Electroless Plating Of Palladium Research Articles

Electroless Plating of Palladium Membranes on Porous Substrates for Hydrogen Separation and the Effects of Process Factors on Plating Rate and Efficiency: A Review

The electroless plating of palladium and palladium alloy membranes is fast becoming an important and enabling technology. This is more so when juxtaposed with the rising demand for high purity hydrogen for applications particularly in proton exchange membrane fuel cells (PEMFC). The effect of process factors such as sensitization and activation during surface modification, concentration of the reducing agent, plating temperature, time, pH, additives, air aeration on plating efficiency, quality of the palladium film and deposit morphology is reviewed with the aim of identifying areas requiring further investigation. The paper also reviews how these process factors could be optimised for better plating efficiency and overall membrane quality. The concentration of the reducing agent has been identified as the limiting factor on plating efficiency albeit other process factors separately impact on the plating efficiency. Furthermore, bulk precipitation caused by concentration of the reducing agent has been identified as a major problem during electroless plating with hydrazine based plating baths. To ameliorate this problem, a multi step addition of the hydrazine reducer in separate portions has been recommended.

Low Temperature Steam Methane Reforming Over Ni Based Catalytic Membrane Prepared by Electroless Palladium Plating

A Pd/Ni-YSZ porous membrane with different palladium loadings and hydrazine as a reducing reagent was prepared by electroless plating and evaluated for the steam methane reforming activity. The steam-reforming activity of a Ni-YSZ porous membrane was greatly increased by the deposition of 4 g/L palladium in the low-temperature range (600 °C). With an increasing amount of reducing reagent, the Pd clusters were well dispersed on the Ni-YSZ surface and were uniform in size (∼500 nm). The Pd/Ni-YSZ catalytic porous membrane prepared by 1 of Pd/hydrazine ratio possessed an abundant amount of metallic Pd. The optimal palladium loadings and Pd/hydrazine ratio increased the catalytic activity in both the steam-reforming reaction and the Pd dispersion.

Electroless plating of ultrathin palladium films: self-initiated deposition and application in microreactor fabrication

We present new electroless palladium plating reactions, which can be applied to complex-shaped substrates and lead to homogeneous, dense and conformal palladium films consisting of small nanoparticles. Notably, autocatalytic and surface-selective metal deposition could be achieved on a wide range of materials without sensitization and activation pretreatments. This provides a facile and competitive route to directly deposit well-defined palladium nanofilms on e.g. carbon, paper, polymers or glass substrates. The reactions proceed at mild conditions and are based on easily accessible chemicals (reducing agent: hydrazine; metal source: PdCl2; ligands: ethylenediaminetetraacetic acid (EDTA), acetylacetone). Additionally, the water-soluble capping agent 4-dimethylaminopyridine (DMAP) is employed to increase the bath stability, to ensure the formation of small particles and to improve the film conformity. The great potential of the outlined reactions for micro- and nanofabrication is demonstrated by coating an ion-track etched polycarbonate membrane with a uniform Pd film of approximately 20 nm thickness. The as-prepared membrane is then employed as a highly miniaturized flow reactor, using the reduction of 4-nitrophenol with NaBH4 as a model reaction.

All electrochemical fabrication of a bilayer membrane composed of nanotubular photocatalyst and palladium toward high-purity hydrogen production

We developed an all-electrochemical technique for fabricating a bilayer structure of a titanium dioxide (TiO2) nanotube array (TNA) and a palladium film (TNA/Pd membrane), which works for photocatalytic high-purity hydrogen production. Electroless plating was used for depositing the Pd film on the TNA surface prepared by anodizing a titanium foil. A 3-μm-thick TNA/Pd membrane without any pinholes in a 1.5-cm-diameter area was fabricated by transferring a 1-μm-thick TNA onto an electroless-plated 2-μm-thick Pd film with a mechanical peel-off process. This ultrathin membrane with sufficient mechanical robustness showed photocatalytic H2 production via methanol reforming under ultraviolet illumination on the TNA side, immediately followed by the purification of the generated H2 gas through the Pd layer. The hydrogen production rate and the apparent quantum yield for high-purity H2 production from methanol/water mixture with the TNA/Pd membrane were also examined. This work suggests that palladium electroless plating is more suitable and practical for preparing a well-organized TNA/Pd heterointerface than palladium sputter deposition.

