Pd-Ni Alloys Research Articles

Elucidating the role of Ni to enhance the methanol oxidation reaction on Pd electrocatalysts

Amongst promising available technologies enabling the transition to renewable energy sources, electrochemical oxidation of alcohols, in a direct fuel cell or in an electrolysis reaction (H2 production), can be an economically and sustainable alternative to currently used technologies. In this work, we highlight the advantages of a Pd-Ni bimetallic electrocatalyst for methanol electrooxidation - a convenient choice due to the low cost of Ni combined with the observed acceptable catalytic performance of Pd. We report a synergistic effort between experiments and theoretical calculations based on density functional theory to provide an in-depth understanding - at the atomistic level - of the origin of the enhanced electrochemical activity of methanol electrooxidation using the bimetallic catalysts Pd3Ni and PdNi over pure Pd. Cyclic voltammograms and High-Performance Liquid Chromatography (HPLC) demonstrate higher activity towards methanol electrooxidation with increased Ni concentration and, furthermore, higher selectivity for CO2. These effects are understood by: 1) changes in the methanol oxidation reaction mechanism. 2) Mitigation or suppression of CO poisoning on the Pd-Ni alloys as compared to the pure Pd catalyst. 3) A stronger tendency towards highly oxidized intermediates for the alloys. These findings elucidate the effects of a bimetallic electrocatalyst for alcohol electrooxidation as well as unambiguously suggest PdNi as a more cost-effective alternative electrocatalyst.

Enhancing Thermal Interface Conductance to Graphene Using Ni-Pd Alloy Contacts.

To identify superior thermal contacts to graphene, we implement a high-throughput methodology that systematically explores the Ni-Pd alloy composition spectrum and the effect of Cr adhesion layer thickness on thermal interface conductance with monolayer graphene. Frequency domain thermoreflectance measurements of two independently prepared Ni-Pd/Cr/graphene/SiO2 samples identify a maximum metal/graphene/SiO2 junction thermal interface conductance of 114 ± (39, 25) MW/m2 K and 113 ± (33, 22) MW/m2 K at ∼10 at. % Pd in Ni-nearly double the highest reported value for pure metals and 3 times that of pure Ni or Pd. The presence of Cr, at any thickness, suppresses this maximum. Although the origin of the peak is unresolved, we find that it correlates with a region of the Ni-Pd phase diagram that exhibits a miscibility gap. Cross-sectional imaging by high-resolution transmission electron microscopy identifies striations in the alloy at this particular composition, consistent with separation into multiple phases. Through this work, we draw attention to alloys in the search for better contacts to two-dimensional materials for next-generation devices.

Fabrication of the Functionalized Carbon Nanomaterials via Catalytic Pyrolysis of Heteroatom-Containing Compounds

Commercial Ni-Cr and specially prepared Ni-Pd alloys were used as a catalyst’s precursor for the synthesis of the heteroatom-doped carbon nanofibers. In order to provide the intercalation of the doping heteroatom into the structure of the carbon product, the synthesis was performed in the one pot regime, when heteroatom-containing substance was subjected to decomposition simultaneously with carbon source compound. Chlorobenzene, 1-bromobutane, 1-iodobutane, and melamine were used as heteroatom-and carbon-containing sources in the experiments carried out in a closed reactor system. 1,2-dichloriethane, being a source of chlorine and carbon, was decomposed in a flow-through reactor system. Additionally, acetonitrile and carbon dioxide were admixed to 1,2-dichloriethane as nitrogen and oxygen sources. It was found that in all the cases, except for halogenated butanes, the amount of the intercalated heteroatom can reach 3-8 at.%. Both the substrate’s nature and the composition of the reaction mixture were found to affect the morphologic features of the carbon nanostructures produced.

