Cold hydrogen delivery in glass fiber composite pressure vessels: Analysis,manufacture and testing

This paper describes Lawrence Livermore National Laboratory (LLNL) and Spencer Composites Corporation (SCC) efforts in demonstrating an innovative approach to hydrogen delivery. This approach minimizes hydrogen delivery cost through utilization of glass fiber pressure vessels at 200 K and 70 MPa to produce a synergistic combination of container characteristics and properties of hydrogen gas: (1) hydrogen cooled to 200 K is ∼35% more compact for a small increase in theoretical storage energy (exergy); and (2) these cold temperatures (200 K) strengthen glass fibers by as much as 50%, expanding trailer capacity without the use of much more costly carbon fiber composite vessels.     

Comparison of infiltrated ceramic fiber paper and mica base compressive seals for planar solid oxide fuel cells

Solid oxide fuel cells using non-glass sealants have become increasingly common. In this paper, fumed silica infiltrated ceramic fiber paper with pre-compression was compared with plain and pre-compressed at 10 MPa hybrid mica as compressive seals. Leakage tests were measured under a 0.1–1.0 MPa compressive load with the pressure gradient varying from 2 to 15 kPa. The results demonstrated that the leakage rate of infiltrated fiber paper was 0.04 sccm cm⁻¹ for a 10 kPa gradient, under 1.0 MPa compressive load, while for mica it was 0.60 and 0.63 sccm cm⁻¹ which indicated that the infiltrated ceramic fiber paper showed a much lower leakage than mica. Long-term thermal cycling tests demonstrated that although the leakage of fumed silica infiltrated fiber paper was slightly higher than that of hybrid mica, it remained stable after 20 thermal cycles and no interlayer was needed. The mass loss of the fiber paper was 1.7 × 10⁻² mg cm⁻² h⁻¹ in a hydrogen environment at 1073 K for 200 h. The leakage of infiltrated fiber paper remained about 0.06 sccm cm⁻¹ after reduction.     

Hydriding/dehydriding properties of MgH2/5 wt.% Ni coated CNFs composite

In this paper, we reported that the prepared nickel coated carbon nanofibers (NiCNFs) by electroless plating method exhibited superior catalytic effect on hydrogen absorption/desorption of magnesium (Mg). It is demonstrated that the nanocomposites of MgH₂/5 wt.% NiCNFs prepared by ball milling could absorb hydrogen very fast at low temperatures, e.g. absorb ∼6.0 wt.% hydrogen in 5 min at 473 K and ∼5.0 wt.% hydrogen in 10 min even at a temperature as low as 423 K. More importantly, the desorption of hydrogen was also significantly improved with additives of NiCNFs. Diffraction scanning calorimetry (DSC) measurement indicated that the peak desorption temperature decreased 50 K and the on-set temperature for desorption decreased 123 K. The composites also desorbed hydrogen fast, e.g. desorb 5.5 wt.% hydrogen within 20 min at 573 K. It is suggested that the new phase of Mg₂Ni, and the nano-sized dispersed distribution of Ni and carbon contributed to this significant improvement. Johnson–Mehl–Avrami (JMA) analysis illustrated that hydrogen diffusion is the rate-limiting step for hydrogen absorption/desorption.     

Changes in hydrogen storage properties of carbon nano-horns submitted to thermal oxidation

The effect of thermal oxidation on the hydrogen storage properties of carbon nano-horns was investigated by gravimetric and electrochemical methods. The pristine nano-horn sample was oxidised at 673 K in air for different periods (15, 30 and 60 min) and the resulting materials were characterised. The N₂ adsorption experiments reveal a marked increase in the surface area, from 267 m² g⁻¹, for the pristine sample, up to 1360 m² g⁻¹ for the sample oxidised for the 60 min period, and a reduction in the average pore diameter. The gravimetric investigation, conducted at low temperature (77 K) showed an increase in the hydrogen storage, from 0.75 wt% for the pristine sample up to 2.60 wt% for the oxidised material. Reproducible and stable hydrogen storage was found for all the samples examined apart from the sample oxidised for 60 min. For the latter, a decrease in the amount of hydrogen stored between the first and second cycles was found. Electrochemical loading of hydrogen in the samples was performed at room temperature (298 K) in alkaline solution by the galvanostatic charge/discharge technique. The results obtained here however show a much lower hydrogen storage level by the samples as compared to the gas storage method, with a maximum value of 0.124 wt% H₂ and with very little dependence on the thermal oxidation treatment.     

