocity distribution and its effect on the temperature distribution are analyzed. The effects of the flow rate at the inlet and of the adsorption factor on the charging process are studied. A computational fluid dynamics (CFD) approach based on finite volume simulations is used. Results show that the temperature near the bottom of the tank is higher than that at the entrance, temperature in the center of the tank is higher than that near the wall and rises somewhat faster along the axial compared to the radial direction. The highest hydrogen absolute adsorption occurs at the entrance of the tank. A good agreement is found between the simulation results and the available experimental data. The maximum magnitude of the axial velocity is much higher than that of the radial component, resulting in more heat energy transfer along the axial direction than radial direction. In addition, the pressure reaches equilibrium earlier when the mass flow is higher, and the temperature reaches a maximum value faster.     

A review on recent advances in hollow spheres for hydrogen storage

Recent advancements in synthesizing materials potential for hydrogen storage have greatly forced the hydrogen storage technology ahead in recent years. Hollow spheres, with unparalleled characteristics like low density and high specific surface area, have emerged as one of the most promising alternatives for hydrogen storage applications. In the present review, the main synthesis approaches of hollow spheres including spray drying, Kirkendall, template-free and, template-assisted methods are surveyed and concisely described. In addition, different types of hollow spheres such as hollow carbons, hollow glasses and other less-common types like Boron nitrides and metal hollow spheres have been tackled with special focus on adsorption/desorption capacities as well as the kinetic of hydrogen storage/release. In addition to the recent progresses, some perspective and outlook on the advancement of hollow spheres and challenges in terms of synthesis methods and hydrogen storage performance were presented.     

In situ deposition of Pd nanoparticles with controllable diameters in hollow carbon spheres for hydrogen storage

A novel in situ synthesis of Pd nanoparticles supported in hollow carbon spheres (HCS) is reported. The size of the nanoparticles can be tuned via application of different Pd precursors. The hydrogen storage properties of Pd supported in HCS under room temperature were examined at partial pressures. We observed significant difference between the storage capacities of two samples containing Pd nanoparticles with different diameter distributions. The results showed that the sample with suitable diameters of Pd nanoparticles was more favorable for the H₂ storage, even lower mass of Pd was used. The maximum hydrogen storage of 0.36 wt % exhibited the sample with Pd nanoparticles with the diameter of 11 nm (measured at 298 K and 24 bar) and it was enhanced by the factor of two in respect to the pristine HCS. The enhanced storage capacity is due to cumulative hydrogen adsorption by HCS and Pd nanoparticles. We also propose the mechanism of hydrogen storage in our material.     

Combination of ZIF-67 derived hollow porous Co9S8 nanocages and MWCNTs for electrochemical hydrogen storage applications

By using zeolitic imidazolate framework of ZIF-67 as the precursor, the hollow porous Co₉S₈ (H–Co₉S₈) nanocages are synthesized via the sulfidation reaction and thermal treatment processes. The ordinary solid Co₉S₈ (S–Co₉S₈) particles are prepared by hydrothermal method. To improve the conductivity and activity of the Co₉S₈ materials, H–Co₉S₈ + MWCNTs and S–Co₉S₈ + MWCNTs composites are fabricated by ball milling. The electrochemical hydrogen storage properties of H–Co₉S₈ and H–Co₉S₈ + MWCNTs electrodes are tested via a three-electrode system for the first time. Ultimately, the H–Co₉S₈ nanocages with hollow porous structure show higher discharge capacity of 667.1 mAh/g than the S–Co₉S₈ particles. The electrochemical performance enhanced after doping with MWCNTs. H–Co₉S₈ + MWCNTs displays the highest discharge capacity of 683.5 mAh/g. Additionally, the preferable high-rate dischargeability, corrosion resistance, and improved kinetic properties are also achieved for H–Co₉S₈ + MWCNTs. H–Co₉S₈ with a unique hollow structure and large specific surface area can offer sufficient electrochemical active sites to anchor hydrogen, meanwhile, MWCNTs with excellent electrical conductivity can further provide fast channels for charge transfer and improve the electrocatalytic activity of Co₉S₈ electrode during the charging/discharging processes.     

Numerical modelling of transient heat transfer of hydrogen composite cylinders subjected to fire impingement

To improve the current design standards of the hydrogen composite cylinders, it is essential to understand the thermal response of the hydrogen composite cylinders subjected to fire impingement. In the present study, a fully coupled conjugate heat transfer model based on a multi-region and multi-physics approach is proposed for modelling the transient heat transfer behaviour of composite cylinders subjected to fire impingement. The fire scenario is modelled using the in-house version of FireFOAM, the large eddy simulation (LES) based fire solver within the frame of OpenFOAM. Three dimensional governing equations based on the finite volume method are written to model the heat transfer through the regions of composite laminate, liner and pressurized hydrogen, respectively. The governing equations are solved sequentially with temperature-dependent material properties and coupled interface boundary conditions. The proposed conjugate heat transfer model is validated against a bonfire test of a commercial Type-4 cylinder and its transient heat transfer behaviour is also studied.     

A novel cryogenic insulation system of hollow glass microspheres and self-evaporation vapor-cooled shield for liquid hydrogen storage

Liquid hydrogen (LH₂) attracts widespread attention because of its highest energy storage density. However, evaporation loss is a serious problem in LH₂ storage due to the low boiling point (20 K). Efficient insulation technology is an important issue in the study of LH₂ storage. Hollow glass microspheres (HGMs) is a potential promising thermal insulation material because of its low apparent thermal conductivity, fast installation (Compared with multi-layer insulation, it can be injected in a short time.), and easy maintenance. A novel cryogenic insulation system consisting of HGMs and a self-evaporating vapor-cooled shield (VCS) is proposed for storage of LH₂. A thermodynamic model has been established to analyze the coupled heat transfer characteristics of HGMs and VCS in the composite insulation system. The results show that the combination of HGMs and VCS can effectively reduce heat flux into the LH₂ tank. With the increase of VCS number from 1 to 3, the minimum heat flux through HGMs decreases by 57.36%, 65.29%, and 68.21%, respectively. Another significant advantage of HGMs is that their thermal insulation properties are not sensitive to ambient vacuum change. When ambient vacuum rises from 10⁻³ Pa to 1 Pa, the heat flux into the LH₂ tank increases by approximately 20%. When the vacuum rises from 10⁻³ Pa to 100 Pa, the combination of VCS and HGMs reduces the heat flux into the tank by 58.08%–69.84% compared with pure HGMs.