Low-pressure H2 Research Articles

Effect of multi-cusp magnetic fields to generate a high-density hydrogen plasma inside a low pressure H2 cylindrical hollow cathode discharge

Based on probe measurements, the plasma density in a low pressure H2 radio-frequency (RF) magnetized cylindrical hollow-cathode capacitively coupled plasma (CCP) is demonstrated to be enhanced by applying a multi-cusp magnetic field (MCMF). CCPs can be used for fabricating functional thin-films, but are currently limited by low plasma densities of less than or about 1016 m−3. It is found that a maximum plasma density of 2.51, 2.88, and 3.14 × 1016 m−3 is obtained at 3, 4 and 5 Pa, respectively. The employed MCMF arrangement contributes to achieving superior plasma uniformity, both in axial and radial direction, at an RF power of 50 W.

Experimental study of hydrogen jet dynamics: Investigating free momentum and impingement phenomena

There is a growing interest in the utilization of hydrogen (H2), as a zero-carbon fuel, in internal combustion engines (ICEs). Accordingly, the primary focus of this study is to investigate low-pressure H2 jet dynamics, which play a vital role in air-fuel mixing especially in direct injection (DI) engines. High-speed z-type schlieren imaging is employed in a constant volume chamber to study the effect of nozzle geometry (single-hole, double-hole, and multi-hole), pressure ratios (PR = injection pressure (Pi)/chamber pressure (Pch)), injection angle (10°, 15°, and 20°), and injection duration (ID) on the H2 jet characteristics. Image post-processing is executed in MATLAB and Python to extract the H2 jet characteristics, including penetration and cross-sectional area. The novelty stems from the comprehensive investigation of H2 jet dynamics and impingement phenomenon under various engine-like conditions. The results indicate that apart from the fact that higher pressure ratios (PRs) improve the air-fuel mixing, the single-hole nozzle induces the fastest H2 jet penetration and the smallest cross-sectional area. Conversely, the double-hole nozzle leads to the slowest penetration and the most expansive cross-sectional area. The performance of the multi-hole nozzle falls between that of the single-hole and double-hole nozzles. Additionally, changing the injection angle results in jet-piston impingement at the periphery, leading to higher H2 concentration in those areas. This negatively affects the formation of an optimal air-fuel mixture. It is also found that changing the injection duration (ID) has no noticeable impact on the H2 jet's behavior.

A Porous Crystalline Nitrone-Linked Covalent Organic Framework.

Herein, we report the synthesis of a nitrone-linked covalent organic framework, COF-115, by combining N, N', N', N'''-(ethene-1, 1, 2, 2-tetrayltetrakis(benzene-4, 1-diyl))tetrakis(hydroxylamine) and terephthaladehyde via a polycondensation reaction. The formation of the nitrone functionality was confirmed by solid-state 13 C multi cross-polarization magic angle spinning NMR spectroscopy of the 13 C-isotope-labeled COF-115 and Fourier-transform infrared spectroscopy. The permanent porosity of COF-115 was evaluated through low-pressure N2 , CO2 , and H2 sorption experiments. Water vapor and carbon dioxide sorption analysis of COF-115 and the isoreticular imine-linked COF indicated a superior potential of N-oxide-based porous materials for atmospheric water harvesting and CO2 capture applications. Density functional theory calculations provided valuable insights into the difference between the adsorption properties of these COFs. Lastly, photoinduced rearrangement of COF-115 to the associated amide-linked material was successfully demonstrated.

Metal Hydride Hydrogen Storage (Compression) Units Operating at Near-Atmospheric Pressure of the Feed H2

