Ternary Alloy Membranes Research Articles

Enhancement for hydrogen transport properties by tailoring lattice matching in V-Pd-Fe ternary alloy membrane

V-based alloy membranes have huge potential for hydrogen separation and purification due to their higher hydrogen permeability, but suffer from hydrogen embrittlement. To address this matter, Pd and Fe have been chosen as alloying additions in V-based membranes to inhibit hydrogen embrittlement and maintain high hydrogen permeation performance based on the lattice-matching strategy. The phase structure, composition, microstructure and hydrogen permeation properties of V-Pd-Fe ternary alloy are investigated systematically, and the V-Fe and V-Pd binary alloys are presented for comparison. The results show that the prepared V-Pd-Fe ternary can match almost perfectly with pure V in lattice constants. Attributing to the lattice-matching strategy, the V-Pd-Fe ternary alloy exhibits more excellent hydrogen permeable properties than that of V-Fe and V-Pd binary alloys. The reduction of hydrogen embrittlement is ascribed to the lower hydrogen solubility that induced by the lattice distortion and electronegativity of Fe and Pd. Meanwhile, the manipulated lattice constant that parallel to pure V maintains high hydrogen permeation performance. Additionally, the designed ternary V87.8Pd8Fe4.2 alloy exhibits exceptional long-term hydrogen permeation stability at 573 and 623 K, and hydrogen flux gradually decreases at 673 and 723 K is observed due to the interdiffusion between Pd film and V87.8Pd8Fe4.2 substrate and defects in the Pd coating. This study offers new scenario and method for optimized hydrogen permeable properties and restrains hydrogen embrittlement in the alloy membrane.

Selective and efficient hydrogen separation of Pd–Au–Ag ternary alloy membrane

The widespread demand for clean energy stimulates great interest to hydrogen energy with high energy density and conversion efficiency. Separation technologies by membranes are increasingly applied for hydrogen separation because of its excellent performance and low consumption. In this work, density functional theory simulations is used to study hydrogen separation of Pd–Au–Ag membrane, and the performance of Pd–Au alloy is also compared and discussed. The results indicate that Pd–Au alloy shows superior selectivity to H2 gas over CO, N2, CH4, CO2 and H2S gases, which is in line with experimental results. In particular, the separation selectivity of Pd–Au–Ag to H2 is significantly greater than those for Pd–Au alloy and several currently reported materials. Moreover, the permeability of H2 in Pd–Au–Ag exceeds the limits for industrial production at deferent temperatures. Our calculations demonstrate that Pd–Au–Ag alloy present excellent performance as a promising membrane for hydrogen separation.

Hydrogen permeation and surface properties of PdAu and PdAgAu membranes in the presence of CO, CO2 and H2S

Using the electroless deposition technique with different deposition sequences, it was possible to obtain a single phase PdAgAu ternary alloy after treatment at 773 K during 7 days. Despite the order of deposition, the samples exhibited similar hydrogen permeation flux at the same temperature and pressure. In the presence of CO, the PdAgAu ternary alloy membranes showed a lower inhibition on the hydrogen permeance compared with the binary PdAu alloy at 623 and 673 K. On the contrary, under CO2 containing streams, the ternary alloy showed a higher inhibition with a complete hydrogen recovery after removing CO2 from the stream. When H2S was introduced in the 13% CO2/13% Ar/74% H2 stream, a higher permeance decrease was observed on both the PdAu and PdAgAu alloy membranes. After removal of H2S, a hydrogen recovery of 60% and 76% was measured for the PdAu and PdAgAu membranes, respectively. Pd surface segregation was observed on the Pd82Ag15Au3–873 K-5 d and the Pd78Au6Ag16–773 K-7 d samples upon exposure to CO containing streams. Instead, silver surface segregation was observed by XPS after exposing the PdAgAu ternary alloy to CO2 containing streams.

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.

