In order to enhance the hydrogen storage properties of Mg, flowerlike NiS particles have been successfully prepared by solvothermal reaction method, and are subsequently ball milled with Mg nanoparticles (NPs) to fabricate Mg-5 wt % NiS nanocomposite. The nanocomposite displays Mg/NiS core/shell structure. The NiS shell decomposes into Ni, MgS and Mg2Ni multiple-phases, decorating on the surface of the Mg NPs after the first hydrogen absorption and desorption cycle at 673 K. The Mg-MgS-Mg2Ni-Ni nanocomposite shows enhanced hydrogenation and dehydrogenation rates: it can quickly uptake 3.5 wt % H2 within 10 min at 423 K and release 3.1 wt % H2 within 10 min at 573 K. The apparent hydrogen absorption and desorption activation energies are decreased to 45.45 and 64.71 kJ mol–1. The enhanced sorption kinetics of the nanocomposite is attributed to the synergistic catalytic effects of the in situ formed MgS, Ni and Mg2Ni multiple-phase catalysts during the hydrogenation/dehydrogenation process, the porthole effects for the volume expansion and microstrain of the phase transformation of Mg2Ni and Mg2NiH4 and the reduced hydrogen diffusion distance caused by nanosized Mg. This novel method of in situ producing multiple-phase catalysts gives a new horizon for designing high performance hydrogen storage material.Keywords: catalytic effects; hydrogen storage; magnesium; multiple-phase catalysts; nanocomposite;

In order to improve hydrogen storage properties of magnesium, (Ti0.85Zr0.15)1.05Mn1.2Cr0.6V0.1Cu0.1 (TiMn2 type) alloy particles have been added into magnesium ultrafine particles produced by a hydrogen plasma-metal reaction approach by ball milling. The (Ti0.85Zr0.15)1.05Mn1.2Cr0.6V0.1Cu0.1 particles are uniformly dispersed on the surface of magnesium. The addition of (Ti0.85Zr0.15)1.05Mn1.2Cr0.6V0.1Cu0.1 alloy improves both the hydrogen storage capacity and kinetics of magnesium. The magnesium–5 wt% (Ti0.85Zr0.15)1.05Mn1.2Cr0.6V0.1Cu0.1 composite can absorb 6.00 wt% H2 within 60 minutes at 523 K and desorb 6.00 wt% H2 within 15 minutes at 623 K. With the increase of (Ti0.85Zr0.15)1.05Mn1.2Cr0.6V0.1Cu0.1, the hydrogenation and dehydrogenation kinetics of the composites improve. The apparent activation energies of magnesium–x wt% (Ti0.85Zr0.15)1.05Mn1.2Cr0.6V0.1Cu0.1 (x = 5, 10, 30) composites for hydrogen absorption and desorption are 67.52, 65.80, 60.99 kJ mol−1 and 121.37, 116.68, 77.25 kJ mol−1, respectively. The enhanced hydrogen storage capacities and kinetics can be attributed to the effective catalysis of the (Ti0.85Zr0.15)1.05Mn1.2Cr0.6V0.1Cu0.1 alloy and ultrafine size of magnesium particles.

Microporous Co nanoparticles (NPs) with pore diameters of 0.38 nm have been prepared by dealloying Co–Al alloy NPs, which were subsequently annealed at different temperatures to synthesize microporous Co3O4–Co nanocomposites as electrode materials for pseudocapacitors. The NPs annealed at 423 K are made of Co3O4 and Co phases, and become pure Co3O4 after being annealed at 473 and 573 K. The pore diameter of the NPs does not change significantly upon increasing the annealing temperature from 423 to 573 K, whereas the specific surface area decreases from 39.25 to 26.68 m2 g−1 due to the sintering effect. The pseudocapacitive behavior of the microporous Co3O4–Co nanocomposites were investigated by cyclic voltammetry (CV) and chronopotentiometry (CP) tests. The microporous Co3O4–Co nanocomposite annealed at 423 K exhibits outstanding pseudocapacitive performance with a high specific capacitance (SC) of 507 F g−1 at 1 A g−1 and good cycling stability (93% retention of its initial specific capacitance after 1000 cycles). The SC value decreases to 77 F g−1 for the sample annealed at 573 K. The charge–discharge mechanism is discussed in terms of the microporous structure and the existence of the Co phase. The novel microporous material may open a new route to high performance pseudocapacitors.

•TiH1.971 reacts with Y2O3 to form Y2Ti2O7 in the Al-containing ODS steel.•Addition of TiH1.971 nanoparticles can prevent the formation of Y-Al-O phases.•Y2Ti2O7 nanoparticles share semicoherent interface with the ferrite matrix.•The mean size of oxide dispersion is reduced to 11.2 ± 7.1 nm with 1.0 wt% TiH1.971.•The tensile strength of the ODS steel enlarges with increasing TiH1.971 content.In order to prohibit the formation of large Y-Al-O precipitates, Ti hydride nanoparticles (NPs) were prepared and used to replace Ti as raw particles to fabricate the oxide dispersion strengthened (ODS) Fe-14Cr-3Al-2W-0.35Y2O3 steels by mechanical alloying (MA) and hot isostatic pressing (HIP). As the content of Ti hydride increases from 0.1 to 0.5 and 1.0 wt%, the oxide nanoprecipitates in the ODS steels changes from Y3Al5O12 phase to Y2Ti2O7 phase (semicoherent with the matrix), and the particle size is successfully reduced. The tensile strength of the ODS steel increases remarkably with increasing Ti hydride content. The sample with 1.0 wt% Ti hydride exhibits a high strength of 1049 MPa at 25 °C and 278 MPa at 700 °C. The creation of Y2Ti2O7 nanoprecipitates by adding Ti hydride NPs opens a new way to control the structure and size of the oxide precipitates in the ODS steels.The creation of Y2Ti2O7 nanoprecipitates by adding Ti hydride nanoparticles remarkably increases the mechanical properties of the Al-containing ODS steels.Download high-res image (356KB)Download full-size image

