Cyclic Hydrogen Research Articles

Effects of differential speed rolling and H2S poison on hydrogen storage performance of ZK60 alloys ball-milled with C, Pd, Ag, and Zr

The commercial ZK60 magnesium alloy was used to investigate hydrogen absorption performance. The ZK60 alloy was severely deformed via differential speed rolling with differential speeds of 6:3 and 9:3. High energy ball milling was used to blend deformed ZK60 powder with 5 wt% activated carbon(C), 0.5 wt% silver (Ag), 0.5 wt%palladium (Pd), and 1 wt% zirconium (Zr) for 20h at 1725 rpm. Hydrogen absorption characteristics at different low temperatures and number of cycles were analyzed using Sievert's apparatus with hydrogen supplied with H2S impurities. The microstructure of the powder was analyzed field emission scanning electron microscope (FESEM). The hydrogen absorption capacity increases with the temperature rise, and maximum capacity(6.02 wt%) was observed in 5C1Zr deformed at 9:3DSR at 200 °C after five cycles. Hydrogen absorption capacity increases after each hydrogenation cycle in 5C0.5Ag and 5C1Zr but remains the same in 5C0.5Pd. The increase in H2S concentration decreases the hydrogen capacity, and increase in the number of cycles further deteriorates absorption capacity when the differential speed ratio is 6:3. The H2S concentration variation has almost no effect at the differential speed of 9:3. The maximum hydrogen absorption kinetics (74.7%) in 10min was observed in 5C1Zr. A more refined dendritic microstructure was observed in ZK60 alloy deformed with a differential speed ratio of 9:3.

Lithium Borohydride Nanorods: Self-Assembling Growth and Remarkable Hydrogen Cycling Properties.

Nanostructured metal hydrides with unique morphology and improved hydrogen storage properties have attracted intense interests. However, the study of the growth process of highly active borohydrides remains challenging. Herein, for the first time the synthesis of LiBH4 nanorods through a hydrogen-assisted one-pot solvothermal reaction is reported. Reaction of n-butyl lithium with triethylamine borane in n-hexane under 50bar of H2 at 40-100°C gives rise to the formation of the [100]-oriented LiBH4 nanorods with 500-800nm in diameter, whose growth is driven by orientated attachment and ligand adsorption. The unique morphology enables the LiBH4 nanorods to release hydrogen from ≈184°C, 94°C lower than the commercial sample (≈278°C). Hydrogen release amounts to 13wt% within 40min at 450°C with a stable cyclability, remarkably superior to the commercial LiBH4 (≈9.1wt%). More importantly, up to 180°C reduction in the onset temperature of hydrogenation is successfully attained by the nanorod sample with respect to the commercial counterpart. The LiBH4 nanorods show no foaming during dehydrogenation, which improves the hydrogen cycling performance. The new approach will shed light on the preparation of nanostructured metal borohydrides as advanced functional materials.

Single-Atom Ni Supported on TiO2 for Catalyzing Hydrogen Storage in MgH2.

As an efficient and clean energy carrier, hydrogen is expected to play a key role in future energy systems. However, hydrogen-storage technology must be safe with a high hydrogen-storage density, which is difficult to achieve. MgH2 is a promising solid-state hydrogen-storage material owing to its large hydrogen-storage capacity (7.6 wt %) and excellent reversibility, but its large-scale utilization is restricted by slow hydrogen-desorption kinetics. Although catalysts can improve the hydrogen-storage kinetics of MgH2, they reduce the hydrogen-storage capacity. Single-atom catalysts maximize the atom utilization ratio and the number of interfacial sites to boost the catalytic activity, while easy aggregation at high temperatures limits further application. Herein, we designed a single-atom Ni-loaded TiO2 catalyst with superior thermal stability and catalytic activity. The optimized 15wt%-Ni0.034@TiO2 catalyst reduced the onset dehydrogenation temperature of MgH2 to 200 °C. At 300 °C, the H2 released and absorbed 4.6 wt % within 5 min and 6.53 wt % within 10 s, respectively. The apparent activation energies of MgH2 dehydrogenation and hydrogenation were reduced to 64.35 and 35.17 kJ/mol of H2, respectively. Even after 100 cycles of hydrogenation and dehydrogenation, there was still a capacity retention rate of 97.26%. The superior catalytic effect is attributed to the highly synergistic catalytic activity of single-atom Ni, numerous oxygen vacancies, and multivalent Tix+ in the TiO2 support, in which the single-atom Ni plays the dominant role, accelerating electron transfer between Mg2+ and H- and weakening the Mg-H bonds. This work paves the way for superior hydrogen-storage materials for practical unitization and also extends the application of single-atom catalysis in high-temperature solid-state reactions.