Preparation and characterization of palladium–ruthenium composite membrane on alumina‐modified PSS substrate

A new Ru/Pd/Al2O3/PSS layered membrane was fabricated by electroless plating of palladium and ruthenium for hydrogen separation. Pd and Ru were successively deposited on a pretreated PSS substrate using palladium and ruthenium plating baths at 333 and 358 K, respectively. EDX, XRD and XPS results confirmed the successful plating of ruthenium. Surface analysis showed that the palladium and ruthenium layers did not alloy significantly at temperatures of 723, 823 and 923 K over 100 h. The hydrogen permeation performance of the Pd–Ru composite membrane followed Sieverts' law, suggesting that diffusion of atomic hydrogen through the dense metal layer was rate‐limiting. The addition of ruthenium had a negligible effect on hydrogen permeability when the Ru weight content was ≤8 wt%. However, when the Ru content was increased to 11 wt%, H2 permeability decreased by 10 %. The Pd–Ru membrane exhibited good chemical stability and high H2/N2 selectivity in long‐term permeation testing.

SYNTHESIS AND CHARACTERIZATION OF PALLADIUM NANOPARTICLES IMMOBILIZED ON TiO2 NANOTUBES AS A NEW HIGH ACTIVE ELECTRODE FOR METHANOL ELECTRO-OXIDATION

Self-organized TiO2 nanotubes/titanium substrate modified with palladium nanoparticles ( Pd/TiO2/Ti electrodes) were prepared by a two-step process consisting of anodizing of titanium plate followed by electroless plating of palladium on resulted TiO2 nanotubes. The morphology and surface analysis of Pd/TiO2/Ti electrodes were investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), respectively. The results indicated that palladium nanoparticles were homogeneously deposited on the surface of TiO2 nanotubes. The electro-catalytic activity of Pd/TiO2/Ti electrodes in the methanol electro-oxidation was studied by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) methods. The results indicate that Pd/TiO2/Ti electrode improve the electro-catalytic activity for methanol oxidation greatly and confirmed the better electro-catalytic activity and stability of these new electrodes. So, the Pd/TiO2/Ti electrodes have a good application potential to fuel cells.

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.

Hydrogen selective thin palladium–copper composite membranes on alumina supports

Abstract Thin and defect-free Pd–Cu composite membranes with high hydrogen permeances and selectivities were prepared by electroless plating of palladium and copper on porous alumina supports with pore sizes of 5 and 100 nm coated with intermediate layers. The intermediate layers on the 100 nm supports were prepared by the deposition of boehmite sols of different particle sizes, and provided a graded, uniform substrate for the formation of defect-free, ultra-thin palladium composite layers. The dependence of hydrogen flux on pressure difference was studied to understand the dominant mechanism of hydrogen transport through a Pd–Cu composite membrane plated on an alumina support with a pore size of 5 nm. The order in hydrogen pressure was 0.98, and indicated that bulk diffusion through the Pd–Cu layer was fast and the overall process was limited by external mass-transfer or a surface process. Scanning electron microscopy (SEM) images of the Pd–Cu composite membrane showed a uniform substrate created after depositing one intermediate layer on top of the alumina support and a dense Pd–Cu composite layer with no visible defects. Cross-sectional views of the membrane showed that the Pd–Cu composite layer had a top layer thickness of 160 nm (0.16 μm), which is much thinner than previously reported.

