A sieverts apparatus for measuring high-pressure hydrogen isotherms on porous materials

A high-pressure Sieverts apparatus, specifically designed to investigate carbon and other low-density materials for hydrogen storage, has been constructed and used to investigate potential storage materials for which the volume of the sample is uncertain or difficult to define. The apparatus can be managed from a computer via a graphical interface and used to measure gas sorption isotherms from 77 K to 873 K, utilising a computer driven piston pressure booster to compress the gas to 340 bar. Based on measurements of activated carbons and graphene-like samples, this article demonstrates the low sensitivity of the apparatus to uncertainty in the sample volume and the quality of data obtained for H₂ adsorption isotherms measured at 296 K and 77 K at pressures up to 300 bar.     

Development of a Sievert apparatus for characterization of high pressure hydrogen sorption materials

A volumetric gas absorption (Sievert) apparatus has been developed to measure hydrogen absorption and desorption at pressures up to 700 bar and temperatures between 240 K and 320 K. The apparatus is designed to reduce uncertainty for high pressure measurements while maintaining proper temperature control in the sample. Pressure-composition isotherms (PCI) and kinetics measurements of a well-studied material, LaNi₅ have been obtained for validation of the apparatus. Measurements of both absorption and desorption PCI curves as well as full absorption kinetics data have been obtained for TiCrMn to examine the performance at high pressures, as well as to examine the thermodynamic hysteresis effect in TiCrMn for applications in metal hydride system design. Due to this hysteresis, the thermodynamics of the absorption reaction differ significantly from those of the desorption reaction, which must be accounted for when considering thermal design of a metal hydride reactor and the suitability of the metal hydride for energy storage applications.     

Study on real-gas equations of high pressure hydrogen

High pressure hydrogen storage has become an important transportation channel in areas of new energy development and utilization. Actual hydrogen demonstrations require the exploration of the physical and chemical properties in detail before the practical employment, which is completely different from the ideal gas under high pressure conditions. However, the existing real-gas state equations are not easy to use in calculation of high pressure hydrogen due to its complex behavior, and may lead to an unacceptable error. In this paper, a real-gas state equation of hydrogen in a simplified form is proposed. Compared with the NIST datum, the results obtained from this equation have a maximum error 1.1% and 3.8% respectively within the temperature ranges of 253 K < T< 393 K and 173 K < T< 393 K. Also, the proposed equation exhibits higher precision for the state parameters of hydrogen than existing models. Based on the real-gas state equation of hydrogen, formulas of thermodynamic properties which are necessary for solving the hydraulic and thermal aspects of gas transfer are also proposed.     

High pressure hydrogen fires

Within the scope of the French national project DRIVE and European project HyPER, high pressure jet flames of hydrogen were produced and instrumented.The experimental technique and measurement strategy are presented. Many aspects are original developments like the direct measurement of the mass flow rate by weighing continuously the hydrogen container, the image processing to extract the flame geometry, the heat flux measurement device, the thermocouples arrangement…Flames were observed from 900 bar down to 1 bar with orifices ranging from 1 to 3 mm. An original set of data is now available about the main flame characteristics and about some thermodynamic aspects of hydrogen releases under high pressure.A brief comparison of some available models is presented.     

An investigation of structural and hydrogen adsorption properties of microporous metal organic framework (MMOF) materials

Microporous metal organic frameworks (MMOFs) have garnered great attraction as adsorbent materials for on-board hydrogen storage. To enhance hydrogen adsorption, we have carried out a systematic study to synthesize, characterize, and modify crystal structures of a number of MMOFs and to investigate their pore characteristics. In addition, their hydrogen adsorption properties at cryogenic and ambient temperature over a range of pressures are analyzed.     

In-situ diffraction techniques for studying hydrogen storage materials under high hydrogen pressure

Diffraction-based methods offer unique advantages for elucidating the pathways by which materials absorb and desorb hydrogen, especially when a phase change or the formation of new compounds is involved. In this case, the hydriding reaction may be followed via the changing crystallography of the phases involved in response to a change in temperature or hydrogen pressure. By using a fast diffractometer, the reaction kinetics may also be correlated to environmental conditions and the degree of completion of the reaction. In this paper we consider and model quantitatively the essential elements of a successful in-situ diffraction experiment with neutrons or X-rays under hydrogen pressures up to several kilobars: a gas manifold to accurately measure hydrogen uptake; a pressure cell designed for maximum detected intensity; means to exclude scattering arising in the cell as much as possible; methodology to correct for attenuation and subtract background intensity from the cell and environment.     