Recent Advances in Reversible Liquid Organic Hydrogen Carrier Systems: From Hydrogen Carriers to Catalysts.

Liquid organic hydrogen carriers (LOHCs) have gained significant attention for large-scale hydrogen storage due to their remarkable gravimetric hydrogen storage capacity (HSC) and compatibility with existing oil and gas transportation networks for long-distance transport. However, the practical application of reversible LOHC systems has been constrained by the intrinsic thermodynamic properties of hydrogen carriers and the performances of associated catalysts in the (de)hydrogenation cycles. To overcome these challenges, thermodynamically favored carriers, high-performance catalysts, and catalytic procedures need to be developed. Here, significant advances in recent years have been summarized, primarily centered on regular LOHC systems catalyzed by homogeneous and heterogeneous catalysts, including dehydrogenative aromatization of cycloalkanes to arenes and N-heterocyclics to N-heteroarenes, as well as reverse hydrogenation processes. Furthermore, with the development of metal complexes for dehydrogenative coupling, a new family of reversible LOHC systems based on alcohols is described that can release H2 under relatively mild conditions. Finally, views on the next steps and challenges in the field of LOHC technology are provided, emphasizing new resources for low-cost hydrogen carriers, high-performance catalysts, catalytic technologies, and application scenarios.

Enhanced cyclic durability of low-cost Ti–V–Cr hydrogen storage alloys by elemental alloying

Low-cost low vanadium (low-V) hydrogen storage materials have high reversible capacities (>2.0 wt%) under moderate conditions, however, they suffer from drastic capacity decay during cycling. In this work, a series of TiCr1.1M0.1(V–Fe)0.6 (M = Mn, Mo and Nb) alloys are prepared by elemental alloying on the basis of the low-cost, low-V alloy TiCr1.2(V–Fe)0.6 alloy, and the modification mechanism of the elemental alloying on the cycling durability of the alloy is systematically investigated. In 100 cycles, the results demonstrated that the original alloy TiCr1.2(V–Fe) 0.6 suffered from poor desorption capacity (1.13 wt%) and lowly capacity retention rate (60.43%). Compared to the addition of Mn and Nb, TiCr1.1Mo0.1(V–Fe)0.6 obtained higher cyclic hydrogen storage capacity (1.32 wt%) and capacity retention (68.04%). In addition, it is found that the addition of Mo can inhibit the formation of the secondary phase during the cycling, and the abundance of the C14 Laves phase maintained at only 2.47% after 100 cycles. According to the microstructural analysis of the alloys during cycling, it is found that the decrease in grain size, the accumulation of micro strain and dislocation density, and the degree of particle pulverization seriously affect the cycling durability of the alloys, resulting in a drastic decrease in the dehydrogenation cycling capacity. Finally, it should be noted that although the improvement in cycle durability with Mo alloying is limited, it is still a positive reference for developing low-cost low-V alloys with good cycle durability.

Influence of the Interaction of Hydrogen with the Phase Boundary of Duplex Stainless Steel on Corrosion

This study simulates the behavior of 2205 duplex stainless steel (DSS) in an actual service environment under hydrogen charging/releasing cycles. Electrochemical and immersion experiments are conducted to compare the pitting susceptibility and corrosion behavior of 2205 DSS under single hydrogen charging and several hydrogen charging/releasing cycles. The results reveal that under single hydrogen charging, pits preferentially initiate and propagate within the austenite phase; this finding is consistent with the results of previous studies. However, under cyclic hydrogen charging/releasing cycles, pits initiate at the phase boundary and propagate along it. Moreover, a hydrogen microprint technique is used to characterize the hydrogen enrichment sites in 2205 DSS. The results demonstrate that pits preferentially initiate at the same hydrogen enrichment sites. The study creates a schematic of hydrogen redistribution and hypothesizes that under actual service conditions, the phase boundary, rather than the austenite phase, is the primary site for pitting corrosion because of its transformation into a hydrogen enrichment site from a hydrogen trap.