A study on the hydrogen storage capacity of Ni-plated porous carbon nanofibers

In this study, we prepared highly porous carbon-nanofiber-supported nickel nanoparticles as a promising material for hydrogen storage. The porous carbons were activated at 1050 °C, and the nickel nanoparticles were loaded by an electroless metal-plating method. The textural properties of the porous carbon nanofibers were analyzed using N₂/77 K adsorption isotherms. The hydrogen storage capacity of the carbons was evaluated at 298 K and 100 bar. It was found that the amount of hydrogen stored was enhanced by increasing nickel content, showing 2.2 wt.% in the PCNF-Ni-40 sample (5.1 wt.% and 6.4% of nickel content and dispersion rate, respectively) owing to the effects of the spill-over of hydrogen molecules onto the metal–carbon interfaces. This result clearly indicates that the presence of highly dispersed nickel particles can enhance high-capacity hydrogen storage.     

Improved hydrogen storage properties of Mg-V nanoparticles prepared by hydrogen plasma-metal reaction

The Mg-10.2 at.% V nanoparticles are prepared by hydrogen plasma-metal reaction (HPMR) method. These nanoparticles are made of Mg, VH₂ and a small amount of MgH₂. The Mg nanoparticles are hexagonal in shape with the particle size in the range of 50-150 nm. The VH₂ nanoparticles are spherical in shape with the particle size around 10 nm, and disperse on the surface of the Mg nanoparticles. After the hydrogen absorption, the mean particle size of MgH₂ decreases to 60 nm, while the V nanoparticles are still about 10 nm. The Mg-V composite nanoparticles can absorb 3.8 wt.% hydrogen in less than 30 min at 473 K and accomplish a high hydrogen storage capacity of 5.0 wt.% in less than 5 min at 623 K. They can release 4.0 wt.% hydrogen in less than 15 min at 573 K. The catalytic effect of the V nanoparticles and the nanostructure and the low oxide content of the Mg particles promote the hydrogen sorption process with the low hydrogen absorption activation energy of 71.2 kJ mol⁻¹.     

Hydrogen adsorption on modified activated carbon

The aim of this work is to investigate hydrogen adsorption on prepared super activated carbon (AC). Litchi trunk was activated by potassium hydroxide under N₂ or CO₂ atmosphere. Nanoparticles of palladium were impregnated in the prepared-AC. Hydrogen adsorption was accurately measured by a volumetric adsorption apparatus at 77, 87, 90 and 303 K, up to 5 MPa. Experimental results revealed that specific surface area of the prepared-AC increased according to KOH/char ratio. The maximum specific surface area reached up to 3400 m²/g and total pore volume of 1.79 cm³/g. The maximum hydrogen adsorption capacity of 2.89 wt.% at 77 K and under 0.1 MPa, was obtained on these materials. The hydrogen adsorption capacity of the 10 wt.% Pd-AC was determined as 0.53 wt.% at 303 K and under 6 MPa. This amount is higher than that on the pristine AC (0.41 wt.%) under the same conditions.     