Hydrogen Solubility of Magnetron Co-Sputtered FCC and BCC PdCuAu Thin Films

Palladium–copper–gold (PdCuAu) ternary alloy membranes are promising alternatives to pure palladium for the purpose of hydrogen separation processes. In the current work, PdCuAu ternary alloys were prepared by magnetron cosputtering deposition. All as-deposited samples showed face-centered cubic (fcc) structure in the composition range of study: 30 ≤ [Pd] ≤ 100, 0 ≤ [Cu] ≤ 66, and 0 ≤ [Au] ≤ 6 (in at%). The body-centered cubic (bcc) phase was prepared from the fcc samples by annealing for 4 h at 400 °C under Ar and was identified in alloys with Pd content between 40 and 46 at%. The hydrogen solubility was evaluated for both fcc and bcc phases using an electrochemical method and an electrochemical in situ X-ray diffraction method, respectively. The alloys’ hydrogen solubility increases with the lattice parameter and palladium content, and decreases with crystallite size and phase transition to bcc. In the same range of composition, the hydrogen solubility of the fcc and bcc phases vary in the same way with...

PdCuAu ternary alloy membranes: Hydrogen permeation properties in the presence of H2S

PdCuAu ternary alloy membranes with different component compositions were synthesized by sequential electroless deposition of components onto porous stainless steel substrates. The ternary with the highest Au content, Pd69Cu14Au17, exhibited the highest hydrogen permeation flux, comparable to that of a Pd91Au9 membrane. Upon exposure to 100ppm H2S/H2 at 673 K for 24h, all PdCuAu membranes experienced flux reductions of ~55%, followed by recovery to ~80% of the initial hydrogen flux upon reintroduction of pure hydrogen at 400°C. Complete flux recovery after H2S exposure required hydrogen treatment at 500°C. X-ray diffraction (XRD) analysis of the H2S-exposed PdCuAu membranes revealed fcc alloy structure with no evidence of bulk sulfide formation. In agreement with the XRD results, sulfur was not detected in the bulk of H2S-exposed samples by energy dispersive spectroscopy (EDS). However, analysis of H2S-exposed PdCuAu alloys by X-ray photoelectron spectroscopy (XPS) depth profiling revealed low, but measureable, amounts of sulfur in the near-surface region, about 10nm in depth. The depth profiles of samples after hydrogen recovery treatment showed significantly reduced sulfur content. These results indicate that H2S exposure causes flux loss in PdCuAu alloys through a surface-poisoning mechanism, and that the surface sulfide can be removed—and flux recovered—by high temperature treatment in hydrogen.

Pd-based binary and ternary alloy membranes: Morphological and perm-selective characterization in the presence of H2S

Pd, Pd90Ag10, Pd91Au9, Pd78Ag9Au13 and Pd75Ag16Au9 alloy membranes were prepared on vacuum-assisted ZrO2-modified porous stainless steel supports by sequential electroless deposition. The membranes were evaluated for permeability in pure H2 and in an H2S/H2 mixture. The membranes displayed a range of permeabilities in pure H2: Pd90Ag10>Pd78Ag9Au13>Pd~Pd75Ag16Au9>Pd91Au9. On exposure to 100ppm H2S/H2 at 673K for 24h, all membranes lost a significant fraction of their H2 permeabilities: Pd (lost the largest fraction, 85%)>Pd90Ag10>Pd75Ag16Au9>Pd78Ag9Au13>Pd91Au9 (60%). When H2S was removed, the membranes recovered the lost permeability to different extents. The Pd91Au9 and Pd78Ag9Au13 membranes displayed the highest fractional recovery of initial H2 permeability (~80%). But, with its higher initial pure H2 permeability, Pd78Ag9Au13 had the highest absolute H2 permeability after recovery. The microstructure, morphology and bulk composition of H2S-exposed samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). XRD revealed the presence of a bulk Pd4S phase on both Pd and Pd90Ag10, the membranes that recovered the least H2 relative flux after their exposure to H2S. In contrast, bulk sulfides did not form on Pd91Au9 or on PdAgAu ternary alloys. In agreement with the XRD results, EDS did not detect sulfur in the bulk of Pd91Au9 or in either of the ternary alloy samples. Our results show that the addition of Au to the high-permeability PdAg binary membrane results in a PdAgAu ternary membrane that minimizes the permanent H2 flux loss associated with H2S exposure by preventing the formation of thick stable sulfides.