Characteristics of heat transfer and temperature rise of hydrogen during rapid hydrogen filling at high pressure

An experiment has been done to measure the rise in temperature of a gas during filling a tank at high pressure. The experimental condition is that filling gases are nitrogen and hydrogen at a pressure of 5 to 35 MPa and at a filling mass of G=45 to 324 g/min for hydrogen. The temperatures are measured either horizontally or vertically at five positions in the tank. It is found that heat loss transferred from compressed gas to the tank wall has a significant effect on the rise in the filled gas temperature. The heat transfer coefficient is estimated after the end of filling and is about α_h=270 W/(m²K) for the hydrogen at 35 MPa. A theoretical procedure is proposed to calculate the temperature increase of the gas on a basis of assumption that the gas temperature in the tank is uniform at any time, and the heat transfer coefficient is given. The calculation shows that the temperature is in reasonable agreement with the measured temperatures by assuming α_h=500 W/(m²K) during the filling of hydrogen at 35 MPa, although the estimated heat loss after the end of filling becomes larger than the actual one. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(1): 13–27, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20140     

High-density automotive hydrogen storage with cryogenic capable pressure vessels

LLNL is developing cryogenic capable pressure vessels with thermal endurance 5–10 times greater than conventional liquid hydrogen (LH₂) tanks that can eliminate evaporative losses in routine usage of (L)H₂ automobiles. In a joint effort BMW is working on a proof of concept for a first automotive cryo-compressed hydrogen storage system that can fulfill automotive requirements on system performance, life cycle, safety and cost. Cryogenic pressure vessels can be fueled with ambient temperature compressed gaseous hydrogen (CGH₂), LH₂ or cryogenic hydrogen at elevated supercritical pressure (cryo-compressed hydrogen, CcH₂). When filled with LH₂ or CcH₂, these vessels contain 2–3 times more fuel than conventional ambient temperature compressed H₂ vessels. LLNL has demonstrated fueling with LH₂ onboard two vehicles. The generation 2 vessel, installed onboard an H₂-powered Toyota Prius and fueled with LH₂ demonstrated the longest unrefueled driving distance and the longest cryogenic H₂ hold time without evaporative losses. A third generation vessel will be installed, reducing weight and volume by minimizing insulation thickness while still providing acceptable thermal endurance. Based on its long experience with cryogenic hydrogen storage, BMW has developed its cryo-compressed hydrogen storage concept, which is now undergoing a thorough system and component validation to prove compliance with automotive requirements before it can be demonstrated in a BMW test vehicle.     

High pressure membrane separator for hydrogen purification of gas from hydrothermal treatment of biomass

For hydrogen purification and green hydrogen production in the context of biomass hydrothermal gasification, a palladium membrane system with microchannels on feed and permeate side was studied. The high pressure in the product gas of the hydrothermal process could potentially be used to generate pressurized pure hydrogen on the permeate side. Stabilizing the membrane by an additional porous metal support, experimental verification of the concept was done at feed pressure up to 50 bar and permeate pressure up to 20 bar. The temperatures were varied between 370 °C and 425 °C. The device was found to be highly selective and efficient for pure hydrogen separation. The membrane was characterized regarding the hydrogen flux and a deviation of the permeation from Sievert's law above 30 bars feed pressure was found. Generally, the microchannels on the feed side minimized concentration polarization effects, leading to high hydrogen fluxes with hydrogen feed mixtures and with real gas samples from hydrothermal gasification.     

