Sequential Electroless Plating Research Articles

Effect of annealing process on the hydrogen permeation through Pd–Ru membrane

In this paper, we report the effect of the annealing process on the hydrogen permeation in/through Pd–Ru membranes. Pd–Ru membranes were deposited via sequential electroless plating method and annealed at different atmospheres and temperatures. The membranes were characterized by XRD, AES, SEM and hydrogen permeation test. The result shows that Ru is amorphous for the as-deposited Pd–Ru membrane. After annealing in H2, N2 atmospheres and vacuum at temperatures higher than 923 K, amorphous Ru transformed into crystalline Ru, and bubble-like cavities appear. The membrane annealed in H2 has larger and more bubble-like cavities compared with those annealed in N2 and vacuum. And the hydrogen permeabilities of Pd–Ru membranes annealed in H2, N2 atmospheres and vacuum decrease by 45–67% compared with that of the original as-deposited one. Furthermore, after annealed in hydrogen permeation process, the Pd–Ru membrane keeps compact and defect-free, and the Ru membrane remains in amorphous state. The hydrogen permeability of such Pd–Ru membrane is 1.2–1.3 times higher than that of the as-deposited one, which is mainly attributed to the dense structure and amorphous Ru in the membrane.

Palladium-copper membrane prepared by electroless plating for hydrogen separation at low temperature

Pd-based membranes are often used to purify hydrogen, but often fail as a result of phase changes at low temperatures. In this study, an electroless plated Pd-Cu membrane was produced to purify hydrogen generated during various low temperature processes. The membrane was fabricated by sequential electroless plating of Pd and Cu with hydrazine as a reducing agent, followed by alloying in a hydrogen atmosphere. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analyses confirmed that the Pd-Cu layer was successfully alloyed, and thickness of the alloy layer was 23.74 µm. The hydrogen permeability of the Pd-Cu membrane prepared in this work was significantly increased compared to the previously published results. The hydrogen permeation flux of 0.6 m3 m−2 h−1 for the Pd-Cu membrane was stable over a period of 10 h at 175 °C without suffering hydrogen embrittlement and was stable over a temperature cycle. Finally, hydrogen temperature-programmed desorption (H2-TPD) confirmed that the desorption properties of hydrogen were changed by using this Pd-Cu alloy.

Apparent activation energy for hydrogen permeation and its relation to the composition of homogeneous PdAu alloy thin-film membranes

Abstract PdAu alloy composite membranes are often fabricated by sequential electroless plating of Pd and Au, but this forms a layered structure that must be annealed to form a homogenous alloy. Using ex situ analysis techniques such as X-ray diffraction (XRD) or energy dispersive X-ray spectroscopy (EDS) to judge the extent of homogenization can be time-consuming as the composite membranes must be cooled to ambient temperatures prior to analysis. However, an in situ alternative is to use the apparent activation energy for H2 permeation (Eact). In this work, 27 – 41 wt% Au films were fabricated to expand upon a range of 0 – 21 wt% that has been previously reported. Homogenization (confirmed by XRD and EDS) was achieved by heat treatment in 3 MPa H2 at 550 °C for up to 120 h. The apparent Eact was found to initially decrease with increasing Au composition from 12.2 kJ mol−1 (pure Pd) to 7.5 kJ mol−1 (21 wt% Au) after which it slowly increased to 9.0 kJ mol−1 (41 wt% Au). The two distinct regimes can be explained using the relation Eact = ΔHH + ED, wherein Eact is the sum of the partial enthalpy of solution of H into the PdAu alloy (ΔHH) and the activation energy for diffusion of H in the alloy (ED). Essentially, the two components of Eact have opposite signs that counteract each other and cause a non-linear trend with increasing Au compositions.

Influence of layer compositions and annealing conditions on complete formation of ternary PdAgCu alloys prepared by sequential electroless and electroplating methods

PdAgCu ternary alloy membranes were synthesized by the sequential electroless plating of Pd following by electroplating of Ag and Cu onto stainless steel substrate. The composition of the composite was varied by changing the deposition times. The fabricated layers were annealed at the temperatures between 500 and 600 °C for 20–60 h. The Energy Dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) were employed to investigate the element distribution in the membrane which provided the insight on membrane alloying process. Complete formation of the alloy could be obtained when the Pd composition was greater than a critical value of 60 wt%, and Ag and Cu contents were in the range of 18–30 wt% and 2–13 wt%, respectively. Deposition times of Ag and Cu were found to affect the completion of alloy formation. Excess amount of the deposited Cu particularly tended to segregate on the surface of the membrane.

