Palladium–ruthenium membranes for hydrogen separation fabricated by electroless co-deposition

Prior published research has claimed that the addition of 4.5 wt% ruthenium to palladium in dense, cold-worked membranes produces desirable properties for hydrogen separation, including greater mechanical strength and increased hydrogen permeability, particularly at higher temperature ranges. Electroless co-deposition onto porous media can be used to produce high-quality composite membranes which take advantage of both the mechanical strength of the support and the high flux of the thin film. The objectives of this investigation were to fabricate Pd–Ru alloy composite membranes, and to examine their properties.     

Novel non-alloy Ru/Pd composite membrane fabricated by electroless plating for hydrogen separation

This study presents a new non-alloy Ru/Pd composite membrane fabricated by electroless plating for hydrogen separation. It shows that palladium and ruthenium can be deposited on an aluminum-oxide-modified porous Hastalloy by using our new EDTA-free plating bath at room temperature and 358 K, respectively. A 6.8 μm thick non-alloy Ru/Pd membrane film could be plated and helium leak test confirmed that the membrane was free of defects. Hydrogen permeation test showed that the membrane had a hydrogen permeation flux of 4.5 × 10⁻¹ mol m⁻² s⁻¹ at a temperature of 773 K and a pressure difference of 100 kPa. The hydrogen permeability normalized value with thickness of the membrane was 1.4 times higher than our pure Pd membrane having similar structure. The EDX profiles of the front and back side membrane, cross-sectional EDX line scanning and XRD profile show that there was no alloying progress between the palladium and ruthenium layer after hydrogen permeation test at 773 K.     

Pd-thickness reduction in electroless pore-plated membranes by using doped-ceria as interlayer

This work presents the use of doped CeO₂ particles with palladium as intermediate barrier for the preparation of fully dense Pd films by Electroless Pore-Plating. The use of doped ceria particles instead of non-doped ones clearly helps to reduce the final palladium thickness required to prepare a fully dense membrane over porous stainless steel supports from 15 to 9 μm (average values by gravimetric analyses), thus saving around 40% of total palladium required in the process. Pure hydrogen permeation tests reveal a consequent increase in the H₂ flux in the range 15–30%, depending on the operation mode. Thus, a H₂ permeance of 6.26·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5 at 400 °C and ΔP = 1 bar is reached, maintaining a really high H₂/N₂ ideal separation factor (≥10,000) and an activation energy within the typical range for these type of membranes, E_a = 13.1 kJ mol⁻¹. Permeation of binary H₂/N₂ gas mixtures and the effect of feeding the mixture from the inner or the outer side of the membrane have been also studied. A significant concentration-polarization effect was observed, being higher when the gas is fed from the inner to the outer side of the membrane. This effect becomes more relevant for the membrane prepared with doped CeO₂, instead of raw CeO₂, due to its lower Pd thickness and higher relative influence of the surface processes. However, it should be emphasized that higher H₂ permeance values were obtained for the entire set of experiments when using the Pd-membranes containing doped ceria. Finally, long-term permeation tests for more than 850 h with pure gases at T = 400 °C and ΔP = 1 bar were also carried out, demonstrating a suitable mechanical stability of membranes at these operating conditions.     

High-flux H2 separation membranes from (Pd/Au)n nanolayers

A novel strategy for the preparation of supported PdAu alloy layers allows the facile and fast fabrication of highly permeable and selective H₂ separation membranes from refractory metals via electroless plating and low-temperature alloying. Homogenous alloying of multiple, separately deposited Pd and Au layers with thickness in the nm range required less than one week at 773 K under atmospheric H₂ as evidenced by X-ray diffraction and H₂ permeation measurements. The H₂ permeation rate JH₂ became stable within a day even, reaching 0.62 mol m⁻² s⁻¹ at 773 K and ΔPH₂ = 100 kPa. The corresponding N₂ leak rate remained constant during a 350 h experiment, resulting in an ideal H₂/N₂ selectivity of 1400 and demonstrating that such membranes tolerate extended operation at that temperature well.     

Preparation of palladium membrane by bio-membrane assisted electroless plating for hydrogen separation

Palladium membrane was prepared on the inner surface of alumina tube by bio-membrane assisted electroless plating combined with osmosis method (BELP). In this preparation technique, an egg-shell film not only served as a semipermeable membrane to form osmotic system for preparing palladium membrane, but also acted as a protection layer to prevent the contamination of the palladium membrane from the osmotic solution. Moreover, the plating solution was circulated through the tube side to promote the mass transfer on the solid–liquid interface between the plating surface and the solution. The detailed depositing process of the palladium membrane was studied by scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDXS). Both long term operation and temperature cycling test carried out for hydrogen and nitrogen permeation confirmed that the palladium membrane was stable.     

