钯膜制备及渗氢性能研究

随着膜分离技术的不断发展,渗氢用钯基膜由于具有优异的透氢速率、透氢选择性及良好的化学和热稳定性,已被广泛应用于氢提纯分离领域。介绍了钯透氢膜的种类、透氢机理和制备方法,总结了钯膜从最初的纯钯膜、钯合金膜到钯复合膜的发展历程和氢渗透性能研究,并重点介绍了以铌钯复合膜为代表的新型Pd/bcc型复合膜氢渗透性能的研究进展。     

Fabrication of defect-free Pd/α-Al2O3 composite membranes for hydrogen separation

Hydrogen production and separation are two important chemical processes. The development of membrane technology has opened up a new possibility for in situ separation of hydrogen from a reaction mixture at elevated temperature in an energy effective way. The availability of a membrane with adequate hydrogen permselectivity and good thermal and mechanical stability is the key for the successful application of membrane technology in hydrogen production and separation. In this paper, a thin-film, defect-free Pd/α-Al₂O₃ composite membrane was fabricated by the electroless plating technique combined with osmosis. The hydrogen permeation performance of the fabricated Pd/α-Al₂O₃ composite membrane was investigated using pure hydrogen at various temperatures from 320–577°C. The hydrogen separation performance was studied using a hydrogen/nitrogen mixture at 467°C. The influence of sweep gas was also investigated.     

金属膜开发应用研究新进展

通过对金属膜研究背景和研究现状进行了较深入的分析,指出目前金属膜研究的热点问题是多孔金属膜(如烧结不锈钢)和致密钯及其合金膜的应用研究是;阐述了钯基金属膜在开发应用方面存在的问题、解决办法以及发展趋势;详细介绍了多孔金属膜和致密钯基复合膜在膜反应器、氢分离器等方面的重要应用;展示了金属膜对于加氢、脱氢、部分氧化等重要反应,以及生产高纯、超高纯氢气等方面的广阔应用前景.     

用于氢相关领域的钯合金膜的研究进展

报道和评估了近年来用于氢渗透、同位素分离、催化等方面的钯合金薄膜的制备新工艺,对氢在薄膜中的溶解、扩散、渗透的影响因素进行了归纳.结合工程应用,对钯合金的应用研究进行了分析,指出了某些钯合金的潜在应用价值和尚待开发和研究的钯合金薄膜.     

Optical switching properties of Pd--Ni thin-film top-capped switchable mirrors

Switchable mirrors based on magnesium--nickel alloy thin films capped with catalytic Pd--Ni alloy thin films were prepared by a DC magnetron sputtering method. Their composition, structure and surface morphology were studied by XPS, XRD and AFM. Herein, the optical switching properties and durability of the switchable mirrors were investigated by varying the Ni content in the Pd--Ni alloys. Comparing pure Pd catalyst with Pd--Ni top-capped switchable mirrors, the latter show better hydrogenation and dehydrogenation kinetics, and the speed of hydrogen desorption is obviously improved with increasing Ni content in the Pd--Ni alloy. The Pd--Ni capped switchable mirrors also have better optical switching durability. The catalytic Pd layer with the addition of Ni does not influence the transmittance (hydride state) and reflectance (metallic state) of the switchable mirrors. In addition, replacing Pd with Pd--Ni alloy decreases the cost of the switchable mirrors: employing nickel in the alloy Pd_89.2Ni_10.8 can save about 11% use of Pd. Therefore, the Pd--Ni alloy can provide a cheaper catalytic thin film, and it is expected to have applications in energy-saving windows, hydrogen sensors and hydrogen storage materials.     

Hydrogen gas sensing performance of Pd-Ni alloy thin films

We investigated the hydrogen (H₂) sensing properties of palladium (Pd)-nickel (Ni) alloy films with varying Ni content and discussed them in light of structural deformations. The Pd-Ni alloys operated reversibly upon H₂ absorption and desorption and their sensitivities decreased linearly with Ni content added to Pd. This was attributed to reduction in the lattice constant and interstitial volume caused by the Ni addition, allowing fewer hydrogen atoms to penetrate into the Pd-Ni alloy with higher Ni content. Interestingly, the response time of the Pd-Ni alloys was much shorter than that of pure Pd, presumably due to the fast permeation of hydrogen atoms through microscopic imperfections in the alloys. Unlike pure Pd, the Pd-Ni alloys showed an almost linear relationship between the sensitivity and H₂ concentration without hysteretic behaviors, enabling the detection of low concentration of H₂ down to 0.01%. These results provide a significant understanding of the role of Ni in the Pd-Ni thin films for improving the H₂ sensing properties of the Pd-based alloy film sensors.     