Synthesis of nitrogen doped segmented carbon nanofibers via metal dusting of Ni-Pd alloy

A single-phase micro-disperse Ni-Pd (5 wt.%) alloy prepared by coprecipitation technique was studied as a catalyst precursor for the synthesis of the nanostructured carbon product. Catalytic synthesis of N-doped carbon nanofibers was implemented by the joint decomposition of C2H4Cl2 and CH3CN vapors in H2 excess at 600 °C. The in situ kinetic experiments performed in a flow gravimetric setup with McBain balances showed that the carbon deposition process is characterized by an induction period (18−20 min). The intensive metal dusting of the Ni-Pd alloyed precursor in reaction conditions was found to lead to its complete disintegration. The obtained submicron-sized Ni-Pd particles were shown by XRD to have the same composition as the starting Ni-Pd (5%) precursor. The growth of carbon filaments accompanied the rapid disintegration of Ni-Pd alloy. The addition of acetonitrile vapors into the reaction mixture was found to enhance carbon yield from 24 (0%) to 40.5 (5 vol.%) and 50.9 (8 vol.%) grams per 1 g of catalyst for 2 h of reaction. Joint catalytic processing of C2H4Cl2 and CH3CN was shown to be sufficient for the production of carbon nanofibers doped with nitrogen. According to XPS and EDX data, the average amount of nitrogen within the obtained N-CNF was about 1.8 wt.%. It was revealed by microscopic studies (SEM, TEM) that the produced N-doped carbon filaments are characterized with a rather regular segmental structure similar to that observed for a reference sample of N-free CNF. The synthesized N-CNF samples are characterized by ID/IG ∼ 1.3 (Raman spectroscopy) and high textural parameters (SBET ∼ 390−450 m2/g, Vpore ∼ 0.6 cm3/g).

Surface topography and composition of NiPd alloys under oblique and normal gas cluster ion beam irradiation

Polycrystalline NiPd and Ni5Pd alloys were irradiated with argon gas cluster ion beam and atomic ion beam. In situ XPS measurements showed surface enrichment with Ni. For cluster ions, the degree of the enrichment was significantly higher, and the ion current density influenced on it. Under oblique cluster ion beam, ripples developed on the surface, and the elements of the alloy redistributed along the surface according to the ripple pattern. For normal cluster ion beam direction, sputtering rate was determined by a crystalline orientation, which limited the smoothing effect.

Pt Nanoparticle Sensitized PdNi Nanofibers As Highly Sensitive and Selective Hydrogen Gas Sensor

Detection of different gases in power transformer oil is essential to accurately examine and understand different problems and faults in the transformer system. Especially, during situations like corona discharge and arcing, evolution of hydrogen gas can be hazardous due to its highly flammable and explosive nature. Therefore, development of high-performance gas sensors targeted for hydrogen gas over a wide range of concentrations is very important.We suggest a facile and effective fabrication method of hydrogen sensing composite material based on palladium and nickel alloy with nanofiber structures originated from electrospinning. PdNi alloy, with further decoration with platinum nanoparticles as catalysts via apo-ferritin templating, shows greatly enhanced sensitivity and response time. Conventionally, Palladium is widely used as hydrogen sensors due to its well-known phase transition to PdHx, α-PdHx at hydrogen concentration below 1%, and β-PdHx at hydrogen concentration above 2%. However, huge volume expansion associated from this transformation limits its lifetime and reduces its long-term performance. In this work, nickel alloying effectively decreases the lattice parameters of the alloy, while increasing the stability during repetitive exposure to high concentration to hydrogen gas. Furthermore, formation of grain boundaries to compensate the lattice contraction induced by nickel alloying, high surface area from its nanofiber structure and gas dissociation and activation properties of platinum nanoparticles improves the sensor’s sensitivity toward hydrogen gas [1]. Nickel in the lattice also acts as pinning points to effectively suppress the grain growth of the alloy during high temperature annealing and reduction processes, which further improves its sensitivity and response time. This facile fabrication and decoration methods allow us to produce a highly sensitive and rapidly responding hydrogen gas sensor with enhanced long-term stability compared to the conventional Pd based hydrogen gas sensors. Reference [1] D. H. Kim, ACS Nano 13, 6071–6082 (2011); doi:10.1021/acsnano.9b02481

Spin-mediated charge-to-heat current conversion phenomena in ferromagnetic binary alloys

