Ultrafine Ni Nanoparticles Research Articles

MOFs-induced encapsulation of ultrafine Ni nanoparticles into 3D N-doped graphene-CNT frameworks as a recyclable catalyst for Cr(VI) reduction with formic acid

Recently, nitrogen-doped carbon encapsulating with transition metal hybrids has attracted extensive interests in catalysis because of its unique microstructure and promising properties. In this work, three dimensional N-doped graphene-CNT frameworks with well encapsulated ultrafine Ni nanoparticles (Ni@N-CNTs/N-G) were developed by a facile two-stage encapsulation strategy by combining Ni-MOFs with melamine as the precursor. In terms of Cr(VI) reduction by using formic acid (HCOOH) as the reductant, N-CNTs/N-G matrix not only protected the encapsulated Ni nanoparticles from poisoning or leaching in strong acid media, but also provided enhanced active sites for Cr(VI) by its rich mesopores and high N content. Among all the products obtained after thermal treatments at different temperatures, Ni@N-CNTs/N-G-800 (pyrolyzed at 800 °C) exhibited superb reduction performance with the efficiency of approximately 99.6%, ascribing to the synergistic effects including the porous 3D framework with large specific surface area, high N-doping level, and large amount of ultrafine Ni nanoparticles. More importantly, its catalytic activity and microstructure rarely changed after 10 times of recycling, suggesting that Ni@N-CNTs/N-G-800 processes excellent stability. This study provides a new strategy of synthesizing transition metal-based catalyst, which can broaden the applicability of MOF materials for heavy metal pollution cleanup.

3D‐Printed Graphene Oxide Framework with Thermal Shock Synthesized Nanoparticles for Li‐CO2 Batteries

AbstractLi‐CO2 batteries have emerged as a promising energy storage technology due to their high theoretical energy density. A thick electrode design is an effective approach for further increasing the energy density on device level by decreasing the weight and volume ratios of inactive materials. Exploring and designing novel thick electrodes with high catalytic activity toward reversible reaction between lithium and carbon dioxide are key challenges to achieve a low charge overpotential, long cycling stability, and high rate performance. Herein, an ultrathick electrode (≈0.4 mm) design for Li‐CO2 batteries by anchoring ultrafine Ni nanoparticles (≈5 nm) on a 3D‐printed reduced graphene oxide framework via thermal shock (1900 K for 54 ms) is demonstrated. The cathode displays low overpotential of 1.05 V at 100 mA g−1, high cycling stability of over 100 cycles, and good rate capability (up to 1000 mA g−1). In particular, a high areal capacity of 14.6 mA h cm−2 can be achieved due to the thick electrode design and uniform distribution of ultrafine catalyst nanoparticles. The strategy of combining an advanced 3D printing technique with fast thermal shock represents a promising direction toward thick electrode design in energy storage devices that are not limited to Li‐CO2 batteries.

In-situ synthesis of graphene decorated with nickel nanoparticles for fabricating reinforced 6061Al matrix composites

Graphene has attracted a lot of interest to be used as reinforcement in Aluminum matrix composites (AMCs) on account of its superior mechanical properties. However, the most serious and challenging issues in graphene-reinforced AMCs are that reinforcements are quite difficult to disperse uniformly in metal matrix and ensure intimate interfacial bonding simultaneously. In this work, an ultrafine Ni nanoparticles (NPs)-decorated graphene hybrid (indicated with Ni-NPs@GNP) was firstly synthesized by an in-situ chemical vapor deposition method to improve the wettability between metal and carbon nanophase, then the Ni-NPs@GNP/6061Al composite powders were obtained by dispersing the Ni-NPs@GNP into 6061Al alloy particles via a short time intermittent ball milling process. Finally, the Ni-NPs@GNP/6061Al bulk composites were fabricated through hot-pressing sintering of the composite powders. It was demonstrated that good dispersion of reinforcements was achieved in the Ni-NPs@GNP/6061Al composite coupled with remarkably enhanced interfacial bonding by introducing Ni NPs on the graphene, which resulted in the formation of Al3Ni intermetallic at the interface and thus improved the interfacial adhesion between 6061Al and graphene. As a result, the Ni-NPs@GNP/6061Al composite with 0.7wt% reinforcement exhibited much enhanced mechanical properties, namely, a high yield strength of 140MPa together with a tensile strength of 213MPa can be achieved, which were 75% and 30% higher than that of the monolithic 6061Al, respectively. This work provides an inspiring strategy for fabricating 6061Al composites with adjustable mechanical properties as well as controllable interfacial bonding.