Uncultivated DPANN archaea are ubiquitous inhabitants of global oxygen-deficient zones with diverse metabolic potential.

Archaea from the DPANN (Diapherotrites, Parvarchaeota, Aenigmarchaeota, Nanoarchaeota, and Nanohaloarchaeota) superphylum have diverse metabolic capabilities and participate in multiple biogeochemical cycles. While metagenomics and enrichments have revealed that many DPANN are characterized by ultrasmall genomes, few biosynthetic genes, and episymbiotic lifestyles, much remains unknown about their biology. We report 33 new DPANN metagenome-assembled genomes originating from the three global marine oxygen-deficient zones (ODZs), the first from these regions. We survey DPANN abundance and distribution within the ODZ water column, investigate their biosynthetic capabilities, and report potential roles in the cycling of organic carbon, methane, and nitrogen. We test the hypothesis that nitrous oxide reductases found within several ODZ DPANN genomes may enable ultrasmall episymbionts to serve as nitrous oxide consumers when attached to a host nitrous oxide producer. Our results indicate DPANN archaea as ubiquitous residents within the anoxic core of ODZs with the potential to produce or consume key compounds.

A First Principles Mechanistic Study of Higher Alcohol Synthesis from Syngas on a Stepped Rhodium Surface

The mechanism of higher alcohol synthesis (HAS) from syngas on a stepped Rhodium surface was explored using first principles calculations based on density functional theory. Results showed that the activation of CO proceeds most energetically feasible via a sequential hydrogenation towards CH2OH, followed by the C–OH bond cleavage yielding CHx species. Because the initial CO hydrogenation step is highly activated, the cascade of elementary steps toward methane formation is highly favored. The formation of C2 oxygenates toward ethanol production is kinetically favored by CO insertion to CH2, or alternatively, by a lower activation barrier CHO insertion to CH3. On the other hand, the C3 species is formed more preferably by CO rather than CHO insertion to a CH3CH2 fragment, indicating the effect of a more extended carbon structure on the reaction mechanism. The overall reaction mechanism for HAS points to a cycle of CO insertion, hydrogenation, and OH elimination steps.Graphical

Autotrophic biofilms sustained by deeply sourced groundwater host diverse bacteria implicated in sulfur and hydrogen metabolism

BackgroundBiofilms in sulfide-rich springs present intricate microbial communities that play pivotal roles in biogeochemical cycling. We studied chemoautotrophically based biofilms that host diverse CPR bacteria and grow in sulfide-rich springs to investigate microbial controls on biogeochemical cycling.ResultsSulfide springs biofilms were investigated using bulk geochemical analysis, genome-resolved metagenomics, and scanning transmission X-ray microscopy (STXM) at room temperature and 87 K. Chemolithotrophic sulfur-oxidizing bacteria, including Thiothrix and Beggiatoa, dominate the biofilms, which also contain CPR Gracilibacteria, Absconditabacteria, Saccharibacteria, Peregrinibacteria, Berkelbacteria, Microgenomates, and Parcubacteria. STXM imaging revealed ultra-small cells near the surfaces of filamentous bacteria that may be CPR bacterial episymbionts. STXM and NEXAFS spectroscopy at carbon K and sulfur L2,3 edges show that filamentous bacteria contain protein-encapsulated spherical elemental sulfur granules, indicating that they are sulfur oxidizers, likely Thiothrix. Berkelbacteria and Moranbacteria in the same biofilm sample are predicted to have a novel electron bifurcating group 3b [NiFe]-hydrogenase, putatively a sulfhydrogenase, potentially linked to sulfur metabolism via redox cofactors. This complex could potentially contribute to symbioses, for example, with sulfur-oxidizing bacteria such as Thiothrix that is based on cryptic sulfur cycling. One Doudnabacteria genome encodes adjacent sulfur dioxygenase and rhodanese genes that may convert thiosulfate to sulfite. We find similar conserved genomic architecture associated with CPR bacteria from other sulfur-rich subsurface ecosystems.ConclusionsOur combined metagenomic, geochemical, spectromicroscopic, and structural bioinformatics analyses of biofilms growing in sulfide-rich springs revealed consortia that contain CPR bacteria and sulfur-oxidizing Proteobacteria, including Thiothrix, and bacteria from a new family within Beggiatoales. We infer roles for CPR bacteria in sulfur and hydrogen cycling.8FE2mu4H1cxgQVBqjGxsC2Video