팔라듐 합금 수소 분리막의 전처리에 관한 연구

A Pd-based hydrogen membranes for hydrogen purification and separation need high hydrogen perm-selectivity. The surface roughness of the support is important to coat the pinholes free and thin-film membrane over it. Also, The pinholes drastically decreased the hydrogen perm-selectivity of the Pd-based composite membrane. In order to remove the pinholes, we introduced various surface pre-treatment such as alumina powder packing, nickel electro-plating and micro-polishing pre-treatment. Especially, the micro-polishing pretreatment was very effective in roughness leveling off the surface of the porous nickel support, and it almost completely plugged the pores. Fine Ni particles filled surface pinholes with could form open structure at the interface of Pd alloy coating and Ni support by their diffusion to the membrane and resintering. In this study, a surface pore-free Pd-Cu-Ni ternary alloy membrane on a porous nickel substrate was successfully prepared by micro-polishing, high temperature sputtering and Cu-reflow process. And permeation and leak tests showed that the Pd-Cu-Ni ternary alloy hydrogen membrane achieved both high permeability of permation flux and infinite selectivity.

Pd–Cu–Ni Ternary Alloy Membrane with High Temperature Durability for Hydrogen Separation and Purification

For successful commercialization, Pd-based membranes used for hydrogen purification and separation need stable thermal durability at high temperatures. In order to meet this requirement, Pd–Cu–Ni ternary alloy hydrogen membranes with a saturated surface concentration were fabricated on a 1-in. porous nickel support using high temperature sputtering and Cu-reflow processes. These membranes had considerably enhanced thermal durability because of their thermally stable surface concentration and morphology.

Predicting, Fabricating, and Permeability Testing of Free-Standing Ternary Palladium−Copper−Gold Membranes for Hydrogen Separation

For hydrogen from coal gasification to be used economically, novel separation processes that produce high-purity H2 must be developed. While binary palladium based alloys have shown promising pure hydrogen flux values, the search for optimal binary or ternary alloys is an involved and costly process due to the immense number of alloy variations that can be prepared and tested. In this paper an approach to identify, fabricate, and experimentally verify the hydrogen permeation performance of PdCu and PdAu binary alloys and ternary alloys of PdCuAu at various copper and gold concentrations to produce robust, poison-tolerant, hydrogen selective free-standing membranes is reported. This approach utilizes three primary tasks of (1) materials modeling and composition selection, (2) fabrication of high-performance binary and ternary alloy membranes, and (3) membrane testing and evaluation that are all operating independently and concurrently. For the binary Pd−Cu system, using a pure Pd membrane as the reference, both the theoretically predicted and experimentally measured additions of copper lowered the hydrogen permeability. For the binary Pd−Au system, the addition of gold slightly lowered permeability in the theoretical model but in the experimental testing was enhanced. For the ternary system, both experimental and theoretical permeabilities were depressed, with Cu exhibiting a larger influence on reducing the permeability.

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.

Study on the Perm-Selectivity of Thin Pd–Cu–Ni Ternary Alloy Membrane for Hydrogen Purification and Separation

In order to meet the requirements of industries dealing with hydrogen, the membranes for hydrogen purification and separation need to be improved for both hydrogen permeability and selectivity. However, it has been difficult to enhance both properties simultaneously because their properties were contrary to each other. In this study, we fabricated a Pd-alloy membrane by using micro-polishing of porous metal support, plasma surface treatment, Pd–Cu sputtering at high temperature, and Cu-reflow process, and achieved both high permeability [10-6 mol/(m2·s·Pa)] and infinite selectivity. This Pd–Cu–Ni ternary alloy membrane could be commercialized for the purification and separation of hydrogen in various applications.

Formation of a defect-free Pd–Cu–Ni ternary alloy membrane on a polished porous nickel support (PNS)

In order to decrease its resistance we enlarged the pore size of a porous nickel support (PNS) by using nickel powder with a larger particle size. The gas permeation test showed that this increased the gas permeation flux compared with the previous support. To make up for the various disadvantages, such as the enlarged surface roughness and pore size, a polishing process was introduced with sandpaper, followed by wet polishing with alumina powder. The polishing treatment was very effective in leveling off the surface of the porous nickel support, but it almost completely plugged the pores. Those pores blocked by the polishing process could be regenerated during Cu-reflow at 973 K by the upward diffusion of nickel and in this way a 12 μm defect-free Pd–Cu–Ni ternary alloy film was formed on the polished porous nickel support. Furthermore, we were able to obtain a three times higher hydrogen permeability than that reported in previous studies, because of the decreased support resistance of the porous nickel support.

