Mingmei Zhang

Synthetic core–shell Ni@Pd nanoparticles supported on graphene and used as an advanced nanoelectrocatalyst for methanol oxidation

In this study, the uniform dispersion of new highly active Ni@Pd core–shell nanoparticle catalysts supported on graphene (Ni@Pd/graphene) was prepared via a two-step procedure involving a microwave synthesis method and a replacement method. Several characterization tools, such as X-ray powder diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) were employed to study the phase structures, morphologies and properties of the Ni@Pd/graphene composite. The results indicated that a uniform dispersion of Ni@Pd core–shell structure nanoparticles on graphene have an average particle size of 4 nm. The Ni@Pd/graphene composite was used as an electrocatalyst for alcohol oxidation in alkaline media for fuel cells. The electrocatalytic activity of Ni@Pd/graphene for ethanol oxidation is 3 times higher than that of the Pd/graphene electrocatalyst at the same Pd loading. The enhanced electrocatalytic properties could be attributed not only to the electric synergistic effect between Pd, Ni and graphene, but also the high use ratio of Pd due to its shell structure.

Nickel core–palladium shell nanoparticles grown on nitrogen-doped graphene with enhanced electrocatalytic performance for ethanol oxidation

Herein, we report a facile two-step strategy for green synthesis of nickel core–palladium shell nanoclusters on nitrogen-doped graphene (Ni@Pd/NG) without any surfactant and additional reducing agent. During the synthesis, nitrogen-doped graphene acted as both the active substance and support by taking advantage of its moderate reducing and highly dispersing capacities. Characterization indicated that a uniform dispersion of Ni@Pd nanoparticles on nitrogen-doped reduced graphene oxide had a 2.8 nm average particle size. Unexpectedly, the as-prepared Ni@Pd/NG hybrid exhibited much greater activity and stability than that of Pd/graphene and commercial Pd/C electrocatalyst at the same Pd loadings. Possible mechanisms for the enhanced electrocatalytic performance of nitrogen-doped reduced graphene oxide after combining with Ni@Pd are proposed. The present study provides an efficient strategy to synthesize highly efficient electrocatalysts.

Ultrafine Co3O4 embedded in nitrogen-doped graphene with synergistic effect and high stability for supercapacitors

Co3O4 embedded in nitrogen-doped graphene (Co3O4/N-G-750) is prepared by a two-step synthetic method: polyol microwave heating method and vacuum tube calcination method. The diameter from 2 nm to 4 nm of the Co3O4 particles can be easily controlled on a nitrogen-doped graphene surface by adjusting the experimental parameters. The electrochemical characteristics of Co3O4/N-G-750 composite have been characterized by cyclic voltammetry (CV) and galvanostatic charge–discharge measurements (GCD) in KOH 6 M electrolyte. The specific capacitance of the electrode modified as-prepared composite exhibited a high specific capacitance of 1288.2 F g−1 at a high discharge current of 1.5 A g−1, as well as excellent cycling stability (91.5% capacitance retention after 5000 cycles). This result indicates Co3O4/N-GO-750 will be an excellent candidate for supercapacitor applications.

Ni/MWCNT-Supported Palladium Nanoparticles as Magnetic Catalysts for Selective Oxidation of Benzyl Alcohol

Well dispersed Pd@Ni bimetallic nanoparticles on multi-walled carbon nanotubes (Pd@Ni/MWCNT) are prepared and used as catalysts for the oxidation of benzyl alcohol. Scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy analysis, and X-ray diffraction were performed to characterise the synthesised catalyst. The results show a uniform dispersion of Pd@Ni nanoparticles on MWCNT with an average particle size of 4.0 nm. The as synthesised catalyst was applied to the oxidation of benzyl alcohol. A 99 % conversion of benzyl alcohol and a 98 % selectivity of benzaldehyde were achieved by using the Pd@Ni/MWCNT (Pd: 0.2 mmol) catalyst with water as a solvent and H2O2 as oxidant at 80°C. The catalytic activity of Pd@Ni/MWCNT towards benzyl alcohol is higher than that of a Pd/MWCNT catalyst at the same Pd loadings. The catalyst can be easily separated due to its magnetic properties.