Preparation of palladium nanoparticles–titanium electrodes as a new anode for direct methanol fuel cells

Pd nanoparticle/Ti electrodes are prepared by electroless plating of palladium on titanium plates. The morphology and surface analysis of Pd nanoparticle/Ti electrodes are investigated using scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively. The results indicate that palladium nanoparticles are homogeneously deposited on the surface of titanium plates. The electro-catalytic activity of Pd nanoparticle/Ti electrodes in the methanol electro-oxidation is studied by cyclic voltammetry and chronoamperometry methods. The results show that the electro-catalytic oxidation of methanol on the Pd nanoparticle/Ti electrode improved compare to pure palladium electrode and confirmed the better electro-catalytic activity and stability of these new electrodes.

Effects of Additives on Nanoscale Electroless Plating of Palladium on a Nonconductive Substrate

not Available.

Autothermal reforming of ethanol in a Pd–Ag/Ni composite membrane reactor

The main objective of this project is to study the hydrogen production reaction from oxidative steam reforming of bio-ethanol in the pertinent characteristics of a palladium–silver alloy membrane reactor. The enhancements of hydrogen permeation and of H 2/N 2 permselectivity were studied in a Ni–Pd–Ag ternary alloy membrane, which was fabricated by successive electroless plating of palladium and silver on stainless steel (PSS) supports modified with nickel electroplating. XRD, SEM, and EDS were used to characterize the surface morphology of the membranes. Ethanol–water mixture ( n water/ n ethanol = 1 or 3) and oxygen ( n oxygen/ n ethanol = 0.2 or 0.7) were fed concurrently into the membrane reactor packed with Zn–Cu commercial catalyst (MDC-3). The reaction temperatures were set at temperatures of 593–723 K and pressures of 3–10 atm. The amount of oxygen added in the feed has a significant effect on the steam reforming reaction of ethanol. At high pressures, autothermal reaction of ethanol with no need for external heating to the composite membrane reactor to produce high purity hydrogen was easily processed.

Palladium nanostructures from galvanic displacement as hydrogen peroxide sensor

Electroless plating of palladium on silicon has been developed, resulting in the formation of palladium films and nanoparticles. The deposition process has been monitored by atomic and Kelvin probe force microscopies (AFM/KPFM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) in order to understand the deposition mechanism. A fabrication process is developed to yield a high density of Pd particles, while ensuring the formation of a palladium thin film underneath. The formed substrates have been used as amperometric sensors without further modification for the determination of hydrogen peroxide concentrations. The substrates are found to exhibit excellent linear electrocatalytic response down to the micromolar range and under an applied potential of 0.0 V, with the lowest quantifiable concentration of 1 μM. The simplicity in substrate fabrication coupled with the potential for integration in microfabrication processes, as well as the low applied potential needed in the measurements, offers the possibility of using the device in enzymatic biosensors with low interference signals.

Electroless plating of palladium on WO 3 films for gasochromic applications

Nowadays, gasochromic Pd/WO 3 coatings as optically switchable materials during H 2 absorption have become more interesting due to their novel applications in smart windows and gas sensor devices. In this study, WO 3 films were fabricated by Pulsed Laser Deposition (PLD) on glass substrates. Using an electroless method, Pd nanoparticles were deposited on the surface of the produced films. The effect of Pd growth time on coloring/bleaching rate was studied for different submerging times (1, 2, 5, 10, 15, 20 and 40 min). The best coloring/bleaching velocity was attained with a growth time of 2 min. The effect of growing time and growth feature of Pd particles was further studied using Scanning Electron Microscope (SEM) and X-ray Photoelectron Spectroscopy (XPS). It was revealed that spherical or agglomerate metallic particles have nucleated upon many surface cracks. The size of particles depends on the growing time and also on the size of cracks. It was observed that hydrogen interaction with a Pd/WO 3 layer provides additional surface cracks leading to gasochromic improvement. Furthermore the effect of substrate on Pd growth and gasochromic response was studied. It was observed that the size and distribution of particles as well as gasochromic response depend strongly on WO 3 substrate characteristics.