Metal hydride (MH) hydrogen storage and compression systems with near-atmospheric H2 suction pressure are necessary for the utilization of the low-pressure H2 produced by solid oxide electrolyzers or released as a byproduct of chemical industries. Such systems should provide reasonably high productivity in the modes of both charge (H2 absorption at PL ≤ 1 atm) and discharge (H2 desorption at PH = 2–5 atm), which implies the provision of H2 equilibrium pressures Peq < PL at the available cooling temperature (TL = 15–20 °C) and, at the same time, Peq > PH when heated to TH = 90–150 °C. This work presents results of the development of such systems based on AB5-type intermetallics characterized by Peq of 0.1–0.3 atm and 3–8 atm for H2 absorption at TL = 15 °C and H2 desorption at TH = 100 °C, respectively. The MH powders mixed with 1 wt.% of Ni-doped graphene-like material or expanded natural graphite for the improvement of H2 charge dynamics were loaded in a cylindrical container equipped with internal and external heat exchangers. The developed units with a capacity of about 1 Nm3 H2 were shown to exhibit H2 flow rates above 10 NL/min during H2 charge at ≤1 atm when cooled to ≤20 °C with cold water and H2 release at a pressure above 2 and 5 atm when heated to 90 and 120 °C with hot water and steam, respectively.

Alloy selection for dual stage metal-hydride hydrogen compressor: Using a thermodynamic model to identify metal-hydride pairs

Metal-hydrides offer a potentially competitive method for compressing hydrogen, particularly where waste heat is available. Metal hydrides are metal alloys or intermetallic compounds that react reversibly with H2. They readily absorb low-pressure H2 at low temperature, and then release H2 at a higher pressure when the temperature is raised. The high pressure H2 is released at a pressure above that expected from standard press-temperature relations. The absorption and desorption pressures of the hydrides are determined by their thermodynamic properties (enthalpy and entropy). To achieve compression ratios above about 10, more than one stage of compression is typically required. The challenge is to find alloy pairs that can work together effectively to achieve the desired compression from the heating/cooling available. Previously, a thermodynamic model has been proposed for identifying suitable metal hydrides that can be paired together to achieve a desired compression. This paper describes methods used previously in the literature to select alloy pairs, and applies the current method to an example selection of 33 hydrides with potential for hydrogen compression. The example application aims to find pairs that can compress a H2 stream from 10 to 350 bar using a temperature range of 30–150 °C, however the theory could readily be adapted to different compression ratios and temperature ranges. For the specific example evaluated none of the potential pairs were able to meet the compression target, however, modification of the parameters (heating/cooling availability) or alloy properties could resolve this issue.

The importance of constructing Triple-functional Sr2P2O7/Ni2P catalysts for smoothing hydrogenation Ring-rearrangement of Biomass-derived Furfural compounds in water

Rational design of catalysts with multi-function was of great importance for speeding mechanism-complicated heterogeneous reaction. Herein, a series of Sr-Ni-P catalysts characterized in (Sr2P2O7)m/Ni2P composite structure (Sr:Ni molar ratio m = 0.15–0.60) were prepared and investigated for hydrogenation ring-rearrangement of four biomass-derived Furfural compounds (FALs) to their Cyclopentanone derivatives (CPOs) in water. By properly manipulate m at 0.40, the superior and reproducible CPOs yields up to 96% were achieved under mild conditions in particular under low-pressure (0.1 MPa) H2. Chemical adsorption measurements disclosed that the attachment of Sr2P2O7 with Ni2P in nanoscale was crucial to construct triple-functional catalytic interface with modulated hydrogen activation (7.5–47.4 µmol/g), acid (196.4–327.3 µmol/g) and base (108.0–214.5 µmol/g) sites. H2-D2 exchange, H2-IR experiments and DFT simulation implied that H2 could be activated through heterolytic dissociation on Sr2P2O7 to participate in reaction; H218O, D2O, D2 isotope-label tracing experiments and DFT mechanism calculation further clarified that besides of H2, H2O was also frequently present in hydrogenation, ring opening, rearrangement and ring re-closing steps and acted as dual donors to provide H and O for CPO; in the favorable thermodynamic feature, a new pathway (with unsaturated dicarbonyl compound as key intermediate) achieved on Sr2P2O7/Ni2P was demonstrated to be more feasible than the reported pathway. The importance of the triple-functional Sr2P2O7/Ni2P catalytic interface for smoothing the aqueous hydrogenation transformation, in particular the function of base site for speeding the transformation was illustrated and discussed.