Microstructural studies of self-supported (1.5–10 μm) Pd/23 wt%Ag hydrogen separation membranes subjected to different heat treatments

The microstructure of self-supported 1.5–10-μm thick Pd/23 wt%Ag membranes grown by magnetron sputtering have been studied after heat treatment and hydrogen permeation tests using electron microscopy and synchrotron X-ray diffraction. After hydrogen flux stabilization and permeance measurements at 300 °C, the membranes were annealed in air at 300 °C or in N₂/Ar at 300/400/450 °C for 4 days and then tested for hydrogen permeation. The permeation results show that changes in permeability depend on the treatment atmosphere and temperature, as well as membrane thickness. Air treatment at ~300 °C generally induced a positive effect on permeation in the thickness range of 1.5–10 μm. Significant microstructural changes, including grain growth, strain relief, void formation, and growth of nodules occurred in the membranes. The changes in microstructure are more severe for the thinner membranes, and may be attributed mainly to the oxidation processes at or near the surface. For samples annealed in N₂/Ar, enhanced permeation was only obtained with treatment at ~450 °C for 5 and 10 μm. The changes in the microstructure generally increased with heat-treatment temperature, and decreased with membrane's thickness. The membrane with enhanced permeation was accompanied by significant grain growth, strain relief, and surface roughening. For all the membranes, the relative changes in the microstructure were substantially more prominent on the permeate surface than on the feed surface. Details of the analysis are presented and discussed.     

渗氢用非对称性复合陶瓷膜的制备技术

简要介绍了渗氢用非对称性复合陶瓷膜的发展状况，着重介绍了载体的制备，载体表面涂覆技术和钯合金膜的沉积技术。     

Fabrication and characterization of dual sputtered Pd–Cu alloy films for hydrogen separation membranes

In this paper, submicron thin Pd–Cu alloy films are deposited using a dual sputtering technique, which allows a high composition control of the layer. The composition, surface morphology and phase structure of the sputtered layers are investigated by energy-dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractiometry (XRD). For example, the XRD data prove that the Pd–Cu layers are an alloy of Pd and Cu. Subsequently, the characterized Pd–Cu alloy layers are deposited on a silicon support structure to create a 750-nm thin Pd–Cu membrane for hydrogen separation. The reported membrane obtained a high flux of 1.6 mol H₂/m² s at a temperature of 725 K, while the selectivity is at least 500 for H₂/He.     

First-principles study on the mechanical,thermal properties and hydrogen behavior of ternary V-Ni-M alloys

Studying hydrogen behavior in alloys and the mechanical properties of alloys are essential to various practical uses,such as separation membranes,as well as hydrogen embrittlement protection.In order to further develop the non-Pd-alloy membranes used in hydrogen separation,the mechanical,thermal properties of V14NiM(M= Al,Fe,Si,Ti,Zn)and hydrogen solubility and diffusion behaviors of V-based ternary alloys were studied by first principles calculation.The results indicated that the hydrogen solution energies of V-Ni-M are greater than pure vanadium.And the mono-vacancy in pure vanadium can capture 6 H atoms while the V-Ni-M alloys can only capture 5 H atoms.Therefore,the V-Ni-M alloys exhibit lower solubility of hydrogen and higher brittleness resistance to embrittlement compared with pure vanadium.And the diffusion coefficients of V-Ni-M alloys are smaller than that of pure vanadium thanks to smaller hydrogen solubility.The hydrogen solubility and hydrogen permeability can maintain relatively balanced.The study of mechanical properties suggests that the V-Ni-Ti has the best resistance to deformation and pure vanadium has the best ductility.Moreover,V-Ni-Si alloy has the smallest thermal expansion coefficient in the temperature range of 473-723 K,which is the temperature of hydrogen separation,indicating that V-Ni-Si is the best for hydrogen separation according to thermal properties.     

