Hydrogenation-dehydrogenation Process Research Articles

Preparation, characterization and modification of magnesium hydride for enhanced solid-state hydrogen storage properties

Magnesium–magnesium hydride (Mg–MgH2) system has attracted attention worldwide recently because of its simple hydrogenation-dehydrogenation process, the cost-effectiveness of the raw materials, and relatively high hydrogen storage capacity compared to the other metal-metal hydride systems. The present study deals with the optimization of the process parameters for the synthesis of magnesium hydride (MgH2) in sizable quantities using commercial-grade magnesium powder, characterization with respect to hydrogen storage capacity, by thermal dehydrogenation and pH-controlled aqueous hydrolysis. The thermal hydrogenation-dehydrogenation and mild acidified aqueous dehydrogenation behaviour of MgH2 were studied systematically to compare the decomposition kinetics and storage capacity. The superior catalytic effect of V2O5 on decreasing the onset-dehydrogenation temperature of MgH2 is demonstrated. The MgH2-5 wt. % mesoporous V2O5 sample starts releasing hydrogen at 220 °C, which is substantially less than the as-synthesized un-catalysed MgH2 under identical conditions which starts releasing hydrogen at 430 °C. The dehydrogenated MgH2-5wt. %V2O5 could be completely re-hydrogenated at 150 °C. Hydrolysis of as-synthesized MgH2 was demonstrated using an aqueous solution using tartaric acid and the dehydrogenation behaviour was co-related with the pH of the solution. More than 90% hydrogen yield was achieved by the hydrolysis of MgH2 in a tartaric acid solution of pH-4. Based on the result, a hydrogen gas dispenser using solid-state magnesium hydride as a hydrogen source is proposed for laboratory applications for the supply of ultra-pure hydrogen for various reactions and crystal growth experiments.

The role of hydrogen in the synthesis of High-entropy alloys and their hydrides

The aim of this work is to present the new technique processes of formation of stable hydrides of High-entropy alloys (HEAs) with high hydrogen content. The essence of the proposed method is the sequential use of self-propagating high-temperature synthesis (SHS) method for producing the metal hydrides, followed by the formation of alloys in the hydride cycle (HC) method. Preliminary, the hydrides of three compositions of metal mixtures were synthesized in SHS: 0.2TiH2+0.2ZrH2+0.2HfH2+0.2VH2+0.2NbH2, 0.3TiH2+0.15ZrH2+0.15HfH2+0.2VH2+0.2NbH2 and 0.3TiH2+0.1ZrH2+0.1HfH2+0.2VH2+0.2NbH2+0.1MgH2. From the synthesized mixtures of metal hydrides, the HEAs were produced in HC. The resultant hard alloys Ti0.2Zr0.2Hf0.2V0.2Nb0.2, Ti0.3Zr0.15Hf0.15V0.2Nb0.2 and Ti0.3Zr0.15Hf0.15V0.2Nb0.2Mg0.1 without crushing combusted in Н2 at РH2 = 5–30 atm. in SHS mode. As a result, the hydrides of HEAs (Ti0.2Zr0.2Hf0.2V0.2Nb0.2)Н2.05, (Ti0.3Zr0.15Hf0.15V0.2Nb0.2)H2.05 and (Ti0.3Zr0.1Hf0.1V0.2Nb0.2 Mg0.1)H182 were synthesized with H2 content between 2.17 and 2.42 wt% and H/Me = 1.82–2.05. The repeating the hydrogenation-dehydrogenation processes for 1–3 times confirmed the exceptional cyclic stability of hydrides and the reversible high hydrogen storage capacity of the alloys. The regularities and the mechanism of formation of HEAs and their hydrides were elucidated. The applicability of combination of SHS and HC methods for synthesis of solid solutions of BCC structure HEAs and of their hydrogen-rich hydrides was demonstrated. The remarkable advantages of the developed efficient, low-energy consuming, waste-free and safe method for the synthesis of HEAs and their hydrides can be of commercial interest and attractive to industry, given the current needs for the development of renewable energy, in particular, the solid hydrogen storage facilities.

