Effects of highly dispersed Ni nanoparticles on the hydrogen storage performance of MgH_(2)

MgH_(2)with a large hydrogen capacity is regarded as a promising hydrogen storage material.However,it still suffers from high thermal stability and sluggish kinetics.In this paper,highly dispersed nano-Ni has been successfully prepared by using the polyol reduction method with an average size of 2.14 nm,which significantly improves the de/rehydrogenation properties of MgH_(2).The MgH_(2)–10wt%nano-Ni sample starts releasing H_(2)at 497 K,and roughly 6.2wt%H_(2)has been liberated at 583 K.The rehydrogenation kinetics of the sample are also greatly improved,and the adsorption capacity reaches 5.3wt%H_(2)in 1000 s at 482 K and under 3 MPa hydrogen pressure.Moreover,the activation energies of de/rehydrogenation of the MgH_(2)–10wt%nano-Ni sample are reduced to(88±2)and(87±1)kJ·mol−1,respectively.In addition,the thermal stability of the MgH_(2)–10wt%nano-Ni system is reduced by 5.5 kJ per mol H_(2)from that of pristine MgH_(2).This finding indicates that nano-Ni significantly improves both the thermodynamic and kinetic performances of the de/rehydrogenation of MgH_(2),serving as a bi-functional additive of both reagent and catalyst.

High-loading, ultrafine Ni nanoparticles dispersed on porous hollow carbon nanospheres for fast (de)hydrogenation kinetics of MgH_(2)

Magnesium hydride(MgH2) is one of the most promising hydrogen storage materials for practical application due to its favorable reversibility, low cost and environmental benign;however, it suffers from high dehydrogenation temperature and slow sorption kinetics.Exploring proper catalysts with high and sustainable activity is extremely desired for substantially improving the hydrogen storage properties of MgH2. In this work, a composite catalyst with high-loading of ultrafine Ni nanoparticles(NPs) uniformly dispersed on porous hollow carbon nanospheres is developed, which shows superior catalytic activity towards the de-/hydrogenation of MgH2. With an addition of 5wt% of the composite, which contains 90 wt% Ni NPs, the onset and peak dehydrogenation temperatures of MgH2are lowered to 190 and 242 ℃, respectively. 6.2 wt% H2is rapidly released within 30 min at 250 ℃. The amount of H2that the dehydrogenation product can absorb at a low temperature of 150 ℃ in only 250 s is very close to the initial dehydrogenation value. A dehydrogenation capacity of 6.4wt% remains after 50 cycles at a moderate cyclic regime, corresponding to a capacity retention of 94.1%. The Ni NPs are highly active,reacting with MgH2and forming nanosized Mg2Ni/Mg2NiH4. They act as catalysts during hydrogen sorption cycling, and maintain a high dispersibility with the help of the dispersive role of the carbon substrate, leading to sustainably catalytic activity. The present work provides new insight into designing stable and highly active catalysts for promoting the(de)hydrogenation kinetics of MgH2.

Effects of PVP on the preparation and growth mechanism of monodispersed Ni nanoparticles

Monodispersed Ni nanoparticles were successfully prepared by chemical reduction with hydrazine hydrate in ethylene glycol. The effect of the amount of polyvinylpyrrolidone （PVP-K30） on the preparation of Ni nanoparticles was investigated. X-ray diffraction （XRD）, transmission electron microscopy （TEM）, and high resolution transmission electron microscopy （HRTEM） were employed to characterize the nickel powders. The average nickel particle size can be controlled from 103 nm to 46 ran with increasing the mass ratio of PVP to NiCl2·6H2O. The particles are spherical in shape and are not agglomerated. A possible extensive mechanism of nickel nanoparticle formation has been suggested.