Micromolding for three-dimensional metal microstructures using stereolithography of photopolymerized resin

If micromachines can be produced with metal microstructures, their application field will be greatly expanded. We have proposed a metal micromolding method based on the stereolithography of photopolymerized resin. In this work, we report our recent successful development of three fundamental processes used in the micromolding method. The electroless plating of palladium with a purity of 93–97% was realized on photopolymerized resin with a view to realizing a shape memory alloy. An electrolytic grinding technique was examined for copper, and step-by-step grinding was realized for the first time using a NaCl solution. A copper replica was successfully extracted from a resin mold by using heat treatment. The results suggested that three-dimensional metal microstructures can be produced with micrometer order accuracy by using the micromolding method.

Fabrication and characterization of (Pd/Ag)–La0.2Sr0.8CoO3−δ composite membrane on porous asymmetric substrates

Perovskite La 0.2 Sr 0.8 CoO 3− δ (LSCO-80) was selected as a model mixed-conductive material for the fabrication of a ceramic electrolyte membrane on porous MgO and ZrO 2 disks. Aiming at overcoming mechanical cracks in the membrane caused by thermal mismatch between the membrane and the asymmetric support, Pd/Ag alloy phase was introduced into the LSCO-80 membrane through a non-powder-blending technique. The alloy phase not only offers relevant plasticity to buffer thermal stress generated in the membrane but also possess adequate chemical stability at high temperature. The metallization was carried out on the LSCO-80 membrane by silver slurry coating and followed by electroless palladium plating. Subsequently, the overlaying metal bi-layer was annealed to allow the formation of Pd/Ag–LSCO-80 composite. The metallization could satisfactorily cure mechanical cracks arisen from sintering of the LSCO-80 powder-packing layer. To pursue further promotion of mechanical stability of the composite membrane at high temperature, the LSCO-80 powder was modified by covering individual particles with a Pd/Ag thin layer, which has been proven to be an effective complement to the above coating approach. In addition to focusing on the alloy-assisted mechanical enhancement, this work has also investigated ionic conduction behavior of three different composite membranes by measuring their AC impedances. The results suggest that the metallization improves anionic oxygen conductivity in the perovskite LSCO-80 lattice at high temperatures. This phenomenon is ascribed to a fast cathodic process wherein the Pd/Ag phase plays the key role.

Fabrication and characterization of (Pd/Ag)–La 0.2Sr 0.8CoO 3− δ composite membrane on porous asymmetric substrates

Perovskite La 0.2Sr 0.8CoO 3− δ (LSCO-80) was selected as a model mixed-conductive material for the fabrication of a ceramic electrolyte membrane on porous MgO and ZrO 2 disks. Aiming at overcoming mechanical cracks in the membrane caused by thermal mismatch between the membrane and the asymmetric support, Pd/Ag alloy phase was introduced into the LSCO-80 membrane through a non-powder-blending technique. The alloy phase not only offers relevant plasticity to buffer thermal stress generated in the membrane but also possess adequate chemical stability at high temperature. The metallization was carried out on the LSCO-80 membrane by silver slurry coating and followed by electroless palladium plating. Subsequently, the overlaying metal bi-layer was annealed to allow the formation of Pd/Ag–LSCO-80 composite. The metallization could satisfactorily cure mechanical cracks arisen from sintering of the LSCO-80 powder-packing layer. To pursue further promotion of mechanical stability of the composite membrane at high temperature, the LSCO-80 powder was modified by covering individual particles with a Pd/Ag thin layer, which has been proven to be an effective complement to the above coating approach. In addition to focusing on the alloy-assisted mechanical enhancement, this work has also investigated ionic conduction behavior of three different composite membranes by measuring their AC impedances. The results suggest that the metallization improves anionic oxygen conductivity in the perovskite LSCO-80 lattice at high temperatures. This phenomenon is ascribed to a fast cathodic process wherein the Pd/Ag phase plays the key role.