High pressure DSC study of hydrogen sorption in MgH2/graphite mixtures: Effects of sintering and oxidation

Hydrogen absorption and desorption properties of ball milled Mg and Mg/graphite materials were analyzed by high pressure differential scanning calorimetry. The influence on hydrogen sorption kinetics of different graphite distribution, oxygen poisoning and magnesium sintering was studied. The Mg/graphite mixture with graphite distributed in the bulk showed better kinetics than the material with graphite located on the surface and Mg without additive. The effect of sintering and oxygen poisoning was a progressive storage capacity loss, due to a kinetic limitation in the case of sintering, and due to irreversible magnesium oxidation in the case of poisoning. The mixtures with graphite exhibited more resistance toward oxygen contamination, particularly in the case where graphite was primarily located on the surface compared to the material with graphite well dispersed in the bulk.     

填埋气体小型变压吸附的试验研究

填埋气体(LFG)作为可再生的清洁能源,对其进行回收利用是非常重要的。变压吸附作为一种气体分离技术,能较好地将CH4与CO2分离。文章对填埋气体的变压吸附进行了小试试验,根据不同操作条件下产品气中甲烷浓度和甲烷回收率来确定最佳操作条件,从而为填埋气体变压吸附的中试试验提供一定的理论依据。     

Simulation and analysis of dual-reflux pressure swing adsorption using silica gel for blue coal gas initial separation

A dual-reflux pressure swing adsorption (DR-PSA) process was proposed and simulated to initially separate the blue coal gas, aiming to capture carbon dioxide (CO₂) and enrich hydrogen (H₂), simultaneously. With a feed flow rate of 7.290 slpm, a light product reflux flow rate of 0.505 slpm and the heavy product reflux flow rate of 3.68 slpm, the developed DR-PSA process could capture CO₂ up to 64.01% with a recovery of 99.60% and enrich H₂ up to 34.66% with a recovery of 97.63% from the blue coal gas (36.2% N₂/28.5% H₂/13.9% CO/12.7% CO₂/8.7% CH₄). In addition, in order to optimize the process, the effects of various operating parameters on the DR-PSA process performance in terms of product purity and recovery were discussed in detail, including the feed position, the light product reflux ratio and the heavy product reflux ratio. Moreover, the dynamic distribution behaviors of pressure, temperature and gas-solid concentration were presented to explain and evaluate the process separation performance in depth under different operating conditions.     

High capacity and reversible hydrogen storage on two dimensional C2N monolayer membrane

Searching advanced materials with high capacity and efficient reversibility for hydrogen storage is a key issue for the development of hydrogen as a clean energy. Here, we have explored the potential application of C₂N monolayer using as a promising material for hydrogen storage through a comprehensive density functional theory (DFT) investigation. Our calculational results indicate that hydrogen molecule can only form weak interaction on neutral C₂N monolayer with the adsorption energy of 0.06 eV. However, if extra charges (5 e^?) are introduced to the system, the adsorption energy of hydrogen molecule on C₂N will be dramatically enhanced to 0.27 eV. Moreover, once the extra charges are moved from the system, the adsorbed hydrogen molecule will be spontaneously released from C₂N monolayer without any barrier. Interestingly, the average adsorption energy for each of the 48 absorbed H₂ molecules is 0.28 eV with the charge injection (8 e^?). This adsorption energy meets the criterion of the Department of Energy (DOE) for hydrogen storage (0.2–0.6 eV). Moreover, C₂N has a high hydrogen storage capacity of 10.5 wt %. Overall, this investigation demonstrates that the new fabricated C₂N can be used as an efficient material for hydrogen storage with high capacity and reversibility by modifying the charges that it carried. The narrow band gap (1.70 eV) of C₂N also ensures the electrochemical methods can be easily realized in experiment.     

NH3BH3 as an internal hydrogen source for high pressure experiments

Aminoborane NH₃BH₃ is proposed as an appropriate material to produce hydrogen in the high-pressure cells designed for the synthesis of hydrides in sizeable amounts at pressures of a few GPa and elevated temperatures. Aminoborane is a non-hydroscopic material and it does not noticeably react with air that permits assembling the high-pressure cells under ambient conditions without any precautions. If heated to 300 °C at any pressure from 0.6 to 9 GPa, aminoborane decomposes to H₂ gas and chemically inert amorphous BN and does not further absorb the liberated hydrogen. Experiments using NH₃BH₃ and AlH₃ alternatively as the internal hydrogen source gave coinciding isotherms of hydrogen solubility in rhodium at 600 °C and pressures up to 9 GPa therefore demonstrating that the partial pressure of impurities (if any) in the H₂ gas generated by NH₃BH₃ is well below the accuracy ±0.3 GPa of determination of the total gas pressure.     