Spin-mediated charge-to-heat current conversion phenomena, i.e., the anomalous Ettingshausen effect (AEE) and the anisotropic magneto-Peltier effect (AMPE), have been investigated in various ferromagnetic Ni-Fe, Ni-Pt, Ni-Pd, and Fe-Pt binary alloys at room temperature. When a charge current is applied to a ferromagnetic conductor, the AMPE modulates the Peltier coefficient depending on the angle between the directions of the charge current and magnetization, while the AEE generates a heat current in the direction perpendicular to both the charge current and magnetization. We observed the strong material dependence of the thermoelectric conversion coefficients and figures of merit of these phenomena. Among the ferromagnetic alloys used in this study, Ni$_{95}$Pt$_{5}$ exhibits the largest AMPE of which the anisotropy of the Peltier coefficient is $\sim 12\%$. In contrast, the magnitude of the AEE signals is moderate in Ni$_{95}$Pt$_{5}$ but largest in Ni$_{75}$Pt$_{25}$ and Ni$_{50}$Fe$_{50}$. We discuss these behaviors by exploring the relations between these charge-to-heat current conversion phenomena and other transport as well as magnetic properties. This systematic study will provide a clue for clarifying the mechanisms of the AMPE and AEE and for enhancing the thermoelectric conversion efficiency of these phenomena.

Redox active Ni-Pd carbonyl alloy nanoclusters: syntheses, molecular structures and electrochemistry of [Ni22-xPd20+x(CO)48]6- (x = 0.62), [Ni29-xPd6+x(CO)42]6- (x = 0.09) and [Ni29+xPd6-x(CO)42]6- (x = 0.27).

A redox active Ni-Pd alloy nanocluster [Ni22-xPd20+x(CO)48]6- (x = 0.62) ([1]6-) was obtained from the redox condensation of [NBu4]2[Ni6(CO)12] with 0.7-0.8 equivalents of Pd(Et2S)2Cl2 in CH2Cl2. Conversely, [Ni29-xPd6+x(CO)42]6- (x = 0.09) ([2]6-) and [Ni29+xPd6-x(CO)42]6- (x = 0.27) ([3]6-) were obtained by employing [NEt4]2[Ni6(CO)12] and 0.6-0.7 equivalents of Pd(Et2S)2Cl2 in CH3CN. The molecular structures of these high nuclearity Ni-Pd carbonyl clusters were determined by single-crystal X-ray diffraction (SC-XRD). [1]6- adopted an M40ccp structure comprising five close-packed ABCAB layers capped by two additional Ni atoms. Conversely, [2]6- and [3]6- displayed an hcp M35 metal core composed of three compact ABA layers. [1]6-, [2]6- and [3]6- showed nanometric sizes, with the maximum lengths of their metal cores being 1.3 nm ([1]6-) and 1.0 nm ([2]6- and [3]6-), which increased up to 1.9 and 1.5 nm, after including also the CO ligands. Ni-Pd distribution within their metal cores was achieved by avoiding terminal Pd-CO bonding and minimizing Pd-CO coordination. As a consequence, site preference and partial metal segregation were observed, as well as some substitutional and compositional disorders. Electrochemical and spectroelectrochemical studies revealed that [1]6- and [2]6- were redox active and displayed four and three stable oxidation states, respectively. Even though several redox active high nuclearity metal carbonyl clusters have been previously reported, the nanoclusters described herein represent the first examples of redox active Ni-Pd carbonyl alloy nanoclusters.

Carbon supported PdNi alloy nanoparticles on SiO2 nanocages with enhanced catalytic performance

Here we present a simple approach for the fabrication of Pd–Ni alloy nanoparticles embedded in a carbon layer on raspberry-like SiO2 hollow nanocages (SiO2@C-PdNi).

Monodisperse NiPd alloy nanoparticles decorated on mesoporous graphitic carbon nitride as a catalyst for the highly efficient chemoselective reduction of α,β-unsaturated ketone compounds

The study reported chemoselective reduction with selectivity (>99%) by the catalytic transfer hydrogenation of α,β-unsaturated ketones with a catalyst of NiPd alloy nanoparticles decorated on mesoporous graphitic carbon nitride (NiPd/mpg-C3N4).

