Improved de/re-hydrogenation properties of MgH2 catalyzed by graphene templated Ti–Ni–Fe nanoparticles

The present investigation deals with the excellent catalytic effect of graphene templated Ti–Ni–Fe nanoparticles (Ti–Ni–Fe@Gr) on de/re-hydrogenation characteristics of MgH₂. The catalytic effect of Ti–Ni–Fe@Gr on MgH2 has also been compared with Ti@Gr, Ni@Gr, and Fe@Gr. It has been found that Ti–Ni–Fe@Gr lowers the onset desorption temperature up to 252 °C with improved kinetics and cyclability for the hydrogen release and absorption from MgH₂. The presence of a multivalence environment around Mg/MgH₂ has been analyzed by XPS analysis which gives the evidence of possible electronic exchange between the catalyst and Mg/MgH₂ during de-/rehydrogenation. Since Mg/MgH₂ and Ti–Ni–Fe are both anchored on graphene template, agglomeration detrimental to cycling is not possible. Thus negligible degradation of 0.22 wt% has been observed even after 24 cycles of de/re-hydrogenation.     

Investigation of the thermodynamic and kinetic properties of La–Fe–B system hydrogen-storage alloys

La–Fe–B hydrogen-storage alloys were prepared using a vacuum induction-quenching furnace with a rotating copper wheel. The thermodynamic and kinetic properties of the La–Fe–B hydrogen-storage alloys were investigated in this work. The P–C–I curves of the La–Fe–B alloys were measured over a H₂ pressure range of 10⁻³ MPa to 2.0 MPa at temperatures of 313, 328, 343 and 353 K. The P–C–I curves revealed that the maximum hydrogen-storage capacity of the alloys exceeded 1.23 wt% at a pressure of approximately 1.0 MPa and temperature of 313 K. The standard enthalpy of formation ΔH and standard entropy of formation ΔS for the alloys' hydrides, obtained according to the van't Hoff equation, were consistent with their application as anode materials in alkaline media. The alloys also exhibited good absorption/desorption kinetics at room temperature.     

Enhanced electrochemical and hydrogen storage properties of La–Mg–Ni-based alloy electrode using a Ni and N co-doped reduced graphene oxide nanocomposite as a catalyst

To enhance the electrochemical property of a La_0.7Mg_0.3(Ni_0.9Co_0.1)_3.5 alloy, a three-dimensional (3D) reduced graphene oxide (rGO)-supported nickel and nitrogen co-doped (Ni–N@rGO) nanocomposite is fabricated by an impregnation method and introduced into the La_0.7Mg_0.3(Ni_0.9Co_0.1)_3.5 alloy. The results show that the reversible hydrogen storage property and the comprehensive electrochemical performance of the La_0.7Mg_0.3(Ni_0.9Co_0.1)_3.5 alloy are enhanced effectively when it is modified by the Ni–N@rGO nanocomposite. The high-rate dischargeability values at a discharge current density of 1500 mA g⁻¹ for the La_0.7Mg_0.3(Ni_0.9Co_0.1)_3.5 alloy and Ni–N@rGO-modified samples are 0.0% and 70.5%, respectively. Additionally, the anodic peak currents for the unmodified alloy electrode is 892 mA g⁻¹. Under the catalytic action of the Ni–N@rGO nanocomposite, the value increases to 2307 mA g⁻¹, which is 2.59 times larger than that of unmodified samples. The results also indicate that the diffusion ability of the hydrogen atom in the alloy electrode body enhances significantly when modified by the Ni–N@rGO nanocomposite. The hydrogen diffusion coefficient for the La_0.7Mg_0.3(Ni_0.9Co_0.1)_3.5 alloy electrode increases from 3.93 × 10⁻¹⁰ cm² s⁻¹ to 6.15 × 10⁻¹⁰ cm² s⁻¹ when is modified by Ni–N@rGO nanocomposite. These improvements in the comprehensive electrochemical properties are mainly attributed to the excellent electrochemical activity and conductivity of the Ni–N@rGO nanocomposite.     

