Yttria promoted metallic nickel catalysts for the partial oxidation of methane to synthesis gas

A metallic Ni catalyst was prepared with nickel sponge, followed by acid treatment. It was further promoted with yttria by an impregnation method. The catalysts were characterized by SEM, BET, XRD, TPR, XPS, etc., and studied in the partial oxidation of methane to syngas. The characterization results showed that the yttria promoted metallic Ni catalysts had high specific surface area and more NiO. The reaction results showed that the yttria promoter increased the CH4 conversion and the selectivity for H2 and CO.

Effects of specific surface area of metallic nickel particles on carbon deposition kinetics

Carbon deposition on nickel powders in methane involves three stages in different reaction temperature ranges. Temperature programing oxidation test and Raman spectrum results indicated the formation of complex and ordered carbon structures at high deposition temperatures. The values of I（D）/I（G） of the deposited carbon reached 1.86, 1.30, and 1.22 in the first, second, and third stages, respectively. The structure of carbon in the second stage was similar to that in the third stage. Carbon deposited in the first stage rarely contained homogeneous pyrolytic deposit layers. A kinetic model was developed to analyze the carbon deposition behavior in the first stage. The rate-determining step of the first stage is supposed to be interfacial reaction. Based on the investigation of carbon deposition kinetics on nickel powders from different resources, carbon deposition rate is suggested to have a linear relation with the square of specific surface area of nickel particles.

Electro-oxidation of Ni(Ⅱ)-citrate complexes at BDD electrode and simultaneous recovery of metallic nickel by electrodeposition

The simultaneous electro-oxidation of Ni(Ⅱ)-citrate and electrodeposition recovery of nickel metal were attempted in a combined electro-oxidation-electrodeposition reactor with a boron-doped diamond(BDD)anode and a polished titanium cathode.Effects of initial nickel citrate concentration,current density,initial p H,electrode spacing,electrolyte type,and initial electrolyte dosage on electrochemical performance were examined.The efficiencies of Ni(Ⅱ)-citrate removal and nickel metal recovery were determined to be 100%and over 72%,respectively,under the optimized conditions(10 m A/cm^(2),pH 4.09,80 mmol/L Na_(2)SO_(4),initial Ni(Ⅱ)-citrate concentration of 75 mg/L,electrode spacing of 1 cm,and 180 min of electrolysis).Energy consumption increased with increased current density,and the energy consumption was 0.032 kWh/L at a current density of 10 m A/cm^(2)(pH 6.58).The deposits at the cathode were characterized by scanning electron microscopy(SEM),energy-dispersive spectrometry(EDS),X-ray diffraction(XRD),and X-ray photoelectron spectroscopy(XPS).These characterization results indicated that the purity of metallic nickel in cathodic deposition was over 95%.The electrochemical system exhibited a prospective approach to oxidize metal complexes and recover metallic nickel.

Partial oxidation of methane to syngas catalyzed by a nickel nanowire catalyst

A nickel nanowire catalyst was prepared by a hard template method, and characterized by transmission electron microscopy （TEM）, N2 physical adsorption, X-ray photoelectron spectrometry （XPS）, X-ray diffraction （XRD） and H2 temperature-programmed reduction （H2-TPR）. The catalytic properties of the nanowire catalyst in the partial oxidation of methane to syngas were compared with a metallic Ni catalyst which was prepared with nickel sponge. The characterization results showed that the nickel nanowire catalyst had high specific surface area and there was more NiO phase in the nickel nanowire catalyst than in the metallic Ni catalyst. The reaction results showed that the nickel nanowire catalyst had high CH4 conversion and selectivities for H2 and CO under low space velocity.

The electrochemical characteristics of AB_(4)-type rare earth-Mg-Ni-based superlattice structure hydrogen storage alloys for nickel metal hydride battery