PdNi nanoparticles decorated on defective mesoporous carbon: An efficient bifunctional electrocatalysts in alkaline direct methanol fuel cells

Defective CMK-3 carbon (CMK-3-D) supported Pd–Ni nanoparticles with different molar ratio and metal loadings have been synthesized. It is found that the PdNi nanoparticles (Pd/Ni molar ratio of 1:1, Pd loading ≤ 10 wt%) are homogeneously distributed on CMK-3-D with particle size of ac. 50 nm, due to the defective carbon support with increased surface areas could provide numerous nucleation active sites for PdNi alloys. Combined the advanced catalytic performance of PdNi with that of defective carbon, the PdNi/CMK-3-D(10) catalyst exhibits remarkable high performance on oxygen reduction reaction. The half-wave potential of PdNi/CMK-3-D(10) catalyst is −0.218 V vs. Ag/AgCl, only 30 mV lower than that of Pt/C catalyst. The more positive onset potential and high limiting current density is comparable to that of Pt/C catalyst. The PdNi/CMK-3-D(10) catalyst also shows an excellent activity on methanol oxidation reaction with a more negative onset potential, higher methanol oxidation current and larger If/Ib ratio. Moreover, due to the defective carbon support provides abundant anchoring sites for PdNi particles, the PdNi/CMK-3-D(10) catalyst has an enhanced catalytic durability on ORR and MOR. This novel combination of PdNi alloy catalyst with defective carbon support would be an efficient bifunctional electrocatalysts in alkaline direct methanol fuel cells.

Dopamine-assisted synthesis of rGO@NiPd@NC sandwich structure for highly efficient hydrogen evolution reaction

We report a facile one-pot solvothermal synthesis of NiPd alloy homogeneously encapsulated between reduced graphene oxide sheets and N-doped carbon layers (rGO@NiPd@NC) with sandwich structure. In this study, dopamine served as both carbon-nitrogen source and green reagent, which cannot only form N-doped carbon layers encasing metal nanoparticles through high-temperature roasting but also co-reduce metal ions to form NiPd alloy. The rGO@NiPd@NC nanocomposite exhibits enhanced hydrogen evolution reaction (HER) activity with a small overpotential of 56 mV at 10 mA cm−2 and a Tafel slope approaching 33 mV dec−1 in acidic aqueous media, which are similar to the HER activity of commercial Pt/C catalyst (52 mV at j = 10 mA cm−2; Tafel slope, 31 mV dec−1). Additionally, the electrocatalyst which reveals excellent electrochemical stability is reflected in that the polarization curve shows negligible difference after 1000 cycles and the current density only slightly decreases within 20 h test, providing more possibilities for practical application in the future.

Interface Nanoengineering of PdNi-S/C Nanowires by Sulfite-Induced for Enhancing Electrocatalytic Hydrogen Evolution.

The interfacial structural design of materials in nanoscale is a promising approach to regulate the physicochemical properties of materials and further optimize material properties for a variety of potential applications. Herein, PdNi-S/C nanowires with inductive sulfite has been successfully crafted through hydrothermal synthesis and applied as a superior hydrogen evolution reaction (HER) catalyst. Based on the autocatalytic mechanism, PdNi alloy nanoparticles were synthesized by controlling reduction kinetics with the presence of formic acid. Meanwhile, the sulfite is selected as an effective inductive agent to form PdNi-S/C nanowires with amorphous interfaces. The morphology, composition, and electronic structure of the synthesized PdNi-S/C were studied in detail. The PdNi-S/C manifests excellent HER performance in alkaline solution with an overpotentials of 67 mV at current density of 10 mA cm-2, a Tafel slope of 69.4 mV dec-1, and significantly long-term durability. The improvement of HER performance of the PdNi-S/C is attributed to the one-dimensional nanowire structure, abundant sulfur vacancies and defects, and the synergistic effect between PdNi-S nanowires with the graphite carbon. Furthermore, this present work offers a novel method for structure adjustment of materials to effectively control their property and catalytic performance.