Electroless Pd membrane deposition on alumina modified porous Hastelloy substrate with EDTA-free bath

This study demonstrates palladium membranes can be electrolessly plated on aluminum oxide-modified porous Hastelloy with hydrazine using an EDTA-free bath. The plating bath temperature affected the membrane surface morphology, with the palladium grain size increasing with increasing temperature. A 7.5 μm thick membrane plating was obtained at room temperature. Helium leak testing confirmed that the membrane was free of defects. Hydrogen permeation test showed that the membrane had a hydrogen permeation flux of 3.3 × 10⁻¹ mol m⁻² s⁻¹ at a temperature of 823 K and at a pressure difference of 100 kPa. There was no measurable interdiffusion between the membrane film and the porous Hastalloy substrate at 823 K. This room temperature membrane plating method provides several advantages such as very high selectivity, stability, favorable energy efficiency and simplicity.     

HI decomposition over PtNi/C bimetallic catalysts prepared by electroless plating

The catalytic decomposition of hydrogen iodide (HI) has drawn increasing attention because it is the key reaction for hydrogen production in the Iodine–sulfur (IS) thermochemical water splitting cycle, which is considered one of the most promising alternative methods for massive hydrogen production with high efficiency and without CO₂ emissions. Because it is very difficult for HI to decompose without the catalysts even at 500 °C, some catalysts have to be used to catalyze this reaction. In this study, four kinds of PtNi bimetallic catalysts supported on activated carbon (PtNi/C) were prepared by electroless plating and their catalytic activities were compared for HI decomposition in a fixed bed reactor at 400 and 500 °C under atmospheric pressure. Their differences in structures, surface areas, and morphology were characterized by XRD, BET and TEM, respectively. The used catalysts were also analyzed by TEM characterization in order to investigate the stability of catalysts. The results showed that the PtNi/C bimetallic catalysts are promising catalysts for HI decomposition because of their high activity and good stability, especially at high reaction temperature.     

Novel intensified catalytic nano-structured nickel–zirconia supported palladium based membrane for high temperature hydrogen production from biomass generated syngas

This Paper is directed on the improvement of the hydrogen permeability of palladium based membranes and their mechanical, chemical and thermal properties by using sandwich type composition based on Nano-Structured supports which at the end of this work demonstrated positive results. It is a new line of research to improve the performance of palladium membranes for hydrogen production and purification. In this study, a novel supported hydrogen selective membrane module was developed which is mechanically, thermally and chemically stable in order to separate hydrogen from syngas. The performance of the sandwiched membrane was evaluated and compared with commercial membrane of the same composition and thickness using hydrogen–nitrogen mixtures followed by the utilization of a syngas. It was shown that the sandwiched membrane had better hydrogen fluxes, good mechanical properties and high chemical stability during 15 days of testing with no failures detected. It also showed a good thermal stability where stable hydrogen concentrations obtained at different temperatures.     

Large-area metallisation wrap through solar cells using electroless plating

In this publication we present a realisation of a large-area metallisation wrap through (MWT) back-contact-solar cell with electroless-plated contacts. The MWT cell is a very promising back-contact solar-cell concept since the additional effort required to process MWT instead of conventional cells is limited to the formation of a small number of holes. In addition, the concept can easily be applied to very large area cells.We introduce a 9.8 cm×9.8 cm MWT solar cell, which reaches an efficiency of 16.1%. Up to this point cell performance is limited by local shunting, which results from non-optimal nickel sintering.     

High-rate discharge characteristics of metal hydride modified by electroless nickel plating based on experimental design approach

In this study, a metal hydride (MH) alloy (MmNi_3.81Mn_0.41Al_0.19Co_0.76) is modified by electroless nickel plating with the controlled variables of plating time (A), temperature (B), amount of MH alloy (C), pH (D), concentration of reducing agent (NaH₂PO₂·H₂O) (E), and complex agent (Na₃C₆H₅O₇·2H₂O) (F). Based on the two-level orthogonal array strategy, the Ni loadings on the modified MH alloy of −20.25–11.83% are strongly affected by the variables of A, D, E, and F, as well as the two-factor interactions of AB, AC, AD, BD, and EF. The utility of the unmodified MH alloy used as the negative electrode material of the Ni–MH battery decreases from 100.6 to 7.6% when increasing the discharge rate from 0.2 to 10 C. The utility at the discharge rate of 10 C can be increased to 54.5% for the MH alloy modified by electroless plating Ni when the plating time, temperature, amount of MH, pH, and concentrations of the reducing agent and complex agent are equal to 10 min, 70 °C, 2 g, 7.0, 15 g L⁻¹, and 30 g L⁻¹, respectively.     