Hydrogen storage properties of Mg–50 vol.%V7.4Zr7.4Ti7.4Ni composite prepared by spark plasma sintering

Hydrogen storage properties of Mg–50 vol.%V7.4Zr7.4Ti7.4Ni composite prepared by spark plasma sintering were investigated based on the PCT measurements, kinetics and DSC estimations and microstructure observations. The results showed that the composite consisted of Mg phase and V-based solid solution, with a small amount of sintering phase at their interface, and could absorb and desorb hydrogen at 303 K and 573 K, with a maximum hydrogen storage capacity of 3.05 wt.% and 2.55 wt.%, respectively. At 573 K it was found that the Mg phase was the basis for the hydrogen absorption/desorption, but with the combination of the V-based solid solution its kinetics was greatly improved, and its hydrogen desorption temperature decreased by about 117 K, which made it possible for hydrogen desorption of Mg phase at 573 K. Meanwhile the sintering phase was considered to be a key factor in improving hydriding properties of the Mg phase, which might act as a catalyst and offer preferable paths for hydrogen diffusion from V-based solid solution to the Mg phase.     

Hydrogen storage properties of Mg–30 wt.% LaNi5 composite prepared by hydriding combustion synthesis followed by mechanical milling (HCS + MM)

A Mg–30 wt.% LaNi₅ composite was prepared by hydriding combustion synthesis followed by mechanical milling (HCS + MM), and the hydriding and dehydriding properties of the HCS + MM product were compared with those of the HCS product and the MM product. The dehydriding temperature onsets of the MM and HCS + MM products were both 470 K, which were lower than that of the HCS product by 100 K. Moreover, the HCS + MM product desorbed faster than the MM product, e.g., the former desorbed completely upon heating to 510 K, whereas the latter did not decompose completely until 590 K. Additionally, the HCS + MM product reached a saturated hydrogen absorption capacity of 3.80 wt.% at 373 K in 50 s, but both the HCS product and the MM product absorbed less than 1.50 wt.% of hydrogen at 373 K in 1800 s. These results suggest the potential of the HCS + MM processing in preparing Mg-based hydrogen storage materials.     

Grand canonical Monte Carlo simulation of hydrogen physisorption in single-walled boron nitride nanotubes

The properties of hydrogen physisorption in single-walled boron nitride nanotubes (SWBNNTs) and single-walled carbon nanotubes (SWCNTs) are investigated in detail by the grand canonical Monte Carlo simulations. A great deal of our computational results show that the hydrogen storage capacity of SWBNNTs is slightly larger than the capacity of SWCNTs at any time when their diameters were equal and in the same conditions, and indicate that the hydrogen storage capacity of SWBNNTs at 293 K and 10 MPa with a diameter of more than 30 nm or at 293 K and 15 MPa with a diameter of more than 25 nm could exceed the 2010 goal of 6 wt%, which is presented by the U.S. Department of Energy. In addition, these results are discussed in theory.     

Sustainable hydrogen production for fuel cells by steam reforming of ethylene glycol: A consideration of reaction thermodynamics

The use of renewable biomass, such as ethylene glycol (EG), for hydrogen production offers a more sustainable system compared to natural gas and petroleum reforming. For the first time, the reaction thermodynamics of steam reforming and sorption enhanced steam reforming of EG have been investigated. Gibbs free energy minimization method was used to study the effect of pressure (1-5 atm), temperature (500-1100 K) and water to EG ratio (WER 0-8) on the production of hydrogen and the formation of associated by-products (CH₄, CO₂, CO, C). The results suggest that hydrogen production is optimum when steam reforming occurs at atmospheric pressure, 925 K and with a WER of 8. Moreover, working at high temperature (>900 K) and with a WER above 6 inhibits almost entirely the production of methane and carbon. The main source of hydrogen in the system is found to be steam reforming of methane and water gas shift reaction by the analysis of the response reactions (RERs). Hydrogen production is governed by the former reaction at low temperatures while the latter one comes into prominence as temperature increases. By coupling with in situ CO₂ capture using CaO, the formation of CO₂ and CO can be avoided and high purity of hydrogen (>99%) can be achieved.     

Fusion reactions in high-density hydrogen: A fast route to small-scale fusion?

