Preparation of a zeolite-palladium composite membrane for hydrogen separation:Influence of zeolite film on membrane stability

With the development of hydrogen energy,palladium-based membranes have been widely used in hydrogen separation and purification.However,the poor chemical stability of palladium composite membranes limits their commercial applications.In this study,a zeolite-palladium composite membrane with a sandwich-like structure was obtained by using a TS-1 zeolite film grown on the surface of palladium membrane.The membrane microstructure was characterized by SEM and EDX.The effects of the TS-1 film on the hydrogen permeability and stability of palladium composite membrane were investigated in details.Benefited from the protection of the TS-1 zeolite film,the stability of palladium composite membrane was enhanced.The results indicate that the TS-1-Pd composite membrane was stable after eight cycles of the temperature exchange cycles between 773 K and 623 K.Especially,the loss of hydrogen permeance for TS-1-Pd composite membrane was much smaller than that of the pure palladium membrane when the membrane was tested in the presence of C3H6atmosphere.It indicated that the TS-1-Pd composite membrane had better chemical stability in comparison with pure palladium membrane,owing to its sandwich-like structure.This work provides an efficient way for the deposition of zeolite film on palladium membrane to enhance the membrane stability.

Enhanced H_(2) permeation and CO_(2) tolerance of self-assembled ceramic-metal-ceramic BZCYYb-Ni-CeO_(2) hybrid membrane for hydrogen separation

Perovskite-type mixed protonic-electronic conducting membranes have attracted attention because of their ability to separate and purify hydrogen from a mixture of gases generated by industrial-scale steam reforming based on an ion diffusion mechanism.Exploring cost-effective membrane materials that can achieve both high H_(2) permeability and strong CO_(2)-tolerant chemical stability has been a major challenge for industrial applications.Herein,we constructed a triple phase(ceramic-metal-ceramic)membrane composed of a perovskite ceramic phase BaZr_(0.1)Ce_(0.7)Y_(0.1)Yb_(0.1)O_(3-δ)(BZCYYb),Ni metal phase and a fluorite ceramic phase CeO_(2).Under H_(2) atmosphere,Ni metal in-situ exsolved from the oxide grains,and decorated the grain surface and boundary,thus the electronic conductivity and hydrogen separation performance can be promoted.The BZCYYbNi-CeO_(2)hybrid membrane achieved an exceptional hydrogen separation performance of 0.53 mL min^(-1)cm^(-2) at 800℃ under a 10 vol% H_(2) atmosphere,surpassing all other perovskite membranes reported to date.Furthermore,the CeO_(2) phase incorporated into the BZCYYb-Ni effectively improved the CO_(2)-tolerant chemical stability.The BZCYYbNi-CeO_(2) membrane exhibited outstanding long-term stability for at least 80 h at 700℃ under 10 vol%CO_(2)-10 vol%H_(2).The success of hybrid membrane construction creates a new direction for simultaneously improving their hydrogen separation performance and CO_(2) resistance stability.

Review of Alloy Membranes/Films for Hydrogen Separation or Purification

Hydrogen separation and purification are two important chemical processes in the extensive application of hydrogen energy. Membrane technology has opened up a potential solution to the problems of separation and purification in an energy effective way. Membranes of adequate hydrogen permeability, good thermal and mechanical stability are the key to successful application of membrane technology in hydrogen separation and purification. In this paper, the relative parameters concerning hydrogen permeability, the development of different types of membranes namely: palladium composite membranes; V-based alloy membranes, specific functionality embraced alloy membranes, metal hydride (MH) thin films and fabrications, were reviewed and discussed. Pd-free membranes are found to be the ideal alternatives. Suitable MH thin films with mono- or multi-layer microstructures produced by novel fabrication techniques, is likely to be the promising candidates due to possessing properties distinct from those of bulk materials in membrane form.

