Nickel Palladium Research Articles

Palladium–nickel nanoparticles loaded on multi-walled carbon nanotubes modified with β-cyclodextrin for electrooxidation of alcohols

β-Cyclodextrin (β-CD) was grafted to the surface of multi-walled carbon tubes (MWCNTs) immobilized on Ti plates to obtain the β-CD-MWCNT/Ti electrode by using the self-assembly method. Binary Pd–Ni nanoparticles were then electrodeposited on the β-CD-MWCNT/Ti to synthesize the PdNi/β-CD-MWCN/Ti electrode. As a comparison, PdNi/MWCNT/Ti and PdNi/Ti electrodes were also prepared under the same condition. SEM images show that compared to the PdNi/MWCNT/Ti and PdNi/Ti, the binary PdNi nanoparticles on the β-CD-MWCNT/Ti are more highly dispersed with smaller sizes of 90–130nm. Electrocatalytic activity of the as-synthesized electrodes towards electrooxidation of ethanol, propanol and butanol in alkaline media was investigated. Results show that the PdNi/β-CD-MWCNT/Ti electrode exhibits very high electroactivity for the alcohol oxidations and presents much enhanced performance compared with other two electrodes. Among the three alcohols, ethanol displays the greatest activity with the highest oxidation current density while butanol shows the lowest oxidation current density.

Synthesis of Ni–Pd nanocubes and nanorods with high selectivity through a modified polyol process

Shape controlled bimetallic nanoparticles are important for catalytic, electrocatalytic, optical, and magnetic applications. This effort describes the synthesis of monodisperse bimetallic nickel–palladium (Ni0.25Pd0.75) nanocubes and nanorods with a combined shape selectivity of over 85%. Composition of the synthesized nanoparticles was determined using STEM-EDX and XRD. The shape control was achieved through the use of poly-vinyl pyrrolidone (PVP) surfactant and solvated bromide ions in 1,5-propanediol under an inert argon atmosphere. The use of bromide ions facilitated the stabilization of (100) and (110) surface facets, yielding nanocubes and nanorods, respectively, while the polymeric capping agent prevented agglomeration. The influence of the bromide ions was verified by using TEM imaging to ascertain the shapes of the synthesized nanoparticles. The reduction temperature used in the synthesis (140°C to 180°C) and the bromide ion-to-metal precursor ratio (15:1 to 50:1) were varied to maximize the shape distribution towards nanocubes and nanorods and to regulate the nucleation and growth phases of the synthesis.

Electrooxidation of Formaldehyde Based on Nickel–Palladium Modified Ordered Mesoporous Silicon

Nickel and palladium nanoparticles were finely dispersed on ordered mesoporous silicon microchannels plate (MCP) by electroless plating. The structure and composition of the resulting Ni-Pd/Si MCP were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). The electrocatalystic properties of Ni-Pd/Si MCP electrode for formaldehyde oxidation have been investigated by cyclic voltammetry. The results show that Ni-Pd/Si MCP has a higher catalytic activity and better steady-state behavior for formaldehyde oxidation. This may be attributed to the synergistic property of high dispersion of Nickel and Palladium nanoparticles and particular properties of mesoporous Si MCP. The present study shows a promising choice of Ni-Pd nanoparticles supported by mesoporous silicon as effective electrocatalyst for formaldehyde electrooxidation in alkaline medium. The results imply that the Ni-Pd/Si MCP nanocomposite has good potential application in formaldehyde fuel cells and sensors.

Investigation of degradation mechanism of palladium–nickel wires during oxidation of ammonia

The process of oxidation of ammonia proceeds in 800–900°C with high reactivity hydrogen discharge. Extremely aggressive environment and temperature require using the most chemically resistant materials with catalysis properties. One of the main groups of those materials is palladium–nickel alloys. In our investigation we focused on analysis of PdNi5 degradation during catalysis process. The investigation was performed on 78μm diameter wires after long exposition to chemically aggressive environment. The samples were prepared with focused ion beam (FIB) system. The observations of surface and wire cross sections were executed using a scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) device, which allowed defining chemical composition. The effect of a grain orientation on sensitivity to reaction with ammonia gas was tested by mapping with electron backscatter diffraction (EBSD) techniques. Significant change of wire cross section after long exposition was determined by 3D X-ray computer tomography (XCT). The obtained results can be basis of further investigation on improvement of strength of PdNi alloys in high temperature chemical application.

