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.     

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 H₂ 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 H₂ permeation rate had become stable. Nonetheless, the membrane exhibited a very high H₂ 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 H₂ adsorption or desorption-limited transport. The composite membrane withstood cycling between 523 and 723 K in H₂ well showing that differing thermal expansion of the joined metallic and ceramic materials stayed within the tolerance range up to 723 K.     

Morphology effect on the electrochemical performance of NiO films as anodes for lithium ion batteries

NiO films were prepared by chemical bath deposition and electrodeposition method, respectively, using nickel foam as the substrate. The films were characterized by scanning electron microscopy (SEM) and the images showed that their morphologies were distinct. The NiO film prepared by chemical bath deposition was highly porous, while the film prepared by electrodeposition was dense, and both of their thickness was about 1 μm. As anode materials for lithium ion batteries, the porous NiO film prepared by chemical bath deposition exhibited higher coulombic efficiency and weaker polarization and its specific capacity after 50 cycles was 490 mAh g⁻¹ at the discharge–charge current density of 0.5 A g⁻¹, and 350 mAh g⁻¹ at 1.5 A g⁻¹, higher than the electrodeposited film (230 mAh g⁻¹ at 0.5 A g⁻¹, and 170 mAh g⁻¹ at 1.5 A g⁻¹). The better electrochemical performances of the film prepared by chemical bath deposition are attributed to its highly porous morphology, which shorted diffusion length of lithium ions, and relaxed the volume change caused by the reaction between NiO and Li⁺.     

Synthesis and hydrogen permeation of Ni-Ba(Zr0.1Ce0.7Y0.2)O3−δ metal-ceramic asymmetric membranes

Ni-Ba(Zr_0.1Ce_0.7Y_0.2)O_3−δ (BZCY) metal-ceramic asymmetric membranes consisted of Ni-BZCY top membrane and porous substrate were successfully prepared and developed as hydrogen permeation membrane for the first time via a method to combine co-pressing technique and two-step sintering process. The uniform fine NiO-BZCY composite powders as the precursor of top membranes were co-synthesized through the citrate-nitrate combustion route (co-synthesis method), which was the key to fabricating Ni-BZCY thin membrane. The homogeneity and phase structure of two phases in powders were characterized using element-map technique and X-ray diffraction analysis, respectively. The fluxes through a metal-ceramic membrane of about 30-μm-thickness were measured as a function of temperature under different feed gas hydrogen partial pressures. The results indicated the asymmetric membrane displayed high hydrogen permeation flux and using 80%H₂/N₂ (with 3% of H₂O) as feed gas and dry high purity argon as sweep gas, a maximum flux of 2.4 × 10⁻⁷ mol cm⁻² s⁻¹ was achieved at 900 °C, exhibiting the predominance of asymmetric structures.     

Preparation and characterisation of porous poly(2,5benzimidazole) (ABPBI) membranes using surfactants as templates for polymer electrolyte membrane fuel cells

The first instance synthesis of porous poly(2,5benzimidazole) (ABPBI) membranes using sodium dodecyl sulfate (SDS) surfactants as templates is reported. The membranes were characterised by SEM, TGA, DSC and tensile tests. The tensile test results revealed that the porous ABPBI membranes exhibited unique mechanical properties compared with the original ABPBI membrane. Moreover, the porous ABPBI membranes showed high proton conductivity at 180 °C with high thermal stability when compared with the original ABPBI. A maximum conductivity of 2.23 × 10⁻² S cm⁻¹ of the porous ABPBI membranes was achieved at 180 °C in dry conditions, double the 1.1 × 10⁻² S cm⁻¹ obtained in the case of the ABPBI membrane. The porous ABPBI membrane demonstrated excellent properties on mechanical strengths, thermal stability and electrochemical performance when compared with those of the original ABPBI membrane, suggestive of a promising polymer electrolyte for fuel cells at high temperature.     