New synthesis method of Pd membranes over tubular PSS supports via “pore-plating” for hydrogen separation processes

A new synthesis method to prepare Pd membranes by novelty modified electroless plating over tubular porous stainless steel supports (PSS) has been developed. This new pore plating method basically consists on feeding both plating solution and reducing agent from opposite sides of support, allowing the preparation of totally hydrogen selective membranes with a significantly lower Pd consumption than the corresponding to the conventional electroless plating procedure. In the latter, both reducing agent and plating solution are added simultaneously in one side of the PSS support. This new plating method has been applied over raw commercial PSS supports and air calcined supports in order to generate a Fe–Cr oxide intermediate layer.     

Development of a H2-permeable Pd60Cu40-based composite membrane using a reverse build-up method

A new reverse build-up method is developed to fabricate an economical H₂-permeable composite membrane. Sputtering and electroplating are used for the formation of a membrane comprised of a 3.7-μm-thick Pd₆₀Cu₄₀ (wt.%) alloy layer and a 13-μm-thick porous Ni support layer, respectively. The H₂-permeation measurements are performed under the flow of a gaseous mixture of H₂ and He at 300–320 °C and 50–100 kPa of H₂ partial pressure. The H₂/He selectivity values exceed 300. The activation energy at 300–320 °C is 10.9 kJ mol⁻¹. The H₂ permeability of the membrane is 1.25 × 10⁻⁸ mol m⁻¹ s⁻¹ Pa^−0.5 at 320 °C after 448 h. The estimated Pd cost of the proposed membrane is approximately 1/8 of the cost for a pure Pd₆₀Cu₄₀ membrane. This study demonstrates that the proposed method allows the facile production of low-cost, Pd-based membranes for H₂ separation.     

Fabrication of Pd/ceramic membranes for hydrogen separation based on low-cost macroporous ceramics with pencil coating

Increasing hydrogen energy utilization has greatly stimulated the development of the hydrogen-permeable palladium membrane, which is comprised of a thin layer of palladium or palladium alloy on a porous substrate. This work chose the low-cost macroporous Al₂O₃ as the substrate material, and the surface modification was carried out with a conventional 2B pencil, the lead of which is composed of graphite and clay. Based on the modified substrate, a highly permeable and selective Pd/pencil/Al₂O₃ composite membrane was successfully fabricated via electroless plating. The membrane was characterized by SEM (scanning electron microscopy), field-emission SEM and metallographic microscopy. The hydrogen flux and H₂/N₂ selectivity of the membrane (with a palladium thickness of 5 μm) under 1 bar at 723 K were 25 m³/(m² h) and 3700, respectively; the membrane was found to be stable during a time-on-stream of 330 h at 723 K.     

One-step electroless deposition of Pd/Pt bimetallic microstructures by galvanic replacement on copper substrate and investigation of its performance for the hydrogen evolution reaction

A facile and one-step method for fabrication of Pd/Pt bimetallic microstructure using galvanic replacement reaction is presented. This electroless deposition was performed without any additive reagent via simple immersion of the copper sheet in cation aqueous solution of Pd and Pt. The as-prepared electrode was characterized by using the techniques of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and cyclic voltammetry and tested for the hydrogen evolution reaction (HER) in the acidic media. Comparison of the HER on the Pd/Pt bimetallic catalysts with different Pd:Pt percentage compositions indicated that the Pd₆₀Pt₄₀ catalyst had the highest HER activity among all the Pd/Pt catalysts and a better performance than the pure Pt. The effects of galvanic replacement time and concentration of H₂SO₄ on the catalytic activity of as-prepared electrode for HER were comparatively investigated.     

Preparation of thin Pd membrane on porous stainless steel tubes modified by a two-step method

Thin Pd membranes for hydrogen filtration were deposited on modified porous stainless steel (PSS) tubes using an electroless plating technique. Alumina oxide (Al₂O₃) particles of two different sizes were subsequently used to modify the non-uniform pore distribution and the surface roughness of the PSS tubes. The principle of the modification was to use large Al₂O₃ particles (∼10 μm) to fill larger pores on the surface, and leave the smaller pores intact. Small Al₂O₃ particles (∼1 μm) were then used to further decrease the surface roughness. The detailed manufacturing steps of the Al₂O₃ modification were investigated and optimized to achieve a continuous dense Pd membrane with a minimum thickness of 4.4 μm on the modified PSS tubes. The highest hydrogen permeance of the membrane was 2.94 × 10⁻³ mol/m²-s-kPa^0.5 at 773 K, with a selectivity coefficient (H₂/He) of 1124 under a pressure difference of 800 kPa. In comparison, the thickness and hydrogen permeance of a dense Pd membrane on unmodified PSS tubes were 31.5 μm and 5.97 × 10⁻⁴ mol/m²-s-kPa^0.5, respectively, at 773 K under an 800 kPa pressure difference. The stability of the membranes at high temperatures was also investigated. The hydrogen permeation flux at 773 K was stable during a test period of 500 h. These results demonstrate that the two-step method modifies the surface of PSS tubes in a relatively simple way and results in thin, dense Pd membranes with high hydrogen permeance and good thermal stability.     