Selective deposition of palladium onto supported nickel – bimetallic catalysts for the hydrogenation of crotonaldehyde

Alumina supported nickel palladium bimetallic catalysts were prepared by a selective redox deposition method and used for the hydrogenation of crotonaldehyde. Supported nickel catalysts, prepared by incipient wetness, were reduced to form a nickel hydride surface prior to contact with palladium(II) salt solutions. Palladium was successfully deposited selectively onto the nickel hydride surfaces, by a redox reaction. Catalysts were prepared using two different palladium(II) salt solutions; (a) pH 1 palladium chloride in hydrochloric acid solution or (b) pH 3 palladium nitrate in nitric acid. The deposition of palladium onto the supported nickel nanoparticles was strikingly different when using the two palladium solutions, with strong alloy formation with the pH 1 solution and a weaker segregated nickel palladium catalyst with the pH 3 solution. Both catalysts were compared with monometallic palladium and nickel supported catalysts for the hydrogenation of crotonaldehyde with the sample prepared at pH 1 being more active.

Palladium catalysts on porous nickel substrates for alcohol fuel cells

Parameters characterizing the active surface of catalytic palladium layers formed from mixed glycinate-chloride and ammonia complexes of palladium(II) were determined. Cyclic voltammetry on a rotating disc electrode was used to study the catalytic activity of nickel substrates and palladium layers in the reaction of methanol and ethanol oxidation in an alkaline medium. It was shown that electrodes with palladium deposited from mixed glycinate-chloride solutions have a higher catalytic activity that those formed from ammonia palladium(II) complexes.

Relationship between the reactions of hydrogen sorption/desorption and methanol oxidation on bifunctional Ni/Pd electrode in alkaline solution

The present paper is aimed at studying the influence of the hydrogen sorption/desorption process occurring on the layered nickel–palladium (Ni/Pd) electrode on the kinetics of the reaction of methanol oxidation in strong alkaline KOH solution. The electrodes were prepared by chemical deposition of a thin layer of porous palladium on a nickel foam support. A scanning electron microscope was used for studying the morphology of both the nickel support and the porous palladium layer. The mechanism of the anodic desorption of hydrogen changes depending on whether or not 6 M KOH electrolyte is admixed with methanol. It was shown that, in the first cycle of the cyclic voltammetry (CV) measurements, the anodic peak current and peak charge related to the oxidative desorption of hydrogen significantly decrease due to the presence of methanol in KOH. This effect is attributed to the obstacles in hydrogen sorption due to the formation of a passivating layer on the Pd surface composed of both adsorbed methanol molecules and the intermediate products involving adsorbed CO. On the other hand, hydrogen desorbing from Pd electrode exerts influence on the kinetics of the reaction of methanol oxidation. Ni/Pd electrode undergoes considerable reactivation due to the potentiostatic saturation with hydrogen at −1.1 V, followed by the ease in hydrogen desorption. The CV measurements proved that, after such a treatment, the peak of hydrogen desorption partially overlaps the double peak of methanol oxidation and, in consequence, the rate of methanol oxidation is enhanced. The positive effect of hydrogen releasing from the electrode on the kinetics of the reaction of methanol oxidation is ascribed to the anti-poison behavior consisting in the reaction of hydrogen radicals with intermediates adsorbed on the Pd surface.

Electrocatalytic hydrodehalogenation of 2,4-dichlorophenol in aqueous solution on palladium–nickel bimetallic electrode synthesized with surfactant assistance

Hydrodehalogenation (HDH) of 2,4-dichlorophenol (2,4-DCP) on a palladium–nickel (Pd–Ni) bimetallic electrode was investigated in this paper. The Pd–Ni bimetallic electrode was prepared on meshed titanium (Ti) substrate by electrochemical deposition with assistance of sodium dodecyl benzene sulfonate (SDBS). Cyclic voltammetry (CV) results revealed that the hydrogen adsorption peak current value of electrode became larger when SDBS was added in electrode preparation process. The structure and composition of the electrode were characterized by scanning electron microscopy (SEM), inductively coupled plasma-atomic emission spectrometry (ICP-AES) and X-ray diffraction (XRD). Dechlorination experiment was conducted on the Pd–Ni(SDBS)/Ti electrode in the presence of 100 mg L−1 (0.61 mmol L−1) 2,4-DCP. The removal efficiency of 2,4-DCP reached 100% with dechlorination current of 5 mA within 70 min in aqueous solution, meanwhile the current efficiency was 33.9%. The Pd–Ni(SDBS)/Ti electrode exhibits a good application prospect for electrocatalytic degradation of 2,4-DCP.

Fabrication, Characterization, and Evaluation of Excess Heat in Zirconium–Nickel–Palladium Alloys

Prior gas loading experiments of Zirconium–Nickel–Palladium alloys have been reported to generate a greater amount of heat with deuterium than with hydrogen. What is intriguing about these experiments was the long-term heat observed. Others, using commercial materials of similar composition, have been unable to observe long-term heat. We also have been unable to observe long-term heat in the commercial materials and materials prepared at NRL. Furthermore, when tested using our gas-loading protocol of measuring both the heat during pressurization and evacuation, these alloys do not show much, if any, excess heat and the majority of the heat observed can be attributed to chemistry.