Low temperature hydrogen transport using a palladium/copper membrane

Results are presented from low temperature hydrogen permeation experiments using a palladium/copper membrane. Inlet pressure was varied from 5 psig to 180 psig, while temperature was varied from 25°C to 275°C. The palladium/copper membranes exhibited flow stability problems at low temperatures and pressures when using ultra high purity hydrogen. A preconditioning step of high temperatures and inlet pressures of pure hydrogen was necessary to stimulate any substantial permeate flows. After pre-conditioning, results showed zero hydrogen flow when using 3–4% hydrogen mixed with helium or argon. It is thought that the inert gas atoms were adsorbed into the membrane surface and thus blocked the hydrogen atom dissolution. When using pure hydrogen at low to moderate temperatures and low pressures, no measurable permeate flow was observed. Also, zero permeate flow was observed at relatively high temperatures (e.g., 150°C) and a low inlet pressure (5 psig). The cause of the zero permeate flow, when using pure hydrogen, was attributed to interface control of the permeation process. Interface control could be due to: (a) insufficient energy to split the hydrogen molecule into hydrogen atoms, or (b) a reversible phase change from beta to alpha of crystals at the near surface.     

Hydrogen transport through thin palladium-copper alloy composite membranes at low temperatures

Hydrogen permeation performance of three thin palladium-copper composite membranes with different thicknesses had been studied between 398 K and 753 K. Hydrogen permeance was obtained up to 2.7 × 10^− 6 mol/(m² s Pa) with an ideal selectivity over 1000 at 753 K. The hydrogen permeation exhibited two different activation energies over the temperature range: lower activation energy of about 9.8 kJ/mol above 548 K, while higher activation energy of about 26.4 kJ/mol below 548 K. After permeation tests, the alloy membranes were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis and in situ X-ray diffraction. Palladium segregation on the surface of these palladium-copper alloys may induce changes of hydrogen permeation performance and thus influence the activation energies.     

Characterization of Ni–Pd alloy as anode for methanol oxidative fuel cell

Electrochemical deposition of Ni–Pd alloy films of various compositions from bath solution containing ethylenediamine (EDA) was carried out to use as anode material for methanol oxidative fuel cell in H₂SO₄ medium. Electronic absorption spectrum of bath solution containing Ni²⁺, Pd²⁺ ions and EDA indicated the formation of a four coordinate square planar metal–ligand complex of both the metal ions. X-ray diffraction (XRD) patterns of the deposited alloy films show an increase in Pd–Ni alloy lattice parameter with increase in Pd content, and indicate the substitution of Pd in the lattice. A nano/ultrafine kind of crystal growth was observed in the alloy film deposited at low current density (2.5 mA cm⁻²). X-ray photoelectron spectroscopic (XPS) studies on the successively sputtered films showed the presence of Ni and Pd in pure metallic states and the surface concentration ratio of Ni to Pd is less than bulk indicating the segregation of Pd on the surface. Electro-catalytic oxidation of methanol in H₂SO₄ medium is found to be promoted on Ni–Pd electrodeposits. The anodic peak current characteristics to oxidation reaction on Ni–Pd was found typically high when compared to pure nickel and the relative increase in surface area by alloying the Ni by Pd was found to be as much as 300 times.     

Nanostructured thin palladium-silver membranes: Effects of grain size on gas permeation properties

Submicron-thick Pd-Ag alloy membranes, prepared on 4 nm pore -alumina support by magnetron sputter deposition, are nanocrystalline with a grain (crystallite) size of about 20 nm. The membranes show good selectivity for hydrogen over helium (about 4000 at 300°C). Hydrogen permeation is dominated by the surface reaction steps in 100–200°C with an activation energy of about 30 kJ/mol. Bulk diffusion resistance becomes important at higher temperatures (>200 °C). Grain size is the most critical parameter affecting the hydrogen permeance of the thin nanostructued Pd-Ag membranes. Increase in Pd-Ag grain size from about 20 to 60 nm results in a substantial improvement in hydrogen permeance with a higher apparent activation energy in 100–300°C. Grain growth appears to increase the hydrogen permeability in the bulk phase of the Pd-Ag membranes. Helium permeance through the grain boundary decreases with increasing temperature or hydrogen partial pressure due to grain expansion. Carbonation and the accompanied grain expansion have detrimental effects on the perm-selectivity of the Pd-Ag membranes.     