Rapid annealing of sequentially plated Pd-Au composite membranes using high pressure hydrogen

In this work, the time-consuming process of annealing Pd-Au alloy composite membranes, fabricated by sequential electroless plating, has been revisited. Composite Pd-Au/YSZ membranes approximately 5µm thick with compositions ranging from 8wt% to 10wt% Au were fabricated by the bi-layer fabrication technique. Using these membranes, we investigated the effect of changing the pressure of the annealing gas (H2) on annealing time at temperatures between 450°C and 550°C. X-ray diffraction (XRD) was used to study the progress of annealing, where it was observed that a ~10wt% Au membrane could be annealed in 9h at 550°C and 3MPa H2 whereas it took 120h to anneal a similar membrane at 550°C and 0.1MPa H2. Another ~10wt% Au membrane was annealed in less than 2 days at 450°C and 3MPa H2. Complete annealing was confirmed using energy dispersive x-ray spectroscopy (EDS) with multiple spot scans throughout the thickness of the membrane indicating a uniform Au composition. Additionally, it was found that the apparent activation energy for hydrogen permeation (Eact) could be used as an in situ parameter to judge the extent of annealing. In this technique, apparent Eact decreases as the membrane anneals, reaching a minimum value which is characteristic of its Au composition. Additional annealing time does not further change the apparent Eact for a membrane with a homogeneous Au distribution.

Controlled deposition of Pd and In on carbon fibers by sequential electroless plating for the catalytic reduction of nitrate in water

Catalysts containing 1.8wt.% of Pd and different In loadings were prepared by sequential electroless plating on activated carbon felts (ACF). Homogeneous structures were obtained, with In particles deposited at the top of a tiny Pd film. The catalyst with the higher In loading (Pd:In ratio of 2.0) presented high activity and good selectivity towards nitrogen, with negligible deactivation after 6h of time-on-stream and three consecutive nitrate pulses. Besides the promising catalytic behavior, PdIn/ACF have the advantages of an open structure, which is highly accessible to the reactants, with no need of separation after the reaction.

Preparation of core–shell microstructures using an electroless plating method

A simple approach for the preparation of core–shell microstructures with an anisotropic shape is proposed in which an Ag nanowire/polyurethane acrylate (AgNW/PUA) composite produced by inverted layer processing is used as a temporary template for the sequential electroless plating of a Cu metal core and Ni shell. Through careful optimization of the metallization conditions, a Cu@Ni core–shell microstructure with an anisotropic shape (i.e., an aspect ratio greater than five) is obtained, which can be easily detached from the template through simple sonication. This technique is therefore considered to be readily applicable to the fabrication of conductive fillers for use in composite structures.

Structural and permeation kinetic correlations in PdCuAg membranes.

Addition of Ag is a promising way to enhance the H2 permeability of sulfur-tolerant PdCu membranes for cleanup of coal-derived hydrogen. We investigated a series of PdCuAg membranes with at least 70 atom % Pd to elucidate the interdependence between alloy structure and H2 permeability. Membranes were prepared via sequential electroless plating of Pd, Ag, and Cu onto ceramic microfiltration membranes and subsequent alloying at elevated temperatures. Alloy formation was complicated by a wide miscibility gap in the PdCuAg phase diagram at the practically feasible operation temperatures. X-ray diffraction showed that the lattice constants of the fully alloyed ternary alloys obey Vegard's law closely. In general, H2 permeation rates increased with increasing Ag and decreasing Cu content of the membranes in the investigated temperature range. Detailed examination of the permeation kinetics revealed compensation between activation energy and pre-exponential factor of the corresponding H2 permeation laws. The origin of this effect is discussed. Further analysis showed that the activation energy for H2 permeation decreases overall with increasing lattice constant of the ternary alloy. The combination of these correlations results in a structure-function relationship that will facilitate rational design of PdCuAg membranes.