High-density atomic hydrogen, which is believed to be a quantum liquid, can be formed by heterogeneous catalysis at the surface of hydrogen-transfer metal oxide catalysts. Extensive studies have been made of the hydrogen phase named H(1), with interatomic distance of 150 pm found by Coulomb explosion measurements. This bond distance corresponds to a material density of 0.5–0.7 kg dm⁻³. The use of this material as fusion target for inertial confinement fusion (ICF) is proposed in J Fusion Energy 2008;27:296–300. A much denser hydrogen (deuterium) material D(−1) also exists with an interatomic distance of 2.3 pm. This material is probably the inverse of metallic D(1), where nuclei and electrons exchange their roles. The ICF process would be greatly simplified if the intended initial multi-laser compression stage was not necessary. The close-packed density of D(−1) is calculated from the bond distance as >130 kg cm⁻³. This is much higher than that required for “fast ignition” laser-driven fusion (>0.3 kg cm⁻³). It may mean that a method already exists to prepare dense hydrogen fuel for small-scale laser-driven fusion. The high energy particles observed experimentally (up to 150 keV/atomic mass unit in the peak or 10⁹ K) indicate that high energy processes exist at relatively low laser intensities.     

Hydrogen production by reforming of liquid hydrocarbons in a membrane reactor for portable power generation—Model simulations

One of the most promising technologies for lightweight, compact, portable power generation is proton exchange membrane (PEM) fuel cells. PEM fuel cells, however, require a source of pure hydrogen. Steam reforming of hydrocarbons in an integrated membrane reactor has potential to provide pure hydrogen in a compact system. In a membrane reactor process, the thermal energy needed for the endothermic hydrocarbon reforming may be provided by combustion of the membrane reject gas. The energy efficiency of the overall hydrogen generation is maximized by controlling the hydrogen product yield such that the heat value of the membrane reject gas is sufficient to provide all of the heat necessary for the integrated process. Optimization of the system temperature, pressure and operating parameters such as net hydrogen recovery is necessary to realize an efficient integrated membrane reformer suitable for compact portable hydrogen generation. This paper presents results of theoretical model simulations of the integrated membrane reformer concept elucidating the effect of operating parameters on the extent of fuel conversion to hydrogen and hydrogen product yield. Model simulations indicate that the net possible hydrogen product yield is strongly influenced by the efficiency of heat recovery from the combustion of membrane reject gas and from the hot exhaust gases. When butane is used as a fuel, a net hydrogen recovery of 68% of that stoichiometrically possible may be achieved with membrane reformer operation at 600 °C (873 K) temperature and 100 psig (0.791 MPa) pressure provided 90% of available combustion and exhaust gas heat is recovered. Operation at a greater pressure or temperature provides a marginal improvement in the performance whereas operation at a significantly lower temperature or pressure will not be able to achieve the optimal hydrogen yield. Slightly higher, up to 76%, net hydrogen recovery is possible when methanol is used as a fuel due to the lower heat requirement for methanol reforming reaction, with membrane reformer operation at 600 °C (873 K) temperature and 150 psig (1.136 MPa) pressure provided 90% of available combustion and exhaust gas heat is recovered.     

Hydrogen sorption in transition metal modified ETS-10

Hydrogen adsorption studies in nickel, rhodium and palladium exchanged and in situ loaded titanosilicate ETS-10 were performed at 77.4 K using a static volumetric adsorption system up to 1 bar, and 303 K in a gravimetric adsorption system up to 5 bar. The hydrogen adsorption isotherms at 77.4 K were reversible with pressure but chemisorption of hydrogen was noticed at 303 K. Rhodium exchanged ETS-10 showed the highest hydrogen adsorption capacity of 82.6 cc/g at 77.4 K. The hydrogen adsorption isotherm analysis at 303 K was repeated up to three adsorption runs to check the repeatability of hydrogen uptake. At 303 K palladium loaded ETS-10 showed the highest hydrogen uptake capacity of 33.1 cc/g. The DRIFT spectra analysis of ETS-10 samples before and after hydrogen adsorption was conducted, which confirmed that the hydrogen adsorbed in transition metal modified ETS-10 at 303 K was due to the chemical interactions in the form of transition metal hydrides inside ETS-10. The absorbed hydrogen at 303 K can be desorbed by heating the ETS-10 sample up to 413 K.     