The effect of temperature and pressure on the hydrogen permeation through Pd-coated Ti26Ni21V53 alloy membrane under different atmospheres

The paper introduces Ti₂₆Ni₂₁V₅₃ alloy membrane as a potential replacement for Pd-based membrane. The pressure–temperature–hydrogen permeation relationships of Pd-coated Ti₂₆Ni₂₁V₅₃ alloy membrane have been investigated under pure hydrogen and mixed hydrogen gas with carbon dioxide and carbon monoxide in a pressure range from 0.5 to 2 atm over a wide temperature range including the typical hydrogen membrane operating temperature range (350–450 °C). The experiments show that the hydrogen flux was directly proportional to the temperature at constant pressure according to an Arrhenius-type relationship, whereas it was not proportional to the square root of hydrogen partial pressure in little accordance with the Sievert's law. The hydrogen permeability values obtained for the Pd-coated Ti₂₆Ni₂₁V₅₃ alloy membrane under present conditions are higher than the pure palladium and those previously published in the Ti–Ni–V ternary systems.     

Sorption, diffusion, and pervaporation characteristics of dimethylformamide/water mixtures using sodium alginate/polyvinyl pyrrolidone blend membranes

Separation of aqueous dimethylformamide (DMF) solutions in the concentration range of 0-100 wt% were studied using sodium alginate (NaAlg)/polyvinyl pyrrolidone (PVP) blend membranes. The NaAlg was blended in different ratios with PVP. Prepared membranes were crosslinked with CaCl₂ for testing in pervaporation (PV) separation of DMF/water mixtures. Effects of feed composition (0-100 wt%), operating temperature (30-50 °C), and membrane thickness were investigated. Best results were obtained at the conditions of 75/25 NaAlg/PVP blend ratio (w/w), 40 °C temperature, 20 wt% DMF concentration, and 70 μm membrane thickness. Blending of PVP with NaAlg increased permeation flux whereas it decreased the separation factor. NaAlg/PVP membranes gave separation factors of 5.5-27 for permeation flux of 0.96-1.81 kg/m²h depending on the operating temperature and the feed mixture composition. Arrhenius plot of permeation flux data versus reciprocal of temperature exhibited linear trends. Permeation activation energy of DMF and water in the PV was calculated as 6.76 and 1.88 kcal/mol, respectively, using an Arrhenius type relationship. Sorption-diffusion properties of the NaAlg/PVP membranes were also investigated at the operating temperature and the feed composition.     

Hydrogen gas sensing with networks of ultrasmall palladium nanowires formed on filtration membranes

Hydrogen sensors based on single Pd nanowires show promising results in speed, sensitivity, and ultralow power consumption. The utilization of single Pd nanowires, however, face challenges in nanofabrication, manipulation, and achieving ultrasmall transverse dimensions. We report on hydrogen sensors that take advantage of single palladium nanowires in high speed and sensitivity and that can be fabricated conveniently. The sensors are based on networks of ultrasmall (<10 nm) palladium nanowires deposited onto commercially available filtration membranes. We investigated the sensitivities and response times of these sensors as a function of the thickness of the nanowires and also compared them with a continuous reference film. The superior performance of the ultrasmall Pd nanowire network based sensors demonstrates the novelty of our fabrication approach, which can be directly applied to palladium alloy and other hydrogen sensing materials.     

钯基合金膜应用研究进展

综述了钯基合金膜应用研究的进展状况 ,着重介绍了钯合金膜的制备方法、影响钯合金膜渗氢性能的因素等 ,并对钯基合金膜存在的技术问题及其发展方向进行了讨论 .     

Hydrogen permeation through internally oxidized Pd alloys

Hydrogen diffusivity and solubility were determined by electrochemical hydrogen permeation tests in samples of Pd_0.97 Al_0.03 and Pd_0.97 Ce_0.03 in the as received and internally oxidized conditions. Internal oxidization caused the appearance of nanosized oxide precipitates in the Pd matrix. The shape and size of precipitates and also the coherence between the precipitates and the matrix were observed by transmission electron microscopy (TEM). Electrochemical hydrogen permeation tests revealed that the presence of oxides increases the apparent hydrogen solubility, S _app, but decreases the hydrogen diffusivity, D _app. The values of D _app were 2.0 × 10⁻¹¹ m² s⁻¹ for vacuum heat treated Pd_0.97 Al_0.03 alloy and 4.0 × 10⁻¹² m² s⁻¹ for internally oxidized Pd_0.97 Al_0.03 alloy. However, the concentration of trapped hydrogen was 49 mol H.m⁻³ for the Pd_0.97 Al_0.03 alloy in the vacuum heat treated condition and 403 mol H.m⁻³ for the Pd_0.97 Al_0.03 alloy in the internally oxidized condition. Both heat treatments were performed at 1073 K for 24 h. The influence of the nature, size and distribution of the precipitates on the hydrogen permeation parameters are discussed in this paper.