Dynamics of H atoms surface recombination in low-temperature plasma

The dynamics of H atom recombination on materials of interest for a EUV lithographer was studied under a long-term low-pressure H2 plasma exposure. The similarity of the experimental plasma with the typical EUV-induced plasma over the multilayer mirrors surface of the EUV lithographic machine is demonstrated by means of 2D PIC MC simulation. The measurement of the temporal dynamics of the H atom surface loss probability (γH) is chosen for testing the surface modification during the treatment. Time-resolved actinometry of H atoms with Kr as the actinometer gas was used to detect the dynamics of the H-atom loss probability on the surface of Al, Ru, RVS, and SiO2. It is demonstrated that significant changes of the materials surface occur only at the very beginning of the treatment and are due to surface heating and cleaning effects. After that no changes in the γH are found, indicating that the surface stays absolutely stable. A special test of sensitivity of the used method to the state of surface was carried out. Dynamics of the γH changes with small O2 addition clearly demonstrate modification of the Al surface due to oxidation with the next removal of oxygen by the H2 plasma treatment. The rate of oxide removal is shown to be determined by plasma parameters such as the ion energy and flux to the surface.

Hydrogen Borrowing: towards Aliphatic Tertiary Amines from Lignin Model Compounds Using a Supported Copper Catalyst.

Upcoming biorefineries, such as lignin-first provide renewable aromatics containing unique aliphatic alcohols. In this context, a Cu-ZrO2 catalyzed hydrogen borrowing approach was established to yield tertiary amine from the lignin model monomer 3-(3,4-dimethoxyphenyl)-1-propanol and the actual lignin-derived monomers, (3-(4-hydroxyphenyl)-1-propanol and dihydroconiferyl alcohol), with dimethylamine. Various industrial metal catalysts were evaluated, resulting in nearly quantitative mass balances for most catalysts. Identified intermediates, side and reaction products were placed into a corresponding reaction network, supported by kinetic evolution experiments. Cu-ZrO2 was selected as most suitable catalyst combining high alcohol conversion with respectable aliphatic tertiary amine selectivity. Low pressure H2 was key for high catalyst activity and tertiary amine selectivity, mainly by hindering undesired reactant dimethylamine disproportionation and alcohol amidation. Besides dimethylamine model, diverse secondary amine reactants were tested with moderate to high tertiary amine yields. As most active catalytic site, highly dispersed Cu species in strong contact with ZrO2 is suggested. ToF-SIMS, N2 O chemisorption, TGA and XPS of spent Cu-ZrO2 revealed that imperfect amine product desorption and declining surface Cu lowered the catalytic activity upon catalyst reuse, while thermal reduction readily restored the initial activity and selectivity demonstrating catalyst reuse.

RF power transfer efficiency of inductively coupled low pressure H2 and D2 discharges

The RF power transfer efficiency and the relevant power absorption mechanisms of inductively heated hydrogen and deuterium plasmas are investigated in the low-pressure region between 0.25 and 10 Pa. The discharges are generated in a cylindrical vessel via a helical coil applying a frequency of 1 MHz and delivered RF powers up to 800 W. The power transfer efficiency η is quantified by a subtractive method that relies on the measurement of the delivered RF power and of the RF current through the plasma coil both with and without discharge operation. By means of optical emission spectroscopy and electrical probe measurements, the key plasma parameters are obtained. For both H2 and D2, the relative behavior of the power transfer efficiency is well comparable, which increases with increasing delivered RF power and describes a maximum at pressures between 1 and 3 Pa where more than of the provided power are absorbed by the plasma. The observed relative dependencies of η on the operational parameters are found to be well explained by an analytical approach that considers the power absorption by the plasma via evaluating the RF plasma conductivity based on the measured plasma parameters. At the parameters present, non-collisional stochastic heating of electrons has to be considered for pressures , while collisional heating dominates at higher pressure. Molecular dissociation is found to have a significant influence on the power transfer efficiency of light molecular discharges. The direct comparison of H2 and D2 identifies the higher atomic density in deuterium to cause a systematically increased power transfer efficiency due to an increased ionization rate in the present electron temperature region.