A Review of the Research Progress and Application of Key Components in the Hydrogen Fuel Cell System

The hydrogen cycle system, one of the main systems used for hydrogen fuel cells, has many advantages. It can improve the efficiency, the water capacity, and the management of thermal fuel cells. It can also enhance the safety of the system. Therefore, it is widely used in hydrogen fuel cell vehicles. We introduce the structure and principles of hydrogen cycle pumps, ejectors, and steam separators and analyze and summarize the advantages of the components, as well as reviewing the latest research progress and industrialization status of hydrogen cycle pumps and ejectors. The technical challenges in hydrogen circulation systems and the development direction of key technologies in the future are discussed. This paper aims to provide a reference for research concerning hydrogen energy storage application technology in hydrogen fuel cell systems.

Synergistic effects between Mn and Co species in CO2 hydrogenation over xCo/MnO catalysts

CO2 hydrogenation technology has great potential for mitigating the greenhouse effect and creating a green economy. The development of catalysts plays a key role in the progress of CO2 hydrogenation technology. In this study, the xCo/MnO catalysts for CO2 hydrogenation reaction were prepared by the impregnation method using MnOx as the catalyst support. And the effects of the Co loading on the CO2 hydrogenation performances of the prepared xCo/MnO catalysts were investigated. The active Co0 species on the xCo/MnO catalysts surface are the main active centers for the CO2 hydrogenation reaction, and the medium basic sites on the xCo/MnO catalysts are the main CO2 adsorption sites. The MnOx support possesses a large number of medium basic sites, which can enhance the CO2 molecules adsorption ability of the xCo/MnO catalysts. An effective regulation of the basic and hydrogenation active site numbers on the xCo/MnO catalysts surface can be achieved by changing the Co loading amount, which in turn can affect the CO2 molecules adsorption, activation and hydrogenation abilities of the xCo/MnO catalysts. Moreover, the Mn1-yCoyO solid solution was found to be formed in the prepared xCo/MnO catalysts, which is conducive to the dispersion of metal Co nanoparticles on the MnO surface and the generation of oxygen-deficient sites. The CO2 desorption amount on the 12Co/MnO catalyst reached 1.76 mmol/g, which provided the catalyst with strong CO2 adsorption and activation abilities, enabling it to exhibit great CO2 hydrogenation performance. Under the conditions of atmosphere and 420 °C, the CO2 conversion and CH4 selectivity on the prepared 12Co/MnO catalyst reached 57.5 % and 78.8 %, separately. Furthermore, the CO2 conversion was able to consistently remain at the initial 57.5 %, and the CH4 selectivity was maintained above 70.0 % in the 10 times CO2 hydrogenation cycle tests on the 12Co/MnO catalyst. Our study highlights the potential of using MnOx as catalyst support in the CO2 hydrogenation reaction, and the findings will provide convenient for the future studies.

Distinct microbial hydrogen and reductant disposal pathways explain interbreed variations in ruminant methane yield.