A Facile Solvothermal Synthesis of Monodisperse Ni Nanoparticles

A simple solvothermal approach was developed to synthesize uniform spherical monodisperse Ni nanoparticles, which can easily disperse in nonpolar solvents to form homogenous colloidal solution. The as-prepared sample was characterized by XRD, TEM, and FTIR. The results indicate that Ni nanoparticles have the structure of face-centered cube and a narrow distribution with a diameter of （3.5±0.5） nm. The FTIR spectrum reveals that the nanoparticles are coated with oleic acid. In the synthetic process, N2H4·H2O was used as a reducing agent and oleic acid as a surfactant. The probable formation mechanism of the spherical nanoparticles was also discussed.

Catalytic reductive amination of furfural to furfurylamine on robust ultra-small Ni nanoparticles

The synthesis of primary amines via reductive amination in the presence of NH_(3)and H_(2),as a green and sustainable process,has attracted much attention.In this paper,we prepared series of Ni/SiO_(2)catalysts with deposition-precipitation and impregnation methods,and their catalytic performances on the reductive amination of a biomass derived compound of furfural to produce furfurylamine were studied.The catalytic activity and the yield were correlated to the structure and the surface properties of catalysts largely.The Ni/SiO_(2)is of high Lewis acidity and small Ni particle with numerous large Ni flat step surface showed high activity and selectivity,it afforded a reaction rate of 12.8 h^(−1)and a high yield to furfurylamine around 98%.These results are superior to the most non-noble metal catalysts reported so far.Moreover,the reaction route was examined with the unit control reactions of the intermediate.To produce furfurylamine selectively,the most suitable catalyst should have the moderate but not the highest activity in activation of hydrogen and hydrogenation in the reductive amination of furfural.This work provides some useful information for the catalytic reductive amination of aldehydes both in the design of catalyst and the reaction route.

Ultrafine Fe-modulated Ni nanoparticles embedded within nitrogen-doped carbon from Zr-MOFs-confined conversion for efficient oxygen evolution reaction

Improvement of the low-cost transition metal electrocatalyst used in sluggish oxygen evolution reaction is a significant but challenging problem. In this study, ultrafine Fe-modulated Ni nanoparticles embedded in a porous Ni-doped carbon matrix were produced by the pyrolysis of zirconium metal–organic–frameworks, in which 2,2′-bipyridine-5,5′-dicarboxylate operating as a ligand can coordinate with Ni^(2+) and Fe^(3+). This strategy allows formation of Fe-modulated Ni nanoparticles with a uniform dimension of about 2 nm which can be ascribed to the spatial blocking effect of ZrO_(2). This unique catalyst displays an efficient oxygen evolution reaction electrocatalytic activity with a low overpotential of 372 mV at 10 mA·cm^(–2) and a small Tafel slope of 84.4 mV·dec^(–1) in alkaline media. More importantly, it shows superior durability and structural stability after 43 h in a chronoamperometry test. Meanwhile, it shows excellent cycling stability during 4000 cyclic voltammetry cycles. This research offers a new insight into the construction of uniform nanoscale transition metals and their alloys as highly efficient and durable electrocatalysts.

Ni nanoparticles encapsulated within H-type ZSM-5 crystals for upgrading palmitic acid to diesel-like fuels

Meso-Ni@HZSM-5 bi-functional catalysts were successfully post-encapsulated with about 3-7 nm Ni nanoparticles within HZSM-5 crystals,which exhibited significantly efficient conversion activity(67.4 g[palmitic acid]g[Ni]^(−1)h^(−1))of palmitic acid and 100%selectivity of hydrocarbons with the outstanding stability during recycling application,compared to the impregnated Ni/HZSM-5 catalyst(14.0 g[palmitic acid]g[Ni]^(−1)h^(−1)).

Capacitance characteristics of metal-oxide-semiconductor capacitors with a single layer of embedded nickel nanoparticles for the application of nonvolatile memory

This paper reports that metal-oxide-semiconductor （MOS） capacitors with a single layer of Ni nanopartictes were successfully fabricated by using electron-beam evaporation and rapid thermal annealing for application to nonvolatile memory. Experimental scanning electron microscopy images showed that Ni nanoparticles of about 5 nm in diameter were clearly embedded in the SiO2 layer on p-type Si （100）. Capacitance-voltage measurements of the MOS capacitor show large flat-band voltage shifts of 1.8 V, which indicate the presence of charge storage in the nickel nanoparticles. In addition, the charge-retention characteristics of MOS capacitors with Ni nanoparticles were investigated by using capacitance-time measurements. The results showed that there was a decay of the capacitance embedded with Ni nanoparticles for an electron charge after 104 s. But only a slight decay of the capacitance originating from hole charging was observed. The present results indicate that this technique is promising for the efficient formation or insertion of metal nanoparticles inside MOS structures.