Using magnetic structure of Co40Pd60/Cu for the sensing of hydrogen

This paper reports on a magnetic device with a [Co40Pd60/Cu]10/Fe structure for use in the detection of H2. In a magneto-optical, transport, and gas-detection system, the proposed device presented sharp, reproducible H2-dependent magnetic/electrical properties. The device's saturation magnetization (induced resistance change) dropped (increased) by a factor of ∼5 when a H2 pressure of 75 kPa is given. Besides, the electrical signal-to-noise ratio of the device can be restored ∼50% by exposing it to a magnetic field of 1000 Oe, even when the sensitivity of the device dropped at a low H2 pressure (0.7 KPa). This demonstrates the applicability of the device for use as a low-pressure H2 detector. Operando x-ray spectroscopy revealed that changes in H2-induced magnetism arose from a Co-Pd charge transfer effect coupled to changes in the local-structure symmetry.

Solvothermal synthesis, nanostructural characterization and gas cryo-adsorption studies in a metal–organic framework (IRMOF-1) material

A nanoporous metal–organic framework material, exhibiting an IRMOF-1 type crystalline structure, was prepared by following a direct solvothermal synthesis approach, using zinc nitrate and terephthalic acid as precursors and dimethylformamide as solvent, combined with supercritical CO2 activation and vacuum outgassing procedures. A series of advanced characterization methods were employed, including scanning electron microscopy, Fourier-transform infrared radiation spectroscopy and X-ray diffraction, in order to study the morphology, surface chemistry and structure of the IRMOF-1 material directly upon its synthesis. Porosity properties, such as Brunauer–Emmet–Teller (BET) specific area (∼520 m2/g) and micropore volume (∼0.2 cm3/g), were calculated for the activated sample based on N2 gas sorption data collected at 77 K. The H2 storage performance was preliminary assessed by low-pressure (0–1 bar) H2 gas adsorption and desorption measurements at 77 K. The activated IRMOF-1 material of this study demonstrated a fully reversible H2 sorption behavior combined with an adequate gravimetric H2 uptake relative to its BET specific area, thus achieving a value of ∼1 wt.% under close-to-atmospheric pressure conditions.

Hydrogen Storage and Selective, Reversible O2 Adsorption in a Metal-Organic Framework with Open Chromium(II) Sites.

A chromium(II)-based metal-organic framework Cr3 [(Cr4 Cl)3 (BTT)8 ]2 (Cr-BTT; BTT(3-) =1,3,5-benzenetristetrazolate), featuring coordinatively unsaturated, redox-active Cr(2+) cation sites, was synthesized and investigated for potential applications in H2 storage and O2 production. Low-pressure H2 adsorption and neutron powder diffraction experiments reveal moderately strong Cr-H2 interactions, in line with results from previously reported M-BTT frameworks. Notably, gas adsorption measurements also reveal excellent O2 /N2 selectivity with substantial O2 reversibility at room temperature, based on selective electron transfer to form Cr(III) superoxide moieties. Infrared spectroscopy and powder neutron diffraction experiments were used to confirm this mechanism of selective O2 binding.

Highly visible-light absorbing black TiO2 nanocrystals synthesized by sol–gel method and subsequent heat treatment in low partial pressure H2

We present here a novel method for producing highly visible-light absorbing black TiO2 nanocrystals by combining sol–gel synthesis and subsequent heat treatment in low partial pressure H2. The synthesized black TiO2 nanocrystals with trivalent titanium, oxygen vacancies and structural defects show a significantly lowered optical bandgap in reference to white TiO2. Photodegradation of methyl orange under visible light irradiation indicates the synthesized black TiO2 is superior to the commercial TiO2-P25. The developed process is simple, cost-effective, safe and allows producing a series of visible spectrum active catalysts without the need for metal doping or decoration.

Programmably Shaped Carbon Nanostructure from Shape-Conserving Carbonization of DNA.

DNA nanostructures are versatile templates for low cost, high resolution nanofabrication. However, due to the limited chemical stability of pure DNA structures, their applications in nanofabrication have long been limited to low temperature processes or solution phase reactions. Here, we demonstrate the use of DNA nanostructure as a template for high temperature, solid-state chemistries. We show that programmably shaped carbon nanostructures can be obtained by a shape-conserving carbonization of DNA nanostructures. The DNA nanostructures were first coated with a thin film of Al2O3 by atomic layer deposition (ALD), after which the DNA nanostructure was carbonized in low pressure H2 atmosphere at 800-1000 °C. Raman spectroscopy and atomic force microscopy (AFM) data showed that carbon nanostructures were produced and the shape of the DNA nanostructure was preserved. Conductive AFM measurement shows that the carbon nanostructures are electrically conductive.