Preparation and characterization of a novel nickel–palladium electrode supported by silicon nanowires for direct glucose fuel cell

Nickel–palladium and silicon nanowires (SiNWs) fabricated by chemical etching and electroless plating (EP) are evaluated as anodes in glucose fuel cells (FC). The effects of processing parameters and structural characteristics such as concentrations of KOH and glucose, medium temperature, and palladium electroless plating on the FC performance are determined. The nickel/silicon electrode exhibits significant activity even without the palladium catalyst and noticeable improvement is observed by incorporating SiNWs. The ordered channels in the SiNWs and coherence rendered by Ni–Pd are important to the enhanced electrode activity. The glucose oxidation current measured from the Ni–Pd/SiNWs electrode is approximately 4.8mA higher than that on the Ni–Pd/Si one. Our results reveal superior electrooxidation performance and long-term stability and Ni–Pd/SiNWs are useful glucose FC anodes in integrated fuel cell applications.

Analysis of electrochemical hydrogen absorption capacity for Pd-Ni nanoparticle incorporated MmNi5−XMX-based metal hydride

SUMMARY In this work are present the results obtained from the electrochemical characterization of a metal hydride type MmNi5−XMX impregnated with palladium, palladium–nickel and nickel nanoparticles as catalytic precursors for hydrogen absorption. The hydrogen absorption was investigated in the charge/discharge mechanism of a metal hydride via electrochemical process. The complete study involved the analysis of linear and anodic polarization, charge/discharge cycles, the application of an electrochemical model and electrochemical impedance spectroscopy to investigate the amount of hydrogen absorbed as a function of the catalytic precursors. The use of Pd nanoparticles showed the best results as catalytic precursor to absorb more hydrogen than other precursor systems. Copyright © 2011 John Wiley & Sons, Ltd.

Effects of nickel ion contents on electrodeposition, composition, structure and properties of palladium–nickel alloys

The effects of nickel ion contents on the electrodeposition, composition, structure and properties of palladium–nickel alloys were studied from a nearly neutral Pd(NH3)2Cl2–NiSO4.6H2O bath by adjusting the Ni2+/Pd2+ ion mole ratios. The results demonstrate that coatings with 17·1–44·0 wt-%Ni can be successfully electrodeposited by simply adjusting the Ni2+/Pd2+ ion mole ratios from 0·5∶1 to 2·5∶1. The coatings are bright, pore-free and crack-free with fine and compact grains. The structure of the coatings is a solid solution in a face-centred cubic structure; its lattice constant gradually decreases with a corresponding increase in the Ni content. The coatings exhibit a comparable corrosion resistance in a 3·5%NaCl solution, where the corrosion potentials Ecorr are between −0·010 and −0·064 V(saturated calomel electrode). Corrosion current densities jcorr slightly increased from 9·8 to 21·3 μA cm−2, with the Ni content increasing from 17·1 to 44·0 wt-%. The microhardness of the coatings increased with a corresponding increase in their Ni contents, and shows the highest value of 511 kg mm−2 with 44·0 wt-%Ni. The coatings exhibit comparable contact resistances of 0·2–0·4 mΩ.

High‐Sensitivity Hydrogen Detection: Hydrogen‐Induced Swelling of Multiple Cracked Palladium Films on Compliant Substrates

Hydrogen sponge: The reversible swelling of palladium–nickel alloys upon hydrogen absorption mechanically closes nanogaps in multiple cracked Pd–Ni films on elastomeric substrate allowing for the electric current to flow across (see picture). When the hydrogen is removed the elastomer elastically returns to its original state reopening numerous potential break junctions along each crack.

Bimetallic Ni/Pd finite systems: Structure and thermodynamics of bimetallic Ni/Pd nanostructures in two and three dimensions

By implementing replica-exchange Monte Carlo simulations within the multihistogram reweighting techniques, the structural and thermodynamic changes in bimetallic nickel–palladium nanostructured systems were studied as a function of composition. Specifically, two- and three-dimensional clusters composed of seven and thirteen atoms, respectively, were described using the embedded atom potential. The lowest energy equilibrium structures were determined, and associated to the degree of mixing in the material. In all cases, melting and order–disorder transitions were revealed by calculating the average constant volume heat capacity as a function of temperature. The change in Helmholtz free energy for the order–disorder transition was determined as a function of composition for each system.