Enhanced performance of direct peroxide–peroxide fuel cells by employing three-dimensional Ni and Co@TiC nanoarrays anodes

Thorn-like Ni@TiC NAs and flake-like Co@TiC NAs electrodes without any conductive agent and binder are simply fabricated by the potentiostatic electrodeposition of Ni and Co catalysts on the TiC nanowire arrays (NAs). The electrocatalytic activity of H₂O₂ oxidation on the Ni@TiC NAs electrodes is better than that on the Co@TiC NAs electrodes. The Ni@TiC NAs electrodes demonstrate a rough surface and have many nano-needles on the rod edges, which assures the high utilized efficiency of Ni catalysts. These particular three-dimensional structures may be very suitable for H₂O₂ electrooxidation. The anodic current of Ni@TiC NAs anode reaches 0.32 A cm^?2 at 0.3 V in 1.0 M H₂O₂ + 4 M KOH solution. The DPFCs employing Ni@TiC NAs anodes display the peak power density of 30.2 mW cm^?2 and open circuit voltage of 0.90 V at 85.1 mA cm^?2 with desirable cell stability at 10 mL min^?1 flow rate and 20 °C, which is much higher than those previously reported.     

Enhanced hydrogen sorption properties of MgH2 when doped with mechanically alloyed amorphous Zr0·67Ni0.33 particles

In the present study, the effect of amorphous Zr_0·67Ni_0.33 additive containing nano-ZrO₂ on the hydrogen sorption kinetics and thermodynamics of Mg/MgH₂ was investigated. The amorphous Zr_0·67Ni_0.33 particles prepared by mechanical alloying of stoichiometric elements were introduced into MgH₂ powder through high-energy milling to produce a MgH₂/Zr_0·67Ni_0.33 composite. Structural and morphological analyses revealed that the nanostructuring effect of the ZrO₂ containing amorphous Zr_0·67Ni_0.33 has led to significant grain-size refinement of MgH₂ to the nanometric scale. As a result, the MgH₂/Zr_0·67Ni_0.33 composite demonstrates enhanced hydrogenation and dehydrogenation kinetics (4.0 wt%/50 s/250 °C and 5.0 wt%/4 min/325 °C, respectively). Meantime, substantially lowered enthalpies (−63.40 and 67.06 kJ/mol H₂ obtained through pressure-composition-isotherm measurements) and reduced desorption temperature (~270 °C) were observed in the composite as compared to the pure MgH₂, possibly due to the dissolution of Ni into MgH₂ lattice during ball milling.     

Enhanced reversibility of the electrochemical Li conversion reaction with MgH2–TiH2 nanocomposites

Nanostructured metallic hydrides are promising anode active materials for the next generations of Li-ion batteries due to their high capacities, adapted working potential and low polarisation. In the present study, nanocomposites made of yMgH₂ and (1 ? y)TiH₂ with molar composition y = 0.2, 0.5 and 0.8 were prepared by mechanical milling of elemental metal powders under hydrogen pressure. Microstructural analysis by X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) shows the co-existence of the two hydrides at the nanoscale with average crystallite sizes comprised between 4 and 11 nm. Galvanostatic and cyclic voltammetry experiments have been performed to investigate the reversibility of the conversion reaction between both hydrides and lithium. All nanocomposites can be fully lithiated for the first discharge, but the reversibility of the reaction strongly depends on the composition. No reformation of any hydride occurs for the TiH₂-rich composite (y = 0.2), TiH₂ is only partially reformed for the equimolar composite (y = 0.5) and both MgH₂ and TiH₂ hydrides are recovered at different extents for the Mg-rich one (y = 0.8). A high reversibility (almost 80%) of TiH₂ is attained in the latter composite with a promising capacity retention (70% over ten cycles) by cycling within a restricted potential window.     