Analysis of H_2S Tolerance of Pd-Cu Alloy Hydrogen Separation Membranes

The presence of a limited amount of H2S in H2-rich feed adversely affects the Pd-Cu membrane permeation performance due to the sulphidization of the membrane surface. A theoretical model was proposed to predict the S-tolerant performance of the Pd-Cu membranes in presence of H2S under the industrial water-gas-shift(WGS) reaction conditions. The ideas of surface coverage and competitive adsorption thermodynamics of H2S and H2 on Pd-Cu surface were introduced in the model. The surface sulphidization of the Pd-Cu membranes mainly depended on the pressure ratio of H2S to H2, temperature and S-adsorbed surface coverage, i.e., the occurrence of sulphidization on the surface was not directly related with the bulk compositions and structures [body centered cubic and face centered cubic(bcc or fcc)] of Pd-Cu alloy membranes because of the surface segregation phenomena. The resulting equilibrium equations for the H2S adsorption/sulphidization reactions were solved to calculate the pressure ratio of H2S to H2 over a wide range of temperatures. A validation of the model was performed through a comparison between lots of literature data and the model calculations over a rather broad range of operating conditions. An extremely good agreement was obtained in the different cases, and thus, the model can serve to guide the development of S-resistant Pd alloy membrane materials for hydrogen separation.

Hydrogen Permeation Characteristics of Pd-CuMembrane in Plasma Membrane Reactor

Hydrogen is an alternative energy source that has the potential to replace fossil fuels.One of the hydrogen applications is as a material for Polymer Electrolyte Membrane Fuel Cells(PEMFC)in fuel cell vehicles.High-purity hydrogen can be obtained using a hydrogen separation membrane to prevent unwanted contaminants from potentially harming the PEMFC components.In this study,we fabricated a plasma membrane reactor and investigated the permeation performance of a hydrogen separation membrane in a plasma membrane reactor utilizing atmospheric pressure plasma.The result showed the hydrogen permeation rate increasing with time as reactor temperature is increased through joule heating.By decreasing the gap length of the reactor from 2 to 1 mm,the hydrogen permeation rate increases by up to 40%.The hydrogen permeation rate increases by 30%when pressure is applied to the plasma membrane reactor by up to 100 kPa.

Preparation of Thin Palladium Composite Membranes and Application to Hydrogen/Nitrogen Separation

Thin palladium composite membranes were prepared by modified electroless plating method on a-alumina supports and a dense Pd/α-Al2O3 composite membrane with high hydrogen flux, good selectivity for hydrogen was obtained. It was tested in a single gas permeation system for hydrogen permeance and hydrogen selectivity over mtrogen. The hydrogen permeance of the corresponding membrane was ashigh as 2.45×10^-6mol·m^-2·s^-1.Pa^-1 and H2/N2 selectivityover700 at 623K and a pressure difference of 0.1MPa. The-main resistance of the composite membrane to H2 permeation lies in the aluminum ceramic support rather than the thin Pd layer.

Fabrication of Ni-alumina Composite Membrane via Powder and Bulk Impregnation Method for Hydrogen Separation

This work reports two preparation methods of Ni-Al2O3 composite to be used as a hydrogen separation membrane. The first method was powder impregnation while the second method was soaking-drying-firing or bulk impregnation. In the first method, the 10 wt pct Nickel （11） nitrate hexahydrate solution was mixed with Al2O3 powder. The mixed powders were dried at 100℃ and uniaxially pressed into a disk shape at 7 MPa. The densification of composite membranes was accomplished by pressureless sintered at 900-1300℃. For the second preparation method, the Al2O3 disk support was prepared firstly by uniaxially pressing Al2O3 powder at 7 MPa and then sintered at 1000-1200℃ for 2 h. After that, the Al2O3 support was soaked into 10 wt pct Ni solution, dried at 100℃ and calcined at 900℃ for 2 h. The soaking-drying-firing sequence was repeated ten times to finally obtain the Ni-Al2O3 membranes. from these two methods were reduced at 910℃ for 2 h After preparation process, the membranes fabricated in hydrogen atmosphere. The effect of the preparation method on properties of membranes in terms of density, porosity, phase and microstructure are discussed

Improved hydrogen separation performance of asymmetric oxygen transport membranes by grooving in the porous support layer

Hydrogen separation through oxygen transport membranes(OTMs)has attracted much attention.Asymmetric membranes with thin dense layers provide low bulk diffusion resistances and high overall hydrogen separation performances.However,the resistance in the porous support layer(PSL)limits the overall separation performance significantly.Engineering the structure of the PSL is an appropriate way to enable fast gas transport and increase the separation performance.There is no relevant research on studying the influence of the PSL on hydrogen separation performance so far.Herein,we prepared Ce0.85Sm0.15O1.925–Sm0.6Sr0.4Cr0.3Fe0.7O3-δ(SDC-SSCF)asymmetric membranes with straight grooves in PSL by tape-casting and laser grooving.A~30%improvement in the hydrogen separation rate was achieved by grooving in the PSLs.It indicates that the grooves may reduce the concentration polarization resistance in PSL for the hydrogen separation process.This work provides a straight evidence on optimizing the structures of PSL for improving the hydrogen separation performance of the membrane reactors.