Methanol and ethanol electrooxidation at 3D ordered silicon microchannel plates electrode modified with nickel–palladium nanoparticles in alkaline

The use of silicon microchannel plates (MCP) modified with nickel–palladium (Ni–Pd) nanoparticles by electroless plating was studied for the electrocatalytic oxidation of methanol and ethanol by cyclic voltammetry and chronoamperometry in alkaline media. The electrocatalyst was characterized by EDS, SEM and cyclic voltammetry, and the effective parameters on electrocatalytic oxidation of the alcohol, i.e. the concentration of KOH and alcohol, medium temperature and working potential limit in anodic direction were investigated. The modified electrode shows a superior electrooxidation performance with the operating temperature increasing and a strong current response to methanol and ethanol even during long-term oxidation of alcohol. All results show that the Ni–Pd/Si–MCP nanocomposite electrode is very attractive for integrated fuel cell applications.

An ultrasonic aerosol therapy nebulizer using electroformed palladium–nickel alloy nozzle plates

Aerosol therapy is a common treatment for traditional lung diseases, particularly asthma and chronic obstructive pulmonary disease (COPD), by using nebulizers as oral drug delivery systems. The nebulized drug droplets can be smaller than 4 μm in diameter and be efficiently absorbed by alveoli through inhalation. An ultrasonic nebulizer with a high frequent vibration through a nebulizer nozzle plate can nebulize large sized drug droplets into small sized drug droplets. Therefore, the dimension of the orifices of the nebulizer nozzle plate is crucial for an efficient aerosol therapy. An ultrasonic nebulizer comprises the palladium–nickel alloy made nozzle plate, a RLC high frequency driving circuit and a PZT transducer was developed and tested. The nozzle plate with 4-μm-diameter nozzle orifices used in this nebulizer is made of electroformed palladium–nickel alloy, which is biocompatible, corrosion resistant, and a stiff material. Using nebulizer spray testing, this study compares the characteristics of the nozzle orifice diameter compared to the nebulized liquid droplet size. The test results successfully demonstrated that the nozzle orifice diameter could affect the nebulized liquid droplet size. In addition, the nebulized liquid droplet size was 3 μm, while the nozzle orifice diameter was 5 μm.

Palladium–nickel alloys loaded on tungsten carbide as platinum-free anode electrocatalysts for polymer electrolyte membrane fuel cells

The strong interaction between PdNi alloys and WC makes PdNi/WC a novel Pt-free electrocatalyst for the anode hydrogen oxidation reaction of polymer electrolyte membrane fuel cells with activity and stability comparable to those of the conventional Pt/C catalysts.

Microstructure in a Ni 60Pd 20P 17B 3 bulk metallic glass compressively fractured at cryogenic temperature

In order to clarify relationship between plasticity and microstructure for a Ni 60Pd 20P 17B 3 bulk metallic glass (BMG) at cryogenic temperature, we investigated the microstructures of both the shear band and fracture surface for the BMG compressively fractured at room temperature (RT) and 77 K (liquid Nitrogen temperature) using transmission electron microscopy (TEM). HRTEM images from the BMG fractured at 77 K clearly reveal that there are nanocrystalline particles around both shear band and fracture surface, but not in undeformed region. The sizes of the particles fractured at 77 K are smaller than those fractured at RT. These particles ranged from 3 to 5 nm in size are thought to consist of an fcc palladium–nickel solid solution phase. The particles with smaller size and the ductile fcc phase may effectively restrain the propagation of shear bands, resulting in enhancement of plastic deformation at cryogenic temperature.

Electrodeposited PdNi 2 alloy with novelly enhanced catalytic activity for electrooxidation of formic acid

Bimetallic palladium–nickel (PdNi 2) alloy catalyst has been prepared for the electrooxidation of formic acid through a simple electrodepositing approach. Scanning Electron Microscopy and X-ray Diffraction revealed that the particle morphology and the crystalline lattice of PdNi 2 alloy were highly different from those of Pd. Although the PdNi 2 catalyst had less noble Pd content, the cyclic voltammetry and chronoamperometry results clearly demonstrated that its catalytic activity was significantly higher than that of Pd. The novel enhancement of catalytic activity was mainly ascribed to the weak absorption strength of intermediates on Pd through the interaction between Pd and additive Ni, which facilitated the formic acid oxidation through direct pathway.

Achieving finer pores and ligaments in nanoporous palladium–nickel thin films

Nanoporous palladium nickel (np-PdNi) was produced by dealloying PdNi alloy thin films. The pore and ligament dimensions were reduced by 50% when surfactants were added to the sulfuric acid etching solution. Changes in film composition and biaxial film stress were used to track the dealloying evolution in the surfactant-modified etching solution. Ultrasonic agitation was also used to enhance dealloying and shortened the required time from 5 h to 1 h, while retaining a pore/ligament size of ∼5 nm.