Preparation of Ni/PZT Core-shell Nanoparticles and Their Electromagnetic Properties

The Ni nanoparticles coated with Pb（Zr,Ti）O3（PZT） were synthesized by a sol-gel method and in situ reaction. And their structure, oxidation resistance, and electromagnetic properties were investigated. The X-ray diffraction patterns（XRD） exhibited that a small amount of impure phase characterized to Ni（OH）2 was detected from the ammonia-treated Ni nanoparticles and the ammonia-treated Ni nanoparticles coated with PZT. After being pre-treated with aqueous ammonia, the PZT coating layer was more uniform and about 10 nm in thickness. The oxidation resistance of the ammonia-treated Ni nanoparticles coated with PZT, compared with that of the non-treated ones, was improved by about 66 ℃. The PZT shell layer prepared by in-situ reaction can greatly reduce the dielectric constant and improve the natural resonance loss at high frequency, so as to obtain the optimal impedance matching performance of the electromagnetic wave transmission.

Aligned Elongation of Ag Nanoparticles Embedded in Silica Irradiated with High Energy Ni Ions

Metallic nanoparticle （NP） shapes have a significant influence on the property of composite embedded with metallic NPs. Swift heavy ion irradiation is an effective way to modify shapes of metallic NPs embedded in an amorphous matrix. We investigate the shape deformation of Ag NPs with irradiation fluence, and 357 MeV Ni ions are used to irradiate the silica containing Ag NPs, which are prepared by ion implantation and vacuum annealing. The UV-vis results show that the surface plasmon resonance （SPR） peak from Ag NPs shifts from 400 to 377nm. The SPR peak has a significant shift at fluence lower than 1 × 10^14 ions/cm2 and shows less shift at fluence higher than 1 × 10^14 ions/cm2. The TEM results reveal that the shapes of Ag NPs also show significant deformation at fluence lower than 1 × 10^14 ions/cm2 and show less deformation at fluence higher than 1 × 10^14 ions/cm2. The blue shift of the SPR peak is considered to be the consequence of defect production and Ag NP shape deformation, Based on the thermal spike model calculation, the temperature of the silica surrounding Ag particles first increases rapidly, then the region of Ag NPs close to the interface of Ag/silica is gradually heated. Therefore, the driven force of Ag NPs deformation is considered as the volume expansion of the first heated silica layer surrounding Ag NPs.

Tribological properties and tribomechanism of nickel nanoparticles in-situ synthesized in rapeseed oil

Nickel(Ni)nanoparticles can be enriched on the surface of iron-based frictional pairs,which provides the possibility to get rid of the competitive adsorption between the polar species of vegetable oil and the surface-active nano-additives thereon.In this paper,nickel acetylacetonate was used as a precursor to in-situ synthesize nickel nanoparticles with an average diameter of about 12 nm in rapeseed oil(RO)as the reducing agent,surface modifier,and solvent as well.The tribological properties of the as-synthesized Ni nanoparticles were evaluated with a four-ball tribometer,and their tribomechanism was investigated based on the characterizations of the tribofilm on rubbed steel surfaces by the scanning electron microscopy(SEM),transmission electron microscopy(TEM),and X-ray photoelectron spectroscopy(XPS).It was found that the Ni nanoparticles in-situ prepared in the RO with a mass fraction of 0.3%can reduce the wear scar diameter(WSD)of the steel ball by 36%.This is because,on the one hand,the Ni nanoparticles are adsorbed on the rubbed steel surfaces to repair or fill up the micro-pits and grooves thereon.On the other hand,Ni nanoparticles participate in tribochemical reactions with atmospheric O and steel substrate to form the tribochemical reaction film on the rubbed steel surfaces with the assistance of friction-induced heat and applied normal load.In addition,an amorphous carbon film is formed on the rubbed surface via the carbonization of base oil under the catalysis of Ni nanoparticles.The adsorbed Ni layer,the tribochemical reaction film,and the carbon layer comprise a composite tribofilm composed of amorphous carbon,polar fatty acid,metallic nickel,iron oxides,and nickel oxides on the rubbed steel surfaces,which contributes to significantly improving the antiwear ability and load-carrying capacity of the RO for the steel-steel sliding pair.