Large-scale computational screening of metal–organic frameworks for D_(2)/H_(2) separation

Deuterium(D_(2)) is one of the important fuel sources that power nuclear fusion reactors. The existing D_(2)/H_(2) separation technologies that obtain high-purity D_(2) are cost-intensive. Recent research has shown that metal-organic frameworks(MOFs) are of good potential for D_(2)/H_(2) separation application. In this work, a high-throughput computational screening of 12020 computation-ready experimental MOFs is carried out to determine the best MOFs for hydrogen isotope separation application. Meanwhile, the detailed structure-performance correlation is systematically investigated with the aid of machine learning. The results indicate that the ideal D_(2)/H_(2) adsorption selectivity calculated based on Henry coefficient is strongly correlated with the 1/ΔAD feature descriptor;that is, inverse of the adsorbility difference of the two adsorbates. Meanwhile, the machine learning(ML) results show that the prediction accuracy of all the four ML methods is significantly improved after the addition of this feature descriptor. In addition, the ML results based on extreme gradient boosting model also revealed that the 1/ΔAD descriptor has the highest relative importance compared to other commonly-used descriptors. To further explore the effect of hydrogen isotope separation in binary mixture, 1548 MOFs with ideal adsorption selectivity greater than 1.5 are simulated at equimolar conditions. The structure-performance relationship shows that high adsorption selectivity MOFs generally have smaller pore size(0.3-0.5 nm) and lower surface area. Among the top 200 performers, the materials mainly have the sql, pcu, cds, hxl, and ins topologies.Finally, three MOFs with high D_(2)/H_(2) selectivity and good D_(2) uptake are identified as the best candidates,of all which had one-dimensional channel pore. The findings obtained in this work may be helpful for the identification of potentially promising candidates for hydrogen isotope separation.

Ultraselective carbon molecular sieve membrane for hydrogen purification

Hydrogen is a green clean fuel and chemical feedstock. Its separation and purification from hydrogencontaining mixtures is the key step in the production of hydrogen with high purity(>99.99%). In this work, carbon molecular sieve(CMS) membranes with ultrahigh permselectivity for hydrogen purification were fabricated by high-temperature(700–900 ℃) pyrolysis of polymeric precursor of phenolphthaleinbased cardo poly(arylene ether ketone)(PEK-C). The evolution of the microstructural texture and ultramicroporous structure and gas separation performance of the CMS membrane were characterized via TG-MS, FT-IR, XRD, TEM, CO2 sorption analysis and gas permeation measurements. CMS membranes prepared at 700 ℃ exhibited amorphous turbostratic carbon structures and high H2 permeability of 5260 Barrer with H2/CH4, H2/N2 and H2/CO selectivities of 311, 142, 75, respectively. When carbonized at900 ℃, the CMS membrane with ultrahigh H2/CH4 selectivity of 1859 was derived owing to the formation of the dense and ordered carbon structure. CMS membranes with ultrahigh permselectivity exhibit an attractive application prospect in hydrogen purification.

High efficiency hydrogen purification through P2C3 membrane:A theoretical study

It is critical to design an effective two-dimensional membrane for hydrogen purification from the mixed gas, due to its wide range of scientific and industrial applications. In this work, we investigate the hydrogen separation performance of P2C3 membranes by density functional theory and molecular dynamics simulations. The results show that the energy barrier of the H2 molecule through the P2C3 film is only 0.18 e V, while the energy barriers of the CO, N2, CO2, and CH4 molecules are 0.77 eV, 0.87 eV, 0.52 eV, and 1.75 eV, respectively. In addition, the P2C3 film has high H2 selectivity toward other gas molecules and high H2 permeability at room temperature. Under 6% tensile strain, 82% hydrogen molecules pass through the film with a H2 permeance of 2.22 × 107 gas permeance unit(GPU), while other molecules cannot across the membrane at all. Therefore, the P2C3 membrane is an excellent material for hydrogen purification.

