High-pressure H2 Research Articles

Kinetics studies of the reversible partial decomposition reaction in Mg(BH4)2

Magnesium borohydride Mg(BH4)2 is a promising candidate for hydrogen storage due to its high hydrogen content and theoretically predicted low decomposition temperature. Hydrogenation of the completely decomposed Mg(BH4)2 requires high temperature, high H2 pressure and long reaction time. However, the partially decomposed compound can be rehydrogenated in much milder conditions. In this work, we study the reversible intermediate decomposition reaction in Mg(BH4)2. Gravimetric and volumetric measurements have shown that Mg(BH4)2 released up to 6.8 wt% H2 below 285 °C with the formation of amorphous MgBxHy intermediate(s), as found by infrared spectroscopic analysis. No crystalline decomposition reaction products were detected by powder X-ray diffraction. Rehydrogenation at 260–280 °C yielded 2.5 wt% uptake and the formation of crystalline Mg(BH4)2. Kinetics modeling suggested that the decomposition is a complex process with possibly several reactions which are limited mostly by diffusion. The rehydrogenation reaction was governed by the Johns–Mehl–Avrami model with the nucleation at a constant rate and diffusion-controlled growth mechanism.

High performance mini-gas chromatography-flame ionization detector system based on micro gas chromatography column.

Monitoring Volatile organic compounds (VOCs) was a very important measure for preventing environmental pollution, therefore, a mini gas chromatography (GC) flame ionization detector (FID) system integrated with a mini H2 generator and a micro GC column was developed for environmental VOC monitoring. In addition, the mini H2 generator was able to make the system explode from far away due to the abandoned use of a high pressure H2 source. The experimental result indicates that the fabricated mini GC FID system demonstrated high repeatability and very good linear response, and was able to rapidly monitor complicated environmental VOC samples.

The H2 Pressure Dependence of Hydrodeoxygenation Selectivities for Furfural Over Pt/C Catalysts

Hydrodeoxygenation of furfural was studied over a 10-wt% Pt/C catalyst at 453 K, under both low- and high-pressure conditions. With vapor-phase furfural as the feed and H2 pressures below 1 bar, decarbonylation to furan is a major product, with the selectivity to furfuryl alcohol and dimethylfuran increasing with increasing H2 pressure. When the reaction is performed at 33 bar, using 1-wt % furfural in 1-propanol solvent and high-pressure H2, no evidence for decarbonylation was observed. At high pressures, the reaction is sequential, with all the furfural proceeding to methylfuran, which in turn reacts to over-hydrogenated products, including 2-methyltetrahydrofuran and 2-pentanone. It is suggested that the hydrogen surface coverage is responsible for the apparent differences in the reaction network at high and low pressures.

Optimization of biomass-based carbon materials for hydrogen storage

Hydrogen is considered as the most promising future fuel, as its combustion generates only water vapor besides energy. However, finding efficient, safe and low cost storage methods is the basic impediment for the adoption of hydrogen as fuel. For this purpose, five biomass-based carbon samples have been successfully prepared through KOH activation procedure. The microstructure of the prepared materials was tuned by varying KOH/precursor weight ratio from 1:1 to 5:1, in order to optimize their hydrogen storage behavior and to clarify the storage mechanism. A careful textural and morphological characterization of the prepared samples (N2 and CO2 adsorption, X-ray diffraction, electron microscopy observations) showed that by increasing the activation ratio the nature of the carbons changes from microporous to micro-mesoporous. Thus, an increase in the surface area was observed which enhanced H2 sorption capacity when high H2 pressures were adopted. At subatmospheric pressure, the role of active sites for H2 adsorption, located in the oriented graphene sheets, was clearly elaborated. Finally, the optimal carbon sample has shown a capacity of 6wt% and 1.22wt% at −196°C and 25°C respectively, and 200bar. These results make biomass-based carbons promising materials for H2 storage application.