Ultra-thin (

Ultrathin (<1μm) Pd–Ag alloy membranes have been successfully coated on the internal surface of YSZ-mixed Al2O3 hollow fibers by sequential electroless plating. The H2 permeance and selectivity of internally-coated (0.8μm thick) Pd–Ag alloy membrane is more than 5μmolm−2s−1Pa−1 and well over 1200, respectively, at 450°C and the pressure difference of 100kPa. The internally-coated Pd–Ag alloy membranes exhibit the significantly improved thermal stability and durability of membranes. This is due to the support layer constrains the thermal expansion of Pd–Ag alloy during the annealing as well as the permeation tests, preventing the delaminating of Pd–Ag alloy membrane, and hence allowing the membranes to tolerate the repeated cyclic permeation tests over at least 5 cycles (10h/cycle) without the significant loss of H2 selectivity. Moreover, mechanical damages (e.g., scratching) of Pd–Ag membrane can also be prevented as the Pd–Ag membrane is not exposed directly to the external surface.

Hydrogen permeability and sulfur tolerance of a novel dual membrane of PdAg/PdCu layers deposited on porous stainless steel

Palladium membrane is the best choice for hydrogen ultra-purification; however, it suffers from difficulties such as hydrogen embrittlement and poisoning with sulfur compounds. In order to overcome these problems, a dense PdAg alloy composite membrane was synthesized using the sequential electroless plating of Pd and Ag onto a porous stainless steel. Then a thin layer of sulfur tolerant PdCu fcc phase was deposited on this layer by electroless plating, too. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were used to study lattice phase, alloying, thickness and elemental composition of the membrane. The membrane's permeation performance was tested at different temperatures between 502 and 553K and a pressure difference up to 90kPa. By lowering the temperature from 553K to 502K, the best pressure exponent changes from 0.5 to 0.7. Hydrogen permeability of 1.77×10−8molm/m2sPa0.5 has been obtained at a temperature of 553K. The membrane sulfur resistance was confirmed by exposure to a combined gas of H2 and H2S.

PdCu membrane integration and lifetime in the production of hydrogen from methane

PdCu membranes prepared by sequential electroless plating were integrated into a hydrogen production and purification process. Hydrogen was produced from methane through catalytic partial oxidation and wet catalytic partial oxidation with Ni-based catalysts. Membrane permeance was measured with thermal cycles in an inert and hydrogen atmosphere at 673 and 773 K. Permeability was 1.98·10−3 mol/(smPa0.5) at 673 K and 2.62·10−3 mol/(smPa0.5) at 773 K. The optimum sweep gas flow required in the membrane module when operating with hydrogen-containing mixtures was selected. Peak hydrogen recovery was obtained using 15–20% of the feed to the module as sweep gas flow. Membranes were then placed downstream of the hydrogen production reactor. The CO and H2O percentages fed to the membrane module did not have a major impact on membrane behavior. Around 60–67% of the hydrogen fed to the membrane module was separated, regardless of its composition.

Preparation of Pd /α–Al2O3 and Pd-Ag/α–Al2O3 Membranes by Electroless Plating and Permeation Measurements

ABSTRACTIn this work, the synthesis of dense Pd/α–Al2O3 and Pd-Ag/α–Al2O3 ceramic composite membranes was done through the sequential electroless plating technique of Pd and Ag. The precursors are solutions of PdCl2 and AgNO3 and N2H4 salts, as reducing agent. The membranes were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS). The permeation tests of H2 and N2 was carried out at 20 psi of pressure and at 25°C, resulted πH2=5.2x10-9 mol H2/m2·s·Pa and πN2=8.2x10-10 mol N2/m2·s·Pa.

Novel PdAgCu ternary alloy: Hydrogen permeation and surface properties

Dense PdAgCu ternary alloy composite membranes were synthesized by the sequential electroless plating of Pd, Ag and Cu on top of both disk and tubular porous stainless steel substrates. X-ray diffraction and scanning electron microscopy were employed to study the structure and morphology of the tested samples. The hydrogen permeation performance of these membranes was investigated over a 350–450 °C temperature range and a trans-membrane pressure up to 100 kPa. After annealing at 500 °C in hydrogen stream followed by permeation experiments, the alloy layer presented a FCC crystalline phase with a bulk concentration of 68% Pd, 7% Ag and 25% Cu as revealed by EDS. The PdAgCu tubular membrane was found to be stable during more than 300 h on hydrogen stream. The permeabilities of the PdAgCu ternary alloy samples were higher than the permeabilities of the PdCu alloy membranes with a FCC phase. The co-segregation of silver and copper to the membrane surface was observed after hydrogen permeation experiments at high temperature as determined by XPS.