Preparation of palladium membrane on Pd/silicalite-1 zeolite particles modified macroporous alumina substrate for hydrogen separation

A palladium composite membrane was successfully fabricated by electroless plating on a macroporous alumina tube. Pd/silicalite-1 zeolite particles were employed to reduce the pore size of the alumina support and improve its surface roughness. Moreover, the Pd⁰ existed in the Sil-1 particle can avoid the time consuming sensitization and activation steps for palladium seeding. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS) and X-ray diffraction (XRD) analysis were conducted for analyzing the detailed microstructure of the palladium composite membrane. The hydrogen permeation performance of the resulting palladium membrane was investigated at temperatures of 623 K, 673 K, 723 K and 773 K. The hydrogen permeance of 1.95 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ with an H₂/N₂ ideal selectivity of 1165 for the palladium membrane was obtained at 773 K. Furthermore, the resulting palladium membrane was stable for a long-term operation of 15 days at 673 K.     

Influence of the type of siliceous material used as intermediate layer in the preparation of hydrogen selective palladium composite membranes over a porous stainless steel support

In this work, several composite membranes were prepared by Pd electroless plating over modified porous stainless steel tubes (PSS). The influence of different siliceous materials used as intermediate layers was analyzed in their hydrogen permeation properties. The addition of three intermediate siliceous layers over the external surface of PSS (amorphous silica, silicalite-1 and HMS) was employed to reduce both roughness and pore size of the commercial PSS supports. These modifications allow the deposition of a thinner and continuous layer of palladium by electroless plating deposition. The technique used to prepare these silica layers on the porous stainless steel tubes is based on a controlled dip-coating process starting from the precursor gel of each silica material. The composite membranes were characterized by SEM, AFM, XRD and FT-IR. Moreover they were tested in a gas permeation set-up to determine the hydrogen and nitrogen permeability and selectivity. Roughness and porosity of original PSS supports were reduced after the incorporation of all types of silica layers, mainly for silicalite-1. As a consequence, the palladium deposition by electroless plating was clearly influenced by the feature of the intermediate layer incorporated. A defect free thin palladium layer with a thickness of ca. 5 μm over the support modified with silicalite-1 was obtained, showing a permeance of 1.423·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5 and a complete ideal permselectivity of hydrogen.     

Effects of iron content on the structural evolution,electrical properties and thermochemical stability of BaCo0.9−xFexNb0.1O3−δ ceramic membrane

Cubic perovskite oxygen permeation materials BaCo_0.9−xFe_xNb_0.1O_3−δ (BCFN, x = 0.1–0.7) are prepared by the conventional solid state reaction process. The crystal structure development, structural stability, electrical conductivity and oxygen permeation flux are investigated. The introduction of iron makes the formation of cubic perovskite structure for BCFN materials much easier. BCFN exhibits a p-type semiconductor and obeys the thermally activated small polarons hopping mechanism. The electrical conductivity of BCFN increases with increasing temperature and decreases with the Fe-doping concentration. The incorporation of Fe decreases slightly the oxygen permeability of BCFN membranes, but enhances significantly the structure stability of the oxygen permeation membrane in reducing atmosphere. A high oxygen permeation flux of 1.7 ml cm⁻² min⁻¹ at 900 °C through 1 mm densified membrane under air/helium condition is obtained for the composition of BaCo_0.6Fe_0.3Nb_0.1O_3−δ.     

Evaluations of hydrogen permeation on TiN-5 wt.%Ni membrane by spark plasma sintering

The TiN-5 wt.%Ni membrane was researched for gasification of coal technique, separating hydrogen from fossil fuel. In general, Pd and Pd-based alloy membranes of separating hydrogen were reported to have the good property of hydrogen selectivity at high temperature, but they has some problems such as hydrogen embrittlement and high material costs. Therefore, materials with good properties of hydrogen selectivity are needed instead of Pd. In this research, we fabricated membranes for hydrogen permeation that are highly resistant to acids, chemically steady, and composed of the economical substance, TiN. Our laboratory investigated hydrogen selectivity. TiN powder was milled for 30, 60, and 240 min by a vibration mill, respectively. Afterwards, the samples underwent operate spark plasma sintering and was characterized by XRD, BET, and SEM. Also, hydrogen selectivity was measured by Sievert’s type hydrogen permeation membrane equipment. In this report, the hydrogen permeability of the TiN-5 wt.%Ni membrane was measured to be 7.8 × 10⁻⁸, 1.7 × 10⁻⁷, and 1.4 × 10⁻⁷ mol/m·s·Pa^1/2 at 473, 573, and 673K under 0.2 MPa H₂ atmosphere, respectively.     