Rare earth-Mg-Ni-based alloys with superlattice structures are new generation negative electrode materials for the nickel metal hydride batteries.Among them,the novel AB_(4)-type superlattice structure alloy is supposed to have superior cycling stability and rate capability.Yet its preparation is hindered by the crucial requirement of temperature and the special composition which is close to the other superlattice structure.Here,we prepare rare earth-Mg-Ni-based alloy and study the phase transformation of alloys to make clear the formation of AB_(4)-type phase.It is found Pr_(5)Co_(19)-type phase is converted from Ce_(5)Co_(19)-type phase and shows good stability at higher temperature compared to the Ce_(5)Co_(19)-type phase in the range of 930-970℃.Afterwards,with further 5℃increasing,AB_(4)-type superlattice structure forms at a temperature of 975℃by consuming Pr_(5)Co_(19)-type phase.In contrast with A_(5)B_(19)-type alloy,AB_(4)-type alloy has superior rate capability owing to the dominant advantages of charge transfer and hydrogen diffusion.Besides,AB_(4)-type alloy shows long lifespan whose capacity retention rates are 89.2%at the 100;cycle and 82.8%at the 200;cycle,respectively.AB_(4)-type alloy delivers 1.53 wt.%hydrogen storage capacity at room temperature and exhibits higher plateau pressure than Pr_(5)Co_(19)-type alloy.The work provides novel AB_(4)-type alloy with preferable electrochemical performance as negative electrode material to inspire the development of nickel metal hydride batteries.

Effect of Overcharge on Electrochemical Performance of Sealed-Type Nickel/Metal Hydride Batteries

The effects of overcharge on electrochemical performance of AA size sealed-type nickel/metal hydride（Ni/MH） batteries and its degradation mechanism were investigated. The results indicated that the relationship between the effects of different overcharge currents on the increasing velocity of inner pressure and the degradation velocity of cycle life and discharge voltage remains in almost direct proportion. After overcharge cycles, the positive electrode materials remain the original structure, but there occur some breaks because of the irreversible expand of crystal lattice. And the negative electrode alloy particles have inconspicuous pulverization, but are covered with lots of corrosive products and its main component is rare earth hydroxide or oxide. These are all the main reasons leading to the degradation behavior of the discharge capacity and cycle life of Ni/MH batteries.

Fabrication of independent nickel microstructures with anodizing of aluminum, laser irradiation, and electrodeposition

Independent microstructures made of Ni metal were fabricated by fivesequential processes: porous anodic oxide film formation, pore sealing, laser irradiation, Nielectroplating, and removal of the aluminum substrate and anodic oxide films. Aluminum plates androds were anodized in an oxalic acid solution to form porous type anodic oxide films, and thenimmersed in boiling distilled water for pore sealing. The anodized and pore-sealed specimens wereirradiated with a pulsed neodymium-doped yttrium aluminum garnet (Nd-YAG) laser beam in a Ni platingsolution to remove anodic oxide film locally by rotating and moving up I down with anXYZ(theta)-stage. Nickel was deposited at the area where film had been removed by cathodicpolarization in the solution before removing the aluminum substrate and anodic oxide films in NaOHsolutions. Cylindrical or plain network structures were fabricated successfully.

NOTCH WEAR OF MACHINING NICKEL BASED ALLOYS WITH CERAMIC TOOLS

The performances of mixed ceramic and sialon ceramic tools in machining nickel based alloy are tested.The negative cutting edge inclination and small tool lead angle are recommended for reducing ceramic tool failure. So called“notching at depth of cut”is not actually at the depth of cutting line, but out of cutting area。 The real reason of notching is caused by shocking of “sawtooth”on sawtooth- shaped burr and fin- shaped edges of chip

Improving sulfur transformation of lean electrolyte lithium-sulfur battery using nickel nanoparticles encapsulated in N-doped carbon nanotubes

Efficient redox reactions of lean electrolyte lithium-sulfur(Li-S)batteries highly rely on rational catalyst design.Herein,we report an electrocatalyst based on N-doped carbon nanotubes(CNT)-encapsulated Ni nanoparticles(Ni@NCNT)as kinetics regulators for Li-S batteries to propel the polysulfide-involving multiphase transformation.Moreover,such a CNT-encapsulation strategy greatly prevents the aggregation of Ni nanoparticles and enables the extraordinary structural stability of the hybrid electrocatalyst,which guarantees its persistent catalytic activity on sulfur redox reactions.When used as a modified layer on a commercial separator,the Ni@NCNT interlayer contributes to stabilizing S cathode and Li anode by significantly retarding the shuttle effect.The corresponding batteries with a 3.5 mg cm^(−2)sulfur loading achieve the promising cycle stability with~85%capacity retention at the electrolyte/sulfur ratios of 5 and 3μL mg^(−1).Even at a high loading of 12.2 mg cm^(−2),the battery affords an areal capacity of 7.5 mA h cm^(−2).