Effect of catalytic Pd coating on the hydrogen storage performances of ZrCo alloy by electroless plating method

The effects of Pd coating with different deposition concentration (PdCl₂ 0.2 g L^?1, 0.6 g L^?1, 1.0 g L^?1) on the surface morphology, microstructure and hydrogen storage performances of ZrCo alloy have been investigated. Results show that spherical Pd particles have been deposited on the surface of ZrCo alloy successfully, which transfer from sparse arrangement to continuous and compact film with increasing deposition concentration of PdCl₂. The hydriding kinetic property of all Pd coated alloys is improved compared with the bare alloy, which is due to the catalyst effect of Pd coating. The hydriding rate of the samples firstly increases and then decreases with increasing deposition concentration, which is closely related to the surface morphology and thickness of Pd coating. The hydriding kinetic property of the samples is greatly improved after 5 cycles, although Pd particles on the alloy surface peel off to some extent. This phenomenon indicates that the accumulated fresh surface during cycling makes a greater contribution to the improved hydriding kinetic property and the catalyst effect of Pd coating is weakened during cycling.     

Toward effective membranes for hydrogen separation: Multichannel composite palladium membranes

Composite palladium membranes can be used as a hydrogen separator because of their excellent permeability and permselectivity. The total membrane area in a hydrogen separator must be reasonably large for industrial use, and it is important that each membrane provides a large enough area. Such a demand can be well met by introducing multichannel composite membranes. In this work, a commercially available microporous ceramic filter with 19 channels was used as a membrane substrate, and the diameter of each channel was 4 mm. A uniform thin palladium layer was fabricated inside the narrow channels by using an electroless plating method, and the resulting membranes were highly permeable and selective. This membrane concept provides a high surface-to-volume ratio without causing significant pressure loss, making the hydrogen separator compact and capable. However, special attention should be paid to cleaning the membrane after electroless plating.     

Decorating carbon nanotubes with Ni particles using an electroless deposition technique for hydrogen storage applications

A facile and low-cost electroless deposition technique is utilized to decorate multi-walled carbon nanotubes (CNTs) with Ni. The obtained composites are attempted to use as hydrogen storage materials, whose performance is evaluated with a high-pressure microbalance. Effects of the concentration of plating solution, deposition time, and reaction temperature on the loading amount, particle size, morphology, and distribution density of Ni are studied using a transmission electron microscope. With proper deposition parameters, highly dispersed Ni nanoparticles with a uniform diameter can be fabricated on CNTs, causing a notable hydrogen spillover reaction on the composite. The optimum hydrogen storage capacity of the prepared Ni-decorated CNTs with a average diameter of 5 nm, measured at 6.89 MPa and 25 °C, is 1.02 wt%, which is almost three times higher than that (0.35 wt%) of pristine CNTs.     

Preparation, testing and modelling of a hydrogen selective Pd/YSZ/SS composite membrane

A palladium selective tubular membrane has been prepared to separate and purify hydrogen. The membrane consists of a composite material, formed by different layers: a stainless steel support (thickness of 1.9 mm), an yttria-stabilized zirconia interphase (thickness of 50 μm) prepared by Atmospheric Plasma Spraying and a palladium layer (thickness of 27.7 μm) prepared by Electroless Plating. The permeation properties of the membrane have been tested at different operating conditions: retentate pressure (1-5 bar), temperature (350-450 °C) and hydrogen molar fraction of feed gas (0.7-1). At 400 °C, a permeability of 1.1 × 10⁻⁸ mol/(s m Pa^0.5) and a complete selectivity to hydrogen were obtained. The complete retention of nitrogen was maintained for all tested experiment conditions, with both single and mixtures of gases, ensuring 100% purity in the hydrogen permeate flux.A rigorous model considering all the resistances involved in the hydrogen transport has been applied for evaluating the relative importance of the different resistances, concluding that the transport through the palladium layer is the controlling one. In the same way, a model considering the axial variations of hydrogen concentration because of the cylindrical geometry of the experimental device has been applied to the fitting of the experimental data. The best fitting results have been obtained considering Sieverts’-law dependences of the permeation on the hydrogen partial pressure.