Enhanced hydrogen storage performance of three-dimensional hierarchical porous graphene with nickel nanoparticles

Three-dimensional hierarchical porous graphene with nickel nanoparticles (3DHPG-Ni) was synthesized through electrostatic assembly method with the assistance of poly (methyl methacrylate) (PMMA) template and subsequent removal of PMMA template by calcination. The morphology, microstructure and hydrogen adsorption properties of 3DHPG-Ni nanocomposites were examined in detail. The obtained 3DHPG-Ni nanocomposite exhibited hierarchical porous structure composed of macro-, meso- and micropores, high specific surface area (925 m² g^?1), large pore volume (0.58 cm³ g^?1) and excellent hydrogen storage capacity. Under the pressure of 5 bar, 3DHPG-Ni nanocomposite showed a maximum hydrogen capacity of 4.22 wt% and 1.95 wt% at 77 K and 298 K, respectively, demonstrating that the as-prepared 3DHPG-Ni nanocomposite was supposed to be a promising material with outstanding properties for practical applications in the field of hydrogen storage. The three-dimensional hierarchical porous structure, evenly distributed Ni nanoparticles and hydrogen spillover effect were responsible for the enhanced hydrogen storage capacities.     

OER properties of Ni–Co–CeO2/Ni composite electrode prepared by magnetically induced jet electrodeposition

Hydrogen production from water electrolysis with catalysts is a simple, effective, and environmentally friendly way. However, the slow kinetics of the oxygen evolution reaction (OER) directly affects the catalytic efficiency of water electrolysis during hydrogen production. While the high cost of noble metal catalysts limits their engineering applications. Therefore, there is an urgent need to develop an economical and abundant catalyst with efficient OER performance to replace noble metal catalysts to reduce costs. In this work, we propose a method for the preparation of composite catalytic electrodes by magnetically induced jet electrodeposition. Ni–Co–CeO₂/Ni composite electrodes with a unique micro-nano structure and a large specific surface area were rapidly obtained through magnetically induced adsorption of nano-mixed particles. It was found that the Ni–Co–CeO₂/Ni composite electrode deposited by magnetically induced electrodeposition exhibited a lower overpotential of 301 mV@10 mA/cm² when the nano-mixed particle concentration was 2 g/L, and the corresponding Tafel slope was as low as 43.72 mV/dec. The key parameters of overpotential and Tafel slope reach or even outperform the best noble metal electrode in the industry, indicating that the Ni–Co–CeO₂/Ni composite electrode had excellent OER catalytic performance. The study demonstrates that magnetically induced jet electrodeposition provides a new method for the preparation of catalytic electrodes, which has important applications in the electrolysis of water for hydrogen production.     

Structural characterization and hydrogen storage properties of MgH2–Mg2CoH5 nanocomposites

Mixtures of XMg–Co containing different amounts of Mg (X = 2, 3 and 7) were reactive milled under hydrogen atmosphere. 2Mg–Co only formed the Mg₂CoH₅ complex hydride, while the mixtures 3Mg–Co and 7Mg–Co formed different contents of Mg₂CoH₅ and MgH₂. Their structural features and hydrogen storage properties were analyzed by different techniques. In-situ synchrotron X-ray diffraction, combined with thermal analysis techniques, (differential scanning calorimetry, thermal gravimetric analysis and quadrupole mass spectrometer) was carried out to observe the behavior of the MgH₂–Mg₂CoH₅ mixtures during the first H-desorption. It was found that the presence of the Mg₂CoH₅ complex hydride has a beneficial effect on the first H-desorption of the MgH₂. Additionally, after first desorption, conventional hydrogenation under high pressure and high temperature of 3Mg–Co and 7Mg–Co samples led to the formation of the Mg₆Co₂H₁₁ complex hydride. The presence of Mg₆Co₂H₁₁ considerably impaired the desorption properties of the nanocomposites.     

Enhanced hydrogen storage properties of Ti–Cr–Nb alloys by melt-spin and Mo-doping

Ti–Cr–Nb hydrogen storage alloys with a body centered cubic (BCC) structure have been successfully prepared by melt-spin and Mo-doping. The crystalline structure, solidification microstructural evolution, and hydrogen storage properties of the corresponding alloys were characterized in details. The results showed that the hydrogen storage capacity of Ti–Cr–Nb ingot alloys increased from 2.2 wt% up to around 3.5 wt% under the treatment of melt-spin and Mo-doping. It is ascribed that the single BCC phase of Ti–Cr–Nb alloys was stabilized after melt-spin and Mo-doping, which has a higher theoretical hydrogen storage site than the Laves phase. Furthermore, the melt-spin alloy after Mo doping can further effectively increase the de-/absorption plateau pressure. The hydrogen desorption enthalpy change ΔH of the melt-spin alloy decreased from 48.94 kJ/mol to 43.93 kJ/mol after Mo-doping. The short terms cycling test also manifests that Mo-doping was effective in improving the cycle durability of the Ti–Cr–Nb alloys. And the BCC phase of the Ti–Cr–Nb alloys could form body centered tetragonal (BCT) or face center cubic (FCC) hydride phase after hydrogen absorption and transform to the original BCC phase after desorption process. This study might provide reference for developing reversible metal hydrides with favorable cost and acceptable hydrogen storage characteristics.     