The Mg-9.3 wt% (TiH1.971-TiH)−0.7 wt% Nb nanocomposite has been synthesized by hydrogen plasma-metal reaction (HPMR) approach to enhance the hydrogen sorption kinetics of Mg at moderate temperatures by providing nanosizing effect of increasing H “diffusion channels” and adding transition metallic catalysts. The Mg nanoparticles (NPs) were in hexagonal shape range from 50 to 350 nm and the average size of the NPs was 177 nm. The small spherical TiH1.971, TiH and Nb NPs of about 25 nm uniformly decorated on the surface of the big Mg NPs. The Mg-TiH1.971-TiH-Nb nanocomposite could quickly absorb 5.6 wt% H2 within 5 min at 573 K and 4.5 wt% H2 within 5 min at 523 K, whereas the pure Mg prepared by HPMR could only absorb 4 and 1.5 wt% H2 at the same temperatures. TiH1.971, TiH and Nb NPs transformed into TiH2 and NbH during hydrogenation and recovered after dehydrogenation process. The apparent activation energies of the nanocomposite for hydrogenation and dehydrogenation were 45.0 and 50.7 kJ mol−1, which are much smaller than those of pure Mg NPs, 123.8 and 127.7 kJ mol−1. The improved sorption kinetics of the Mg-based nanocomposite at moderate temperatures and the small activation energy can be interpreted by the nanostructure of Mg and the synergic catalytic effects of Ti hydrides and Nb NPs.

•Nickel Sulfides/Graphene was produced by co-reducing Ni2+ and graphene oxide.•Mg-5wt%NiS/rGO nanocomposite is prepared by ball milling Mg and NiS/rGO.•It shows best desorption properties compared with samples catalyzed by NiS and rGO.•Nickel sulfides in situ change to MgS, Mg2Ni and Ni multiple catalysts.•MgS, Mg2Ni, Ni and rGO synergistically catalyze the hydrogen desorption of Mg.Nickel sulfides decorated reduced graphene oxide (rGO) has been produced by co-reducing Ni2+ and graphene oxide (GO), and is subsequently ball milled with Mg nanoparticles (NPs) produced by hydrogen plasma metal reaction (HPMR). The nickel sulfides of about 800 nm completely in situ change to MgS, Mg2Ni and Ni multiple catalysts after first hydrogenation/dehydrogenation process at 673 K. The Mg-5wt%NiS/rGO nanocomposite shows the highest hydrogen desorption kinetics and capacity properties, and the catalytic effect order of the additives is NiS/rGO, NiS and rGO. At 573 K, the Mg-NiS/rGO nanocomposite can quickly desorb 3.7 wt% H2 in 10 min and 4.5 wt% H2 in 60 min. The apparent hydrogen absorption and desorption activation energies of the Mg-5wt%NiS/rGO nanocomposite are decreased to 44.47 and 63.02 kJ mol−1, smaller than those of the Mg-5wt%rGO and Mg-5wt%NiS samples. The best hydrogen desorption properties of the Mg-5wt%NiS/rGO nanocomposite can be explained by the synergistic catalytic effects of the highly dispersed MgS, Mg2Ni and Ni catalysts on the rGO sheets, and the more nucleation sites between the catalysts, rGO sheets and Mg matrix.Download high-res image (331KB)Download full-size image

•Nanoporous Ni@NiO NPs are prepared by chemical dealloying and annealing methods.•Particle size increases with annealing temperature whereas pore volume decreases.•The capacitance value decreases with the increasing annealing temperature.•The sample passivated at room temperature has the largest capacitance of 641 F/g.•The charge–discharge mechanism is explained by nanopore and core@shell structure.Nanoporous Ni nanoparticles (NPs) have been successfully prepared by a facile two-step process, hydrogen plasma-metal reaction (HPMR) and chemical dealloying. Via the subsequent passivation at room temperature, an oxide layer is generated outside the Ni NPs as the result of surface oxidation. The passivated Ni@NiO NPs of 48 nm exhibit a highly porous structure with pore volume of 0.812 cm3/g. The NPs are subsequently annealed at different temperatures to adjust the content of Ni and NiO. With the increase of the annealing temperature from 423 to 573 K, the particle size increases from 54 to 61 nm and the pore volume decreases from 0.432 to 0.02 cm3/g. The specific capacitance (SC) of the Ni@NiO NPs decreases with the increasing annealing temperature, and the passivated sample with a large pore volume and low resistance has the highest SC of 641 F/g at a charge–discharge current density of 1 A/g. The passivated sample also shows an energy density of 25.95 W h/kg, a power density of 2.7 kW/kg, and good stable specific capacitance retention of 73% after 1000 cycles. The charge–discharge mechanism is discussed in terms of pore architecture and core@shell structure.Download high-res image (311KB)Download full-size imageThe capacitance value of the nanoporous Ni@NiO NPs decreases with the increasing annealing temperature, and the sample passivated at room temperature exhibits the largest capacitance of 641 F/g.