Ruminants are essential for global food security, but these are major sources of the greenhouse gas methane. Methane yield is controlled by the cycling of molecular hydrogen (H2), which is produced during carbohydrate fermentation and is consumed by methanogenic, acetogenic, and respiratory microorganisms. However, we lack a holistic understanding of the mediators and pathways of H2 metabolism and how this varies between ruminants with different methane-emitting phenotypes. Here, we used metagenomic, metatranscriptomic, metabolomics, and biochemical approaches to compare H2 cycling and reductant disposal pathways between low-methane-emitting Holstein and high-methane-emitting Jersey dairy cattle. The Holstein rumen microbiota had a greater capacity for reductant disposal via electron transfer for amino acid synthesis and propionate production, catalyzed by enzymes such as glutamate synthase and lactate dehydrogenase, and expressed uptake [NiFe]-hydrogenases to use H2 to support sulfate and nitrate respiration, leading to enhanced coupling of H2 cycling with less expelled methane. The Jersey rumen microbiome had a greater proportion of reductant disposal via H2 production catalyzed by fermentative hydrogenases encoded by Clostridia, with H2 mainly taken up through methanogenesis via methanogenic [NiFe]-hydrogenases and acetogenesis via [FeFe]-hydrogenases, resulting in enhanced methane and acetate production. Such enhancement of electron incorporation for metabolite synthesis with reduced methanogenesis was further supported by two in vitro measurements of microbiome activities, metabolites, and public global microbiome data of low- and high-methane-emitting beef cattle and sheep. Overall, this study highlights the importance of promoting alternative H2 consumption and reductant disposal pathways for synthesizing host-beneficial metabolites and reducing methane production in ruminants.

General definition of hydrogen energy and related electrochemical technologies

Electrochemical energy conversion, based on the transformation between electrical energy and chemical energy, is crucial for the storage and utilization of renewable electrical energy, as well as the eco-friendly production of valuable fuels and chemicals. Here we put forward a general definition of hydrogen energy that covers the energy storage/release in any hydrogen-involved chemical bonds, such as H–H, C–H, and N–H bonds. Given that H2 gas, hydrocarbons, and hydronitrogens are not only high-energy-density fuels but also important industrial feedstock s, the successful implementation of efficient energy storage/release in the H–H (hydrogen cycle), C–H (carbon cycle), and N–H (nitrogen cycle) bonds are of great significance in establishing sustainable energy systems and reducing dependence on fossil fuels, which contributes to address global energy crisis and environmental problems. We provide a concise overview of the current development status of some key low-temperature (< 100 °C) electrochemical technologies relevant to general hydrogen energy, including fuel cells, water electrolysis, CO2 electrolysis, and N2 electrolysis. This discussion aims to elucidate the major challenges and future trends in this field.

Growth mechanism of aromatic prebiotic molecules: insights from different processes of ion-molecule reactions in benzonitrile-ammonia and benzonitrile-methylamine clusters.

Benzonitrile (BN, C6H5CN) has been detected in the cold molecular cloud Taurus molecular cloud-1 (TMC-1) in 2018, which is suggested to be a precursor in the formation of more complex nitrogen-containing aromatic interstellar compounds. In this study, we utilized mass-selected infrared (IR) photodissociation spectroscopy and quantum chemical calculations to investigate the structures and gaseous ion-molecule reactions of benzonitrile-ammonia (BN-NH3) and benzonitrile-methylamine (BN-MA) clusters. The spectral observations indicate that the cyclic hydrogen bonding structure predominates in both neutral clusters. After VUV (118 nm) single-photon ionization, a new C-N covalent bond formed between BN and NH3 in the (BN-NH3)+ cluster. However, proton sharing constitutes the primary structure of the (BN-MA)+ cluster. The two nitrogen-containing interstellar molecules react with BN to yield distinct products due to difference in charge distribution and molecular polarity in the ionized clusters. The reactions of BN with other molecules contribute to our understanding of the growth mechanisms of complex interstellar molecules.

Systematic analysis of electronic barrier heights and widths for concerted proton transfer in cyclic hydrogen bonded clusters: (HF)n, (HCl)n and (H2O)n where n = 3, 4, 5.