Surface Reactions of H2O2, H2, and O2 in Aqueous Systems Containing ZrO2

In radiolysis of water, three molecular products are formed (H2O2, O2, and H2). It has previously been shown that aqueous hydrogen peroxide is catalytically decomposed on many oxide surfaces and that the decomposition proceeds via the formation of surface-bound hydroxyl radicals. In this work, we have investigated the behavior of aqueous H2 and O2 in contact with ZrO2. Experiments were carried out in an autoclave with high H2 pressure and low O2 pressure (40 and 0.2 bar, respectively). In the experiments the concentration of H-abstracting radicals was monitored as a function of time using tris(hydroxymethyl)aminomethane (Tris) as scavenger and the subsequent formation of formaldehyde to probe radical formation. The plausible formation of H2O2 was also monitored in the experiments. In addition, density functional theory (employing the hybrid PBE0 functional) was used to search for reaction pathways. The results from the experiments show that hydrogen-abstracting radicals are formed in the aqueous H2-/O2-sy...

A gasdynamic gun driven by gaseous detonation.

A gasdynamic gun driven by gaseous detonation was developed to address the disadvantages of the insufficient driving capability of high-pressure gas and the constraints of gunpowder. The performance of this gasdynamic gun was investigated through experiments and numerical simulations. Much more powerful launching capability was achieved by this gun relative to a conventional high-pressure gas gun, owing to the use of the chemical energy of the driver gas. To achieve the same launching condition, the initial pressure required for this gun was an order of magnitude lower than that for a gun driven by high-pressure H2. Because of the presence of the detonation, however, a more complex internal ballistic process of this gun was observed. Acceleration of projectiles for this gun was accompanied by a series of impulse loads, in contrast with the smooth acceleration for a conventional one, which indicates that this gun should be used conditionally. The practical feasibility of this gun was verified by experiments. The experiments demonstrated the convenience of taking advantage of the techniques developed for detonation-driven shock tubes and tunnels.

Efficiency of silane gas generation in high-rate silicon etching by narrow-gap microwave hydrogen plasma

The silicon (Si) etching characteristics and the related efficiency of the etched Si to generate SiH4 gas in narrow-gap high-pressure microwave H2 plasma have been investigated. It was found that cooling of the Si sample is effective to obtain a high etching rate even under high pressure conditions, and the excess temperature increase of both the gas and Si sample can be suppressed even at an input power density of more than 250 W cm−3, probably because of the narrow plasma gap. The local etching depth monotonically increased with increasing H2 pressure and input plasma power, whereas the etching weight decreased with increasing H2 pressure. By simultaneously increasing the H2 pressure and input power, a maximum Si etching rate of 38 μm min−1 was achieved. This is considered to be related to the high H density generated in the narrow-gap microwave plasma at relatively low temperatures. The energy efficiency of Si etching and the utilization efficiency of the etched Si and H2 gas for SiH4 formation are discussed. Lower input power is favorable for high energy efficiency of Si etching. The Si utilization efficiency, which is defined as the molar ratio of generated SiH4 to etched Si, increases with decreasing average gas residence time in the plasma, whereas H2 utilization efficiency is independent of the gas residence time.

Communication: Dynamical and structural analyses of solid hydrogen under vapor pressure.

Nuclear quantum effects play a dominant role in determining the phase diagram of H2. With a recently developed quantum molecular dynamics simulation method, we examine dynamical and structural characters of solid H2 under vapor pressure, demonstrating the difference from liquid and high-pressure solid H2. While stable hexagonal close-packed lattice structures are reproduced with reasonable lattice phonon frequencies, the most stable adjacent configuration exhibits a zigzag structure, in contrast with the T-shape liquid configuration. The periodic angular distributions of H2 molecules indicate that molecules are not a completely free rotor in the vapor-pressure solid reflecting asymmetric potentials from surrounding molecules on adjacent lattice sites. Discrete jumps of librational and H-H vibrational frequencies as well as H-H bond length caused by structural rearrangements under vapor pressure effectively discriminate the liquid and solid phases. The obtained dynamical and structural information of the vapor-pressure H2 solid will be useful in monitoring thermodynamic states of condensed hydrogens.

H2 Stimulated Raman Scattering in a Multi-pass Cell with a Herriott Configuration**Supported by the National Natural Science Foundation of China under Grant Nos 11304311 and 11475177.