Study on Physical and Chemical Behaviors of Rare Earths in Preparing Ceramic Tube Supported Palladium Film by Electroless Plating

The rare earths of ytterbium, lanthanum, praseodymium, neodymium and their binary mixtures were respectively added into the traditional electroless plating solution to prepare thin palladium film on the inner surface of porous ceramic tube. The experimental results shows that the addition of rare earths increases palladium deposition rates and the binary mixtures are superior to the single rare earths and the mixture of ytterbium-lanthanum is the most efficient. Adding the mixture of ytterbium-lanthanum can also reduce the plating temperature by 10 ~ 20℃, shrink the metal crystal size and improve the film densification compared to those by traditional electroless plating. A thin palladium film with 5μm was prepared and the film made a highly pure hydrogen with a molar fraction of more than 99.97% from a H2-N2 gas mixture. More attentions were paid to analyze the physical and chemical behaviors of the rare earths in palladium film preparation.

Effects of Sn residue on the high temperature stability of the H_2-permeable palladium membranes prepared by electroless plating on Al_2O_3 substrate after SnCl_2–PdCl_2 process: A case study

The stability of composite palladium membranes is of key importance for their application in hydrogen energy systems. Most of these membranes are prepared by electroless plating, and beforehand the substrate surface is activated by a SnCl_2–PdCl_2 process, but this process leads to a residue of Sn, which has been reported to be harmful to the membrane stability. In this work, the Pd/Al_2O_3 membranes were prepared by electroless plating after the SnCl_2–PdCl_2 process. The amount of Sn residue was adjusted by the SnCl_2 concentration, activation times and additional Sn(OH)_2coating. The surface morphology, cross-sectional structure and elemental composition were analyzed by scanning electron microscopy(SEM), metallography and energy dispersive spectroscopy(EDS), respectively. Hydrogen permeation stability of the prepared palladium membranes were tested at450–600 °C for 400 h. It was found that the higher SnCl_2 concentration and activation times enlarged the Sn residue amount and led to a lower initial selectivity but a better membrane stability. Moreover, the additional Sn(OH)_2coating on the Al_2O_3 substrate surface also greatly improved the membrane selectivity and stability.Therefore, it can be concluded that the Sn residue from the SnCl_2–PdCl_2 process cannot be a main factor for the stability of the composite palladium membranes at high temperatures.

Preparation and Gas Permeation of Supported γ-Al_2O_3 Membranes Used as Substrate Layer for Microporous Membranes

γ-Al2O3 membranes were successfidly deposited on the top of porous α-Al2O3 support by sol-gel process and characterized by means of XRD , SEM, N2 adsorption and gas permeation. The γ-Al2O3 membranes, free of pin-holes and cracks, adhere tightly to the supports and have a thlekness of about 7μm. When sintered at 400 ℃ , γ-Al2O3 membranes have a rutrrow pore size distribution, with a pore diameter of 3.6nm, and the transport of both H2 and CO2 in supported γ-Al2O3 membrane is governed by Knudsen mechanism, with H2 permeance of 3.3× 10^-6 molm^-2Pa^-1s^-1 and H2/ CO2 permselectivity close to the ideal Knudsen value at 50 ℃ . The γ-Al2O3 membranes are suitable for being used as the substrates of microparoas membranes .

Platinum single atom catalysts for hydrogen isotope separation during hydrogen evolution reaction

Electrolysis of water is widely used for hydrogen isotope separation and the development of hydrogen evolution reaction(HER)catalysts with high selectivity and activity is of key importance.Herein,we propose single atom catalysts(SACs)as promising catalysts for efficient hydrogen isotope separation.Pt SACs and Pt nanoparticles(NPs)have been fabricated on nanoarray-structured nitrogen-doped graphite foil(NGF)substrate by a polyol reduction method.The as prepared Pt1/NGF electrode exhibits high activity and selectivity toward HER with a low overpotential of 0.022 V at 10 mA·cm^(-2) and a high separation factor of 6.83 for hydrogen and deuterium separation,much better than Pt NPs counterpart.Density functional theory(DFT)calculations ascribe the high activity and selectivity to the constructed Pt-N_(2)C_(2) structure.This work develops a new opportunity for the design and application of high-efficiency and stable SACs toward hydrogen isotope separation by electrolysis of water.