Surface characterization of Pd–Ag composite membranes after annealing at various temperatures

Pd–Ag films (∼24% Ag, 20–26 μm thick) were deposited by sequential electroless plating onto porous tubular stainless steel substrates. Intermediate α- and γ-Al 2O 3 oxide layers were employed to modify the support pore size and to prevent intermetallic diffusion of the stainless steel components into the Pd–Ag layer. The aluminum oxides were applied to the substrate porous system by a vacuum assisted-coating method. Composite membranes annealed at temperatures between 500 and 600 °C were characterized for film structure (XRD), morphology (SEM), bulk and surface component distribution (EDS, XPS), and hydrogen permeance. Pd–Ag alloy formation progressed as annealing temperature was increased to 600 °C. Composition measurements within the Pd–Ag layer revealed preferential segregation of the Ag component to the top surface; this result is consistent with Ag's lower surface free energy. No diffusion of stainless steel components into the Pd–Ag layer was observed, demonstrating the effectiveness of the oxide interdiffusion barrier. Hydrogen permeation tests of membranes annealed at 500 °C displayed high permeability and H 2/N 2 selectivity at operating temperatures between 400 and 450 °C. Permeabilities were higher but selectivities were lower for membranes annealed at 550 °C. This performance deterioration may be related to defects within the Pd–Ag layer caused by growth of dendritic Ag deposits.

Novel PdAgCu ternary alloy as promising materials for hydrogen separation membranes: Synthesis and characterization

The use of the sequential electroless plating method allowed us to obtain the PdAgCu ternary alloy on top of dense stainless steel (SS) 316 L disks. The XRD analysis indicated that initially the nucleation of the two phases of the alloy (FCC and BCC) takes place, but the FCC/BCC ratio increases with the annealing time at 500 °C in H 2 stream. After 162 h, the film contained only the FCC phase, which presents promising properties to be applied in the synthesis of hydrogen selective membranes. SEM cross-section results showed that a dense, continuous, defect-free film was deposited on top of the SS support, and the EDS data indicated that no significant gradient was present on the thickness of the film. XPS and LEIS allowed us to determine that Cu and Ag surface segregation takes place after annealing up to 500 °C/5 days. In the top-most surface layer, Ag enrichment takes place as determined by ARXPS experiments which can be the result of the lower surface tension of Ag compared to that of Cu and Pd. Increasing the annealing temperature results in an increase of the Ag surface segregation while the Cu concentration in the top-most surface layer decreases.

Preparation and performance of thin-layered PdAu/ceramic composite membranes

Preparation of 3–5 μm thick, hydrogen-selective PdAu layers via sequential electroless plating of Pd and Au onto ceramic microfiltration membranes was investigated employing a cyanide-free Au plating bath. The Au deposition rate was strongly dependent on bath temperature and alkalinity reaching an optimum at 333 K and pH 10. Homogenous alloying of the separate metal layers under atmospheric H 2 proved to be a protracted process and required approximately a week at 873 K for a PdAu layer as thin as 3 μm. After 300 h annealing at 823 K the 5 μm thick PdAu layer of a composite membrane still exhibited a Au gradient declining from 7.4 at.% at the top surface to 5.5 at.% at the support interface despite that the H 2 permeation rate had become stable. Nonetheless, the membrane exhibited a very high H 2 permeability of e.g. 1.3 × 10 −8 mol m m −2 s −1 Pa −0.5 at 673 K, but it decreased much faster with temperature below 573 K than above, likely due to a change from bulk H diffusion-controlled to H 2 adsorption or desorption-limited transport. The composite membrane withstood cycling between 523 and 723 K in H 2 well showing that differing thermal expansion of the joined metallic and ceramic materials stayed within the tolerance range up to 723 K.