Stimulated raman scattering (SRS) is an effective method for expanding the spectral range of high power lasers, especially in the regime of near IR and middle IR. We report the SRS of high pressure H2 with a multiple-pass cell configuration. The SRS with the multiple-pass cell configuration is found to be very efficient for reduction of threshold of the first Stokes (S1). Due to the coherent SRS (CSRS) process, the multiple-pass cell configuration is more effective for reduction of the threshold for the second Stokes (S2) SRS and for increasing the conversion efficiency of S2. This contributes to the relatively low conversion efficiency of S1 for the multiple-pass cell configuration. Multiple-pass cell SRS is also found to be very effective for improving the beam quality and the stability of S1.

Well-dispersed Pt on TiO2: A highly active and selective catalyst for hydrogenation of 3-nitroacetophenone

Pt nanoparticles with size between 2 and 7nm supported on TiO2 were prepared by a deposition–precipitation method. These catalysts were characterized by nitrogen sorption, powder X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The effects of Pt loading and reaction conditions on the hydrogenation properties of 3-nitroacetophenone over Pt/TiO2 were investigated. The results show that the catalytic performance of Pt/TiO2 for 3-nitroacetophenone hydrogenation to 3-aminoacetophenone is better than those of Rh/TiO2 and Rh/SiO2. The specific activity of Pt in the Pt/TiO2 for 3-nitroacetophenone hydrogenation increases nearly two times when the Pt loading in the Pt/TiO2 decreases from 1.5wt% to 0.3wt%. The selectivity to 3-aminoacetophenone can be up to 100% at complete conversion of 3-nitroacetophenone over the 0.3wt% Pt/TiO2 even at high temperature and H2 pressure. The high activity and excellent selectivity of the 0.3wt% Pt/TiO2 are primarily derived from Pt nanoparticles and TiO2 support as well as the interaction between them. The reaction conditions also have a pronounced effect on the catalytic performance. Higher reaction temperature, H2 pressure and polar solvent are favorable for 3-nitroacetophenone hydrogenation to 3-aminoacetophenone over the 0.3wt% Pt/TiO2.

Microwave-Assisted Conversion of Levulinic Acid to γ-Valerolactone Using Low-Loaded Supported Iron Oxide Nanoparticles on Porous Silicates

The microwave-assisted conversion of levulinic acid (LA) has been studied using low-loaded supported Fe-based catalysts on porous silicates. A very simple, productive, and highly reproducible continuous flow method has been used for the homogeneous deposition of metal oxide nanoparticles on the silicate supports. Formic acid was used as a hydrogen donating agent for the hydrogenation of LA to effectively replace high pressure H2 mostly reported for LA conversion. Moderate LA conversion was achieved in the case of non-noble metal-based iron oxide catalysts, with a significant potential for further improvements to compete with noble metal-based catalysts.

Ruthenium-Catalyzed Straightforward Synthesis of 1,2,3,4-Tetrahydronaphthyridines via Selective Transfer Hydrogenation of Pyridyl Ring with Alcohols.

Through a ruthenium-catalyzed selective hydrogen transfer coupling reaction, a novel straightforward synthesis of 1,2,3,4-tetrahydronaphthyridines from o-aminopyridyl methanols and alcohols has been developed. The synthetic protocol proceeds in an atom- and step-economic fashion together with the advantages of operational simplicity, broad substrate scope, production of water as the only byproduct, and no need for external reducing reagents such as high pressure H2 gas, offering a highly practical approach for accessing this type of structurally unique products.

Genome Wide Re-Annotation of Caldicellulosiruptor saccharolyticus with New Insights into Genes Involved in Biomass Degradation and Hydrogen Production.