Investigation of the Effect of Milling Time on Elemental Powders of Oxi‐Reduction Nickel and Hydrogenation–Dehydrogenation Titanium

Mechanical alloying (MA) is widely applied in the synthesis of blended elemental or prealloyed powders. This work evaluates the effect of milling time on elemental nickel and titanium powders produced by oxi‐reduction and the hydrogenation–dehydrogenation process, respectively. The powders are characterized by scanning electron microscopy, X‐ray diffraction, particle size, powder yield, and differential scanning calorimetry. It is observed that increasing the milling time promotes the formation of a structure composed of thin lamellae of nickel and titanium, which results in the beneficial effect of lowering the temperature for the formation of the intermetallic of the Ni–Ti system and in the powder yield achieved. The reduction of milling time in the MA process of NiTi alloys enhances technological efficiency by decreasing their overall processing time.

Gas-phase applications of metal hydrides

Applications of metal hydrides (MHs) utilise a reversible interaction of hydride-forming metals, alloys and intermetallic compounds with hydrogen. The reversible process of the formation-decomposition of the MH when interacting with hydrogen allows to utilise several unique features of the hydrogenation-dehydrogenation process. These features enable efficient storage of hydrogen gas resulting in a high volumetric efficiency of hydrogen storage while also storing thermal energy and converting it to the energy of compressed hydrogen gas or utilising the hydrides for the electrochemical energy conversion and storage. Thus, MH applications are very important as the components of the hydrogen energy systems integrating hydrogen supply from the metal hydride store and PEM fuel cells. Compact and safe hydrogen storage together with utilisation of the waste heat opens up for the commercial market of the hydrogen energy systems of green energy storage and supply.

Catalytic applications of cobalt/cobalt oxide nanoparticles in heterocyclic compounds

Worldwide interest is growing in the various catalytic uses of cobalt/cobalt oxide nanoparticles in the synthesis of heterocyclic compounds. This review covers the last seven-year (2017–2023) reports on the catalytic applications of cobalt/cobalt oxide nanoparticles in heterocyclic compounds. For several chemical reactions involving N-Heterocycles, we described Co/CoO nanoparticles that were doped with other elements and coordinated with nitrogen in the current work. An excellent performance for reversible hydrogenation-dehydrogenation processes is attributed to a well-designed Co metal catalyst with a reductive N-formylation of N-heterocyclic arenes, an organic pathway for hydrogen storage. There have also been reports of various MCR for heterocycles utilising Co/CoO NPs as the catalyst. In addition to the solvent-free, selective aza-heterocycle synthesis using cobalt described above, intra-molecular ring-closing processes for the synthesis of organic heterocycles have also recently been discovered. In this context numerous studies on a variety of topics, including the oxygenation of alcohols to aldehyde, esters, and nitriles, aryl halide biaryl coupling reactions, radical trans-annulations, multicomponent coupling reactions, cyclization, and cyclo-propanations have been described.

Способы хранения и аккумулирования водорода

Due to the depletion of natural fossil energy carriers, hydrogen is becoming a promising alternative fuel, the advantages of which are inexhaustible reserves and its high energy and environmental indicators. The undeveloped infrastructure for the supply of hydrogen fuel to consumers, the problems of storage/accumulation of hydrogen hinder the development of hydrogen energy. (Research purpose) The research purpose is in considering modern methods of storage and accumulation of hydrogen, comparing their advantages and disadvantages. (Materials and methods) The article presents the state of the issue on scientific and information sources and patent information published in the open press. Authors considered storage methods for a number of parameters, the main of which are: volume and mass content of hydrogen; storage conditions and hydrogenation-dehydrogenation processes; cyclic stability and cost. The article presents a patent search in the information search system of the database of the Federal Institute of Industrial Property by keywords. Authors studied the abstracts and applications of Russian inventions, formulas of Russian utility models. Mechanical stresses in capillaries were determined using the moment-free theory of shells. (Results and discussion) The article presents the results of studies on the storage of gaseous and liquid hydrogen, in inorganic and organic carriers, carriers based on nanomaterials, in microspheres and adsorbents, capillary structures and energy storage substances. The hydrides do not require maintaining a low temperature and provide a volume density of 100-150 grams per liter, comparable to liquid hydrogen. A cost-effective method of storing hydrogen in microspheres and adsorbents is one of the promising methods for storing hydrogen gas under pressure in capillary or multicapillary structures made of glass, quartz, basalt and other materials. The density of hydrogen exceeds the density of liquid at a pressure of 200 megapascals. (Conclusions) Depending on the scale, purposes of storage and accumulation, it is possible to give preference to the method of storing hydrogen in liquid form, in multicapillary structures and various types of hydrogen carriers.