Hydrothermal catalytic deoxygenation of palmitic acid over nickel catalyst

Fatty acid has recently received considerable interest as a possible precursor for producing renewable hydrocarbon. In this study, we investigated hydrothermal catalytic deoxygenation of palmitic acid to produce paraffin over a Ni/ZrO2 catalyst with no or low-pressure (100psi) external supply of H2. The results show that the presence of water greatly improved conversion of palmitic acid and paraffin yield. Significant improvement was attributed to the formation of in-situ H2. Without an external H2 supply, a 64.2C% conversion of palmitic acid was achieved in the presence of water, while only a 17.2C% conversion was achieved without water. The results also show that the presence of water suppressed the side reactions of palmitic acid, specifically ketonization and esterification. We concluded that, compared with decarboxylation and hydrodeoxygenation, decarbonylation was the major route for palmitic acid deoxygenation catalyzed by Ni/ZrO2. Varieties of shorter-chain paraffin (C8–C14) were formed through hydrogenolysis, which also produced a considerable amount of CH4. A viable reaction pathway for hydrothermal catalytic deoxygenation of palmitic acid in the presence of Ni/ZrO2 was suggested. The results show that hydrogenolysis and decarbonylation were the major reactions that occurred. This study demonstrates that this hydrothermal catalytic process is a promising approach for producing liquid paraffin (C8–C15) from fatty acids under no or low-pressure H2.

Porous carbon derived via KOH activation of a hypercrosslinked porous organic polymer for efficient CO2, CH4, H2 adsorptions and high CO2/N2 selectivity

Microporous carbon having Brunauer-Emmett-Teller (BET) surface area of 2186m2g−1 and micropore volume of 0.85cm3g−1 has been synthesized via KOH induced high temperature carbonization of a non-conjugated hypercrosslinked organic polymer. Owing to the templating and activation by KOH, we have succeeded in making a microporous carbon from this porous polymer and the resultant carbon material showed high uptake for CO2 (7.6mmolg−1) and CH4 (2.4mmolg−1) at 1atm, 273K together with very good selectivity for the CO2/N2 (30.2) separation. Furthermore, low pressure (1atm) H2 (2.6wt%, 77K) and water uptake (57.4wt%, 298K) ability of this polymer derived porous activated carbon is noteworthy.

Spectroscopic diagnostics of active screen plasma nitriding processes: on the interplay of active screen and model probe plasmas

In a reactor used for active screen plasma nitriding (ASPN) the interplay of two plasma types, (i) the plasma of the cylindrical active screen driven in a pulsed dc mode (f = 1 kHz, 60% duty cycle) and (ii) the plasma at an internal model probe driven in a cw dc mode, ignited in a low pressure H2–N2 gas mixture (p = 3 mbar) containing small amounts of CH4 and CO2 have been studied by tunable diode laser infrared absorption (TDLAS) and optical emission spectroscopy (OES) techniques. Applying in situ TDLAS the evolution of the carbon containing precursors, CH4 and CO2, and of the reaction products, NH3, HCN, CO and H2O, has been monitored. The degree of dissociation of the carbon containing precursor molecules varied between 70% and 92%. The concentrations of the reaction products were found to be in the range 1012…1015 molecules cm−3. By analyzing the development of the molecular concentrations at changes of gas mixtures and plasma power values, it was found that (i) HCN and NH3 are the main products of plasma conversion in the case of methane admixture and (ii) CO, HCN and NH3 in the carbon dioxide case. The fragmentation efficiencies of methane and carbon dioxide (RF(CH4) ≈ 1…2 × 1015 molecules J−1, RF(CO2) ≈ 0.5…1.0 × 1016 molecules J−1) and the respective conversion efficiencies to the product molecules (RC(product) ≈ 1013–1015 molecules J−1) have been determined for different gas mixtures and plasma power values, while the influence of probe and screen plasmas, i.e. the phenomena caused by the interplay of both plasma sources, was analyzed. The additional usage of the plasma at the model probe has a sensitive influence on the generation of the reaction products, in particular that of NH3 and HCN. With the help of OES the rotational temperature of the screen plasma could be determined, which increases with power from 770 K to 950 K. Also with power the ionic component of nitrogen molecules, i.e. the intensity of the -(0-0) band of the first negative system, increases strongly in relation to the intensity of the neutral component, represented by the N2-(0-0) band of the second positive system. In addition, the behavior of the emission of the plasma at the model probe has been studied during the off phase of the plasma of the active screen leading to a direct comparison of the emission characteristics of both plasma sources.

