PdCu Membranes Research Articles

Hydrogen transport through Mo2C/PdCu composite membranes

First-principle calculations have been adopted to systematically investigate the adsorption and dissociation of H2 on Mo2C (100) and (001) surfaces, as well as the fluxes of hydrogen dissociative adsorption on the Mo2C surfaces and the hydrogen across the Mo2C(100)/PdCu(110) and Mo2C(001)/PdCu(110) interfaces. It is observed that the adsorption and dissociation of H2 as well as the hydrogen flux on the Mo2C (100) surfaces are energetically more favorable than on the Mo2C (001) surfaces. Calculations also reveal that the hydrogen flux across the Mo2C(100)/PdCu(110) and Mo2C(001)/PdCu(110) interfaces is one and six order of magnitude greater than the hydrogen desorption flux on the permeation side of PdCu, respectively. In other words, the hydrogen diffusion in BCC PdCu bulk and hydrogen desorption are the dominant steps of hydrogen transport through Mo2C/PdCu composite membranes, rather than the hydrogen diffusion across the Mo2C/PdCu interfaces. The calculational findings are consistent with the similar experimental observations in the literature, and provide a profound understanding regarding the hydrogen transport across Mo2C-coated PdCu membrane.

Hydrogen Permeation Characteristics of Pd-Cu Membrane in Plasma Membrane Reactor

Hydrogen Permeation Characteristics of Pd-Cu Membrane in Plasma Membrane Reactor

Fundamental properties of hydrogen at PdCu–Mo2C interfaces from first principles calculations

First principles calculation have been carried out to comparatively examine the hydrogen solubility, hydrogen diffusion, and hydrogen permeability, as well as the interface strength at the PdCu(110)-Mo2C(001) interfaces region. It is found that the addition of Mo2C as a coating and support could increase the hydrogen solubility of BCC PdCu membrane. On the contrary, the formation of PdCu(110)-Mo2C(001) interfaces would hinder the hydrogen diffusion, and hydrogen diffusion through the PdCu region of Mo2C(001)/PdCu(110) interface is relatively easier than that of PdCu(110)/Mo2C(001) interface. Moreover, when the Mo2C is used as the catalytic layers, the formation of Mo2C(001)/PdCu(110) interface would be profit for hydrogen permeation. Calculations also reveal that the interface strength would be reduced when hydrogen permeation across the PdCu(110)-Mo2C(001) interfaces region. The predicted results could provide a deep understanding of the effects of formations of PdCu(110)-Mo2C(001) interfaces on hydrogen behaviors, and Mo2C/PdCu composite membranes could be regarded as a nice candidate for hydrogen permeation.

Analysis of hydrogen embrittlement in palladium–copper alloys membrane from first principal method using density functional theory

Hydrogen embrittlement has significant effects on membrane properties, and it is vital to develop countermeasures to avoid this problem from the start. The impact of hydrogen on pure palladium and palladium-copper alloys used for hydrogen purification/separation was investigated in this study. It was discovered that the lattice parameter and crystalline structure of pure Pd change from 3.92 Å to 5.55 Å and from cubic structure to triclinic structure, respectively. The presence of hydrogen atoms in the crystalline structure is responsible for this alteration. The absorption enthalpy of Pure Pd and PdCu of −4.38eV and −4.86eV, respectively, showed that a PdCu membrane with a lower enthalpy value increased anti-hydrogen brittleness. Due to hydrogen exposure, the mechanical characteristics of pure palladium were considerably affected. This study demonstrates that the mean peak on EF of Pd–Cu (0.259eV) is lower than that of pure Pd (0.955eV) when exposed to hydrogen, indicating more stability and lower hydrogen embrittlement in Pd–Cu alloy than pure Pd. Density functional theory-based simulation is used to analyse what happened at the grain boundary, the causes of hydrogen embrittlement, and possible ways to prevent it.

Gas-Transport Characteristics of PdCu-Nb-PdCu Membranes Modified with Nanostructured Palladium Coating.

A method for obtaining composite gas-diffusion PdCu–Nb–PdCu membranes modified with a nanostructured crystalline coating was developed to increase the performance of Nb-based membranes. A modifying functional layer with a controlled size and composition was synthesized by electrochemical deposition, which made it possible to determine a certain geometric shape for palladium nanocrystallites. Developed PdCu–Nb–PdCu membranes have demonstrated flux values up to 0.232 mmol s−1 m−2 in the processes of diffusion purification of hydrogen at 400 °C. A very significant difference in the hydrogen fluxes through the modified and non-modified composite PdCu–Nb–PdCu membranes reached 1.73 times at the lower threshold temperature of 300 °C. Cu doping of protective layer did not affect the selective properties of the membranes, which was confirmed by the obtained high selectivity values up to 1323, and made it possible to reduce the noble metal content. The research data indicate that the modification of the membrane surface significantly accelerates the hydrogen transfer process at sufficiently low temperatures due to the acceleration of dissociative–associative processes on the surface. The reported approach demonstrates new possibilities for creating productive and cost-efficient membranes based on niobium.