Enhancement of the hydrogen storage characteristics of Mg by reactive mechanical grinding with Ni,Fe and Ti

Mg-10wt%Ni-5wt%Fe-5wt%Ti powder was prepared by reactive mechanical grinding using a planetary ball mill. The Mg-10wt%Ni-5wt%Fe-5wt%Ti powder exhibited high hydriding and dehydriding rates even at the first cycle, and its activation was completed after two hydriding–dehydriding cycles. After the reactive mechanical grinding, the particle size of the powder was reduced, as compared with those of the starting materials. The hydrogen storage properties were measured at temperatures of 473 K, 573 K and 623 K. The activated Mg-10wt%Ni-5wt%Fe-5wt%Ti powder absorbed 5.31 wt% and 5.51 wt% of hydrogen for 5 min and 1 h, respectively, at 573 K under 12 bar H₂. It desorbed 5.18 wt% of hydrogen at 573 K under 1.0 bar H₂ for 1 h. The initial hydrogen absorption rate increased when passing from 473 K to 573 K, but decreased at 623 K. The hydrogen desorption rate increased rapidly with increasing temperature from 473 K to 623 K. The hydrogen storage capacity was about 6.72 wt% at 573 K.     

Synthesis,characterization and hydrogen adsorption properties of metal–organic framework Al-TCBPB

In this work, a new metal–organic framework (MOF) was synthesized by using a large organic ligand 1,3,5-tris[4′-carboxy(1,1′-biphenyl)-4-yl] benzene (abbreviated as TCBPB) and aluminum as the metal that forms the secondary building unit (SBU) by solvothermal method. The MOF, named as Al-TCBPB, was characterized with pore textural properties, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Raman and FT-IR spectroscopy. Hydrogen adsorption was measured volumetrically at ambient pressure and temperatures of 77, 88 and 298 K and at high pressure (up to 9 MPa) for temperatures 77 and 298 K. Pore textural properties revealed a high BET surface area of 2311 m²/g, narrow bimodal pore widths of 11.8 Å and 20 Å and a total pore volume of 0.80 cm³/g. PXRD identified the crystal structure as monoclinic with space group c2/m. This MOF adsorbs 1.53 and 0.83 wt.% of hydrogen at 77 and 88 K, respectively, and pressures up to ambient conditions. At higher pressure of 9 MPa, it demonstrated an excess adsorption of 4.8 and 1.4 wt.% at 77 and 298 K, respectively; these high-pressure data fit well with modified Dubinin–Astakov (D–A) analytical model. The heat of adsorption values of Al-TCBPB vary between 5.9 and 4.9 kJ/mol for the hydrogen adsorption loading of 0.1–0.8 wt.% and decreases monotonically to approximately 2 kJ/mol when the adsorption loading becomes 4.8 wt%.     

Zirconia supported catalysts for bioethanol steam reforming: Effect of active phase and zirconia structure

Three new catalysts have been prepared in order to study the active phase influence in ethanol steam reforming reaction. Nickel, cobalt and copper were the active phases selected and were supported on zirconia with monoclinic and tetragonal structure, respectively. To characterize the behaviour of the catalysts in reaction conditions a study of catalytic activity with temperature was performed. The highest activity values were obtained at 973 K where nickel and cobalt based catalysts achieved an ethanol conversion of 100% and a selectivity to hydrogen close to 70%. Nickel supported on tetragonal zirconia exhibited the highest hydrogen production efficiency, higher than 4.5 mol H₂/mol EtOH fed. The influence of steam/carbon (S/C) ratio on product distribution was another parameter studied between the range 3.2–6.5. Nickel supported on tetragonal zirconia at S/C = 3.2 operated at 973 K without by-product production such as ethylene or acetaldehyde. In order to consider a further application in an ethanol processor, a long-term reaction experiment was performed at 973 K, S/C = 3.2 and atmospheric pressure. After 60 h, nickel supported on tetragonal zirconia exhibited high stability and selectivity to hydrogen production.     