The MP2 and CCSD(T) methods are paired with correlation consistent basis sets as large as aug-cc-pVQZ to optimize the structures of the cyclic minima for (HF)n, (HCl)n and (H2O)n where n = 3-5, as well as the corresponding transition states (TSs) for concerted proton transfer (CPT). MP2 and CCSD(T) harmonic vibrational frequencies confirm the nature of each minimum and TS. Both conventional and explicitly correlated CCSD(T) computations are employed to assess the electronic dissociation energies and barrier heights for CPT near the complete basis (CBS) limit for all 9 clusters. Results for (HF)n are consistent with prior studies identifying Cnh and Dnh point group symmetry for the minima and TSs, respectively. Our computations also confirm that CPT proceeds through Cs TS structures for the C1 minima of (H2O)3 and (H2O)5, whereas the process goes through a TS with D2d symmetry for the S4 global minimum of (H2O)4. This work corroborates earlier findings that the minima for (HCl)3, (HCl)4 and (HCl)5 have C3h, S4 and C1 point group symmetry, respectively, and that the Cnh structures are not minima for n = 4 and 5. Moreover, our computations show the TSs for CPT in (HCl)3, (HCl)4 and (HCl)5 have D3h, D2d, and C2 point group symmetry, respectively. At the CCSD(T) CBS limit, (HF)4 and (HF)5 have the smallest electronic barrier heights for CPT (≈15 kcal mol-1 for both), followed by the HF trimer (≈21 kcal mol-1). The barriers are appreciably higher for the other clusters (around 27 kcal mol-1 for (H2O)4 and (HCl)3; roughly 30 kcal mol-1 for (H2O)3, (H2O)5 and (HCl)4; up to 38 kcal mol-1 for (HCl)5). At the CBS limit, MP2 significantly underestimates the CCSD(T) barrier heights (e.g., by ca. 2, 4 and 7 kcal mol-1 for the pentamers of HF, H2O and HCl, respectively), whereas CCSD overestimates these barriers by roughly the same magnitude. Scaling the barrier heights and dissociation energies by the number of fragments in the cluster reveals strong linear relationships between the two quantities and with the magnitudes of the imaginary vibrational frequency for the TSs.

Introducing a novel crystal form of pyruvic acid thiosemicarbazone and its sodium salt

The reaction of thiosemicarbazide and sodium pyruvate has been thoroughly studied and the novel crystal form of pyruvic acid thiosemicarbazone (H2pt) and its sodium salt was obtained. Compounds were characterized by IR spectra, melting points, elemental analysis, conductometric measurements and single-crystal X-ray analysis. A detailed comparative analysis of crystal structures of these compounds is given, as well as comparison with some of the earlier known complexes containing H2pt. The two novel crystal structures exhibit notably different hydrogen bonding patterns, mutually and in comparison with previously reported crystal form of H2pt. All crystal structures are stabilized by extensive network of N?H???O, O?H???O and N?H???S hydrogen bonds. The cyclic hydrogen bonding motif involving the thioureido moieties of the ligand is the only one which repeats in each structure.

Strong metal-support interactions of TiO2 interface-loaded Pt constructed under different atmospheres for adjusting the hydrogen storage reaction performance of N-ethylcarbazole.

In this study, two series of samples (rT-Pt/TiO2 prepared with a hydrogen pretreatment and Tr-Pt/TiO2 prepared with an oxygen pretreatment) were prepared by treating commercial TiO2 supports in different atmospheres to establish different TiO2 interfacial structures, followed by the addition of platinum nanoparticles (NPs) for the catalyzed hydrogenation/dehydrogenation cycle of N-ethylcarbazole (NEC). The kinetic analysis and reaction mechanism were investigated by combining XRD, Raman, CO-DRIFT, HRTEM, XPS, H2-TPD and DFT calculations. It was found that the performance of the samples for the NEC system's cyclic hydrogen storage could be modulated by treating the TiO2 interfacial structure with different atmospheres varying the extent of strong metal-support interaction (SMSI). In addition, a turnover frequency (TOF) of 191.52 min-1 for dehydrogenation was achieved at 170 °C, which is better than the previously reported catalysts. Experimental studies (characterization and kinetic studies) and DFT calculations confirmed that the SMSI of the Tr-Pt/TiO2 series samples promoted the escape of H2 and enhanced the catalytic activity for 4H-NEC in the 12H-NEC dehydrogenation reaction. In the NEC hydrogenation reaction, the rT-Pt/TiO2 series samples were pretreated with H2 before loading platinum metal, which led to the early activation of Ti4+ in their carriers, and thus suppressed the SMSI effect of the reduction process after loading platinum. This process caused the interface formed by rT-Pt/TiO2 to have a higher energy barrier to 6H-NEC, which is an intermediate product of the NEC hydrogenation process, and this interrupted the hydrogenation process of 6H-NEC.