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.

Lamp Processing of the Surface of PdCu Membrane Foil: Hydrogen Permeability and Membrane Catalysis

Lamp Processing of the Surface of PdCu Membrane Foil: Hydrogen Permeability and Membrane Catalysis

Performance evaluation of hydrogen permeation through pd/cu membrane at different plasma system conditions

The interest of hydrogen separation using palladium-based membranes has been raised due to their high permeability and selectivity. In this study, the performance of hydrogen permeation using dielectric barrier discharge (DBD) plasma in a microchannel plate reactor (MPR) was investigated. Pure hydrogen gas was injected into the MPR reactor at H2 flow rate of 0.1 L/min. The effect of plasma only, plasma-catalyst, plasma-heating, and the electrode gap distance (EGD) on the performance of H2 permeation through Pd-Cu membrane was experimentally analyzed. The results showed that these parameters have an important influence on hydrogen permeation through Pd-Cu membrane. Small amount of permeated hydrogen gas was observed in the sole DBD plasma experiments when plasma applied at ambient temperature. Furthermore, a significant enhancement of hydrogen permeation rate at high input power was registered in the plasma-catalyst experiment because of the plasma creates an increase in the surface gas temperature increased subsequently catalyst temperature which enhanced the catalytic material activity. The best hydrogen permeation rate was achieved in the plasma-heating experiment and electrode gap distance of 4.5 mm. Moreover, it was found that the electrode gap distance (EGD) has an important role in enhancing the hydrogen permeation under DBD plasma. Additionally, it was found that at large electrode gap distance (4.5 mm) has the long residence time which improved the hydrogen permeability and H2 permeation rate reach the maximum value of 102.7%. Also, it can be concluded that the DBD plasma should be used with catalyst and a suitable electrode gap distance.

H2 purification process with double layer bcc-PdCu alloy membrane at ambient temperature

Pure Pd membranes could be used for H2 purification only at high temperature (over 573 K) due to tendency to embrittlement when exposed to hydrogen at lower temperatures especially when approaching ambient temperature. To solve this problem, a double layer bcc-PdCu alloy membrane was prepared by alternating electrodeposition of Pd and Cu on a ceramic support membrane that allowed to be operated down to room temperature. The H2 flux and N2 leak rate (JN2) remained stable during 200 h continuous operation in H2 at 303 K. Kinetic characteristics of the supported bcc PdCu membranes were explored over a wider temperature range as well. The marginal hydrogen solubility in bcc PdCu alloys and considerable H diffusivity guaranteed the excellent low-temperature tolerance and favorable H2 permeability, rendering them promising candidates for processes that require H2 separation at ambient temperatures.

High-temperature ethanol steam reforming in PdCu membrane reactor

Membrane-assisted steam reforming of ethanol is an intriguing option for on-site H2 production from biomass in refueling stations for automotive fuel cells. The energy consumption for H2 compression and thus fuel costs can be significantly reduced if this process could deliver H2 at elevated pressures. Thermodynamic analyses show that reforming temperatures above 823 K are needed for attaining H2 partial pressures that will enable operation without sweep gas and allow appreciable compression energy savings. Reforming of a 6:1 steam/ethanol mixture was practically driven to completion at 873 K and 1.3 MPa employing thin, supported Pd and PdCu membranes without sweep gas. Both H2 yield and H2 recovery factor remained stable during 10 day continuous testing of these membranes. The H2 yield reached nearly 94% with ca. 92% H2 separated by the PdCu membrane, for example. However, purity of the permeated H2 declined from about 97% to nearly 91% in the Pd membrane reformer whereas it remained steady at 98% when using the PdCu membrane. In addition, the twice as high single gas H2 permeation rate of the Pd membrane was reduced by ca. 85% during reforming due to inhibition by unstable carbon compounds while that of the PdCu membrane was diminished by less than 60%. Hence, the relative H2 permeability of the two membranes was virtually inverted under reforming conditions. In consequence, PdCu membranes are clearly the better option for integration into high-temperature ethanol steam reformers.