•The Y2Ti2O7-dispersed Fe–Cr–Al alloys show enhanced oxidation resistance.•Al plays dominant role in improving oxidation resistance by forming Al2O3 scale.•Y2Ti2O7 nanoprecipitates are of importance to form stable Al2O3 scale.•The concentration of Al in Fe-14Cr ODS alloy should not be less than 4.5 wt.%.Aluminum was added at different percentages of 1.5, 3 and 4.5 wt.% into the Y2Ti2O7-dispersed Fe-14Cr ferritic alloy to improve its oxidation resistance. The oxidation behavior of the oxide dispersion strengthened (ODS) alloys was investigated at 1100 °C in air up to 200 h. Al plays the key role in improving the oxidation resistance of the ODS alloys by generating alumina protection scale. Y2Ti2O7 is of importance to form stable alumina layer. To produce a compact and continuous alumina layer on the surface of Fe-14Cr ODS alloys, the concentration of Al should not be less than 4.5 wt.%.

•Microporous Ni/NiO nanoparticles are prepared by chemical dealloying method.•They possess micropores of 0.6–1.2 nm with a surface area of 68.9 m2/g.•They show minimum microwave reflection coefficient of −49.1 dB and bandwidth of 5.8 GHz.•Microwave absorption mechanism is explained by micropore and core/shell structures.The fabrication of microporous metal materials with many potential applications is challenging due to their high chemical activities and the difficulty in controlling the pore size. By adjusting the reaction condition and the composition of the Ni–Al nanoparticle precursor, we have successfully produced the microporous Ni nanoparticles (NPs) of 22 nm by chemical dealloying method. During the passivation process, the microporous Ni NPs covered with NiO shell are generated as the result of surface oxidation. The micropores range from 0.6 to 1.2 nm in diameter with a large surface area of 68.9 m2/g. Due to the elimination of Al atoms during dealloying process, the crystalline size of the microporous Ni NPs is sharply decreased to 2–5 nm. The specific architecture offers the microporous Ni/NiO NPs a small microwave reflection coefficient (RC) and a wide absorption bandwidth (RC ≤ −10 dB) of −49.1 dB and 5.8 GHz, much better than the nonporous counterpart of −24.1 dB and 3.7 GHz. The enhanced microwave absorption performance has been interpreted in terms of the micropore structure, core/shell structure and nanostructure effects.

Surface modification is an effective way to induce new magnetic phenomena in nanostructured materials. Herein, FeAl nanoparticles (NPs) with a mean diameter of 38 nm are produced by the hydrogen plasma-metal reaction (HPMR) approach. Via the subsequent passivation process, an oxide layer is generated outside the FeAl NPs as the result of surface oxidation. The 3 nm-thick amorphous-like oxide layer consists mainly of Al2O3 together with a small amount of Fe2O3. An Fe-enriched zone is created between the oxide layer and the FeAl core due to the much higher diffusion rate of Al than Fe towards the particle surface during the passivation process, which can be explained by the Kirkendall effect. The FeAl@(Al, Fe)2O3 NPs surprisingly display a superparamagnetic property with a blocking temperature (TB) of 250 K and a saturation magnetization of 36 emu g−1 at 4.2 K. They also exhibit high microwave absorption performance with a minimum reflection loss (RL) value of −22.6 dB at a thickness of 1.7 mm, and a broad absorption bandwidth of 8.3 GHz corresponding to the RL below −10 dB. Formation of the oxide layer plays a dominant role in inducing the superparamagnetic property and high microwave absorption performance in FeAl@(Al, Fe)2O3 NPs. Specific core@shell NPs may open a new way to tune the magnetic and electromagnetic properties of metallic nanomaterials through surface modification.

With the intention of improving the hydrogenation/dehydrogenation kinetics of Mg, Mg-7.5 wt % Nb nanocomposite has been prepared by hydrogen plasma-metal reaction approach. The spherical Nb nanoparticles (NPs) of 12 nm are uniformly decorated on the surface of Mg NPs. The Mg–Nb nanocomposite can quickly uptake 4.0 wt % H2 in 10 min and reach a saturation value of 5.7 wt % H2 in 60 min at 473 K. Furthermore, it can also release 4.0 wt % H2 in 60 min at 573 K. The reversible hydrogen storage capacity is as high as 7.0 wt % at 673 K. Nb NPs transform into NbH during hydrogenation and recover after dehydrogenation process. They restrain the growth of Mg and work as catalysts to accelerate the hydrogen transportation in the Mg-based nanocomposite by decreasing the activation energies of hydrogenation/dehydrogenation to 70.9 and 86.4 kJmol–1, respectively. The catalytic mechanism of Nb NPs is explained in terms of spillover, d-electrons and electronegativity effects. The nanosizing effects of both Mg and Nb and the catalytic effect of Nb NPs give rise to the improved hydrogen storage properties of the Mg–Nb nanocomposite at moderate temperatures.

Nanoporous metal materials with many potential applications have been synthesized by a chemical dealloying approach. The fabrication of nanoporous metal nanoparticles (NPs), however, is still challenging due to the difficulties in producing suitable nanoscale precursors. Herein, nanoporous Co NPs of 31 nm have been successfully prepared by dealloying Co–Al NPs, and surprisingly they possess micropores in a range from 0.7 to 1.7 nm and a large surface area of 50 m2 g−1. The crystalline size of the microporous NPs is 2–5 nm. Through the passivation process, the microporous Co NPs covered with CoO (Co@CoO) are generated as a result of the surface oxidation of Co. They exhibit better microwave absorption properties than their nonporous counterpart. An enhanced reflection loss (RL) value of −90.2 dB is obtained for the microporous Co@CoO NPs with a thickness of merely 1.3 mm. The absorption bandwidth corresponding to the RL below −10 dB reaches 7.2 GHz. The microwave absorption mechanism is discussed in terms of micropore morphology, core@shell structure and nanostructure. This novel microporous material may open new routes for designing high performance microwave absorbers.