The influence of the CO inhibition effect on the estimation of the H2 purification unit surface

The CO inhibition effect on H₂ permeance through commercial Pd-based membranes was analysed by means of permeation measurements at different CO compositions (0–30% molar) and temperatures (593–723 K) with the aim to determine the increase of the membrane area in order to compensate the H₂ flux reduction owing to the CO inhibition effect. The permeance of H₂ fed with carbon monoxide was observed to decrease with respect to the case of pure hydrogen. At 647 K the H₂ permeance of a pure feed of 316 μmol m⁻² s⁻¹ Pa^−0.5 reduces progressively until 275 μmol m⁻² s⁻¹ Pa^−0.5 when 15% or more of CO is present in the system, until it reaches a plateau at 20%. The inhibition effect occurring when CO is present in the feed stream reduces with the progressive temperature increase; the reduction of the permeance decreases exponentially by 23% at 593 K and by 3% at 723 K with 10% of CO. The inhibition effect is seen to be reversible. An H₂ flux profile in a Sieverts' plot shows the effect produced by the increase of the CO composition along the Pd-based membrane length. The H₂ flux profile allows the area of a Pd-based membrane to be evaluated in order to have the same permeate flow rate of H₂ when it is fed with CO or as a pure stream. Moreover, a qualitative comparison between the H₂ flux profiles and a previously proposed model has been carried out.     

Poly(styrene sulfonic acid)/poly(vinyl alcohol) copolymers with semi-interpenetrating networks as highly sulfonated proton-conducting membranes

Poly(styrene sulfonic acid)/poly(vinyl alcohol) proton-conducting membranes with semi-interpenetrating networks (semi-IPNs) were prepared using a modified two-step crosslinking strategy. We previously employed sulfosuccinic acid (SSA) and glutaraldehyde (GA) as crosslinking agents to form a dense hydrophobic layer at the outer membrane surface. Although the proton conductivity of the resulting membrane increased with the content of SSA, the methanol permeability also increased. In this study it was found that the introduction of a sufonating agent, with a high molecular weight, i.e. poly(styrene sulfonic acid) (PSSA), at a PSSA/poly(vinyl alcohol) (g g⁻¹) ratio greater than 0.72, increased the density of the tangled IPN structures that effectively impede the membrane's permeability to MeOH, while enhancing its proton conductivity. The synthesized semi-IPN membranes exhibited high proton conductivities (up to 5.88 × 10⁻² S cm⁻¹ at room temperature, i.e. greater than those of Nafion membranes) and high resistances to MeOH permeation (ca. 1 × 10⁻⁷ cm² S⁻¹, that is approximately one order of magnitude lower than that of Nafion membranes).     

Water–gas shift reaction in a Pd membrane reactor over Pt/Ce0.6Zr0.4O2 catalyst

A water–gas shift (WGS) Pt/Ce_0.6Zr_0.4O₂ catalyst has been prepared, which exhibits much faster kinetics than conventional high-temperature ferrochrome catalysts in the temperature range most suitable for operation of WGS Pd membrane reactors, i.e. above 623 K. The performance of the Pt catalyst was tested in a reactor furnished with a supported, 1.4 μm thick high-flux Pd membrane using feeds obtained by autothermal reforming of natural gas. CO conversion remained above thermodynamic equilibrium up to feed space velocities of 9100 l kg⁻¹ h⁻¹ at 623 K, P_total = 1.2 MPa and steam-to-carbon ratio S/C = 3, but H₂ recovery decreased from 84.8% at GHSV = 4050 l kg⁻¹ h⁻¹ to 48.7% at the highest space velocity. This rapid decline of separation performance is attributed to slow H₂ diffusion through the catalyst bed, suggesting that external mass flow resistance has a significant impact on the H₂ permeation rate in such membrane reactors. This could be minimized by the development of WGS catalysts with even faster kinetics which would allow further reduction of the catalyst bed height.     