Nanoporous spongy graphene: Potential applications for hydrogen adsorption and selective gas separation

In the present work, a nanoporous (pore width~0.7nm) graphene-based sponge-like material with large surface area (~350m2/g) was synthesized by wet chemical reduction of graphene oxide in combination with freeze-drying. Surface morphology and elemental composition were studied by scanning and transmission electron microscopy combined with energy dispersive X-ray spectroscopy. Surface chemistry was qualitatively examined by Fourier-transform infrared spectroscopy, while the respective structure was investigated by X-ray diffraction analysis. Textural properties, including Brunauer–Emmet–Teller (BET) surface area, micropore volume and surface area as well as pore size distribution, were deduced from nitrogen gas adsorption/desorption data obtained at 77K and up to 1bar. Potential use of the spongy graphene for gas storage and separation applications was preliminarily assessed by low-pressure (0–1bar) H2, CO2 and CH4 sorption measurements at different temperatures (77, 273 and 298K). The adsorption capacities for each gas were evaluated up to ~1bar, the isosteric enthalpies of adsorption for CO2 (28–33kJ/mol) and CH4 (30–38kJ/mol) were calculated using the Clausius–Clapeyron equation, while the CO2/CH4 gas selectivity (up to 95:1) was estimated using the Ideal Adsorbed Solution Theory (IAST).

Low-Pressure H2, NH3 Microwave Plasma Treatment of Polytetrafluoroethylene (PTFE) Powders: Chemical, Thermal and Wettability Analysis

Functionalization of Polytetrafluoroethylene (PTFE) powders of ~6 μm particle size is carried out using low-pressure 2.45 GHz H2, NH3 microwave plasmas for various durations (2.5, 10 h) to chemically modify their surface and alter their surface energy. The X-ray Photoelectron Spectroscopy (XPS) analyses reveal that plasma treatment leads to significant defluorination (F/C atomic ratio of 1.13 and 1.30 for 10 h NH3 and H2 plasma treatments, respectively vs. 1.86 for pristine PTFE), along with the incorporation of functional polar moieties on the surface, resulting in enhanced wettability. Analysis of temperature dependent XPS revealed a loss of surface moieties above 200 °C, however, the functional groups are not completely removable even at higher temperatures (>300 °C), thus enabling the use of plasma treated PTFE powders as potential tribological fillers in high temperature engineering polymers. Ageing studies carried over a period of 12 months revealed that while the surface changes degenerate over time, again, they are not completely reversible. These functionalised PTFE powders can be further used for applications into smart, high performance materials such as tribological fillers for engineering polymers and bio-medical, bio-material applications.

Characterization of hydrogen environment anisotropic thermal etching and application to GaN nanostructure fabrication

We report a new GaN etching technique with high anisotropy involving a thermal decomposition reaction in a low-pressure H2 environment. A GaN microridge stripe structure (5 µm in width and 1.2 µm in height) with extremely smooth sidewalls was fabricated at 1,050 °C and a H2 pressure of 10 Pa for 15 min using a SiO2 mask. The activation energy of the vertical etching was calculated to be 62–77 kcal/mol. In the GaN nanoridge stripe structure, the side etching under the SiO2 mask was less than 5 nm in depth and showed top width and height of ∼40 and ∼180 nm, respectively. The sidewall was extremely smooth and tilted by ∼15° from the m-plane along the a-axis, while being slightly rough and tilted by ∼30° from the a-plane along the m-axis. The () planes were relatively stable in this etching technique.