Distribution Of Ni Nanoparticles Research Articles

Nitrogen-Doped Graphene-Supported Nickel Nanoparticles Reveal Low Dehydrogenation Temperature and Long Cyclic Life of Magnesium Hydrides.

Magnesium hydride (MgH2) is a promising hydrogen storage candidate due to its large capacity; however, high dehydrogenation temperature and slow kinetic rates are the main bottlenecks. Herein, we proposed a strategy for designing nitrogen-doped graphene-supported Ni nanoparticles (NPs) (Ni@NC) to tackle these problems. The results showed that the MgH2 + 15 wt % Ni@NC nanocomposite reduced the on-set dehydrogenation temperature to 195 °C, which was 175 °C lower than pristine MgH2. In addition, MgH2 + 15 wt % Ni@NC achieved 1.7 and 6.5 wt % desorption capacities at 225 and 300 °C, respectively, while absorbing 5.5 wt % hydrogen at 100 °C. The MgH2 + 15 wt % Ni@NC nanocomposite showed high cyclic stability, achieving 98.0% capacity retention after 100 cycles at 270 °C with negligible loss in capacity. This remarkable hydrogen storage performance can be attributed to the homogeneous distribution of Ni NPs on N-doped graphene layers, in situ formed Mg2NiH2 NPs, and multiphasic regions, promoting the nucleation and growth process during hydrogenation/dehydrogenation, which stabilized and improved the cyclic stability. This strategy paves the way to developing high-performance MgH2 for large-scale applications.

Ni-TiO2 catalysts derived from metal-organic framework for efficient photo-thermal CO2 methanation

Catalytic reduction of CO2 to high value-added chemicals such as methane is crucial in the development of renewable energy and waste disposal. Photo-thermal CO2 methanation has been received great attention, because the synergistic effect of photo and thermal lead to efficient CO2 reduction at low temperature. Herein, we reported the synthesis of Ni nanoparticles (NPs) supported on TiO2 (Ni-TiO2) derived from MIL-125 (Ti-MOFs) for photo-thermal CO2 methanation. The nanoparticle sizes and electron densities of metallic Ni, defects and chemical properties, photo-thermal and photo-electric characteristics of the catalysts have been systematically characterized by XRD, TEM, CO2/H2-TPD, XPS, photoluminescence and photocurrent. For the Ni-TiO2, the conversion of CO2 was 56 % under the full spectrum irradiation (1200 mW/cm2) at 325 °C, which was about 1.8 times of that without light irradiation. The selectivity of methane nearly 99 % with a production rate was 95.7 mmol/(gcat∙h), which was about 2.7 times of that without light irradiation. Meanwhile, the catalysts showed excellent stability without any activity decay during the four cycles testing (32 h). The main reasons for the high catalytic performance for photo-thermal CO2 methanation were attributed to the uniform distribution of Ni NPs with synergistic effect of large specific surface area of TiO2 with abundant moderate strength alkaline sites. In addition, good photo-thermal and photo-electric conversion ability make the catalysts possess more photo-generated charge carriers and reduce its recombination.

Interfacial Coupling of Graphene with Nickel Nanoparticles for Water Splitting and Urea Oxidation: A Spectroelectrochemical Investigation.

Nickel nanoparticle and graphene interfaces of various stoichiometries were created through electrodeposition techniques. The catalytic behavior of the electrodeposited films was investigated through spectro-electrochemical methodologies. UV-vis absorbance spectra of the electrodeposited films are significantly different in the air and alkaline medium. Furthermore, UV-vis and Raman spectroscopy confirmed the coupling of Ni nanoparticles (Ni-NP) with the graphene framework, along with NiO and Ni(OH)2 . A combination of Raman and impedance spectroscopy revealed that the surface adsorption and charge transfer properties of the electrodeposited films are entirely dependent on the defects on graphene structure as well as distribution of Ni-NP on graphene. The electrodeposited films possess heterogeneous catalytic properties with a low overpotential of 50 mV (10 mA/cm-2 ) for hydrogen evolution reaction, as well as 601 mV and 391 mV (at 50 mA/cm-2 ) for the oxygen evolution reaction and urea oxidation reaction, respectively. In addition, eelectrodeposited samples show extraordinary overall water splitting performance by achieving a current density of 10 mA/cm2 at a very low applied potential of 1.38 V. This synergistic coupling of Ni and graphene renders the electrodeposited samples promising candidates as electrodes for overall water splitting in alkaline and urea-supplemented solutions.