Production of hydrogen by methane catalytic decomposition over Ni–Cu–Fe/Al2O3 catalyst

Catalysts with high nickel concentrations 75%Ni–12%Cu/Al₂O₃, 70%Ni–10%Cu–10%Fe/Al₂O₃ were prepared by mechanochemical activation and their catalytic properties were studied in methane decomposition. It was shown that modification of the 75%Ni–12%Cu/Al₂O₃ catalyst with iron made it possible to increase optimal operating temperatures to 700–750 °C while maintaining excellent catalyst stability. The formation of finely dispersed Ni–Cu–Fe alloy particles makes the catalysts stable and capable of operating at 700–750 °C in methane decomposition to hydrogen and carbon nanofibers. The yield of carbon nanofibers on the modified 70%Ni–10%Cu–10%Fe/Al₂O₃ catalyst at 700–750 °C was 150–160 g/g. The developed hydrogen production method is also efficient when natural gas is used as the feedstock. An installation with a rotating reactor was developed for production of hydrogen and carbon nanofibers from natural gas. It was shown that the 70%Ni–10%Cu–10%Fe/Al₂O₃ catalyst could operate in this installation for a prolonged period of time. The hydrogen concentration at the reactor outlet exceeded 70 mol%.     

Efficient catalytic properties of Co–Ni–P–B catalyst powders for hydrogen generation by hydrolysis of alkaline solution of NaBH4

The aim of the present work is to study the catalytic efficiency of amorphous Co–Ni–P–B catalyst powders in hydrogen generation by hydrolysis of alkaline sodium borohydride (NaBH₄). These catalyst powders have been synthesized by chemical reduction of cobalt and nickel salt at room temperature. The Co–Ni–P–B amorphous powder showed the highest hydrogen generation rate as compared to Co–B, Co–Ni–B, and Co–P–B catalyst powders. To understand the enhanced efficiency, the role of each chemical element in Co–Ni–P–B catalyst has been investigated by varying the B/P and Co/Ni molar ratio in the analyzed powders. The highest activity of the Co–Ni–P–B powder catalyst is mostly attributed to synergic effects caused by each chemical element in the catalyst when mixed in well defined proportion (molar ratio of B/P = 2.5 and of Co/(Co + Ni) = 0.85). Heat-treatment at 573 K in Ar atmosphere causes a decrease in hydrogen generation rate that we attributed to partial Co crystallization in the Co–Ni–P–B powder. The synergic effects previously observed with Co–Ni–B and Co–P–B, now act in a combined form in Co–Ni–P–B catalyst powder to lower the activation energy (29 kJ mol⁻¹) for hydrolysis of NaBH₄.     

Molten salt-promoted Ni–Fe/Al2O3 catalyst for methane decomposition

Bimetallic Ni–Fe/Al₂O₃ catalysts were prepared by the molten salt method, and the catalytic performance of the Ni–Fe/Al₂O₃ catalysts with the KCl–NiCl₂ melt for methane decomposition was evaluated at 800 °C. The catalysts and carbon products were characterized by XRD, SEM/EDS, XRF and Raman spectroscopy techniques. The results show that molten salt-promoted Ni–Fe/Al₂O₃ catalysts exhibit high activity and long-term stability up to 1000 min time on stream without any deactivation. The carbon products over the molten salt-promoted Ni–Fe/Al₂O₃ catalysts are in the form of small granular particles instead of filamentous carbon for the catalyst without molten salt. The promotional effect of the molten salt may attribute to the higher wettability of the Fe–Ni alloy by molten salt, which can prevent the catalysts from deactivation due to carbon encapsulation.     