Surface analysis of nickel nanomaterials electrodeposited on graphite surface

Pure Nickel (Ni) and Nickel-Palladium (Ni-Pd) alloy were electrodeposited on graphite surface via pulse electrolysis in dimethyl sulfoxide in form of rods and nanoparticles with a diameter of ~100-350 and ~10-35 nm, respectively. X-ray photoelectron spectroscopy (XPS) spectra of Ni 2p 3/2 region for these nanomaterials suggests on their surface Ni 2+ precursor while after Ar + ion-etching metallic nickel starts to be dominated. Both Pd 0 and Pd 2+ for XPS spectra of Pd 3d 5/2 and 3d 3/2 were observed after electrodeposition. Scanning electron microscope-energy dispersive X-ray and XPS analysis confirmed electrodeposition of nickel nanomaterials in non-aqueous electrolyte. Using a lower concentration of Ni 2+ precursor, nanoparticles with an average particle size of ~10-23 nm were prepared on a graphite surface.

Noble Metals Alloys Deposition from Non-Aqueous Solvents

Binary alloys of Pd and Pt were successfully deposited from 1-butyl-3-methyl imidazolium tetrafluoroborate (BMIM-BF4-Cl) ionic liquid and from a deep eutectic solvent (DES) based on a mixture of choline chloride and urea (ChCl-UA) at ambient atmosphere conditions. Ag, Ni and Sn were used as alloy components. Cyclic voltammetry experiments on glassy carbon electrode showed the reduction and dissolution of the alloys in the investigated solvents. Pulse plating and potentiostatic deposition techniques were used to deposit PdAg, PdNi, PdSn and PdPt alloys on cylindrical Cu substrate. The composition of the layers could be varied either by the concentration of the metals in the electrolyte solution or by changing the deposition mode (pulsed current or potentiostatic deposition). In order to determine the surface morphology and the thickness of the electrodeposited noble metal alloy films, a high resolution scanning electron microscope (SEM/EDX) and an energy dispersive X-ray fluorescence spectrometer (XRF) were used. The surface morphology of the layers was remarkable affected by the composition of the alloys. Scanning electron micrographs of the different electrodeposits showed that Pd alloys deposited by pulse current were generally nodular and relatively compact, whereas the films deposited by potentiostatic deposition were less dense and covered with dendrite-like and sharp-edged crystallites. The addition of a second metal (e.g. Ag+ or Sn2+) to a basic Pd or Pt electrolytes enhanced the overall metal deposition rate in comparison to solutions without alloying components and caused a remarkable increase of the layer thickness of the alloys. XRD measurements confirm that it was possible to deposit different binary metal alloys from both non-aqueous electrolytes by applying different deposition techniques. First adhesion tests and measurements of the microhardness of Pd-Ag deposits showed good properties of the produced alloy films. Also the hydrogen embrittlement of selected samples was proved by a hydrogen analyzer. These results confirmed that the quantity of hydrogen was negligible in the Pd alloy films produced from ionic liquids in comparison to films obtained from conventional aqueous solutions.

Enhanced accuracy of palladium-nickel alloy based hydrogen sensor by in situ temperature compensation

The influence of working temperature on the accuracy of the PdNi alloy thin film hydrogen sensor was investigated. The PdNi hydrogen sensor was fabricated on a silicon chip together with a Pt temperature sensor by DC sputtering. The PdNi hydrogen sensor shows excellent response to H2 with concentration from 0.02% to 40% at room temperature. Results show that the response of PdNi hydrogen sensor is nonlinearly related to the hydrogen concentration and working temperature. And correction method only based on considering the baseline temperature correction cannot obtain high measurement accuracy in the whole range area. Therefore, in order to improve the full range detection accuracy of PdNi hydrogen sensor, a modified algorithm which takes baseline and sievert constant temperature compensation into account is presented in this work. After applying the algorithm, the PdNi hydrogen sensor exhibits enhanced H2 sensing accuracy and stability even in violent temperature fluctuate situations.