Hydrogen flux of BCC and FCC PdCuAg membranes

First-principles calculations have been used to study the effects of Ag addition on adsorption and dissociation of H2 on BCC and FCC PdCu surfaces as well as hydrogen diffusion and recombinative hydrogen desorption through the PdCu membranes. It is found that the Ag addition makes it energetically difficult for the adsorption of H2 on PdCu surfaces and hydrogen diffusion through PdCu, while could help the recombinative desorption of H atoms from both BCC (110) and FCC (111) surfaces of PdCu. Moreover, substitution of Ag for Pd or Cu would impede or improve the dissociation of H2 on PdCu surface. Calculations also reveal that the overall hydrogen flux of BCC Pd8Cu8 (Pd8Cu7Ag) membranes is determined by the recombinative desorption and diffusion when the membrane thickness is smaller and bigger than 10.31 (4.73) μm, respectively. In addition, hydrogen diffusion is the dominant step of hydrogen permeation of FCC PdCu and PdCuAg as well as BCC Pd7Cu8Ag membranes. The present results not only agree well with experimental observations in the literature, but also deepen the understanding of the effect of Ag alloying on hydrogen permeation through PdCu membranes.

4-2-2 電解めっきによるPdCu水素透過膜の開発

4-2-2 電解めっきによるPdCu水素透過膜の開発

Effects of Synthesis Conditions on the PdCu Membrane Structure

In this study, it was aimed to plate PdCu alloy layer on porous glass supports by using electroless plating technique. It was also aimed to achieve coexistence of fcc (face-centered cubic) and bcc (body-centered cubic) phases on the alloy membrane layer. The fcc and bcc phases were seen together in the structures of the membranes synthesized at all three bath temperatures (30 °C, 40 °C and 50 °C), but, it was shown that the most suitable coating rate was achieved when the coating bath temperature was 40 °C. The appropriate composition of PdCu (74% Pd, 26% Cu) was achieved by following a synthesis procedure as follows: Coating in Pd bath three times for 60 minutes each followed by coating in Cu bath at the low formaldehyde concentration (5 mL/L) for 15 minutes. Hydrogen flux in the membrane was measured as 1.9x10-6 mol/cm2s. After flux measurements, it was determined that the membrane structure changed and the fcc (200) structure, which did not previously exist in the structure, was formed.

Adsorption, diffusion, and permeation of hydrogen at PdCu surfaces

Ab initio calculations have been utilized to comparatively study the adsorption, dissociation, diffusion, and permeation of hydrogen at FCC (111) and BCC (110) surfaces of Pd50Cu50. It is found that the adsorption of H2 on BCC (110) surface seems thermodynamically more stable with more negative adsorption energy than that on FCC (111) surface, while the dissociation energy of H2 on BCC (110) surface is much bigger. Furthermore, the BCC (110) or FCC (111) surface of Pd50Cu50 possesses much higher hydrogen permeability and lower hydrogen diffusivity than its corresponding Pd50Cu50 bulk. In addition, the BCC (110) surface of Pd50Cu50 should be preferred in actual applications as a result of its excellent hydrogen permeability. The present findings are in nice agreement with experimental results in the literature, and could deepen the comprehension of hydrogen permeation through PdCu membranes.

Palladium-copper membrane modules for hydrogen separation at elevated temperature and pressure

Two Pd-Cu alloy membrane modules were designed to recover high-purity hydrogen from a mixture at elevated temperature and pressure. Permeation and separation behavior were studied experimentally and theoretically using pure hydrogen gas and a binary mixture of H2/CO2 (58.2: 41.8 in vol%) at 250–350 °C and 800–1,200 kPa. The Pd-Cu membrane modules presented a maximum permeation flux at the highest temperature (350 °C) and pressure (1,200 kPa) both for pure H2 gas and the binary mixture. When the permeate and retentate flowed in the same direction in the membrane module (co-current flow), a temperature gradient and permeation flux variations were observed and the permeance of the H2/CO2 mixture was 2.263×10−4 mL/(cm2·s·Pa0.5) at 250 °C and 3.409×10−4 mL/(cm2·s·Pa0.5) at 350 °C. On the other hand, when the retentate flowed in the opposite direction to the permeate flow (counter-current flow), the temperature gradient and permeation flux variations were significantly reduced and the permeation flux improved by about 11% from that of the co-current flow module. The well-distributed temperature profile inside the module and increased hydrogen pressure difference through the membrane layer shortened the time to reach the steady state in the counter-current Pd-Cu membrane module, thus enhancing the membrane performance. The results of this study can contribute towards developing an efficient Pd-Cu membrane reactor.