Hydrogen storage in Nickel dispersed boron doped reduced graphene oxide

Graphene oxide (GO) based derivatives have been explored for hydrogen storage application, owing to their high surface area, low density and tunable pore size. However, under ambient conditions as desired for transport application, their storage capacity is poor. The use of nanohybrids of graphene oxide decorated with catalyst nanoparticles is emerging as a promising strategy to store atomic forms of hydrogen by invoking the spillover mechanism (in addition to storing molecular forms of hydrogen). Also, doping the substrate (GO) with light heteroatoms such as boron (B) have been envisaged for improving the enthalpy of adsorption of molecular hydrogen on the substrate. In the current work, GO based hybrids namely boron doped reduced graphene oxide (B-rGO) and Ni nanoparticle dispersed B-rGO (Ni-B-rGO) has been synthesized via freeze drying and hydrothermal route. The presence of various phases in the samples was identified using X-ray diffraction. Field-emission scanning electron microscopy was used to study the morphology; especially the 'wrinkling' in the GO based structures. The size and distribution of Ni nanoparticles was studied using transmission electron microscopy (size ∼1–2 nm and inter-particle distance of ∼20 nm). Raman spectroscopy was used to quantify the degree of disorder in the samples and additionally to demonstrate the existence of adsorbed molecular hydrogen. Fourier transform infrared spectroscopy studies showed the presence of various functional groups on carbon and further revealed the presence of atomic hydrogen generated by the spillover mechanism. X-ray photoelectron spectroscopy studies augmented the investigations to show the surface composition of Ni-B-rGO sample. The samples were further characterized for their hydrogen storage capacity using Sieverts apparatus (pressure-composition-isotherms) at three temperatures (77 K, 273 K and 298 K) and 20 bar H2 pressure. The B-rGO sample, showed promising storage capacity of ∼0.24 wt.% at 298 K, which increased to ∼0.58 wt.% at 273 K; which further increased to 8.2 wt.% at 77 K. The storage capacity of the Ni-B-rGO hybrid at the three temperatures (77 K, 273 K and 298 K) are: ∼6.9 wt.%, ∼0.41 wt.% and 0.16 wt.%, respectively.

Synthesis of biomimetic monolithic biochar-based catalysts for catalytic decomposition of biomass pyrolysis tar

Catalytic reforming of tar is an urgent technique for fuel gas production from biomass. In this paper, using monolith pinewood as the raw material, biomimetic monolithic biochar-based catalysts with the inherited 3D porous structure were prepared via simple impregnation and carbonization to explore their catalytic performance on biomass pyrolysis tar decomposition. Regular flow-through channels (20–50 μm) were achieved in the axial direction of the catalysts with irregular pores in the cross direction. High-density and well-dispersed Ni0 nanoparticles were formed and encapsulated on the wall of channels by in-situ reactions during biomass carbonization. The channels ensured the quick passing through of the gas flow and thus the diffusion steps could be effectively reduced, thereby reducing the coke deposition and aggregation of Ni particles. Based on their unique structure, the catalysts exhibited high activity and good stability for the biomass tar decomposition. At 800 °C, the catalyst (PC@0.3Ni) reached a high tar conversion of over 92% with excellent stability during five consecutive tests, leading to a higher yield of the product gas, especially the yields of H2 and CO. The distribution of Ni nanoparticles on the spent PC@0.3Ni was almost the same as the fresh catalyst with a similar particle size range.

Self-supported bifunctional electrocatalysts with Ni nanoparticles encapsulated in vertical N-doped carbon nanotube for efficient overall water splitting

To satisfy the practical requirements of electrochemical water splitting, developing a flexible, effective and sustainable approach for scalable production of bifunctional electrocatalyst for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a tremendous issue to be rationally addressed. Herein, a solid-state diffusion strategy with Ni foam and N-doped carbon layers is applied to prepare multi-interfacial, self-supported and N-doped carbon nanotube (NCNT) encapsulated Ni nanoparticles (NPs) array bifunctional electrocatalyst (NCNT-NP@NF). Prominently, this NCNT-NP@NF is scalable to meet the application requirements and can be used as a binder-free electrode for direct the water splitting. The optimal sample demonstrate outstanding HER/OER performance in 1.0 M KOH, with low overpotential (η10) at 10 mA cm−2 during HER (96.1 mV) and OER (240 mV) process, which is extremely superior to the most reported metal-based electrocatalysts and even better than commercial IrO2 (400 mV at 10 mA cm−2 for OER). Strikingly, when these bifunctional electrocatalysts are employed in a dual-electrode electrolyzer for water splitting, the NCNT-NP@NF only needs cell voltage of 1.54 V to drive overall water splitting in 1.0 M KOH, and displays excellent long-term stability (150 h for water splitting). Moreover, experiments combined with density functional theory (DFT) calculations clarify that the remarkable electrochemical activity and stability are mainly attribute to the synergistic effect of the uniform distribution of Ni NPs, heteroatomic doping, as well as district confinement effect of NCNT leading to enhanced electronic multi-interfacial transmission, all these factors co-accelerate electrocatalytic kinetics. Accordingly, this solid-state diffusion method possesses a favorable potential to construct a multi-interfacial and self-supported electrocatalysts in the fields of sustainable supply of clean energies.