•The Mg–9.2wt%TiH1.971–3.7wt%TiH1.5 nanocomposite was prepared.•The Ti hydrides nanoparticles of 13 nm were dispersed on the Mg nanoparticles.•TiH1.971 and TiH1.5 nanoparticles cooperatively catalyzed the hydrogenation of Mg.•The nanocomposite absorbed 4.3 wt% H2 in 10 min at room temperature.•The apparent activation energy for hydrogen absorption was 12.5 kJ mol−1.In order to improve the hydrogen sorption kinetics of Mg at room temperature, the Mg–9.2wt%TiH1.971–3.7wt%TiH1.5 nanocomposite is successfully prepared by hydrogen plasma-metal reaction (HPMR) method and hydrogenation/dehydrogenation at 673 K. The Mg nanoparticles are hexagonal in shape with the size in the range of 50–190 nm. The spherical Ti hydrides nanoparticles of about 13 nm are uniformly dispersed on the surface of Mg nanoparticles. During hydrogenation/dehydrogenation cycle, the Ti hydrides nanoparticles restrain the growth of Mg nanoparticles. The Mg–TiH1.971–TiH1.5 nanocomposite quickly absorbs 4.3 wt% H2 in 10 min at room temperature and reaches a saturation value of 5.0 wt% in 60 min. The apparent activation energies for hydrogen absorption and desorption are 12.5 and 46.2 kJ mol−1, respectively. The improved kinetics and reduced activation energy are explained in terms of the nanostructure of Mg and the synergic catalytic effect of TiH1.971–TiH1.5 nanoparticles.The Mg–9.2wt%TiH1.971–3.7wt%TiH1.5 nanocomposite is successfully prepared by hydrogen plasma-metal reaction (HPMR) method and hydrogenation/dehydrogenation at 673 K. The spherical Ti hydrides nanoparticles of about 13 nm are uniformly dispersed on the surface of the Mg nanoparticles. The Mg–TiH1.971–TiH1.5 nanocomposite quickly absorbs 4.3 wt% H2 in 10 min at room temperature and reaches a value of 5.0 wt% in 60 min. The apparent activation energies for hydrogen absorption and desorption are 12.5 and 46.2 kJ mol−1, respectively. The improved kinetics and reduced activation energy are explained in terms of the nanostructure of Mg and the synergic catalytic effect of TiH1.971–TiH1.5 nanoparticles.

•We prepared Mg–10.6 wt. % La–3.5 wt. % Ni composite nanoparticles by HPMR method.•The LaH3 and Mg2Ni nanoparticles disperse on the surface of Mg.•Single crystalline Mg nanoparticles change into polycrystalline after activation.•These nanoparticles show high hydrogen sorption kinetics and storage capacities.•The hydrogen absorption activation energy of the nanoparticles is 39.1 kJ mol−1.The Mg–10.6 wt. % La–3.5 wt. % Ni nanoparticles are prepared by hydrogen plasma-metal reaction method. These nanoparticles are made of Mg, LaH3 and a small amount of Mg2Ni. The as-prepared Mg nanoparticles of 180 nm are single crystalline and quasi-spherical in shape, and they change into polycrystalline after activation. LaH3 and Mg2Ni nanoparticles are nearly spherical in shape with the mean particle size of 15 nm, and disperse on the surface of Mg. The Mg–10.6La–3.5Ni nanoparticles can absorb 3.2 wt. % H2 in less than 15 min at 523 K and accomplish a high hydrogen storage capacity of 6.5 wt. % H2 in less than 10 min at 673 K, almost reaching the theoretical gravimetric capacity. They can release 4.2 wt. % H2 in 3 min at 623 K. The synergistic catalytic effect of LaH3 and Mg2Ni nanoparticles, the nanostructure and the low oxide content of Mg nanoparticles promote the hydrogen sorption process with the low hydrogen absorption activation energy of 39.1 kJ mol−1.The Mg–10.6 wt. % La–3.5 wt. % Ni nanoparticles are prepared by HPMR. LaH3 and Mg2Ni nanoparticles disperse on the surface of Mg. Single crystalline Mg nanoparticles change into polycrystalline after activation. The Mg–10.6La–3.5Ni nanoparticles can absorb 3.2 wt. % H2 in less than 15 min even at 523 K and accomplish a high hydrogen storage capacity of 6.5 wt. % H2 in less than 10 min at 673 K. They can release 4.2 wt. % H2 in 10 min at 623 K. The catalytic effect of LaH3 and Mg2Ni nanoparticles, the nanostructure and the low oxide content of Mg nanoparticles promote the hydrogen sorption process with the low hydrogen absorption activation energy of 39.1 kJ mol−1.

•We prepared a series of Mg–La–Pd trilayer films by magnetron sputtering method.•The La 3 nm film possessed the fastest sorption rate compared with other films.•The hydrogenation of the La 3 nm film saturated within 14 s at 298 K.•The La 3 nm film released 80% of hydrogen within 60 min at 298 K.•The maximum discharge capacity of the La 3 nm film was 377.8 mAh g−1.A series of Mg–La–Pd trilayer films (La = 0.5–9 nm) have been prepared by magnetron sputtering method. When the thickness of La layer is larger than 3 nm, the distribution of La element becomes homogeneous. The hydrogen storage properties of the films under 0.1 MPa H2 and at 298 K are investigated by measuring their resistance and optical transmittance during the hydrogenation. The hydrogenation of the La 3 nm film saturates within 14 s and possesses the fastest absorption kinetics compared with other Mg–La–Pd films. The further increase of La thickness decreases the hydrogenation rate due to the decreased hydrogen diffusion rate through this layer. The La 3 nm film also exhibits the fast hydrogen desorption rate in air at room temperature. It releases 80% of hydrogen within 60 min. The electrochemical properties of the Mg–La–Pd films have been carried out in 6 M KOH with a three-electrode cell. Among these films, the La 3 nm film possesses the largest anodic area and anodic peak current, as well as the highest maximum discharge capacity of 377.8 mAh g−1.