Preparation of palladium-coated V and V–15Ni membranes for hydrogen purification by electroless plating technique

A simple electroless palladium plating treatment on V and V–15Ni alloy was attempted to prepare sandwich-type membranes for hydrogen purification. The obtained coating on the membranes was characterized using SEM–EDX and AFM, and hydrogen permeability and hydrogen diffusion coefficients for the plated membranes were determined. Sensitizing–activating treatment with SnCl 2 and PdCl 2 solutions before the electroless plating treatment enabled palladium to cover the membranes densely. The V membrane with electroless palladium plating, whose hydrogen permeability was 5.0×10 −7 mol H 2 m −1 s −1 Pa −1/2 at 623 K , showed cracking during the hydrogen permeation experiment at 473 K . Hydrogen permeability for the V–15Ni membrane with electroless palladium plating was 3.4×10 −8 mol H 2 m −1 s −1 Pa −1/2 at 623 K , which was comparable to that of the sample coated by the conventional methods including evaporation and electrochemical plating. The long-period permeation test showed that the V–15Ni membrane with electroless palladium plating possessed satisfactory durability to be used as hydrogen purification material.

Electroless plating of palladium and copper on polypyrrole films

A novel process for the metallization of polypyrrole (PPY) film surface through consecutive electroless plating of palladium and copper in the complete absence of the SnCl2 sensitization step was demonstrated. X-ray photoelectron spectroscopy (XPS) technique was used to characterize the polymer surface at each stage of the metallization process. It was found that only the fully reduced PPY film could reduce palladium ions to palladium metal (Pd(0)) in substantial amounts from either the Pd(NO3)2 or PdCl2 acid solution. The palladium metal was necessary for catalyzing the subsequent electroless plating of copper. The reduction of Pd(II) ions in acid solution to Pd(0) on the film surface was accompanied by a simultaneous increase in intrinsic oxidation state and doping level of the film. The copper plating process after the palladium uptake step was highly dependent on the [Pd]/[N] ratio on the film. Through XPS and Auger photoeletron spectroscopy measurements, it was postulated that during the electroless copper plating process, the Cu(II) ions were first reduced to Cu(I) on the PPY film surface before complete reduction to copper metal.

Effects of electroless plating chemistry on the synthesis of palladium membranes

The effects of plating chemistry on palladium deposition, plating efficiency and membrane microstructure have been studied for two palladium electroless plating solutions, hydrazine-based and hypophosphite-based plating baths. The electroless plating kinetics of palladium onto seeded supports have been determined for hypophosphite-based plating bath, and a simple kinetic model has been developed. The model provides an accurate prediction of deposition rate and film thickness as a function of plating parameters. Most importantly, the experimental results demonstrated that plating chemistry plays a vital role on both plating performance and film microstructure.

Electroless plating of palladium and copper on polyaniline films

Electroless plating of copper on polyaniline (PANI) films of different intrinsic oxidation states, viz., the emeraldine base (EB), the nigraniline (NA) and the leucoemeraldine (LM) states, in the complete absence of surface sensitization by SnCl 2 was explored. The process consisted of two steps. The first step involved electroless deposition of palladium on PANI film in Pd(NO 3) 2 nitric acid solution. The Pd-laden films were subsequently used for the electroless plating of copper. It was found that electroless deposition of Pd and Cu occurred efficiently only on the fully reduced LM film surface. X-ray photoelectron spectroscopy was employed for the characterization of surface compositions and chemical states of the polymer films and the metals during the two electroless deposition processes. The quantitative changes in N1s core-level spectra and the evolution of Pd 3d and Cu 2p core-level spectra on the polymer films during the two-step process were carefully monitored. In Pd(NO 3) 2 nitric acid solution, all three types of the PANI films were protonated. Nevertheless, coupled Pd reduction occurred only on the LM film surface. The metallic Pd atoms on the LM film surface initiated the subsequent electroless plating of copper. The reduction of Cu(II) ions to Cu metal proceeded via the Cu(I) state. The effect of [Pd]/[N] mole ratio of the Pd-laden LM film on the rate of electroless plating of copper was also investigated.