Improving spreadability of hydrogenation–dehydrogenation Ti powder via surface treatment using silane-based compounds

Ti powder is manufactured using several methods such as sponge screening, hydrogenation–dehydrogenation (HDH), and atomization. Manufacturing of Ti powder using HDH process is approximately 70% less expensive than that using gas atomization. The irregularly shaped particles of Ti powder fabricated using the HDH process have a lower spreadability than the spherical particles of Ti powder produced using atomization. Hence, HDH Ti powder cannot be used in powder bed fusion (PBF) method, which is an additive manufacturing process. Therefore, in this study, the spreadability of HDH Ti powder was improved by changing the powder surface from hydrophilic to hydrophobic using silane-based chemicals. The flowability, shape, and purity of the surface-treated Ti powder were analyzed, and the surface bonding characteristics of the powder were studied using X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. The hydrophobic modification was confirmed by measuring the contact angle of the powder with water. For evaluating the improvement in spreadability of the powder, a recoating tester with the actual PBF driving method was created. The results indicated that the proposed method can be used in additive manufacturing and can reduce the cost of HDH Ti powder while improving the spreadability of the powder particles.

The functioning mechanism of Al valid substitution for Co in improving the cycling performance of Zr–Co–Al based hydrogen isotope storage alloys

In order to optimize the hydrogen isotope storage properties of ZrCo alloy and promote its application in the storage and delivery system (SDS), ZrCo alloy is modified by partial substitution of Co with Al and subsequent melt spinning process. The microstructure and hydrogen isotope storage properties, especially the cycling performance, of ZrCo1-xAlx (x = 0–0.15) samples were thoroughly investigated. It is found that all as-cast Al-substituted alloys are consisted of a main phase of ZrCo, while the segregation of Al element at grain boundary is more serious with the increase of Al doping content, which restrains the valid substitution content of Al for Co in ZrCo phase. The initial activation performances of the Al-substituted alloys are enhanced and excellent hydriding kinetics are maintained. With the increase of Al substitution content in ZrCo phase of ZrCo1-xAlx (x = 0–0.15) alloys, the initial saturated hydrogen capacities of α solid-solution phase are improved significantly, which is attributed to the decline of valence electron concentrations (VEC) for Al-substituted alloys. Further analysis shows that the hydrogenation-dehydrogenation process of ZrCo1-xAlx (x = 0–0.15) alloys after multiple cycles has been altered as intercalation and de-intercalation of hydrogen atoms between ZrCo phase and α phase, leading to cycling capacity stabilization. More importantly, the improved terminal saturated hydrogen capacities of α phase in the Al-substituted alloys, which represents enhanced final cycling stable capacities, is linked with the increase of initial saturated hydrogen capacities of α phase after Al substitution for Co in ZrCo phase. In addition, the valid substitution content of Al for Co in ZrCo phase is further increased without any element segregation for ZrCo0.9Al0.1 alloy processed by melt spinning, which behaves further optimized final cycling stable capacity of 0.93 wt%, and its variation of the hydrogenation and dehydrogenation paths is similar to those of the above samples. In this work, the mechanism of cycling capacity stabilization has been explored in detail, which provides guidance to improve the cycling stability of ZrCo-based hydrogen isotope storage alloys from point of phase structure of ZrCo alloy.

Structural Changes in С36 Laves Phase Intermetallic Compound TiCr2 During Hydrogenation–Dehydrogenation Process

The paper deals with melting of titanium and chromium metal powders in plasma of abnormal glow discharge which results in the formation of the hexagonal С36 Laves phase compound TiCr2 with a = 4.928 A and c = 15.983 A lattice parameters. The hydrogenation–dehydrogenation process is used to prepare the powder of C36 Laves phase intermetallic compound TiCr. The hydrogenation–dehydrogenation process is performed at 100°C, 2 atm hydrogen pressure and 30 min ageing followed by vacuum cooling. The prepared metal powder is characterized by rounded lamellar and coarse particles 6 ± 2 μm and 21 ± 7 μm in size, respectively.