•Mg–5 wt.% LaNi5 nanocomposite showed excellent sorption kinetics.•The nanocomposite could absorb 3.5 wt.% H2 in less than 5 min at 473 K.•The storage capacity was as high as 6.7 wt.% at 673 K.•The apparent activation energy for hydrogenation was 26.3 kJ mol−1.Mg (200 nm) and LaNi5 (25 nm) nanoparticles were produced by the hydrogen plasma-metal reaction (HPMR) method, respectively. Mg–5 wt.% LaNi5 nanocomposite was prepared by mixing these nanoparticles ultrasonically. During the hydrogenation/dehydrogenation cycle, Mg–LaNi5 transformed into Mg–Mg2Ni–LaH3 nanocomposite. Mg particles broke into smaller particles of about 80 nm due to the formation of Mg2Ni. The nanocomposite showed superior hydrogen sorption kinetics. It could absorb 3.5 wt.% H2 in less than 5 min at 473 K, and the storage capacity was as high as 6.7 wt.% at 673 K. The nanocomposite could release 5.8 wt.% H2 in less than 10 min at 623 K and 3.0 wt.% H2 in 16 min at 573 K. The apparent activation energy for hydrogenation was calculated to be 26.3 kJ mol−1. The high sorption kinetics was explained by the nanostructure, catalysis of Mg2Ni and LaH3 nanoparticles, and the size reduction effect of Mg2Ni formation.

•MgH2 is one of the most attractive candidates for hydrogen storage.•Many strategies were used to improve the hydrogen storage properties of MgH2.•Mg-based nanocomposites enhance the sorption kinetics and storage capacity.•Nanocomposites improve the stability of Mg during absorption/desorption cycling.MgH2 is one of the most attractive candidates for on-board H2 storage. However, the practical application of MgH2 has not been achieved due to its slow hydrogenation/dehydrogenation kinetics and high thermodynamic stability. Many strategies have been adopted to improve the hydrogen storage properties of Mg-based materials, including modifying microstructure by ball milling, alloying with other elements, doping with catalysts, and nanosizing. To further improve the hydrogen storage properties, the nanostructured Mg is combined with other materials to form nanocomposite. Herein, we review the recent development of the Mg-based nanocomposites produced by hydrogen plasma-metal reaction (HPMR), rapid solidification (RS) technique, and other approaches. These nanocomposites effectively enhance the sorption kinetics of Mg by facilitating hydrogen dissociation and diffusion, and prevent particle sintering and grain growth of Mg during hydrogenation/dehydrogenation process.

With the purpose of improving the hydrogen sorption kinetics of Mg at moderate temperatures, the Mg–TiH1.971–VH2 nanocomposite is synthesized by means of the hydrogen plasma–metal reaction (HPMR) approach. The nanocomposite is consequently hydrogenated and dehydrogenated at 673 K to synthesize Mg–9.6 wt % Ti–2.9 wt % V nanocomposite. The Mg Nanoparticles (NPs) in hexagonal shape range from 30 to 300 nm. The spherical Ti and V NPs of about 23 nm are uniformly distributed on the surfaces of the Mg NPs. The Mg–Ti–V nanocomposite quickly absorbs 4.7 wt % H2 within 5 min at 473 K and 2.5 wt % H2 within 10 min at 373 K. The apparent activation energies for hydrogenation and dehydrogenation are 29.2 and 73.8 kJ mol–1, respectively. During the hydrogenation/dehydrogenation cycle, the Ti and V NPs restrain the growth of Mg NPs. The dehydrogenation of TiH1.971 to Ti is interpreted as the catalytic impact of V NPs. The improved sorption kinetics at moderate temperatures and the reduced activation energy derive from the nanostructure of Mg and the synergic catalytic impact of Ti and V NPs.

The Pd nanoparticles of 10 nm have been prepared by dealloying method. They can absorb/desorb hydrogen or deuterium completely in a few seconds at room temperature. There is no apparent isotope effect on the sorption kinetics. The activation energies of hydrogen and deuterium absorption are 23.2 and 23.7 kJmol−1, respectively. The diffusion coefficients of hydrogen and deuterium in the Pd nanoparticles are similar at 423 K. However, the deuterium isotherm shows higher plateau pressure and narrower gap than the hydrogen isotherm at the same temperature. When the temperature increases to 473 K, no phase transformation can be detected for both hydrogen and deuterium. The particle size and structure effects on the hydrogen/deuterium sorption process are discussed.Graphical abstractThe Pd nanoparticles of 10 nm have been prepared by dealloying method. They can absorb/desorb hydrogen or deuterium completely in a few seconds at room temperature, and there is no apparent isotope effect on the kinetics. In addition, the diffusion coefficients of hydrogen and deuterium in the Pd nanoparticles are similar at 423 K. However, the deuterium isotherm shows higher plateau pressure and narrower gap than the hydrogen isotherm at the same temperature. The particle size and structure effects on the hydrogen/deuterium sorption process are discussed.Highlights► We prepared the Pd nanoparticles of 10 nm by dealloying method. ► They can absorb/desorb hydrogen or deuterium quickly at room temperature. ► There is no apparent isotope effect on the sorption kinetics of Pd nanoparticles. ► The diffusion coefficients of hydrogen and deuterium in Pd are similar. ► Deuterium isotherm shows higher plateau pressure and narrower gap than hydrogen.