The effect of Cu reflow on the Pd–Cu–Ni ternary alloy membrane fabrication for infinite hydrogen separation

A Pd–Cu–Ni ternary alloy membrane was fabricated by sputtering and a Cu reflow process. The sputtering method has been used for deposition of a thin, impurity-free Pd alloy membrane. However, the low selectivity of hydrogen has been a major drawback for commercialization of membranes prepared by sputtering methods. In this work, a Cu reflow process was introduced as a solution to this problem. The adoption of the Cu reflow process makes possible a dense and void-free surface, and leads to a dramatic increase of the selectivity of hydrogen to an infinite level. The crystal structure and surface microstructure of the membrane were subjected to high temperature X-ray diffraction and field emission scanning electron microscope analyses to investigate the effect of Cu reflow on the Pd–Cu–Ni ternary alloying process. With respect to the analysis, the Cu film deposited on the top Pd layer commenced reflowing-behavior at 350 °C, and the initial Pd–Cu alloy was formed and surface voids were completely filled at 500 °C. After final heat treatment at 650 °C for 2 hr, the nickel element of the support actively diffused into the Pd–Cu film layer. As a consequence, the Pd–Cu film and Ni support layer were completely integrated as an alloy membrane with a functional gradient. The results of a permeation test using a single gas (H 2 and N 2) at a pressure difference of 280 kPa indicated that the selectivity of hydrogen was at an infinite level due to the void free and dense surface of the membrane. The permeability was revealed to be 0.077 mol·m − 2 ·s − 1 . The performance of the membrane formed by sputtering and the Cu reflow process was not degraded after a long working-period of 3 weeks at severe conditions of various temperature and pressure difference. This is most likely due to the excellent stability of the Pd–Cu–Ni ternary alloy, as it is composed of metals with high mutual chemical affinity and is has been fabricated under dry vacuum conditions without any contamination by impurities.

Long-term hydrogen permeation tests of Pd–Cu–Ni/PNS with temperature cycles from room temperature to 773 K

Pd–Cu–Ni ternary alloy membranes were fabricated on a porous nickel support by sputtering followed by the Cu-reflow method. The weight composition of Pd:Cu:Ni was 88.9:7.4:3.7 and the thickness was 12 μm. α–β phase transition tests were carried out using hydrogen gas in the temperature range from 373 to 623 K using feed side pressures of 0.052 and 0.138 MPa. There were neither peaks nor shoulders in the hydrogen flux across the entire temperature range, meaning that the α–β phase transition did not occur below the critical points of the Pd–H system, i.e. 565 K, 1.97 MPa. The durability of the membranes was demonstrated by performing temperature cycles from room temperature to 773 K at a feed side pressure of 0.138 MPa and this was attributed to the phase stability of the α-phase even at room temperature.

The effect of support resistance on the hydrogen permeation behavior in Pd–Cu–Ni ternary alloy membrane deposited on a porous nickel support

This paper shows the effect of support resistance on the pressure exponent. Pd–Cu–Ni ternary alloy film is formed on the newly developed porous nickel support which has Knudsen diffusion. Permeation flux of hydrogen was measured at 673, 723 and 773 K under two different permeation directions, i.e. support to film (SF mode) and film to support (FS mode). It was found that the permeation direction had an effect on the hydrogen permeation flux and the pressure exponent as well. For both of permeation directions, the interface pressure of Pd alloy film and porous nickel support was determined and it was affected by permeation direction. The obtained interface pressure was used to clarify the reason why the pressure exponent was deviated from the Sieverts’ law and it was found that the reason is the support resistance rather than surface reaction.

Characterization of Pd–Cu–Ni ternary alloy membrane prepared by magnetron sputtering and Cu-reflow on porous nickel support for hydrogen separation

Pd–Cu–Ni alloy membrane was successfully deposited 4 μm in thickness on porous nickel support by multitarget sputtering and Cu-reflow technique. The surface of porous nickel support needed not to be modified because it has very uniform and small pore distribution as 33 nm. From the XRD and SEM analysis, it was clarified that the fabricated Pd–Cu–Ni ternary alloy film had Pd–Cu–Ni alloy character and no defects on the surface of thin membrane. The weight composition of Pd:Cu:Ni was 89:4.5:6.5 from EDS analysis. As a result of single gas permeation test using H 2 and N 2, hydrogen permeance increased with an increase of operating temperature and transmembrane pressure difference. Furthermore, hydrogen separation factor with single gas test was infinity indicating pinhole-free palladium-based alloy membrane. In additions, it was so stable that the morphology of the surface was not changed and there were no indications of metal interdiffusion during time-on-stream test for 10 days with the cycling of operating temperature and transmembrane pressure difference.