The first observation of Ni nanoparticle exsolution from YSZ and its application for dry reforming of methane

Ni nanocatalysts produced through exsolution have shown strong resistance to particle sintering and carbon coking in a beneficial dry reforming of methane(DRM)reaction utilizing greenhouse gases such as CH_(4)and CO_(2).However,most of the existing oxide supports for exsolution have been limited to perovskite oxide,while studies on fluorite support have been rarely conducted due to the limited solubility despite its excellent redox stability.Here we demonstrate that 3 mol%Ni can be successfully dissolved into the yttria-stabilized zirconia(YSZ)lattice and be further exsolved to the surface in a reducing atmosphere.The YSZ decorated with exsolved Ni nanoparticles shows enhanced catalytic activity for DRM reaction compared to the conventional cermet type of bulk Ni-YSZ.Moreover,the catalytic activity is extremely stable for about 300 h without significant degradation.Overall results suggest that the YSZ-based fluorite structure can be utilized as one of the support oxides for exsolution.

Regulating the intrinsic electronic structure of carbon nanofibers with high-spin state Ni for sodium storage with high-power density

Carbon nanofibers(CNFs)with high specific surface area show great potential for sodium storage as a hard carbon material.Herein,CNFs anchored with Ni nanoparticles(CNFs/Ni)were prepared through chemical vapor deposition and impregnation reduction methods,in situ growing on the three-dimensional porous copper current collector(3DP-Cu).The coupling effect of high-spin state Ni nanopar-ticles leads to the increase of defect density and the expansion of lattice spacing of CNFs.Meanwhile,the 3DP-Cu ensures a high loading capacity of CNFs and short ion/electron transport channels.As an integral binder-free anode,the 3DP-Cu/CNFs/Ni exhibits excellent electrochemical performance,which demon-strates a high specific capacity with 298.5 mAh g^(-1)at 1000 mA g^(-1)after 1500 cycles,and a high power density with 200 mAh g^(-1)over 1000 cycles at 5000 mA g^(-1).Density functional theory calculation re-sults show that the high-spin state Ni regulates the electronic structure of CNFs,which significantly reduces the adsorption energy for Na^(+)(-2.7 Ev)and thus enables high-rate capability.The regulation of the electronic structure of carbon materials by high-spin state metal provides a new strategy for developing high-power carbonaceous anode materials for sodium-ion batteries.

N-doped carbon nanotubes formed in a wide range of temperature and ramping rate for fast sodium storage

Herein,nickel@nitrogen-doped carbon nanotubes(Ni@NCNTs)are prepared by a simple and reliable method with Ni-based complex as single-source precursor.Significantly,the formation of CNTs is not susceptible to the calcination temperature and ramping rate and Ni@NCNTs can be attained from 430 to 900℃in an inert atmosphere.Then they are the first time to be applied as the anode material for sodium-ion batteries.The presence of Ni nanoparticles(NPs)facilitates the solid electrolyte interface film over the anode surface and improves the capacity retention of the host material,especially at the high rates.Furthermore,Na+diffusion is reinforced after the introduction of Ni NPs.Ni@NCNTs obtained at 500℃(Ni@NCNTs-500)exhibit the best capacity retention and rate capability.Kinetics analyses demonstrate the faster electron transportation and ion diffusion than others prepared at other temperatures.The surficial capacitance storage favors the fast electrochemistry kinetics.It delivers a high specific capacity(192 mA h g^−1 at 0.5 A g^−1),excellent cycling stability(103 mA h g^−1 after 10,000 cycles at 10 A g^−1),and outstanding high-rate capability up to 20 A g^−1(118 mA h g^−1).The related full cells confirm a high energy density of 140 Wh kg^−1 at 38.16 W kg^−1 and 44.27 W h kg^−1 at 762 W kg^−1.