Investigation of sulfonated polysulfone membranes as electrolyte in a passive-mode direct methanol fuel cell mini-stack

This paper reports on the development of polymer electrolyte membranes (PEMs) based on sulfonated polysulfone for application in a DMFC mini-stack operating at room temperature in passive mode. The sulfonated polysulfone (SPSf) with two degrees of sulfonation (57 and 66%) was synthesized by a well-known sulfonation process. SPSf membranes with different thicknesses were prepared and investigated. These membranes were characterized in terms of methanol/water uptake, proton conductivity, and fuel cell performance in a DMFC single cell and mini-stack operating at room temperature. The study addressed (a) control of the synthesis of sulfonated polysulfone, (b) optimization of the assembling procedure, (c) a short lifetime investigation and (d) a comparison of DMFC performance in active-mode operation vs. passive-mode operation.The best passive DMFC performance was 220 mW (average cell power density of about 19 mW cm⁻²), obtained with a thin SPSf membrane (70 μm) at room temperature, whereas the performance of the same membrane-based DMFC in active mode was 38 mW cm⁻². The conductivity of this membrane, SPSf (IEC = 1.34 mequiv. g⁻¹) was 2.8 × 10⁻² S cm⁻¹. A preliminary short-term test (200 min) showed good stability during chrono-amperometry measurements.     

Ethanol steam reforming reaction in a porous stainless steel supported palladium membrane reactor

In this experimental work, the ethanol steam reforming reaction is performed in a porous stainless steel supported palladium membrane reactor with the aim of investigating the influence of the membrane characteristics as well as of the reaction pressure. The membrane is prepared by electroless plating technique with the palladium layer around 25 μm deposited onto a stainless steel tubular macroporous support. The experimental campaign is directed both towards permeation and reaction tests. Firstly, pure He and H₂ are supplied separately between 350 and 400 °C in the MR in permeator modality for calculating the ideal selectivity αH₂/He. Thus, the MR is packed with 3 g of a commercial Co/Al₂O₃ catalyst and reaction tests are performed at 400 °C, by varying the reaction pressure from 3.0 to 8.0 bar. Experimental results in terms of ethanol conversions as well as recovery and purity of hydrogen are given and compared with some results in the same research field from the open literature.As best result of this work, 100% ethanol conversion is reached at 400 °C and 8 bar, recovering a hydrogen-rich stream consisting of more than 50% over the total hydrogen produced from reaction, having a purity around 65%.     

Effect of Pd concentration on electroless dense Pd-PSS membrane fabrication

Abstract

This work addresses the effect of palladium solution concentration on combinatorial plating characteristics of surfactant and sonication coupled electroless plating baths for the fabrication of dense palladium films on porous stainless steel substrates. All plating experiments were carried out using palladium solution concentration of 0·005 and 0·01M plating baths with cetyltrimethylammonium bromide surfactant at four critical micelle concentrations and loading ratio of 203 cm² L^?1. The evaluated combinatorial plating characteristics include selective conversion, plating efficiency, plating rate, Pd film thickness and per cent pore densification. The enhancement in palladium solution concentration was found to be insignificant to provide better combinatorial plating characteristics, and the plating bath consisting of 0·005M Pd solution concentration has provided 99·98% per cent pore densification with a Pd film thickness of 8·81 μm and plating efficiency of 80·69%.     