•The oxide dispersion strengthened alloys show enhanced oxidation resistance.•Al plays the dominant role in improving the oxidation resistance.•Cr and Y are of importance in forming the stable Al2O3 scale.•The respective concentrations of Al and Cr should be larger than 2 and 14 wt.%.The oxidation of six oxide dispersion strengthened (ODS) ferritic alloys was investigated at 1050 °C in air up to 200 h. Al plays the dominant role in improving the oxidation resistance of the ODS alloys. Cr and Y are of importance in forming the stable Al2O3 scale. To produce the dense alumina layer with enhanced adherence to the metal substrate, the concentrations of Al and Cr should be larger than 2 and 14 wt.%, respectively.

The MgxNi100−x films of 100 nm have been prepared by magnetron co-sputtering Mg and Ni targets, and a Pd layer of 10 nm was deposited on these films by magnetron sputtering a Pd target. Mg2Ni and MgNi2 are directly generated during the co-sputtering process in the Mg84Ni16/Pd and Mg48Ni52/Pd films. The hydrogen storage properties of the films under 0.1 MPa H2 at 298 K were investigated. The hydrogenation of the Mg84Ni16/Pd film saturates within 45 s and exhibits the faster absorption kinetics compared with Mg94Ni6/Pd and Mg48Ni52/Pd films. The electrochemical properties of the MgxNi100−x/Pd films were investigated in 6 M KOH with a three-electrode cell. The Mg84Ni16/Pd film can be activated just at the first cycle. The maximum discharge capacity of the Mg84Ni16/Pd film is 482.7 mAh g−1, the highest among these films.

The Zr65Al10Ni10Cu15 amorphous ribbon and bulk samples were prepared by the single roller melt-spinning technique and the copper-mold casting, respectively. The hydrogen absorption properties of the ribbon and bulk samples were evaluated at 473 and 523 K under 4 MPa using a Sieverts-type apparatus. For both ribbon and bulk samples, the hydrogen absorption kinetics increase with the increase of temperature, and the hydrogen concentration approaches the saturation value of 0.7 and 0.8 wt.% at 473 and 523 K, respectively. The electrical resistivity of the hydrogenated sample decreases with the increasing temperature with a negative slope, similar as the melt-spun sample. The electrical resistivity increases with the increasing hydrogen content in the amorphous sample mainly due to the diffraction effect from the absorbed hydrogen atoms. The electrical resistivities of the sample with of 0.8 wt.% H are 294 μΩ·cm at 293 K and 316 μΩ·cm at 5 K. The compressive strength of the bulk amorphous alloy is not changed apparently by the absorbed hydrogen. However, the plastic deformation decreases from 3.2% for the as-cast bulk sample to 1.3% for the sample with 0.8 wt.% H due to the lower free volume after the hydrogenation. The hardness value enlarges slightly with the increase of hydrogen content.Highlights► Zr65Al10Ni10Cu15 amorphous alloy exhibited a fast hydrogen absorption rate. ► The hydrogenated alloy had a negative temperature coefficient of resistivity. ► The electrical resistivities increased with the increasing hydrogen content. ► The compressive strength was not changed apparently by the hydrogenation. ► The plasticity decreased slightly with the increasing hydrogen content.

Fe-25 wt% Y2O3 composite powders have been fabricated by mechanical milling (MM) Fe powders of 100 μm in diameter and Y2O3 nanoparticles in an argon atmosphere for the milling periods of 4, 8, 12, 24, 36, and 48 h, respectively. The features of these powders were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe micro analyzer (EPMA) and transmission electron microscopy (TEM). The experimental results showed that the mean particle size and crystalline size of MM powders decreased with the milling time increasing. All the elements distributed homogenously inside the powders after 48 h of MM. The lattice constant of the matrix α-Fe kept constant with the milling time, and no solid solution took place during MM process. After 8 h of MM, the α-Fe in each powder became nanocrystalline. After 48 h of MM, Y2O3 changes from nanostructure into amorphous structure, and the crystalline size of α-Fe further decreased to 10 nm. The Y2O3 in the powders mechanically milled for 48 h kept the amorphous structure after being annealed at 400 °C, and starts to crystallize when the powders are annealed at 600 °C. The amorphous Y2O3 contains a small amount of Fe, and crystalline FeYO3 appears at 800 °C.

In order to improve the hydrogen storage properties of Mg, Mg@Mg17Al12 ultrafine particles (UFPs) with 7, 22 and 27 at% Al have been successfully prepared by a hydrogen plasma–metal reaction (HPMR) approach. These UFPs are nearly spherical in shape with an average size of about 150 nm. The Mg particle core is a single crystal, and the Mg17Al12 particle shell of 2–5 nm thickness effectively suppresses the formation of MgO. The formation mechanism of the core–shell structure is interpreted in terms of Mg–Al phase transformation. The Mg17Al12 shell disproportionates into MgH2 and Al upon hydrogenation, and is recovered after hydrogen release. The morphology and size of these UFPs are not obviously changed during the sorption cycle, whereas the Mg particle core changes from single crystal into the polycrystalline form of 2–4 nm size. The hydrogen sorption kinetics and storage capacity of the Mg@Mg17Al12 UFPs decreased with increasing Al content. Mg–7 at.% Al can absorb 5.7 wt% H2 at 523 K and 7.0 wt% H2 at 673 K. It can release 6.0 wt% H2 within 30 minutes at 623 K and 6.2 wt% H2 within 3 minutes at 673 K. The catalytic effect and oxidation resistance of the Mg17Al12 shell, and the nanostructure of the Mg core accelerate the hydrogen diffusion, with low hydrogen absorption and desorption activation energies of 49.3 and 105.5 kJ mol−1, respectively.