Nitrogen-doped carbon nanotube-encapsulated nickel nanoparticles assembled on graphene for efficient CO2 electroreduction

Exploring 3 D hybrid nanocarbons encapsulated with metal nanoparticles(NPs)are recently considered as emerging catalysts for boosting CO2 electroreduction reaction(CRR)under practical and economic limits.Herein,we report a one-step pyrolysis strategy for fabricating N-doped carbon nanotube(CNT)-encapsulated Ni NPs assembled on the surface of graphene(N/NiNPs@CNT/G)to efficiently convert CO2 into CO.In such 3 D hybrid,the particle size of Ni NPs that coated by five graphitic carbon layers is less than 100 nm,and the amount of N dopants introduced into graphene with countable CNTs is determined to 7.27 at%.Thanks to unique CNT-encapsulated Ni NPs structure and N dopants,the achieved N/NiNPs@CNT/G hybrid displays an exceptional CRR activity with a high Faradaic efficiency of 97.7%and large CO partial current density of 7.9 mA/cm2 at-0.7 V,which outperforms those reported metallic NPs loaded carbon based CRR electrocatalysts.Further,a low Tafel slope of 134 mV/dec,a turnover frequency of 387.3 CO/h at-0.9 V,and tiny performance losses during long-term CRR operation are observed on N/NiNPs@CNT/G.Experimental observations illustrate that the Ni NPs encapsulated by carbon layers along with N dopants are of great importance in the conversion of CO2 into CO with high current density.

Size-effect on Ni electrocatalyst:The case of electrochemical benzyl alcohol oxidation

The nanoparticles(NPs)of Ni with different sizes endows its distinctive physical and chemical properties,which represents a typical strategy for the development of high-performance catalysts.However,the size effect of metallic Ni-NPs on electrocatalytic performance remains ambiguous.Herein,the Ni-NPs with different sizes supported on nitrogen doped carbon(NC)has been synthesized by controlling the pyrolysis temperature,leading to the synthesis of Ni@NC-500(8.3 nm),Ni@NC-280(1.9 nm)and Ni@NC-200(1.0 nm).The electrooxidation of benzyl alcohol(BA)over these nanocatalysts shows the yield of benzoic acid was 99%,82%,55%on Ni@NC-280,Ni@NC-200 and Ni@NC-500,respectively.The experimental and theoretical simulation demonstrate that the difference in the adsorption strength of reactant molecules by Ni-NPs is responsible for their different performance,where the Ni@NC-280 exhibits an optimal adsorption configuration between Ni@NC-280 electrode and BA.This work provides a new angle for designing and synthesizing efficient electrocatalysts,which may be extended to the exploration of various promising electrocatalytic systems.

Stabilization of Cu/Ni Alloy Nanoparticles with Graphdiyne Enabling Efficient CO_(2) Reduction

Electrocatalysis has become an attractive strategy for the artificial reduction of CO_(2) to high-value chemicals.However,the design and development of highly selective and stable non-noble metal electrocatalysts that convert CO_(2) to CO are still a challenge.As a new type of two-dimensional carbon material,graphdiyne(GDY),is rarely used to explore the application in carbon dioxide reduction reaction(CO_(2)RR).Therefore,we tried to use GDY as a substrate to stabilize the copper-nickel alloy nanoparticles(NPs)to synthesize Cu/Ni@GDY.Cu/Ni@GDY requires an overpotential(−0.61 V)to 10 mA/cm^(2) for the formation of CO,and it shows better activity than Au and Ag,achieving a higher Faraday efficiency of about 95.2%and high stability of about 26 h at an overpotential(−0.70 V).The electronic interaction between GDY substrate and Cu/Ni alloy NPs and the large specific surface area of GDY is responsible for the high performance.