Cross-linked PEEK-WC proton exchange membrane for fuel cell

The low cost proton exchange membrane was prepared by cross-linking water soluble sulfonated-sulfinated poly(oxa-p-phenylene-3,3-phthalido-p-phenylene-oxa-p-phenylene-oxy-phenylene) (SsPEEK-WC). The prepared cross-linked membrane became insoluble in water, and exhibited high proton conductivity, 2.9 × 10⁻² S/cm at room temperature. The proton conductivity was comparable with that of Nafion^® 117 membrane (6.2 × 10⁻² S/cm). The methanol permeability of the cross-linked membrane was 1.6 × 10⁻⁷ cm²/s, much lower than that of Nafion^® 117 membrane.     

Cathode development for alkaline fuel cells based on a porous silver membrane

Porous silver membranes were investigated as potential substrates for alkaline fuel cell cathodes by the means of polarization curves and electrochemical impedance spectroscopy measurements. The silver membranes provide electrocatalytic function, mechanical support and a means of current collection. Improved performance, compared to a previous design, was obtained by increasing gas accessibility (using Teflon AF instead of PTFE suspension) and by adding a catalyst (MnO₂ or Pt) in the membrane structure to increase the cathode activity. This new cathode design performed significantly better (∼55 mA cm⁻² at 0.8 V, ∼295 mA cm⁻² at 0.6 V and ∼630 mA cm⁻² at 0.4 V versus RHE) than the previous design (∼30 mA cm⁻² at 0.8 V, ∼250 mA cm⁻² at 0.6 V and ∼500 mA cm⁻² at 0.4 V) in the presence of 6.9 M KOH and oxygen (1 atm(abs)) at room temperature. The hydrophobisation technique of the porous structure and the addition of an extra catalyst appeared to be critical and necessary to obtain high performance. A passive air-breathing hydrogen-air fuel cell constructed from the membranes achieves a peak power density of 65 mW cm⁻² at 0.40 V cell potential when operating at 25 °C showing a 15 mW cm⁻² improvement compared to the previous design.     

Zirconium phosphate as the proton conducting material in direct hydrocarbon polymer electrolyte membrane fuel cells operating above the boiling point of water

Zirconium phosphate (ZrP) was investigated as a possible proton conductor material in direct hydrocarbon polymer electrolyte membrane (PEM) fuel cells that operate at greater temperatures than conventional PEM fuel cells. Amorphous zirconium phosphate was synthesized in this work by precipitation at room temperature via reaction of ZrOCl₂ with H₃PO₄ aqueous solutions. The conductivity of the synthesized ZrP materials were 7.04 × 10⁻⁵ S cm⁻¹ for ZrP oven dried in laboratory air at 70 °C and 3.57 × 10⁻⁴ S cm⁻¹ for ZrP powder dried first at 70 °C in laboratory air and then processed at 200 °C with continuous H₂O injection at an H₂O/N₂ molar ratio of 6. This work showed that by maintaining appropriate water content in the vapour phase at processing conditions, it was possible to alter the composition of zirconium phosphate to a sufficiently hydrated state, and thereby avoid the normal decrease in conductivity with increasing temperature.     

Covalent-ionically cross-linked polyetheretherketone proton exchange membrane for direct methanol fuel cell

In this paper, the proton exchange membrane prepared by covalent-ionically cross-linking water soluble sulfonated-sulfinated poly(oxa-p-phenylene-3,3-phthalido-p-phenylene-oxa-p-phenylene-oxy-phenylene) (SsPEEK-WC) is reported. Compared with covalent cross-linked PEEK-WC membrane, this covalent-ionically cross-linked PEEK-WC membrane exhibits extremely reduced water uptake and methanol permeability, but just slightly sacrificed proton conductivity. The proton conductivity of the covalent-ionically cross-linked PEEK-WC membrane reaches to 2.1 × 10⁻² S cm⁻¹ at room temperature and 4.1 × 10⁻² S cm⁻¹ at 80 °C. The methanol permeability is 1.3 × 10⁻⁷ cm² s⁻¹, 10 times lower than that of Nafion^® 117 membrane. The results suggest that the covalent-ionically cross-linked PEEK-WC membrane is a promising candidate for direct methanol fuel cell because of low methanol permeability and adequate proton conductivity.