Mg-2 at.% La-2.6 at.% Al composite nanoparticles are prepared by hydrogen plasma–metal reaction (HPMR) method. The electron microscopy and X-ray diffraction studies reveal that these nanoparticles are made of single crystalline Mg of about 160 nm, and a little amount of polycrystalline Al2La of 15 nm dispersing on the surface of Mg. The addition of Al effectively reduces the oxidation of Mg nanoparticles. After hydrogenation, Al2La disproportionates into single crystalline LaH3 of 15 nm. The composite nanoparticles can absorb 5.0 wt.% H2 in 30 min even at 473 K, and the storage capacity is as high as 6.8 wt.% at 673 K. They can also release 6.0 wt.% H2 in less than 10 min at 673 K. The catalytic effect of LaH3 nanoparticles, nanocrystalline structure and low oxide content of Mg accelerate the hydrogen sorption process of Mg–La–Al composite nanoparticles with a low hydrogen absorption activation energy of 23.1 kJ mol−1.Highlights► We prepared Mg–La–Al composite nanoparticles by hydrogen plasma–metal reaction. ► These composite nanoparticles can absorb 5.0 wt.% hydrogen in 30 min at 473 K ► The hydrogen absorption activation energy is as low as 23.1 kJ mol−1. ► The LaH3 nanoparticle and the nanostructured Mg improve the sorption process.

The hydrogen absorption properties of Zr65Al10Ni10Cu15 amorphous alloy with a wide supercooled liquid region were evaluated using a Sieverts-type apparatus. The amorphous alloy absorbs 0.34, 0.80 and 0.85 wt.% hydrogen within 10, 6 and 5 min at 373, 473 and 523 K, respectively. According to Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory, the hydrogen absorption activation energy of the amorphous alloy was 1.27 kJ mol−1. The pressure–composition (P–C) isotherms of the amorphous Zr65Al10Ni10Cu15 alloy at 573, 623 and 673 K did not show a plateau, and the hydrogen absorption capacities were 0.8, 1.3 and 1.7 wt.%, respectively. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analysis demonstrated that the thermal stability of the amorphous alloy was improved with an enlarged supercooled liquid region after the hydrogen uptake below 473 K, but was decreased after the hydrogenation above 523 K. The alloy still kept the amorphous structure after hydrogenation at 573 K, and transformed into the crystalline phases of ZrH2, ZrNi and AlCu after the hydrogenation at 673 K.Highlights► Zr65Al10Ni10Cu15 amorphous alloy exhibited a fast hydrogen absorption rate. ► The hydrogen absorption activation energy was 1.27 kJ mol−1. ► The P–C isotherms at 573, 623 and 673 K did not show a plateau. ► The alloy kept the amorphous structure after the hydrogenation at 573 K. ► The hydrogenation below 473 K improved the thermal stability of the alloy.

The Mg–10.2 at.% V nanoparticles are prepared by hydrogen plasma–metal reaction (HPMR) method. These nanoparticles are made of Mg, VH2 and a small amount of MgH2. The Mg nanoparticles are hexagonal in shape with the particle size in the range of 50–150 nm. The VH2 nanoparticles are spherical in shape with the particle size around 10 nm, and disperse on the surface of the Mg nanoparticles. After the hydrogen absorption, the mean particle size of MgH2 decreases to 60 nm, while the V nanoparticles are still about 10 nm. The Mg–V composite nanoparticles can absorb 3.8 wt.% hydrogen in less than 30 min at 473 K and accomplish a high hydrogen storage capacity of 5.0 wt.% in less than 5 min at 623 K. They can release 4.0 wt.% hydrogen in less than 15 min at 573 K. The catalytic effect of the V nanoparticles and the nanostructure and the low oxide content of the Mg particles promote the hydrogen sorption process with the low hydrogen absorption activation energy of 71.2 kJ mol−1.Highlights► We have prepared Mg–V composite nanoparticles by hydrogen plasma–metal reaction. ► These nanoparticles show high hydrogen sorption rate and storage capacity. ► The catalytic V nanoparticles and the nanostructured Mg promote the sorption process.

•Microporous Ni/NiO nanoparticals were prepared by chemically dealloying method.•They possessed micropores of 0.7–1.6 nm with a surface area of 69.5 m2/g.•They showed high microwave absorption intensity and wide absorption bandwidth.•Microwave absorption mechanism was explained by micropore and core/shell structures.The Al3Ni2@Al nanoparticles (NPs) were prepared from Ni45Al55 master alloy by hydrogen plasma-metal reaction method, and were subsequently dealloyed to produce porous Ni@NiO NPs of 36 nm. The pore size ranges from 0.7 to 1.6 nm, leading to large specific surface area of 69.5 m2/g and big pore volume of 0.507 cc/g. The saturation magnetization (MS) and coercivity (HC) of the microporous Ni@NiO NPs are 11.5 emu/g and 5.2 Oe. They exhibit high microwave absorption performance with a minimum reflection coefficient (RC) of −86.9 dB and an absorption bandwidth of 2.6 GHz (RC≤−10 dB) at thickness of 4.5 mm. The enhanced microwave absorption properties are attributed to the synergistic effect of the magnetic Ni core and dielectric NiO shell, and the micropore architecture. The NPs with micropore morphology and core/shell structure open a new way to modify the microwave absorption performance.The microporous Ni/NiO nanoparticles prepared by chemically dealloying Al3Ni2@Al NPs exhibit high microwave absorption intensity (−86.9 dB) and wide absorption bandwidth (2.6 GHz for RC≤−10 dB).Download high-res image (383KB)Download full-size image