Ni(OH)_(2) nanoparticles encapsulated in conductive nanowire array for high-performance alkaline seawater oxidation

Design and development of high-efficiency and durable oxygen evolution reaction(OER)electrocatalysts is crucial for hydrogen production from seawater splitting.Herein,we report the in situ electrochemical conversion of a nanoarray of Ni(TCNQ)2(TCNQ=tetracyanoquinodimethane)on graphite paper into Ni(OH)_(2) nanoparticles confined in a conductive TCNQ nanoarray(Ni(OH)_(2)-TCNQ/GP)by anode oxidation.The Ni(OH)_(2)-TCNQ/GP exhibits high OER performance and demands overpotentials of 340 and 382 mV to deliver 100 mA·cm^(−2) in alkaline freshwater and alkaline seawater,respectively.Meanwhile,the Ni(OH)_(2)-TCNQ/GP also demonstrates steady long-term electrochemical durability for at least 80 h under alkaline seawater.

In-situ growth of Ni nanoparticle-encapsulated N-doped carbon nanotubes on carbon nanorods for efficient hydrogen evolution electrocatalysis

Searching for inexpensive,efficient and durable electrocatalysts with earth-abundant elements toward the hydrogen evolution reaction(HER)is of vital importance for the future sustainable hydrogen economy,yet still remains a formidable challenge.Herein,a facile template-engaged strategy is demonstrated for the direct in-situ growth of Ni nanoparticles and N-doped carbon nanotubes on carbon nanorod substrates,forming a hierarchically branched architecture(abbreviated as Ni@N-C NT/NRs hereafter).The elaborate construction of such unique hierarchical structure with tightly encapsulated Ni nanoparticles and open configuration endows the as-fabricated Ni@N-C NT/NRs with abundant well-dispersed active sites,enlarged surface area,reduced resistances of charge transfer and mass diffusion,and reinforced mechanical robustness.As a consequence,the optimal Ni@N-C NT/NR catalyst demonstrates superior electrocatalytic activity with relatively low overpotential of 134 mV to deliver a current density of 10 mA·cm^-2 and excellent stability for HER in 0.1 M KOH,holding a great promise for practical scalable H2 production.More importantly,this work offers a reliable methodology for feasible fabrication of robust high-performance carbon-based hierarchical architectures for a variety of electrochemical applications.

Nickel embedded porous macrocellular carbon derived from popcorn as sulfur host for high-performance lithium-sulfur batteries

Due to the demands for high performance and ecological and economical alternatives to conventional lithium-ion batteries(Li Bs),the development of lithium-sulfur(Li-S)batteries with remarkably higher theoretical capacity(1675 m A h g-1)has become one of the extensive research focus directions worldwide.However,poor conductivity of sulfur,critical cyclability problems due to shuttle of polysulfides as intermediate products of the cathodic reaction,and large volume variation of the sulfur composite cathode upon operation are the major bottlenecks impeding the implementation of the next-generation Li-S batteries.In this work,a unique three-dimensional(3D)interconnected macrocellular porous carbon(PC)architecture decorated with metal Ni nanoparticles was synthesized by a simple and facile strategy.The as-fabricated Ni/PC composite combines the merits of conducting carbon skeleton and highly adsorptive abilities of Ni,which resulted in efficient trapping of lithium polysulfides(Li PSs)and their fast conversion in the electrochemical process.Owing to these synergistic advantageous features,the composite exhibited good cycling stability(512.3 mA h g^(-1)after 1000 cycles at 1 C with an extremely low capacity fading rate 0.03%per cycle),and superior rate capability(747.5 mA h g^(-1)at 2 C).Accordingly,such Ni nanoparticles embedded in a renewable puffed corn-derived carbon prepared via a simple and effective route represent a promising active type of sulfur host matrix to fabricate high-performance Li-S batteries.