Caldicellulosiruptor saccharolyticus has proven itself to be an excellent candidate for biological hydrogen (H2) production, but still it has major drawbacks like sensitivity to high osmotic pressure and low volumetric H2 productivity, which should be considered before it can be used industrially. A whole genome re-annotation work has been carried out as an attempt to update the incomplete genome information that causes gap in the knowledge especially in the area of metabolic engineering, to improve the H2 producing capabilities of C. saccharolyticus. Whole genome re-annotation was performed through manual means for 2,682 Coding Sequences (CDSs). Bioinformatics tools based on sequence similarity, motif search, phylogenetic analysis and fold recognition were employed for re-annotation. Our methodology could successfully add functions for 409 hypothetical proteins (HPs), 46 proteins previously annotated as putative and assigned more accurate functions for the known protein sequences. Homology based gene annotation has been used as a standard method for assigning function to novel proteins, but over the past few years many non-homology based methods such as genomic context approaches for protein function prediction have been developed. Using non-homology based functional prediction methods, we were able to assign cellular processes or physical complexes for 249 hypothetical sequences. Our re-annotation pipeline highlights the addition of 231 new CDSs generated from MicroScope Platform, to the original genome with functional prediction for 49 of them. The re-annotation of HPs and new CDSs is stored in the relational database that is available on the MicroScope web-based platform. In parallel, a comparative genome analyses were performed among the members of genus Caldicellulosiruptor to understand the function and evolutionary processes. Further, with results from integrated re-annotation studies (homology and genomic context approach), we strongly suggest that Csac_0437 and Csac_0424 encode for glycoside hydrolases (GH) and are proposed to be involved in the decomposition of recalcitrant plant polysaccharides. Similarly, HPs: Csac_0732, Csac_1862, Csac_1294 and Csac_0668 are suggested to play a significant role in biohydrogen production. Function prediction of these HPs by using our integrated approach will considerably enhance the interpretation of large-scale experiments targeting this industrially important organism.

New Direct Alcohol and Hydrogen Fuel Cells for Naval and Aeronautical Applications (PILCONAER)

In the current context of demand for reliable, low cost and low environmental impact energy sources, many countries and companies are mostly focused on fuel cells (FC) in fields as transportation and stationary power generation and portable devices. Lately, FCs have begun to be applied in naval and aeronautical systems due to its high efficiency, low noise and environmental advantages. These applications could range from propulsion systems to auxiliary power units (APU). The main problems associated with the use of FCs in these areas are the current high cost due to the materials used, i.e. Nafion and Pt, the lack of durability testing in these specific conditions, security issues to flammability and high H2 pressures and low availability as a fuel, or the toxicity of methanol used as a fuel, and specific parameters such as weight in aircraft applications and volume in marine applications. Currently it is working on each of these issues, and at this point the ethanol as direct fuel is considered crucial. The use of ethanol as fuel has the advantage of easy transportation, storage and refueling, and is nontoxic. Bioethanol is a promising energy source, produced from raw materials containing sugar or starch. These raw materials exists in all parts of the world and is renewable, which involves the use of local energy sources contributing to the diversification of energy supply, reducing import dependence, increasing security of supply and generating new opportunities for agriculture. The main objective of the proposal is the development of low power stacks (stacks) fed with methanol (DMFC) and ethanol (DEFC) based on the development of new catalysts and membranes. The materials are considered first from the point of view of application in FCs fed with H2 (PEMFC) to be optimized and used on FCs fed directly with alcohols. An important particular objective is the development of cells fed with ethanol in alkaline medium in order to eliminate the use of Pt as the catalyst and increase the efficiency of the electrochemical FC while cost is decreased. The proposed development of new FCs fed with alcohols, especially ethanol, is considered a technology of sustainable use, further commitment to the restoration of the natural environment and biodiversity conservation. The consortium combines groups: skilled in synthesis and characterization of materials (CSIC); expert in the development and evaluation of FC stacks (UPM and INTA) and with the ability to develop physical and mathematical models to predict the behavior of the fuel cell equipped for the MEAs fabricated (UCM). Four companies have shown interest in the proposal, as well as participation according to preliminary results.

Diiron azadithiolates as models for the [FeFe]-hydrogenase active site and paradigm for the role of the second coordination sphere.