Vacuum activation assisted hydrogenation-dehydrogenation for preparing high-quality zirconium powder

ABSTRACTThe vacuum activation assisted hydrogenation-dehydrogenation (HDH) method was applied to fabricate the high-purity and ultrafine nuclear grade zirconium powders. An additional vacuum activation process was specially used prior to the hydrogenation to suppress the oxygen content and increase the hydrogen content. It was found that this extra process was not only efficient in shortening the length of the whole process, but also critical in improving the quality of Zr powders. The detailed investigations on the mechanism indicated that the merits could be both attributed to the removal of the oxygen sources on the sponge zirconium surface and the formation of micro-cracks on the ZrO2 film. By adjusting the parameters of the vacuum activation assisted HDH process, the oxygen content of the intermediate material ZrH2 was decreased down to 0.16 wt.%, while the hydrogen content was increased up to 2.14 wt.%, nearly approaching to the theoretical value. Based on this high-quality ZrH2 bulks, the Zr powders with oxygen content of 0.21 wt.% and D50 of ~2.9 μm could be fabricated after the ball-milling and dehydrogenation process. An efficient approach to produce high-quality Zr powders was systematically investigated in this paper to satisfy with the demand of the nuclear industry.

Characteristics of Ti6Al4V Powders Recycled from Turnings via the HDH Technique

The objective of this research is for Ti6Al4V alloy turnings, generated during the machining of implants, to produce powders for the fabrication of Ti base coating via the cold spray method. In order to decrease the cost of powder production and increase the recycling rate of the turnings, the hydrogenation-dehydrogenation (HDH) process has been utilised. The HDH process consists of the following sequence: surface conditioning of the turnings, hydrogenation, ball milling (for powder production), and dehydrogenation. Afterwards, the properties of the recycled powder were analysed via phase, chemical, and morphological examinations, and size and flowability measurements. Usability of the powder in additive manufacturing applications has been evaluated via examining the characteristics of the deposit produced from this powder by the cold spray method. In short, promising results were obtained regarding the potential of the recycled powders in additive manufacturing after making minor adjustments in the HDH process.

Electrochemical Corrosion Behavior of Air-Exposed Zr–Mn–Cr–Ni–V Alloy

Scanning electron microscopy and electron microprobe analysis show that the ZrMnCrNiV alloy has a dendritic structure and is chemically inhomogeneous. The corrosion mechanism for the unexposed alloy and the alloy exposed in air for 7 and 15 days, followed by aging in a 30% KOH solution, is the same: corrosion originates at the interphase boundary and propagates along it, which is typical of pitting corrosion. If the alloy is preliminary exposed in air, its surface has a greater number of pittings, but all of them are smaller in area and depth, making the corrosion process more uniform. In hydrogenation–dehydrogenation of this alloy, even more uniform distribution of smaller corrosion areas is observed. Studies of the corrosion resistance of this alloy in a KOH solution carried out by atomic adsorption spectrometry show that the alloy powder exposed in air has higher corrosion resistance compared to the unexposed powder. Electrochemical corrosion studies of the alloy conducted in the anodic region using the method of polarization curves indicate that the corrosion rate for the unexposed and exposed alloys is controlled by the rate at which passivating films form. The most extensive passivation region is observed in the alloy exposed in air for 15 days. It shows adequate corrosion resistance in a 30% KOH solution. The cyclic resistance studies for the electrodes produced from the alloy powder exposed for 10 days, at a discharge to potential difference E = –1.0 V and E = –0.8 V, demonstrate that oxidation in the hydrogenation-dehydrogenation process affects the cyclic resistance. It is found that there is liming time for exposing the alloy in air (as an ingot and/or powder) after which the cyclic resistance deteriorates.