Development of a High Stability Pd-Ni Alloy Thin-Film Coated SAW Device for Sensing Hydrogen.

A Pd-Ni alloy thin-film coated surface acoustic wave (SAW) device is proposed for sensing hydrogen. The Pd-Ni thin-film was sputtered onto the SAW propagation path of a SAW device with a delay line pattern to build the chip-sized hydrogen sensor. The prepared sensor chip was characterized by employing a differential oscillation loop. The effect of the Pd-Ni film thickness on sensing performance was also evaluated, and optimal parameters were determined, allowing for fast response and high sensitivity. Excellent working stability (detection error of 3.7% in half a year), high sensitivity (21.3 kHz/%), and fast response (less than 10 s) were achieved from the 40 nm Pd-Ni alloy thin-film coated sensing device.

Room temperature synthesis of PdxNi100−x nanoalloy: superior catalyst for electro-oxidation of methanol and ethanol

Bimetallic Pd–Ni alloy nanoparticles with tunable dimensions, unique composition and excellent electrocatalytic activity towards methanol and ethanol oxidation reaction (MOR and EOR) in alkali, were successfully synthesized by co-reduction of metal precursors in strong alkali medium at room temperature. X-ray diffraction profiles typically signify alloy structure of the particles. Microscopy, diffraction and spectroscopy studies further conform the successful formation of Pd–Ni nanoalloy of determined diameter and morphology. The compositions of this alloy nanoparticles can be easily tuned by typically varying the Pd2+/Ni2+ molar ratio. The mol% of Ni present in the Pd–Ni bimetallic nanoalloy portrays a key role on the catalytic activity for MOR and EOR in alkali. Pd70Ni30/C catalyst exhibits the optimum synergic catalytic activity with improved oxidation of carbonaceous intermediates. Chronoamperometric study satisfactorily proves that Pd70Ni30/C is quite stable at ambient temperature and can be used as anode for MOR and EOR.

Solid solution palladium-nickel bimetallic anode catalysts by co-sputtering for direct urea fuel cells (DUFC)

A solid solution Pd–Ni alloy co-sputtered on carbon paper (Pd–Ni/C) is explored as a catalyst in the flow-through porous anode of a direct urea fuel cell (DUFC). The catalytic performances of urea electro-oxidation in an alkaline medium are investigated by cyclic voltammetry and chronoamperometry. In order to minimize the effect of morphological variation by the Pd–Ni composition, the island structure with a uniform size or electrochemical surface area was prepared. The Pd–Ni/C electrode shows a much higher electrocatalytic activity and lower onset oxidation potential toward urea electro-oxidation compared to the Ag–Ni/C and Pt–Ni/C electrodes prepared by the same procedure. When the DUFC with a cell configuration of Pd–Ni/C anode and Pd/C cathode operates at room temperature, an open circuit voltage of 0.59 V was obtained with 0.33 molL−1 urea solution as anolyte and humidification oxygen as the catholyte. The DUFC also exhibits a maximum power density of 1.12 mWcm−2. The electrocatalytic activity by the developed solid solution is largely attributed to high intrinsic electronic conductivity, excellent porous network structures and a synergetic effect by the constituting bimetallic elements. This work develops a simple type of anode catalyst for DUFC, which can possibly open a promising approach for urea-rich wastewater treatment.

Formation of nano-porous Pd(Ni) structure produced by dealloying Zr-Al-Ni-Pd base glassy alloys and their electrochemical properties

In this work bulk metallic glasses of Zr55Al10Ni10Pd25, Zr50Al10Ni15Pd25 and Zr40Al10Ni25Pd25 in rod forms were prepared by copper mold casting technique. The glass-forming ability, thermal stability and corrosion behavior were examined with the aim to investigate the possibility of synthesizing nanoporous Pd(Ni) alloy structure which are exhibiting good electrochemical characteristics by the dealloying treatment of Zr-Al-Ni-Pd bulk metallic glasses in acid solution. After chemical treatments, the glassy rods exhibit open, three-dimensional, and separated nanopores structure. The size of nanopores (NP) is increased with increasing Zr content due to the enhanced dealloying kinetics.