Hydrogen generation from the hydrolysis of aluminum promoted by Ni–Li–B catalyst

In this study, the high activity Ni–Li–B catalysts were fabricated through wet chemical reduction method. Their morphological structures, crystallinity, surface area and composition were examined by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) method and energy-dispersive X-ray spectroscopy (EDS). The aluminum-water reaction tests were explored in the range of temperatures from 35–75 °C. It was found that water could react with aluminum to generate hydrogen gas. The yield and hydrogen generation rate were significantly increased when all prepared catalysts were added into the reaction. The Ni–Li–B (X_LiCl = 0.1 g) catalyst exhibited the highest cumulative hydrogen volume of 201.3 ml with an average hydrogen production rate of 0.50 ml min⁻¹ at 55 °C. This phenomenon could be pointed to the emergence of the micro galvanic cell formed by the Ni–Li–B, Li/Ni–Li–B, Li and Al, which accelerated aluminum to rapidly react with water.     

A study on catalytic activity of modified Ni–Re/Al-SBA-15 catalyst for hydrodenitrogenation of o-toluidine

To elucidate the influence of Al content and effect of Ni loading on the structure and catalytic activity for hydrodenitrogenation reaction of o-toluidine, a series of mesoporous Al-SBA-15 supported Ni–Re sulphided catalysts were prepared. The textural and chemical properties of support and catalyst were analysed using XRD, N₂-sorption studies, DRS UV–Vis, SEM, HRTEM, NH₃-TPD, TPR and XPS. These characterizations indicate that the incorporation of Al content into the SBA-15 framework leads to the formation of moderate acid sites, which shows enhanced catalytic activity. The maximum catalytic activity in 1 wt%Ni-5wt%Re/Al-SBA-15(10) catalyst is due to fine dispersion of Re and Ni over the support, strong metal–support interaction, high degree of sulphidation and more sulphur atoms on the surface.     

Facile synthesis of snowflake-like magnetic Fe–Ni alloy with high magnetic properties

Abstract

Snowflake-like Fe–Ni alloy has been synthesised via a facile hydrothermal approach without any soft and hard template. The structure of the snowflake-like Fe–Ni alloy was characterised by means of scanning electron microscopy (SEM), X-ray diffraction and energy dispersive X-ray spectroscopy. The dendrite trunk lengths of the snowflake-like Fe–Ni alloy were about 2·5–7·0 μm, and those of the branch trunk ranged from 250·0 to 650·0 nm. Furthermore, it was found that the formation and morphology of Fe–Ni alloy strongly depended on the reaction time. Moreover, the magnetic and electrical properties of Fe–Ni alloy with various morphologies were compared. Moreover, the result showed that the snowflake-like Fe–Ni alloy indicated enhancement of their ferromagnetic and electrical properties, which was attributed to their anisotropic shape.     

In-situ hydrodeoxygenation of phenol by supported Ni catalyst – explanation for catalyst performance

In-situ hydrodeoxygenation of phenol with aqueous hydrogen donor over supported Ni catalyst was investigated. The supported Ni catalysts exerted very poor performance, if formic acid was used as the hydrogen donor. Catalyst modification by loading K, Na, Mg or La salt could not make the catalyst performance improved. If gaseous hydrogen was used as the hydrogen source the activity of Ni/Al₂O₃ was pretty high. CO₂ was found poisonous to the catalysis, due to the competitive adoption of phenol with CO₂. If formic acid was replaced by methanol, the catalyst performance improved remarkably, with major products of cyclohexanone and cyclohexanol. The better effect of methanol enlightened the application of the supported Ni catalyst in in-situ hydrodeoxygenation of phenol.     

Influence of gaseous hydrogen on the tensile properties of Fe–36Ni INVAR alloy

No loss in tensile ductility was found for Invar 36 alloy tested in a gaseous hydrogen atmosphere (1 MPa, −50 °C). Fractography revealed no indication of hydrogen assisted damage. Deformation mechanisms of Invar 36 are published in the open literature. Comparing the tensile test results as well as the deformation mechanisms with those of other iron based stable austenitic alloys indicate that the inherent deformation mechanism of Invar 36 comprising of a high portion of dislocation cross slip is an important reason for the negligible loss in tensile ductility under the presence of hydrogen.