Electrochemical Properties of Zr–Mn–Cr–Ni–V Alloy in Long-Term Cycling After Air Oxidation

A zirconium-containing alloy was subjected to air oxidation to examine its influence on the lattice parameters and cyclic resistance. The samples made of freshly prepared alloy powder and of powder oxidized in air for 7, 15, and 30 days were studied. Cyclic voltammetry was used to analyze in detail the current–voltage characteristics and X-ray diffraction was employed to determine the lattice parameters. The freshly prepared alloy was found to be very unstable and significantly lose its activity in the hydrogenation–dehydrogenation process. This results from oxidation of the alloy, which induces interfacial stresses and causes mechanical damage of the electrodes. Air oxidation of the alloy powder followed by compaction of the electrodes stabilizes its electrochemical properties and, as a result, increases the cyclic resistance. According to X-ray diffraction, the phase ratio after air oxidation remains practically unchanged, and the lattice expansion (within 1%) can be attributed to measurement errors.

Atomically Thin Interfacial Suboxide Key to Hydrogen Storage Performance Enhancements of Magnesium Nanoparticles Encapsulated in Reduced Graphene Oxide.

As a model system for hydrogen storage, magnesium hydride exhibits high hydrogen storage density, yet its practical usage is hindered by necessarily high temperatures and slow kinetics for hydrogenation-dehydrogenation cycling. Decreasing particle size has been proposed to simultaneously improve the kinetics and decrease the sorption enthalpies. However, the associated increase in surface reactivity due to increased active surface area makes the material more susceptible to surface oxidation or other side reactions, which would hinder the overall hydrogenation-dehydrogenation process and diminish the capacity. Previous work has shown that the chemical stability of Mg nanoparticles can be greatly enhanced by using reduced graphene oxide as a protecting agent. Although no bulklike crystalline MgO layer has been clearly identified in this graphene-encapsulated/Mg nanocomposite, we propose that an atomically thin layer of honeycomb suboxide exists, based on first-principles interpretation of Mg K-edge X-ray absorption spectra. Density functional theory calculations reveal that in contrast to conventional expectations for thick oxides this interfacial oxidation layer permits H2 dissociation to the same degree as pristine Mg metal with the added benefit of enhancing the binding between reduced graphene oxide and the Mg nanoparticle, contributing to improved mechanical and chemical stability of the functioning nanocomposite.

One-Pot Synthesis of Functionalized Carbazoles via a CAN-Catalyzed Multicomponent Process Comprising a C-H Activation Step.

The microwave-promoted three-component reaction between o-nitrochalcones, primary amines and β-dicarbonyl compounds in the presence of Ce(IV) ammonium nitrate constitutes the first example of a multicomponent carbazole synthesis. This reaction furnishes highly substituted and functionalized carbazole derivatives via a double annulation process that generates two C-C and two C-N bonds, with water as the only side product. Mechanistically, this transformation has some unusual features that include an intramolecular coupled hydrogenation-dehydrogenation process, the functionalization of a C-H group by direct attack onto a nitrogen function and a CAN-catalyzed reduction via hydride transfer from ethanol. The mechanisms of these reactions were studied with the aid of computational techniques.

Production of spherical powders on the basis of group IV metals for additive manufacturing

The method of production of group IV powders for additive manufacturing is presented. Powders are produced in the hydrogenation-dehydrogenation process followed by plasma spheroidization of prepared polygonal powders. The dependence of composition of hydrides on amount of absorbed hydrogen is established for the group IV metals; it allows optimizing the technological parameters of processes for hydrogenation and grinding. It is shown that spherical powders of titanium, Ti–6Al–4V, and Zr–10% Ti of mass fractions of 40–70 μm and not less than 40 μm with calculated spheroidization level achieving 96% may be produced in Ar + 8 vol % H2 thermal plasma flow generated by an arc-jet plasma generator. The average roundness factor is 1.01.

