A metal hydride–polymer composite for hydrogen storage applications

To address the issue of the breakdown into fine powders that occurs in the practical use of metal hydrides, the possibility of using a polymeric material as a matrix that contains the active metal particles was experimentally assessed. A ball milling approach in the tumbling mode was used to develop a metal hydride–polymer composite with a high metal to polymer weight ratio. The alloy powder was blended with the polymer and a coating of the metal particles was obtained. The composite was consolidated by hot pressing and the pellets were characterized in terms of their hydriding–dehydriding properties. The materials did not show significant losses in either loading capacity or kinetic properties. The polymeric matrix resulted as being stable under hydrogen cycling. Further, from SEM observation it was confirmed that the metal powders remained embedded in the polymeric matrix even after a number of cycles and that the overall dimensional integrity was retained.     

Fracture analysis of hydrogen storage composite cylinders with liner crack accounting for autofrettage effect

An understanding of fracture behavior is crucial to the safe installation and operation of high-pressure composite cylinders for hydrogen storage. This work has developed a comprehensive finite element model to investigate axial surface flaws in cylinder liners using the fracture mechanics and a global–local finite element technique. Since the autofrettage process has a strong influence on cylinder fracture behavior, it is also considered in this analysis. The simulation process is broken down into three steps in order to precisely extract fracture parameters and incorporate the autofrettage effect. In the first step, the global model performs the autofrettage simulation to study the residual stress with consideration of both material hardening and the Bauschinger effect. In the second step, the global model uses residual stress to compute displacement for the local model. Finally, in the third step, the local model extracts the values of stress intensity factor and J-integral. Comparison is conducted on the fracture parameters with various autofrettage levels and crack shapes. The vicinity of the crack front is also studied by the size and shape of the plastic zone, and the validity of stress intensity factor and J-integral dominances is examined.     

Safety approach for composite pressure vessels for road transport of hydrogen. Part 2: Safety factors and test requirements

Composite pressure vessels for transporting hydrogen on roads are a promising and efficient solution for supplying refueling stations. The safety factors of current ISO design standards are perceived as being restrictive for design. In this paper, new safety factors are calculated based on a probabilistic approach and by extending the methods used in the DNV Offshore standard DNV-OS-C501 “Composite Components”. Short-term and long-term conditions are addressed.     

Analysis of heat conducting enhancement measures on the composite for hydrogen storage by incorporation of activated carbon with MOFs

Experiments and numerical simulations were conducted for evaluating measures for enhancing adsorption capacity and heat conducting of an on board MOFs hydrogen storage system by cryo-adsorption. Solvothermal method was employed to synthesize MIL-101(Cr) composite by incorporating activated carbon. The composite was undergone structure characterization, structural morphology observation, thermal conductivity measurement and measurement of isotherm of hydrogen adsorption at 77.15 K within 0–6 MPa. Effect of adding expanded natural graphite (ENG) and equipping a honeycomb heat exchanging device (HHED) on mitigating the thermal effect on a 0.5 L hydrogen storage vessel packed with composite was investigated within a flow rate of hydrogen required by a ship's power unit. It shows that the sample incorporated by 1 wt% activated carbon respectively obtained about 14.5%, 26.2% and 5.7% increment in specific surface area, micropore volume and the maximum excess adsorption amount. Results also reveal that, within the flow rate 5 L·min^?1-25 L min^?1, the mean relative error between the experimental data and those from simulations is less than 1.61%, and the reduction in temperature fluctuation of the storage system is about 5 °C and 4 °C on charge and discharge process while equipping the HHED, which accordingly brought about 17%, 24.3%, 18.5% increment in accumulated amount of charge and discharge as well as the useable capacity ratio (UCR) of the system. It suggests that equipping a HHED is a more promising method for weakening the thermal effect on MOFs-hydrogen storage systems.     

Effect of substituting Mn for Ni on the hydrogen storage and electrochemical properties of ReNi2.6−xMnxCo0.9 alloys

ReNi_2.6−xMn_xCo_0.9 (x = 0.0, 0.225, 0.45, 0.675, 0.90) alloys were prepared by induction melting. The effects of partially substituting Mn for Ni on the phase structure and electrochemical properties of the alloys were investigated systematically. In the alloys, (La, Ce)₂Ni₇ phase with a Ce₂Ni₇-type structure, (Pr, Ce)Co₃ phase with a PuNi₃-type structure, and (La, Pr)Ni₅ phase with a CaCu₅-type structure were the main phases. The (La,Pr)Ni phase appeared when x increased to 0.45, and the (La, Pr)Ni₅ phase disappeared with further increasing x (x > 0.45). The hydrogen-storage capacity of the ReNi_2.6−xMn_xCo_0.9 (x = 0.0, 0.225, 0.45, 0.675, 0.90) alloys initially increased and reached a maximum when Mn content was x = 0.45, and then decreased with further increasing Mn content. The ReNi_2.6−xMn_xCo_0.9 (x = 0.0, 0.225, 0.45, 0.675, 0.90) alloy exhibited a hydrogen-storage capacity of 0.81, 0.98, 1.04, 0.83 and 0.53 wt.%, respectively. Electrochemical studies showed that the maximum discharge capacity of the alloy electrodes initially increased from 205 mAh/g (x = 0.0) to 352 mAh/g (x = 0.45) and then decreased to 307 mAh/g (x = 90). The hydrogen absorption rate first increased and then decreased with addition of Mn element. The ReNi_2.15Mn_0.45Co_0.9 alloy showed faster hydrogen absorption kinetics than that of the other alloys. The presence of Mn element slowed hydrogen desorption kinetics.     