Thermodynamic analysis of hydrogen production via autothermal steam reforming of selected components of aqueous bio-oil fraction

From a technical and economic point of view, autothermal steam reforming offers many advantages, as it minimizes heat load demand in the reformer. Bio-oil, the liquid product of biomass pyrolysis, can be effectively converted to a hydrogen-rich stream. Autothermal steam reforming of selected compounds of bio-oil was investigated using thermodynamic analysis. Equilibrium calculations employing Gibbs free energy minimization were performed for acetic acid, acetone and ethylene glycol in a broad range of temperature (400–1300 K), steam to fuel ratio (1–9) and pressure (1–20 atm) values. The optimal O₂/fuel ratio to achieve thermoneutral conditions was calculated under all operating conditions. Hydrogen-rich gas is produced at temperatures higher than 700 K with the maximum yield attained at 900 K. The ratio of steam to fuel and the pressure determine to a great extent the equilibrium hydrogen concentration. The heat demand of the reformer, as expressed by the required amount of oxygen, varies with temperature, steam to fuel ratio and pressure, as well as the type of oxygenate compound used. When the required oxygen enters the system at the reforming temperature, autothermal steam reforming results in hydrogen yield around 20% lower than the yield by steam reforming because part of the organic feed is consumed in the combustion reaction. Autothermicity was also calculated for the whole cycle, including preheating of the organic feed to the reactor temperature and the reforming reaction itself. The oxygen demand in such a case is much higher, while the amount of hydrogen produced is drastically reduced.     

Biocatalyzed hydrogen production in a continuous flow microbial fuel cell with a gas phase cathode

A single liquid chamber microbial fuel cell (MFC) with a gas-collection compartment was continuously operated under electrically assisted conditions for hydrogen production. Graphite felt was used for anode construction, while the cathode was made of Pd/Pt coated Toray carbon fiber paper with a catalyst loading of 0.5 mg cm⁻². To achieve hydrogen production, the MFC was connected to a power supply and operated at voltages in a range of 0.5–1.3 V. Either acetate or glucose was used as a source of carbon. At an acetate load of 1.67 g (L_A d)⁻¹, the volumetric rate of hydrogen production reached 0.98 L_STP (L_A d)⁻¹ when a voltage of 1.16 V was applied. This corresponded to a hydrogen yield of 2 mol (mol-acetate)⁻¹ with a 50% conversion efficiency. Throughout the experiment, MFC efficiency was adversely affected by the metabolic activity of methanogenic microorganisms, which competed with exoelectrogenic microorganisms for the carbon source and consumed part of the hydrogen produced at the cathode.     

Biohydrogen production from household solid waste (HSW) at extreme-thermophilic temperature (70 °C) – Influence of pH and acetate concentration

Hydrogen production from household solid waste (HSW) was performed via dark fermentation by using an extreme-thermophilic mixed culture, and the effect of pH and acetate on the biohydrogen production was investigated. The highest hydrogen production yield was 257 ± 25 mL/gVS_added at the optimum pH of 7.0. Acetate was proved to be inhibiting the dark fermentation process at neutral pH, which indicates that the inhibition was caused by total acetate concentration not by undissociated acetate. Initial inhibition was detected at acetate concentration of 50 mM, while the hydrogen fermentation was seriously inhibited at acetate concentration of 200 mM. At 200 mM acetate concentration, the hydrogen yield was 36 ± 25 mL/gVS_added, which was almost 7 times lower than the yield of 254 ± 13 mL/gVS_added, which was achieved at lower acetate concentration (5–25 mM). Additional to the negative effect on the hydrogen yield, acetate was resulting in the longer lag phase during batch fermentations. The lag phase was more than 100 h at acetate concentration of more than 150 mM, while it was only 3–4 h at 5–25 mM acetate.