Tank volume and energy consumption optimization of hydrogen cycle test system

The hydrogen cycle test is the most complex type test of high-pressure hydrogen storage cylinders for hydrogen fuel cell vehicles, and it is quite challenging to develop a hydrogen cycle test system for this test. The volume of gas source tank and recovery tank can be described on the basis of thermodynamic model with considering of hydrogen mass, pressure, and temperature. The optimal volumes for the tanks are determined by applying the objective function. The sum of pressure drops in each level of the source tanks is used to evaluate the test energy consumption and the optimal pressure at each stage of hydrogen charging and discharging is obtained to minimize the test energy consumption. The tank volume calculation method and energy consumption optimization method proposed in this paper not only reduce the hydrogen consumption and energy consumption during the operation of the hydrogen cycle test system, but also improve the safety and economy of the system.

Effect of Ti0.9Zr0.1Mn1.5V0.3 alloy catalyst on hydrogen storage kinetics and cycling stability of magnesium hydride

As a high-capacity hydrogen storage material, MgH2 still has the problem of high operating temperature and slow reaction kinetics. In this work, an TiMn2-based Laves phase alloy (Ti0.9Zr0.1Mn1.5V0.3, denoted as Ti–Mn) was first synthesized by arc melting and then employed to regulate the hydrogen storage properties of MgH2, with the carbon nanotubes (CNTs) as an aid agent to facilitate the hydrogen diffusion and heat transfer. It was shown that the introduction of Ti–Mn/CNTs can remarkably improve the hydrogen storage properties of MgH2. The MgH2 + 10 wt% Ti–Mn + 1 wt% CNTs composite has an initial dehydrogenation temperature of 195 °C and can absorb hydrogen at room temperature. As for the kinetics, it can release 6.1 wt% H2 in 5 min at 300 °C, and absorb 4.8 wt% H2 in 10 min at 150 °C. It still has a reversible capacity of 6.2 wt% after 100 cycles. Combination of Ti–Mn alloy and CNTs is more effective than Ti–Mn alloy or CNTs alone for regulating MgH2. Ti–Mn/CNTs does not alter the overall thermodynamics of MgH2. However, local destabilization of Mg–H bonds induced by the MgH2/Ti–Mn interfaces was observed experimentally and confirmed theoretically, which partially contributes to the enhanced hydrogen storage of MgH2. In addition, the active transition metals contained in the alloy was believed to accelerate the hydrogen dissociation and delivery during the hydrogen storage process. This work not only achieves the synergistic improvement of hydrogen storage of MgH2 by combination of Ti–Mn alloy and CNTs, but also presents the local destabilization mechanism to explain the improved hydrogen storage of MgH2 by Ti–Mn alloy experimentally and theoretically.

Microstructure and hydrogenation properties of RETMMg15 (RE= Nd, Gd; TM= Cu, Ni) alloys

In this study, five RETMMg15 (RE = Nd and/or Gd, TM = Ni and/or Cu) alloys have been successfully synthesized by induction melting of pure elements and characterized by XRD, BSE-SEM and EDXS. Their hydrogen storage properties have been studied from kinetic and thermodynamic points of view. The synthesized alloys NdNiMg15, NdCuMg15 and GdCuMg15 were composed of a RETMMg15 main phase with lesser proportions of α-Mg phase and other ternary phases. It has been found that substituting half of the RE (or TM) element by another RE (or TM) element leads to the formation of two solid solutions with composition: Nd0.5Gd0.5CuMg15 and NdCu0.5Ni0.5Mg15. Upon first hydrogenation, all alloys decomposed into binary or ternary hydrides. Next hydrogenation cycles allowed to store reversibly around 4.5 %wt. hydrogen. All alloys presented reduced MgH2 formation enthalpies as compared to pure Mg which is explained in term of “chemical milling”.