Surface modification is an effective way to induce new magnetic phenomena in nanostructured materials. Herein, FeAl nanoparticles (NPs) with a mean diameter of 38 nm are produced by the hydrogen plasma-metal reaction (HPMR) approach. Via the subsequent passivation process, an oxide layer is generated outside the FeAl NPs as the result of surface oxidation. The 3 nm-thick amorphous-like oxide layer consists mainly of Al2O3 together with a small amount of Fe2O3. An Fe-enriched zone is created between the oxide layer and the FeAl core due to the much higher diffusion rate of Al than Fe towards the particle surface during the passivation process, which can be explained by the Kirkendall effect. The FeAl@(Al, Fe)2O3 NPs surprisingly display a superparamagnetic property with a blocking temperature (TB) of 250 K and a saturation magnetization of 36 emu g−1 at 4.2 K. They also exhibit high microwave absorption performance with a minimum reflection loss (RL) value of −22.6 dB at a thickness of 1.7 mm, and a broad absorption bandwidth of 8.3 GHz corresponding to the RL below −10 dB. Formation of the oxide layer plays a dominant role in inducing the superparamagnetic property and high microwave absorption performance in FeAl@(Al, Fe)2O3 NPs. Specific core@shell NPs may open a new way to tune the magnetic and electromagnetic properties of metallic nanomaterials through surface modification.

In order to improve the hydrogen storage properties of Mg, Mg@Mg17Al12 ultrafine particles (UFPs) with 7, 22 and 27 at% Al have been successfully prepared by a hydrogen plasma–metal reaction (HPMR) approach. These UFPs are nearly spherical in shape with an average size of about 150 nm. The Mg particle core is a single crystal, and the Mg17Al12 particle shell of 2–5 nm thickness effectively suppresses the formation of MgO. The formation mechanism of the core–shell structure is interpreted in terms of Mg–Al phase transformation. The Mg17Al12 shell disproportionates into MgH2 and Al upon hydrogenation, and is recovered after hydrogen release. The morphology and size of these UFPs are not obviously changed during the sorption cycle, whereas the Mg particle core changes from single crystal into the polycrystalline form of 2–4 nm size. The hydrogen sorption kinetics and storage capacity of the Mg@Mg17Al12 UFPs decreased with increasing Al content. Mg–7 at.% Al can absorb 5.7 wt% H2 at 523 K and 7.0 wt% H2 at 673 K. It can release 6.0 wt% H2 within 30 minutes at 623 K and 6.2 wt% H2 within 3 minutes at 673 K. The catalytic effect and oxidation resistance of the Mg17Al12 shell, and the nanostructure of the Mg core accelerate the hydrogen diffusion, with low hydrogen absorption and desorption activation energies of 49.3 and 105.5 kJ mol−1, respectively.

Co/C nanoparticles (NPs) with a size of 45 nm have been prepared by an arc plasma method under a mixed methane and argon atmosphere. They display a uniform carbon shell of 3 nm in thickness and have a low graphitization degree. The saturation magnetization (MS) and coercivity (HC) of the NPs are 159.9 emu g−1 and 275.7 Oe, respectively. The microwave absorption properties of the Co/C NPs mixed with paraffin wax (PW) at 25, 50 and 75 wt% NPs have been investigated in the range of 2–18 GHz. The Co/C-PW composite with 50 wt% NPs exhibits the best microwave absorption performance. It has a minimum reflection loss (RL) value of −43.4 dB at a thickness of 2.3 mm, and the absorption bandwidth for RL ≤ −20 dB is as large as 7.2 GHz, which is the highest value among the reported Co-based absorbers. The high microwave absorption performance is interpreted in terms of impedance matching, core/shell structure and nanosize effects. The carbon-coated magnetic metal NPs prepared by methane plasma arc are potential microwave absorbers with strong absorption intensity and wide absorption bandwidth.

The MgxNi100−x films of 100 nm have been prepared by magnetron co-sputtering Mg and Ni targets, and a Pd layer of 10 nm was deposited on these films by magnetron sputtering a Pd target. Mg2Ni and MgNi2 are directly generated during the co-sputtering process in the Mg84Ni16/Pd and Mg48Ni52/Pd films. The hydrogen storage properties of the films under 0.1 MPa H2 at 298 K were investigated. The hydrogenation of the Mg84Ni16/Pd film saturates within 45 s and exhibits the faster absorption kinetics compared with Mg94Ni6/Pd and Mg48Ni52/Pd films. The electrochemical properties of the MgxNi100−x/Pd films were investigated in 6 M KOH with a three-electrode cell. The Mg84Ni16/Pd film can be activated just at the first cycle. The maximum discharge capacity of the Mg84Ni16/Pd film is 482.7 mAh g−1, the highest among these films.

25 nm carbon-coated microporous Co/CoO nanoparticles (NPs) were synthesized by integrating chemical de-alloying and chemical vapor deposition (CVD) methods. The NPs possess micropores of 0.8–1.5 nm and display a homogeneous carbon shell of about 4 nm in thickness with a low graphitization degree. The saturation magnetization (MS) and coercivity (HC) of the NPs were 70.3 emu g−1 and 398.4 Oe, respectively. The microporous Co/CoO/C NPs exhibited enhanced microwave absorption performance with a minimum reflection coefficient (RC) of −78.4 dB and a wide absorption bandwidth of 8.1 GHz (RC ≤ −10 dB), larger than those of the nonporous counterparts of −68.3 dB and 5.8 GHz. The minimum RC values of the microporous Co/CoO/C NPs at different thicknesses were much smaller than the nonporous counterparts. The high microwave absorption mechanism of the microporous Co/CoO/C nanocomposite can be interpreted in terms of the interfacial polarization relaxation of the core/shell and micropore structures, the effective permittivity modification of the air in the micropores and the polarization relaxation of the defects in the low-graphitization carbon shell and the porous Co NPs. Our study demonstrates that the microporous Co/CoO/C nanocomposite is an efficient microwave absorber with high absorption intensity and wide absorption bandwidth.