Low-temperature hydrogen desorption from Mg(BH4)2 catalysed by ultrafine Ni nanoparticles in a mesoporous carbon matrix

Homogenously dispersed, ultrafine Ni nanoparticles (Ni NPs) have been grown in a mesoporous carbon (MC) matrix (MC-Niinsitu) and efficiently catalyze low-temperature hydrogen desorption from Mg(BH4)2. The onset desorption temperature (Tonset) of this MC-Niinsitu-Mg(BH4)2 system is 44 °C compared to 275 °C (Tonset) for pure Mg(BH4)2. This is the lowest value reported for hydrogen desorption from this metal hydride. The activation energy (Ea) of MC-Niinsitu-Mg(BH4)2 was determined to be 21.3 kJ/mol which is less than half the value of 45.9 kJ/mol for pure Mg(BH4)2. We ascribe this reduction to the synergistic effects of nanoconfinement and the homogeneously dispersed, ultrafine Ni NPs active sites in the mesoporous carbon.

Enhanced hydrogen generation by cocatalytic Ni and NiO nanoparticles loaded on graphene oxide sheets

Cocatalytic ultrafine Ni and NiO nanoparticles (2 to 3 nm diameter) were uniformly loaded on graphene oxide (GO) sheets using a simple chemical method. Water splitting activity from aqueous methanol solution under UV-Visible light illumination was enhanced, approximately 4-fold for NiO/GO and 7-fold for Ni/GO, compared to bare GO. The highest activity (shown by Ni/GO) is attributed to the minimal electron–hole recombination resulting from the easy transfer of photogenerated electrons from the GO photocatalyst to the Ni cocatalyst. The relatively lower activity of NiO/GO may be due to the less efficient electron trapping ability of the NiO surface. A mechanism for the hydrogen gas evolution is proposed. This work revealed that a cocatalyst loaded on high surface area GO sheets can significantly enhance the evolution of hydrogen from aqueous methanol solution. We believe that this study offers a route to green energy harvesting using readily available low cost materials in combination with simple, versatile and scalable techniques. It also encourages the utilization of new graphene based materials which are adaptable to a wide variety of applications in areas such as fuel cells, lithium ion batteries and sensors.

Research on nickel morphology of dependence on the microwave‐assisted polyol method

AbstractThe structures, morphology and magnetic properties of the ultrafine Ni nanoparticles prepared by microwave‐assisted polyol method was investigated, using X‐ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM), respectively. The XRD results suggested that Ni nanoparticles with an fcc structure were successfully synthesized. It was interesting to note that the Ni nanoparticles are ideally spherical, which were examined by the TEM. As immersed in different solutions, we can get different shape nickel particles with different conditions. Especially, the experimental results indicated that nanohair nickel particles were ferromagnetic.

Structure and magnetic properties of oxygen-stabilized tetragonal Ni nanoparticles prepared by borohydride reduction method

We report a comprehensive study on the structure and magnetic properties of ultrafine Ni nanoparticles prepared by the borohydride reduction method. A spontaneous surface oxide layer of NiO encapsulates the Ni particles, as these have been prepared under ambient atmosphere. From the x-ray diffraction (XRD) pattern, the ``as-prepared'' sample has been identified as Ni in a tetragonal crystal structure, stabilized by the incorporation of oxygen atoms in the Ni lattice. On annealing this sample in air at different temperatures, the XRD patterns showed an interesting feature: unexpected fcc Ni peaks appeared together with the usual NiO peaks. Anomalous behavior is also observed in the $M\text{\ensuremath{-}}H$ curves, with the as-prepared sample showing a linear response with field and low values of magnetization and the annealed samples showing ferromagnetism with large coercivity $(290\phantom{\rule{0.3em}{0ex}}\mathrm{Oe})$ and high magnetization values. These surprising and seemingly contradictory observations have been coherently explained on the basis of a proposed phenomenological model. Furthermore, we attribute the observed low magnetization values of the as-prepared sample to an antiferromagnetic superexchange interaction between some of the Ni atoms, mediated by the dissolved oxygen atoms in the Ni lattice.