Porosity, Microstructure, and Mechanical Properties of Ti-6Al-4V Alloy Parts Fabricated by Powder Compact Forging

Ti-6Al-4V alloy powders produced using a hydrogenation–dehydrogenation process and a gas atomization process, respectively, were rapidly consolidated into near-net-shaped parts by powder compact forging. The porosity, microstructure, and tensile mechanical properties of specimens cut from regions at different distances from the side surfaces of the forged parts were examined. The regions near the side surfaces contained a fraction of pores due to the circumferential tensile strain arising during the powder compact forging process, and the porosity level decreased rapidly to zero with increasing the distance from the side surface. The forged parts had a fully lamellar structure with the α + β colony sizes and α lamella thickness changing little with the distance from the side surface. The specimens cut from the regions near the side surfaces had a lower yield strength and tensile strength. The correlation of porosity with the yield strength of the specimens suggested that the reduction of load bearing areas due to the porosity and unbonded or weakly bonded interparticle boundaries was not the only reason for the lower strength, and the stress concentration at the pores and associated with their geometry also played an important role in this. It is likely that the effect of stress concentration on yield strength reduction of the forged part increases with oxygen content. The Hall–Petch relationship of the yield strength and the average α lamella thickness suggested that the strength of the fully dense and fully consolidated forged parts was increased by oxygen solution strengthening.

Micro-alloyed Mg2Ni for better performance as negative electrode of Ni-MH battery and hydrogen storage

The effect of vanadium doping on the kinetics and thermodynamics of hydrogenation–dehydrogenation process of Mg2Ni have been investigated. Two samples, Mg2Ni-5 wt.% V and Mg2Ni-10 wt.% vanadium were prepared by ball milling process. The hydrogenation–dehydrogenation kinetics along with pressure–composition isotherm (PCT) of vanadium doped and pure-Mg2Ni samples were studied. The sample Mg2Ni-5 wt.% V has shown improved hydrogenation–dehydrogenation kinetics with extended plateau region as compared to pure-Mg2Ni under similar conditions. Marginal changes in the enthalpies of hydrogenation–dehydrogenation have been observed on vanadium addition. The improved properties could be beneficial for the viable commercial applications of Mg2Ni as a negative electrode of metal-hydride batteries and as a material for hydrogen storage.

Ti-based solid solution carbonitrides prepared from Ti-alloy scraps via a hydrogenation-dehydrogenation process and high-energy milling

Ti-based solid-solution carbonitrides (Ti,Al,V)(CN) and (Ti,Al,Mo,V)(CN), were synthesized successfully using Ti-6Al-4V (Ti-64) and Ti-8Al-1Mo-1V (Ti-811) alloy scraps via hydrogenation-dehydrogenation and highenergy milling processes. A single phase of (Ti,Al,V)(CN) could be readily synthesized by the high-energy milling of Ti-64 alloy with graphite in a nitrogen atmosphere regardless of the carbon content. On the other hand, for the Ti-811 alloy, metallic Mo and various Mo-less carbides, in this case Ti2AlC, Ti3AlC2, and Ti3AlC, were also formed in addition to (Ti,Al,Mo,V)(CN) due to the low nitrogen affinity of Mo. The solid-solution carbonitrides consolidated by spark plasma sintering revealed excellent mechanical properties (HV: 19.1-20.6 GPa, KIC: 5.2-6.4 MPa·m1/2) due to the alloying effect of Al, Mo, and V in Ti(CN). These values are superior to those of typical Ti(CN)–based ceramic composites (HV: 16-20 GPa, KIC: 3.2-5.5 MPa·m1/2). We believe that the suggested method would be a valuable option for the production of Ti-based solid-solution carbonitrides with decent mechanical properties economically.

Preparation of Ti-Mo-Si alloy powders with enhanced high-temperature oxidation resistance using Ti-10Mo scraps

To recycle Ti alloy scraps and enhance the functionality of the recycled scraps, we manufactured low-oxygen contented Ti-Mo-Si powders using two types of ternary Ti alloy ingots which were prepared by vacuum arc melting of Ti-Mo scrap with different amounts of Si. The weight ratio of Ti-Mo scrap was Ti:Mo=9:1 and Si contents in two alloy ingots were 1 and 2 wt%. The alloy powders were prepared by the hydrogenation-dehydrogenation process and the oxygen atoms were removed by the deoxidation in solid state method. We confirmed that the deoxidation process effectively reduced the oxygen content of Ti-Mo-Si alloy powder from 3,350 ppm to 1,700 ppm. In addition, we confirmed that the high-temperature oxidation resistance was increased by adding Si to Ti-Mo alloys. Thermal gravimetric analysis showed that the weight gain of powders by the oxidation was reduced from 8.85% for Ti-Mo to 7.5% for Ti-Mo-Si at 1,500 °C.