The [FeFe] hydrogenases (H2ases) catalyze the redox reaction that interconverts protons and H2. This area of biocatalysis has attracted attention because the metal-based chemistry is unusual, and the reactions have practical implications. The active site consists of a [4Fe-4S] cluster bridged to a [Fe2(μ-dithiolate)(CN)2(CO)3](z) center (z = 1- and 2-). The dithiolate cofactor is [HN(CH2S)2](2-), called the azadithiolate ([adt(H)](2-)). Although many derivatives of Fe2(SR)2(CO)6-xLx are electrocatalysts for the hydrogen evolution reaction (HER), most operate by slow nonbiomimetic pathways. Biomimetic hydrogenogenesis is thought to involve intermediates, wherein the hydride substrate is adjacent to the amine of the adt(H), being bonded to only one Fe center. Formation of terminal hydride complexes is favored when the diiron carbonyl models contain azadithiolate. Although unstable in the free state, the adt cofactor is stable once it is affixed to the Fe2 center. It can be prepared by alkylation of Fe2(SH)2(CO)6 with formaldehyde in the presence of ammonia (to give adt(H) derivatives) or amines (to give adt(R) derivatives). Weak acids protonate Fe2(adt(R))(CO)2(PR3)4 to give terminal hydrido (term-H) complexes. In contrast, protonation of the related 1,3-propanedithiolate (pdt(2-)) complexes Fe2(pdt)(CO)2(PR3)4 requires strong acids. The amine in the azadithiolate is a kinetically fast base, relaying protons to and from the iron, which is a kinetically slow base. The crystal structure of the doubly protonated model [(term-H)Fe2(Hadt(H))(CO)2(dppv)2](2+) confirms the presence of both ammonium and terminal hydrido centers, which interact through a dihydrogen bond (dppv = cis-C2H2(PPh2)2). DFT calculations indicate that this H---H interaction is sensitive to the counterions and is strengthened upon reduction of the diiron center. For the monoprotonated models, the hydride [(term-H)Fe2(adt(H))(CO)2(dppv)2](+) exists in equilibrium with the ammonium tautomer [Fe2(Hadt(H))(CO)2(dppv)2](+). Both [(term-H)Fe2(Hadt(H))(CO)2(dppv)2](2+) and [(term-H)Fe2(adt(H))(CO)2(dppv)2](+) are highly active electrocatalysts for HER. Catalysis is initiated by reduction of the diferrous center, which induces coupling of the protic ammonium center and the hydride ligand. In contrast, the propanedithiolate [(term-H)Fe2(pdt)(CO)2(dppv)2](+) is a poor electrocatalyst for HER. Oxidation of H2 has been demonstrated, starting with models for the oxidized state ("Hox"), for example, [Fe2(adt(H))(CO)3(dppv)(PMe3)](+). Featuring a distorted Fe(II)Fe(I) center, this Hox model reacts slowly with high pressures of H2 to give [(μ-H)Fe2(adt(H))(CO)3(dppv)(PMe3)](+). Highlighting the role of the proton relay, the propanedithiolate [Fe2(pdt)(CO)3(dppv)(PMe3)](+) is unreactive toward H2. The Hox-model + H2 reaction is accelerated in the presence of ferrocenium salts, which simulate the role of the attached [4Fe-4S] cluster. The redox-complemented complex [Fe2(adt(Bn))(CO)3(dppv)(FcP*)](n+) catalyzes both proton reduction and hydrogen oxidation (FcP* = (C5Me5)Fe(C5Me4CH2PEt2)).

Research on Unitized Regenerative Fuel Cell Stack with Producing High Pressure H2 and O2 in WE Mode