Improved electrochemical hydrogen storage properties of Mg-Y thin films as a function of substrate temperature

Pd-capped Mg78Y22 thin films have been prepared by direct current magnetron co-sputtering system at different substrate temperatures and their electrochemical hydrogen storage properties have been investigated.It is found that rising substrate temperature to 60 ℃ can coarsen the surface of thin film,thus facilitating the diffusion of hydrogen atoms and then enhancing its discharge capacity to 1725 mAh·g-1.Simultaneously,the cyclic stability is effectively improved due to the increased adhesion force between film and substrate as a function of temperature.In addition,the specimen exhibits a very long and flat discharge plateau at about —0.67 V,at which nearly 60%of capacity is maintained.The property is favorable for the application in metal hydride/nickel secondary batteries.The results indicate that rising optimal substrate temperature has a beneficial effect on the electrochemical hydrogen storage of Mg-Y thin films.

ELECTRODE CHARACTERISTICS OF NANOCRYSTALLINE LaNi_5 PREPARED BY MECHANICAL ALLOYING

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Effects of Annealing Temperature on Microstructure and Electrochemical Properties of Perovskite-type Oxide LaFeO3 as Negative Electrode for Metal Hydride/Nickel（MH/Ni） Batteries

We reported the effects of annealing temperatures on microstructure and electrochemical properties of perovskite-type oxide LaFeO3 prepared by stearic acid combustion method. X-Ray diffraction（XRD） patterns show that the annealed LaFeO3 powder has orthorhombic structure. Scanning electron microscopy（SEM） and transmission electron microscopy（TEM） images show the presence of homogeneously dispersed, less aggregated, and small crystals（30--40 nm） at annealing temperatures of 500 and 600 ℃. However, as the annealing temperature was increased to 700 and 800 ℃, the crystals began to combine with each other and grew into further larger crystals（90--100 nm）. The electrochemical performance of the annealed oxides was measured at 60 ℃ using chronopotentiometry, potentiodynamic polarization, and cyclic voltammetry. As the annealing temperature increased, the discharge capacity and anti-corrosion ability of the oxide electrode first increased and then decreased, reaching the optimum values at 600 ℃, with a maximum discharge capacity of 563 mA-h/g. The better electrochemical performance of LaFeO3 annealed at 600℃ could be ascribed to their smaller and more homogeneous crysals.

Superior electrochemical performance of La-Mg-Ni-based alloys with novel A_(2)B_(7)-A_(7)B_(23) biphase superlattice structure

Nickel metal hydride(Ni-MH) rechargeable batteries hold an important position in the new-energy vehicle market owing to their key technology advantages. Their negative electrode materials—hydrogen storage alloys(HSAs) are always on the spotlight and are the key to compete with the burgeoning Li-ion batteries. Here, for the first time we report a series of biphase supperlattice HSAs with a(La,Mg)_(2)Ni_7 matrix phase and a novel(La,Mg)_(7)Ni_(23) secondary phase. The biphase alloys show discharge capacities of402–413 m Ahg^(-1) compared with 376–397 mAhg^(-1) of the other multi-or single-phase alloys. These values are among the highest for superlattice HSAs. In addition, the alloy with 15.4 wt.%(La,Mg)_(7)Ni_(23) phase exhibits good high rate dischargeability due to the proper compromise between the amount of crystal boundaries and equilibrium plateau voltage. The cycling stability of the biphase alloys is lower than that of the single-phase alloy but is till higher than the multiphase alloy. The novel superlattice biphase alloys with superior overall electrochemical properties are expected to inspire further design and development of HSAs as advanced electrode materials for power batteries.

Wide gap active brazing of ceramic-to-metal-joints for high temperature applications

Applications like solid oxide fuel cells and sensors increasingly demand the possibility to braze ceramics to metals with a good resistance to high temperatures and oxidative atmospheres. Commonly used silver based active filler metals cannot fulfill these requirements, if application temperatures higher than 600℃ occur. Au and Pd based active fillers are too expensive for many fields of use. As one possible solution nickel based active fillers were developed. Due to the high brazing temperatures and the low ductility of nickel based filler metals, the modification of standard nickel based filler metals were necessary to meet the requirements of above mentioned applications. To reduce thermally induced stresses wide brazing gaps and the addition of A1203 and WC particles to the filler metal were applied. In this study, the microstructure of the brazed joints and the thermo-chemical reactions between filler metal, active elements and WC particles were analyzed to understand the mechanism of the so called wide gap active brazing process. With regard to the behavior in typical application oxidation and thermal cycle tests were conducted as well as tensile tests.