Electroless deposition of Ni nanoparticles on carbon nanotubes with the aid of supercritical CO2 fluid and a synergistic hydrogen storage property of the composite

A hybrid synthesis protocol that combines electroless plating and the supercritical CO₂ (scCO₂) technique is developed for the first time to decorate multi-walled carbon nanotubes (CNTs) with Ni nanoparticles. The scCO₂ fluid, which is immiscible with aqueous plating solution, renders a heterogeneous Ni deposition reaction and suppresses the lateral growth of Ni, which leads to the formation of nanoparticles. A uniform dispersion of tightly anchored particles, a few nanometers in diameter, on CNTs can be achieved. Since the electroless deposition process can be easily manipulated, large-scale production should be realizable. The constructed CNT/Ni nano-composite exhibits a synergistic property in hydrogen storage performance, which is evaluated using a high-pressure microbalance. The deposited nanoparticles enhance the hydrogen spillover reaction on CNTs, tripling the hydrogen storage amount at room temperature as compared to pristine CNTs.     

A quasi-Delphi study on technological barriers to the uptake of hydrogen as a fuel for transport applications—Production, storage and fuel cell drivetrain considerations

The introduction of hydrogen in transport, particularly using fuel cell vehicles, faces a number of technical and non-technical hurdles. However, their relative importance is unclear, as are the levels of concern accorded them within the expert community conducting research and development within this area. To understand what issues are considered by experts working in the field to have significant potential to slow down or prevent the introduction of hydrogen technology in transport, a study was undertaken, primarily during 2007. Three key technology areas within hydrogen transport were selected - hydrogen storage, fuel cell drivetrains, and small-scale hydrogen production - and interviews with selected experts conducted. Forty-nine experts from 34 organisations within the fuel cell, automotive, industrial gas and other related industries participated, in addition to some key academic and government figures. The survey was conducted in China, Japan, North America and Europe, and analysed using conventional mathematical techniques to provide weighted and averaged rankings of issues viewed as important by the experts. It became clear both from the interviews and the subsequent analysis that while a primary concern in China was fundamental technical performance, in the other regions cost and policy were rated more highly. Although a few individual experts identified possible technical showstoppers, the overall message was that pre-commercial hydrogen fuel cell vehicles could realistically be on the road in tens of thousands within 5 years, and that full commercialisation could take place within 10-15 years, without the need for radical technical breakthroughs. Perhaps surprisingly, the performance of hydrogen storage technologies was not viewed as a showstopper, though cost was seen as a significant challenge. Overall, however, coherent policy development was more frequently identified as a major issue to address.     

Design of electrocatalysts with reduced Pt content supported on mesoporous NiWO4 and NiWO4-graphene nanoplatelets composite for oxygen reduction and hydrogen oxidation in acidic medium

Herein, a new direct synthesis route leading to a mesoporous NiWO₄ with crystalline framework and NiWO₄ - graphene nanoplatelets (GNP) composite is reported. Ni and W assembled into a mesoporous tungstate type of symmetry by co-precipitation synthesis route and its composite with GNP were used as supports for electrocatalysts, with reduced Pt content (8 wt.%), in oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) in acidic medium. A comprehensive assessment of the modifications related to the crystalline and porous structures, morphological aspects as well as the surface chemistry aiming to explain the electrochemical properties was performed. It was found that the presence of GNP during the synthesis process leads, mainly, to the enhanced growth of NiWO₄ nanocrystallites, as well as induces changes in the surface chemistry. The electrochemical results show that the introduction of GNPs into the NiWO₄ composite support leads to a significant improvement in the activity of the Pt electrocatalyst in ORR and HOR compared to both initial NiWO₄ and Pt/NiWO₄ samples, as well as mechanical mixtures of these catalysts with carbon. Mass activity for hydrogen oxidation, determined in a mixed kinetic-diffusion controlled region, obtained on the 8 wt.% Pt/NiWO₄-GNP catalyst was significantly higher compared to the commercial 20 wt.% Pt/C Quintech catalyst. Our comprehensive structural and surface chemistry assessments indicate this composite material as a viable electrocatalyst for PEMFCs using a broader type of fuels.     

Direct synthesis of nanocrystalline titanium dioxide/carbon composite and its catalytic effect on NaAlH4 for hydrogen storage

Nanocrystalline titanium dioxide/carbon composite (TiO₂/C) was synthesized through a direct solution-phase carburization using tetrabutyl titanate (Ti(OBu)₄) and resol as precursors. The prepared TiO₂/C composite was mainly in the anatase structure with an average particle size under 20 nm, which was then introduced in NaAlH₄ as a catalyst through ball milling. The desorption curves show that both nanocrystalline TiO₂/C and TiO₂ can obviously improve the kinetics of NaAlH₄, while NaAlH₄ with 3 mol% TiO₂/C exhibits better cycling stability than NaAlH₄ with 3 mol%TiO₂. The hydrogen storage capacity of NaAlH₄ with TiO₂/C remains stable after 5th cycle, and about 94% of initial hydrogen is released, while the capacity of NaAlH₄ with TiO₂ decreases continuously during cycling, and only 88% of initial hydrogen is released after 10th cycle. Furthermore, NaAlH₄ with 3 mol%TiO₂/C exhibits good reversibility at relatively low hydrogen pressures, and it can reload 4.16 and 1.63wt% hydrogen at 50 and 30 bar hydrogen pressures, respectively.