Insights into heat management of hydrogen adsorption for improved hydrogen isotope separation of porous materials

Separating high-purity hydrogen isotopes from their mixture still remains a huge challenge due to almost the identical physicochemical properties.Much importance has been attached to tune microstructure of porous materials,while heat management during hydrogen isotope separation tends to be ignored.Herein,a porous material 5 A molecular sieve(5 A)is mixed with graphene(GE)under ball grinding to enhance its thermal conductivity for hydrogen isotope separation.The thermal conductivity increases from 0.19 W m^(-1)K^(-1)of neat 5 A,0.75 W m^(-1)K^(-1)of 5 A/GE2(2 wt%GE)to 1.23 W m^(-1)K^(-1)of 5 A/GE8.In addition,introducing GE into 5 A promotes hydrogen adsorption and D_(2)/H_(2)adsorption ratio.5 A/GE2 shows the highest D_(2)adsorption capacity(5.40 mmol/g)and the largest D_(2)/H_(2)adsorption ratio(1.07)among the composites.It also displays a high efficiency of heat transfer that contributes to a low energy consumption due to the shortened cycle time during hydrogen isotope separation.This work offers new insights into material design for improved hydrogen isotope separation,which is greatly crucial to scientific and industrial applications,such as fuel self-sustaining in fusion reactors.

Self-template synthesis of double-layered porous nanotubes with spatially separated photoredox surfaces for efficient photocatalytic hydrogen production

Improving charge carriers separation to achieve high photoconversion efficiency in heterogeneous photocatalysts is highly desirable.Herein,heterostructured ZnS@CdS double-layered porous nanotubes(PNTs),in which the spatially separated reduction and oxidation reaction sites lie on the outer and inner shell,respectively,are fabricated through a robust self-template conversion strategy.After selective photo-deposition of Ni and CoO_x as dual cocatalysts,Ni nanoparticles as electron collectors and reduction reaction sites are loaded on the outer shell,while CoO_x nanoparticles as hole collectors and oxidation reaction sites are loaded on the inner shells.As a result,a novel CoO_x/ZnS@CdS/Ni photocatalyst is obtained and shows high visible-light-driven photocatalytic hydrogen production activity owing to the synergistic effect of self-template-derived thin mesoporous heterojunctions and photo-depositionderived spatially separated dual cocatalysts,which can significantly provide driving force for the ordered transfer of photogenerated electrons and holes toward opposite direction and promote the surface catalytic reaction.Additionally,the facile strategy can be broadened to the preparation of CoO_x/ZnSe@CdSe/NiPNTs with enhanced photocatalytic activity.

The competitive and synergistic effect between adsorption enthalpy and capacity in D_(2)/H_(2)separation of M_(2)(m-dobdc)frameworks

Hydrogen isotope separation is a challenging task due to their similar properties.Herein,based on the chemical affinity quantum sieve(CAQS)effect,the D_(2)/H_(2)separation performance of M_(2)(m-dobdc)(M=Co,Ni,Mg,Mn;m-dobdc^(4-)=4,6-dioxido-1,3-benzenedicarboxylate),a series of honeycomb-shaped MOFs with high stability and abundant open metal sites,are studied by gases sorption and breakthrough experiments,in which two critical factors,gas uptake and adsorption enthalpy,are taken into consideration.Among these MOFs,Co_(2)(m-dobdc)exhibits the longest D_(2)retention time of 180 min/g(H_(2)/D_(2)/Ne:1/1/98)at 77 K because of its second-highest adsorption enthalpy(10.7 kJ/mol for H_(2)and 11.8 kJ/mol for D_(2))and the best sorption capacity(5.22 mmol/g for H_(2)and 5.49 mmol/g for D_(2))under low pressure of 1 kPa and 77 K,which make it a promising material for industrial hydrogen isotope separation.Moreover,the results indicate that H_(2)and D_(2)capacities under low pressure(about 1 kPa)dominate the final D_(2)/H_(2)separation property of MOFs.

A two-dimensional microporous metal–organic framework for highly selective adsorption of carbon dioxide and acetylene

Solvothermal reaction of 3-aminoisonicotinic acid（Haina） and Cu（NO_3）_2·2.5H_2O gave a novel twodimensional（2D） microporous metal–organic framework, [Cu（aina）_2（DMF）]·DMF（1, DMF = N,N-dimethylformamide）. Single-crystal X-ray crystallographic study of compound 1 revealed that Cu（II）ions are linked by ainaàligands forming square grid-like layers, which stack together via multiple hydrogen bonding interactions. The solvent-free framework of 1a displayed considerable porosity（void = 46.5%） with one-dimensional（1D） open channels（4.7 ？ ？ 4.8 ？） functionalized by amino groups.Gas sorption measurements of 1 revealed selective carbon dioxide（CO_2） and acetylene（C_2H_2） adsorption over methane（CH_4） and nitrogen（N_2） at ambient temperature.