氢存储技术

日益严峻的能源危机和环境污染，使得发展清洁的可再生能源成为各个国家的重要议题。氢能源以其可再生性和良好的环保效应成为未来最具发展潜力的能源载体。氢的储存是发展氢能技术的难点之一。文章介绍了高压、液化、金属氢化物和碳质吸附等储氢技术的研究现状，并对储氢技术的发展趋势进行了讨论。     

High pressure polymer electrolyte water electrolysis: Test bench development and electrochemical analysis

A test bench for a polymer electrolyte water electrolysis (PEWE) cell for high pressure operation of up to 100 bar in differential and balanced pressure mode is described. Important aspects referring to the design, safety and operability of the test bench and the design of a small scale electrolysis cell are described. The electrolyzer cell comprises a special compression mechanism which allows accommodating porous transport layers of different thickness and setting of the compression pressure independent of the clamping pressure. In order to analyze the electrochemical results with respect to the overpotentials, a power source with integrated high frequency resistance (HFR) as well as electrochemical impedance spectroscopy (EIS) measurement capabilities is implemented. The versatility of the test environment is demonstrated by comparing the DC, HFR and EIS data as a function of operating pressure, temperature (up to 70 °C) and current density (up to 4 A/cm²). With respect to pressurized operation of PEWE cells, only the differential pressure mode (hydrogen pressurized) shows the expected isothermal compression behavior, for balanced pressure operation a different characteristic is observed.     

High pressure cryo-storage of hydrogen by adsorption at 77 K and up to 50 MPa

In this paper, we focused on hydrogen adsorption on large surface area solids, combining optimal extreme conditions i.e. very high pressure and low temperature for gas storage process purpose. Therefore, a new volumetric device is elaborated to obtain excess adsorption isotherms at 77 K up to 500 bar. Two activated carbons with different micro-porosities are analysed in the view of hydrogen storage investigation. Also, the results are compared to zeolite adsorption properties. Based on these results, the total mass and volumetric storage capacity are calculated using the bulk density relationship. Thereby, we obtained high storage in situ capacities equal to 5.2 wt% and 54.5 kgH₂/m³. Further, we also considered practical application aspects related to hydrogen storage process in highly porous packed materials.     

Two-dimensional thermal analysis of liquid hydrogen tank insulation

Liquid hydrogen (LH₂) storage has the advantage of high volumetric energy density, while boil-off losses constitute a major disadvantage. To minimize the losses, complicated insulation techniques are necessary. In general, Multi Layer Insulation (MLI) and a Vapor-Cooled Shield (VCS) are used together in LH₂ tanks. In the design of an LH₂ tank with VCS, the main goal is to find the optimum location for the VCS in order to minimize heat leakage. In this study, a 2D thermal model is developed by considering the temperature dependencies of the thermal conductivity and heat capacity of hydrogen gas. The developed model is used to analyze the effects of model considerations on heat leakage predictions. Furthermore, heat leakage in insulation of LH₂ tanks with single and double VCS is analyzed for an automobile application, and the optimum locations of the VCS for minimization of heat leakage are determined for both cases.     

Hydrogen adsorption properties of carbide-derived carbons at ambient temperature and high pressure

Properties of the adsorbed hydrogen phase have been studied for hydrogen adsorption in three carbide derived carbons: SiC-CDC, steam/CO₂ activated SiC-CDC and TiC-CDC. Using the excess hydrogen uptake isotherm at hydrogen pressures above 120 MPa where adsorption has finished, the adsorbate volume has been determined and the adsorbate density has been calculated at ambient temperatures. Absolute adsorption isotherms have been constructed by assuming the adsorbate volume is equivalent to the pore volume and is therefore constant. This study indicates that all three CDCs had the same maximum adsorbate density, with the adsorption proportional to the total pore volume.