H 2O 2 synthesis over PdAu membranes

2–3 μm thick PdAu membranes have been prepared by sequential electroless plating on porous ceramic tubes followed by annealing at 823 K under H 2. Gas phase H 2 permeation rates had stabilized after 250 h annealing even though the alloy layers still remained inhomogeneous as evidenced by X-ray diffraction analyses after conclusion of all other experiments. The H 2 permeability of a Pd 90.5Au 9.5 membrane reached 1.2 × 10 −8 mol m −1 s −1 Pa −0.5 at 673 K. A marked discontinuity in the temperature dependence of the H 2 permeation rate at 573 K signals a change from diffusion to adsorption or desorption-limited H 2 transport through the membrane below that threshold. H 2O 2 was directly synthesized from the elements over these PdAu membranes in O 2-saturated, acidic water/ethanol mixtures while feeding H 2 through the membrane. The H 2O 2 formation rate increased from 19.5 to 97.5 mmol m −2 h −1 between 277 and 363 K in water at 300 kPa H 2 feed pressure even though the H 2O 2 selectivity decreased from 56% to 30% in parallel. H 2O 2 yield and selectivity improved both with H 2 feed pressure, however. H 2O 2 formation rate and selectivity increased also moderately with ethanol content, but the PdAu layer tended to delaminate from the ceramic support if the ethanol content was raised above 50%.

Impact of the fcc/bcc phase transition on the homogeneity and behavior of PdCu membranes

The Pd–Cu phase diagram is discontinuous in the immediate vicinity of the body centered cubic (bcc) Pd 47.3Cu 52.7 alloy, which is a promising material for H 2 separation membranes. Hence PdCu/ceramic composite membranes have been prepared by sequential electroless plating of the metals to investigate the influence of concomitant face centered cubic (fcc) phases on the behavior of such membranes. Structural and compositional segregation was observed during cycling of a bcc Pd 48Cu 52 membrane through the fcc/bcc miscibility gap between 723 and 873 K. Transient bcc and fcc phases with low Pd content also appeared in the initial formation stages of an fcc Pd 63Cu 37 membrane during alloying of Pd and Cu layers at 723 and 773 K. Both phenomena could be sources of persistent stoichiometric heterogeneity in supported bcc PdCu membranes, which considerably reduces their H 2 permeability. An fcc/bcc Pd 46Cu 54 mixed phase membrane withstood 30 temperature cycles between room temperature and 673 K well, although a slight increase of the leak flow was observed. The widening of the leaks is tentatively attributed to mechanical stress caused by the incommensurate lattice expansion of hydrogenated fcc and bcc PdCu grains. A formation mechanism for the frequently observed pinholes in bcc PdCu membranes is proposed based on the discrepancy between the hydrogen solubility in bcc and fcc PdCu alloys. As a consequence coexisting fcc phases could reduce the life time of bcc PdCu membranes in H 2 atmospheres.

Preparation and thermal treatment of3 Pd/Ag composite membrane on a porous α-alumina tube by sequential electroless plating technique for H 2 separation

Pd/Ag/α-Al 2O 3 composite membranes were prepared by sequential electroless plating technique. The prepared membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spec-troscopy, and inductively coupled plasma atomic emission spectroscopy techniques (ICP-AES). Effects of annealing time, Ag content, and air treatment on the hydrogen permeation flux and morphology of the alloys were investigated. The results of the investigation showed that the prepared type of tube had a good potential as substrate for membrane preparation. In addition, a uniform defect-free alloy was prepared by annealing at 550°C in H 2 atmosphere. The permeation results showed an increase in H 2 permeation flux by increasing the Ag content and the annealing time. In addition, the air treatment of the prepared membranes at 400°C for 1 h changed the morphology of the alloy and substantially enhanced the hydrogen flux.

Hydrogen production from oxidative steam reforming of ethanol in a palladium–silver alloy composite membrane reactor

In this investigation, we studied the oxidative steam reforming reaction of ethanol in a Pd–Ag/PSS membrane reactor for the production of high purity hydrogen. Palladium and silver were deposited on porous stainless steel (PSS) tube via the sequential electroless plating procedure with an overall film thickness of 20 μm and Pd/Ag weight ratio of 78/22. An ethanol–water mixture ( n water/ n ethanol = 1 or 3) and oxygen ( n oxygen/ n ethanol = 0.2, 0.7 or 1.0) were fed concurrently into the membrane reactor packed with Zn–Cu commercial catalyst (MDC-3). The reaction temperatures were set at 593–723 K and the pressures at 3–10 atm. The hydrogen flux in the permeation side increased proportionately with increasing pressure; however, it reduced slightly when increasing oxygen input. This is probably due to the fast oxidation reaction that consumes hydrogen before the onset of the steam reforming reaction. The effect of oxygen plays a vital role on the ethanol oxidation steam reforming reaction, especially for a Pd–Ag membrane reactor in which a higher flux of hydrogen is required. The selectivity of CO 2 increased with increasing flow rate of oxygen, while the selectivity of CO remained almost the same.