Formation of cobalt silicide nanoparticles on graphene with a synergistic effect and high stability for ethanol oxidation

Stable cobalt silicide (CoSi) with an average diameter of less than 4 nm is uniformly decorated with graphene by a chemical vapor deposition method. Palladium (Pd) is then supported on the CoSi–G composite (Pd/CoSi–G) using an intermittent microwave heating reduction method and this composite is used as an electrocatalyst for ethanol oxidation in alkaline media. The Pd/CoSi–G catalyst exhibits 1.8 and 4.3 times the peak current density compared with Pd loaded on graphene and Vulcan XC-72 carbon, respectively. The significant increase in catalytic activity can be contributed to CoSi benefitting the formation of smaller and highly dispersed Pd particles and the synergistic effect between CoSi and Pd. The novel multi-effects of Pd on CoSi make Pd/CoSi–G a highly active, durable and low-cost fuel cell electrocatalyst candidate.

Angstrom-scale vanadium carbide rods as Pt electrocatalyst support for efficient methanol oxidation reaction

Angstrom-scale vanadium carbide rods combined with carbon (denoted as C–V8C7 (rods)) are synthesized through an ion-exchange route. The angstrom-scale C–V8C7 (rods) show better promotion effect on Pt than the nanoscale C–V8C7 (particles) towards methanol oxidation reaction (MOR). Furthermore, Pt particle loading on C–V8C7 (rods) (denoted as Pt/C–V8C7 (rods)) show much higher MOR activity and stability than commercial Pt/C electrocatalyst. The present method is imagined to be adopted to easily synthesize other angstrom-scale materials.

Preparation and Characterization of Nickel(Ni)-Silver(Ag) Core-Shell Nanoparticles for Conductive Pastes

Nickel(Ni)-silver(Ag) core-shell nanoparticles with different shell thickness were synthesized with Ni nanoparticles by liquid phase reduction technique form water solution. The product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and inductively coupled plasma spectroscopy (ICP). The results showed that the Ni nanoparticles are in sphere shape and the average diameter is 104nm , the nickel(Ni)-silver(Ag) core-shell nanoparticles has good crystallinity and the thinkness of Ag nanoshells could be effectively controlled by changing the concentration of silver nitrate. The product can be used for nickel-based conductive paste preparation because of the surface character of Ag and the magnetic property of Ni

Preparation of nickel–silver core–shell nanoparticles by liquid-phase reduction for use in conductive paste

Nickel–silver (Ni–Ag) core–shell nanoparticles (NPs) were prepared by depositing Ag on Ni nanocores using the liquid-phase reduction technique in aqueous solution, and their properties were characterised using various experimental techniques. The core–shell NPs had good crystallinity, and the thicknesses of the Ag nanoshells could be tuned effectively. The oxidation resistance of the Ag surface and the electroconductive properties of the Ni core allowed these Ni–Ag core–shell NPs to be used in a conductive paste. Thick films composed of Ni–Ag core–shell NPs were screen-printed on a polycrystalline silicon substrate then sintered at temperatures ranging from 500 °C to 800 °C. Stable resistivity was obtained when the sintering temperature was higher than 650 °C, and the electrical properties of the Ni–Ag core–shell paste were close to those of pure Ag paste. Thus, the Ni–Ag NPs can partly replace pure Ag NPs in conductive pastes.

Synthesis of Ni@MWCNTs Magnetic Nanocatalysts and their Catalytic Activity towards 4-Nitrophenol Reduction

A well-dispersed Ni nanoparticles on multi-walled carbon nanotubes (Ni@MWCNTs) was prepared by chemical vapor deposition (CVD) method using a vacuum quartz tube furnace at the temperature of 600°C. The scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) were performed to characterize the synthesized catalyst. It shows an unfirom dispersion of Ni nanoparticles on MWCNTs with the average particle size of 8.6 nm. The as synthesized catalyst was applied in a redox reaction of 4-nitrophenol, which showed very high catalytic activity, stability and well conversion. The catalyst can be easily separated due to the magnetical performance

Facile Synthesis of Nicore - Agshell Bimetallic Nano Particles for Conductive Paste

Ni-Ag core-shell nano particles have been facilely prepared by redox-transmetalation reaction of silver ions on the surface of nickle nano particles. As characterized by transmission electron microscopy (TEM), the as-synthesized core-shell particles were mono-dispersed and exhibited a narrow size distribution ranging from 200nm to 300nm. XRD analyses indicated both Ni core and Ag shell had an fcc structure. Furthermore, the thickness of silver shell was controllable via changing the mole ratio of Ag to Ni, which could show benefits for potential applications in optical, catalytic and electronic fields.