A unitized regenerative fuel cell (URFC) is an electrochemical energy storage device that combines a fuel cell and a water electrolyzer in a single system. The URFC is an excellent clean, quite energy source and are promising energy storage systems for uninterrupted power supplies, solar powered aircraft, and satellites. In the paper, the high pressure unitized regenerative fuel cell was developed and validated with a capacity of producing hydrogen and oxygen at a pressure of up to 5MPa in the water electrolysis mode. The bifunctional performance of URFC stack in the hydrogen and oxygen fuel cell (FC) and water electrolysis (WE) modes and the generated gases pressure influence on URFC stack were investigated. The main electrochemical element is bifunctional membrane electrode assembly (MEA) with an active area of 200cm2 which consists of polymer electrolyte membrane from Dupont and the electrode layer on both sides of the membrane by catalyst coated on membrane technique (CCM). Oxygen electrode layer was prepared by Pt/IrO2mixing catalysts. Hydrogen electrode layer was prepared by 40%Pt/C (J.M.). The diffusion layer of MEA was the porous sintered metal foil with corrosion resistance. Primary test results illustrated that high pressure URFC stack exhibited the promising bifunctional performance. The static seal level of URFC stack was up to 10MPa and the dynamic gas pressure reached 5MPa in the water electrolysis mode. Figure1 showed that the stack output electric power was greater than 1.2kW at a current density of 1000mA/cm2in the fuel cell mode. Figure 2 showed that the generated gases pressure had few influence on the performance of the stack in the water electrolysis mode under working conditions. The single cell voltage was 5~12mV higher at the generated gases pressure of up to 5MPa when the current density was less than 700mA/cm2. However the single cell voltage was 5~10mV lower at the generated gases pressure of up to 5MPa when the current density greater than 700mA/cm2. The stack showed good pressure adaptability. The round-trip energy conversion efficiency of high pressure URFC stack was greater than 45% at the current density of 500mA/cm2. In addition, the cycling test of the stack during URFC operation was performed in both fuel cell and water electrolysis modes. The results indicated that high pressure URFC stack had the promising cycling stability. Further research and validation are still underway. Figure 1

Iridium catalyzed reversible dehydrogenation – Hydrogenation of quinoline derivatives under mild conditions

The potential of a hydrogen-based energy economy is limited by the fact that hydrogen gas is difficult to store and transport. Storing hydrogen in the form of liquid organic hydrogen-carriers (LOHCs) is a highly attractive alternative to current options but it requires the development of catalytic means of reversibly hydrogenating and dehydrogenating these carriers under mild conditions and ideally using a single catalyst for both processes. We report the optimization of two families of previously reported hydrogenation catalysts for the reverse reaction, dehydrogenation of N-heterocyclic substrates. These complexes are capable of catalyzing both dehydrogenation and hydrogenation reactions in alternation, giving high yields in both directions. Importantly, our complexes do not require high temperatures, high pressures of H2 or strong base for the hydrogenation step.

Biomass hydrolysis inhibition at high hydrogen partial pressure in solid-state anaerobic digestion

In solid-state anaerobic digestion, so-called ss-AD, biogas production is inhibited at high total solids contents. Such inhibition is likely caused by a slow diffusion of dissolved reaction intermediates that locally accumulate. In this study, we investigated the effect of H2 and CO2 partial pressure on ss-AD. Partial pressure of H2 and/or CO2 was artificially fixed, from 0 to 1 557mbars for H2 and from 0 to 427mbars for CO2. High partial pressure of H2 showed a significant effect on methanogenesis, while CO2 had no impact. At high PH2, the overall substrate degradation decreased with no accumulation of metabolites from acidogenic bacteria, indicating that the hydrolytic activity was specifically impacted. Interestingly, such inhibition did not occur when CO2 was added with H2. This result suggests that CO2 gas transfer is probably a key factor in ss-AD from biomass.

One-step Conversion of Furfural into 2-Methyltetrahydrofuran under Mild Conditions.

One-step direct conversion of biomass-derived furfural to 2-methyltetrahydrofuran was realized under atmospheric pressure over a dual solid catalyst based on two-stage-packed Cu-Pd in a reactor; this is the first report that one-step conversion of furfural resulted in high yield of 2-methyltetrahydrofuran (97.1 %) under atmospheric pressure. This strategy provided a successive hydrogenation process, which avoids high H2 pressure, uses the reactor efficiently, and eliminates the product-separation step. Therefore, it could enhance the overall efficiency as a result of low cost and high yield.

Verification of electron doping in single-layer graphene due to H2 exposure with thermoelectric power

We report the electron doping of single-layer graphene (SLG) grown by chemical vapor deposition (CVD) by means of dissociative hydrogen adsorption. The transfer characteristic showed n-type doping behavior similar to that of mechanically exfoliated graphene. Furthermore, we studied the thermoelectric power (TEP) of CVD-grown SLG before and after exposure to high-pressure H2 molecules. From the TEP results, which indicate the intrinsic electrical properties, we observed that the CVD-grown SLG is n-type doped without degradation of the quality after hydrogen adsorption. Finally, the electron doping was also verified by Raman spectroscopy.