Optimization of a Multi-tube Annular Membrane Methanol Reformer for Fuel Cell-Powered Vehicles

A new multi-tube annular membrane methanol reformer (MTAMMR) integrated with the preheating system under sufficient consideration of the effect of heat integration presented. The MTAMMR consists of a bundle of annular membrane methanol reformers (AMMRs). The AMMR is a concentric annular cylinder to carry out the endothermic methanol steam reforming (MSR) and the exothermic preferential oxidation (PROX) reactions in the outer and the inner tubes, respectively. With the aid of the Pd-Cu membrane covered on the surface, the counter-current type AMMR under the proper operating conditions can ensure the high methanol conversion as well as the high hydrogen yield. Through a series of optimization algorithms for minimizing the weight of the MTAMMR as well as minimizing the total energy (electricity) demand of the preheating system, the lightest weight of MeOH-to-H2 processor is probably 95.5 kg. Finally, the conceptual methanol-electric hybrid power configuration demonstrated to promote the possibility of the MeOH-to-H2 processor applied for a hybrid power vehicle.

Design, modeling, and optimization of a lightweight MeOH-to-H2 processor

The conceptual design, modeling, and optimization of a MeOH-to-H2 processor by an integration of a multi-tube annular membrane methanol reformer (MTAMMR) and the preheating system are presented. The annular membrane methanol reformer (AMMR) is a packed-bed reactor consisting of two concentric cylinders and its surface is covered with the Pd-Cu membranes. When the methanol steam reforming and the preferential oxidation reactions are carried out in the outer and the inner tubes, respectively, the counter-current axial flow in the annular gap can ensure the thermally self-sustaining operation. Under sufficient consideration of the effect of heat integration, three plate-fin heat exchangers (PFHEs) are taken into account in the preheating system. Through a series of optimization algorithms for maximizing the H2 permeation rate of each AMMR and minimizing the total energy demand of the preheating system, respectively, the optimal operating conditions and specifications of MeOH-to-H2 processor are obtained. Finally, it is successfully found that the perfect weight of the optimized MeOH-to-H2 processor is close to the H2 tank weight for 2016 Toyota Mirai vehicle if the PFHEs use titanium material.

Microscopic Insights into Hydrogen Permeation Through a Model PdCu Membrane from First-Principles Investigations

Palladium-based alloys are commonly used in industry as a membrane material for the purification of hydrogen. In this work, we report a systematic theoretical study of all of the processes associat...

Thin PdCu membrane for hydrogen purification from in-situ produced methane reforming complex mixtures containing H2S

A 0.9 µm PdCu (69 wt% Pd) membrane prepared by an electroless plating method on a ceramic tubular support was tested in hydrogen sulfide containing streams. H2S/H2 mixtures with 40 and 100 ppmv of H2S were tested in order to observe the reversibility of sulfur addition. The membrane permselectivity operating in H2S/complex mixtures with around 32 ppmv of H2S in CH4, CO, CO2 and H2 was also tested. The streams were in-situ produced by Methane Steam Reforming and Methane Catalytic Partial Oxidation reactions. Prior to the tests with H2S, the hydrogen flux of the membrane at 773 K and 2 bar of pressure difference was 0.92 mol m−2 s−1. Membrane hydrogen flux decreased by around 50–80% in the tests with H2S/H2 mixture, but it recovered to the original values after removing H2S. In H2S/complex mixtures operation, the flux decrease was smaller due to concentration polarization phenomena. Although no sulfide compounds where detected on the membrane by SEM−EDX, XRD or XPS, the H2S or the employed temperatures seem to induce Cu segregation to the membrane surface.

High-temperature stability of Pd alloy membranes containing Cu and Au

High-temperature stability of Pd-based membranes benefits their application in steam reformers and sulfur-contaminated H2 streams because both membrane reforming efficiency and sulfur tolerance of Pd alloys increase much with temperature. Hence, we investigated PdCu, PdAu, and PdCuAu membranes supported on porous ceramic tubes between 500°C and 650°C. Remarkably, PdCu membranes were much more stable than Au-containing ones. The H2 permeation rates of some PdAu and PdCuAu membranes declined at 550°C with substantially increasing N2 fluxes. This was triggered by severe morphological deformation of the Au alloy films into stoichiometrically inhomogeneous, cavernous structures. The H2 fluxes of the PdCu membranes started to decline at 650°C with leak flows increasing slightly. Moreover, the PdCu layer morphology remained dense and compositionally homogeneous even after testing for up to 4800h between 500 and 650°C. The strikingly different high-temperature stability can be understood by considering the divergent surface segregation tendencies of Cu and Au and their differing impact on hydrogen solubility in Pd alloys. As a result, Au may desorb much more easily from membranes than Cu leading to structural instability above 500°C during operation in H2. The instability of PdAu membranes at high temperatures may be mitigated by addition of sufficient Cu to obtain ternary membranes with good H2 permeability and better thermal stability.