Effect of Size and Distribution of Ni Nanoparticles on γ-Al2O3 in Oleic Acid Hydrodeoxygenation to Produce n-Alkanes

To contribute to the search for an oxygen-free biodiesel from vegetable oil, a process based in the oleic acid hydrodeoxygenation over Ni/γ-Al2O3 catalysts was performed. In this work different wt % of Ni nanoparticles were prepared by wetness impregnation and tested as catalytic phases. Oleic acid was used as a model molecule for biodiesel production due to its high proportion in vegetable oils used in food and agro-industrial processes. A theoretical model to optimize yield of n-C17 was developed using size, distribution, and wt % of Ni nanoparticles (NPs) as additional factors besides operational conditions such as temperature and reaction time. These mathematical models related to response surfaces plots predict a higher yield of n-C17 when physical parameters of Ni NPs are suitable. It can be of particular interest that the model components have a high interaction with operation conditions for the n-C17 yields, with the size, distribution, and wt % of Ni NPs being the most significant. A combination of these factors statistically pointed out those conditions that create a maximum yield of alkanes; these proved to be affordable for producing biodiesel from this catalytic environmental process.

Novel route to control the size, distribution and location of Ni nanoparticles in mesoporous silica for steam reforming of propylene glycol in microchannel reactor

Highly dispersed and size controlled Ni nanoparticles (NPs) in SBA-15 were synthesized by thermolysis of sucrose as a new delivery conveyor and sacrificial template. The Ni/SBA-15 catalysts were characterized systematically to elucidate their morphological structure and surface properties. It was found that the sucrose contributes majorly to control the size and higher distribution of Ni NPs by prevents their sintering into mesoporous nanochannels. The catalytic performance of Ni/SBA-15 catalysts was investigated by steam reforming of propylene glycol in microchannel reactor. As compared with conventional Ni-impregnated catalyst, the catalyst prepared with sucrose assisted route improves the coking and sintering resistance in steam reforming reaction of propylene glycol.

Synthesis Route towards Fine and Monodisperse Ni Nanoparticles via Hot-Injection Approach

Manipulation of adding sequences have been found to influence the reaction rate, thus made it easier to produced controllable Ni nanoparticles. Hot-injection approach shown capability to significantly reduce the production time of Ni nanoparticles compared to the conventional one-pot synthesis. With minor modification on conventional polyol method, narrow, monodispersed and highly yield spherical nickel (Ni) nanoparticles were successfully produced at synthesis temperature of 60°C. Three mixing methods were investigated to study its efficiency towards producing rapid and narrower size distribution of Ni nanoparticles. Reduction processes were proposed each of the method. As-synthesized Ni nanoparticles were characterized with Transmission Electron Microscopy (TEM), Scanning Transmission Electron Microscopy (STEM) and Fourier transform infrared spectroscopy (FTIR) to analyze the size, morphology and interaction of reactants. Fine particles size distribution revealed that when hydrazine was first heated, reaction rate improved tremendously.

Back Cover: Importance of Size and Distribution of Ni Nanoparticles for the Hydrodeoxygenation of Microalgae Oil (Chem. Eur. J. 30/2013)

Back Cover: Importance of Size and Distribution of Ni Nanoparticles for the Hydrodeoxygenation of Microalgae Oil (Chem. Eur. J. 30/2013)

Magnetic Properties of Self-Assembled Ni Nanoparticles in Two Dimensional Structures

A pulsed laser deposition technique has been used to synthesize a uniform distribution of Ni nanoparticles of controllable size in Al2O3 thin film matrix. The ability to control particle size in confined layers provides a very convenient means to tune the magnetic properties from superparamagnetic to ferromagnetic. The coercivity of these particles was measured at various temperatures as a function of particle size. The results indicate that the magnetic transition from single- to multi-domain region occurs at a larger particle size at higher temperature than at lower temperature. Stronger magnetic interaction among particles at lower temperatures is believed to lead to the formation of smaller sized domains for any given particle size in order to minimize the interaction energy.

Magnetic resonance study of Ni nanoparticles in single-walled carbon nanotube bundles

We present a detailed study of the electron magnetic resonance (EMR) properties of Ni nanoparticles (NPs) placed in the bundles of single-walled carbon nanotubes produced by arc discharge with Ni catalyst. The behavior of EMR signals has been investigated in the 10–300K temperature range for the initial powderlike materials and those diluted in a nonmagnetic matrix. The magnetic response evolves between two modes, ferromagnetic and superparamagnetic, depending on both the temperature and distribution of Ni nanoparticles in the sample. The behavior of EMR spectra shows that the initial materials retain the ferromagnetic character of the NP ensemble even at room temperature. This is most likely due to dipole-dipole interactions and macroscopic demagnetizing fields stemming from powderlike composition of the samples. For the diluted materials, the actual superparamagnetic signal is observed at room temperature. As temperature is reduced, the behavior of the EMR parameters reflects a gradual transition from free rotated magnetic moments of NPs to those ordered along the “easy” magnetic axes (blocked state). In the 300–130K temperature range, anomalous temperature dependence of the resonance magnetic field Hres was observed. It is examined in terms of competition between the single-particle anisotropy energy and dipole interactions between the Ni nanoparticles. Finally, a transition to a blocked state occurs at blocking temperature estimated as Tb≈40K. At lower temperatures, both the dense and diluted samples behave identically.