Characterization of Pd–Cu membranes fabricated by surfactant induced electroless plating (SIEP) for hydrogen separation

Pd–Cu composite membranes on microporous stainless steel (MPSS) substrate were fabricated using surfactant induced electroless plating (SIEP). In the SIEP method, dodecyl trimethyl ammonium bromide (DTAB), a cationic surfactant, was used in Pd- and Cu-baths for the sequential deposition of metals on MPSS substrates. The SIEP Pd–Cu membrane performance was compared with membranes fabricated by conventional electroless plating (CEP). The pre- and post-annealing characterizations of these membranes were carried out by SEM, XRD, EDX and AFM studies. The SEM images showed a significant improvement of the membrane surface morphology, in terms of metal grain structures and grain agglomeration compared to the CEP membranes. The SEM images and helium gas-tightness studies indicated that dense and thinner films of Pd–Cu can be produced with shorter deposition time using SIEP method. From XRD, cross-sectional SEM and EDS studies, alloying of Pd–Cu was confirmed at an annealing temperature of 773 K under hydrogen environment. These membranes were also studied for H₂ perm-selectivity as a function of temperature and feed pressure. SIEP membranes had significantly higher H₂ perm-selectivity compared to CEP membranes. Under thermal cycling (573 K – 873 K – 573 K), the SIEP Pd–Cu membrane was stable and retained hydrogen permeation characteristics for over three months of operation.     

Structure and hydrogen permeability of V–15Ni alloy

The structure of the V–15Ni at.% alloy before and after hydrogen permeability tests was investigated by means of XRD and SEM with EDS analysis. We have found that decomposition of supersaturated V-based solid solution with variable Ni content occurred during testing. The volume fraction of the solid solution decreased and the fraction of V₃Ni phase increased during permeability testing, thus bringing the alloy to nearly equilibrium. The membrane without Pd coating showed satisfactory hydrogen fluxes with a significant impact of the surface dissociation rate of hydrogen. The shape of hydrogen permeation curves at the downstream side of the membrane at various temperatures was unusual. We attribute it to the high concentration of dissolved hydrogen in the metal lattice and its effect on the hydrogen diffusivity and solubility. In addition, the multiphase structure with non-uniform distribution of nickel both between the phases and within the BCC solid solution (and, consequently, different hydrogen concentrations) may cause dilatation or compressing effect on neighbouring micro-volumes of the alloy.     

Pd–Ni hydrogen sponge for highly sensitive nanogap-based hydrogen sensors

We have successfully fabricated sub-100 nm nanogaps in Pd–Ni alloy thin films on an elastomeric substrate by simple stretching. The nanogaps-containing Pd–Ni films were utilized as hydrogen-sensing sponges and their performance was demonstrated to dominate over the performance of similar mobile thin films comprised of pure Pd in major aspects such as the response time, sensitivity in high H₂ concentrations, and H₂ detection limit. Notably, Pd_87.5Ni_12.5 hydrogen sensing sponges showed ultra-high sensitive and reversible On-Off behaviors and low detection limit of ∼100 ppm, which were attributed to the reduced nanogap width and the enhanced volume expandability of Pd–Ni lattice. The effects of Ni added to Pd and a search for an optimum Ni concentration were also systematically studied.     

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.     

Mechanical property and hydrogen permeability of ultrafine-grained Pd–Ag alloy processed by high-pressure torsion

A process of high-pressure torsion (HPT) was used to produce an ultrafine-grained Pd–Ag alloy, and to improve mechanical property and hydrogen permeability simultaneously. Hardness values of the HPT-processed sample were much higher than those of a cold-rolled sample which is strengthened by dislocation accumulation. Additionally, in contrast to the degradation of hydrogen permeability in the cold-rolled sample due to a high density of dislocations which act as trapping sites of hydrogen atoms, the hydrogen permeability in the HPT-processed sample was improved due to a high density of high-angle grain boundaries which act as a fast diffusion path. The ultrafine-grained structure in the Pd–Ag alloy was retained during permeation testing at 300 °C due to the addition of silver.     

Comparative study on the numerical simulation of hydrogen separation through palladium and palladium–copper membranes

The hydrogen (H₂) diffusion through palladium (Pd) and Pd–copper (Cu) membranes was numerically investigated by developing a two-dimensional computational fluid dynamics model for predicting the performance of H₂ separation. The momentum and mass transport phenomena in the laminar flow conditions were solved at different operating conditions in a vertical cylindrical-type reactor. The effect of feed-gap distance, H₂ concentration, and reactor heating temperature on the H₂ permeation processes were simulated and compared for both Pd-based membranes. The concentration, velocity, and convective and diffusion mass transfer flux distributions were analyzed using the designed model. The H₂ concentration was proportional to the feed-gap distance/cross-sectional area. The smaller the feed-gap distance, the greater the probability of a H₂ molecule being adsorbed by the membrane surface and the ionization energy increasing, leading to further H₂ dissociation through the Pd-based membranes. It was found that the diffusion flux of all feed concentrations was substantially decreased 50 s after the start of the permeation process. Moreover, the diffusion flux of the Pd–Cu40% membrane was relatively larger than that of the pure Pd membrane under the same operating conditions. The distributions of the convective flux, diffusion mass transfer flux, and concentration of the Pd–Cu40% membrane were substantially increased up to 350 °C, then fell to a lower value at higher temperatures. The simulation results were validated with the experimental results, with analysis indicating a good agreement with the experimental results under the same operating conditions. It can be concluded that the simulation modeling for Pd-based membranes was able to predict the optimum operating conditions at high H₂ diffusion rates.     

Design of hydrogen permeable Nb–Ni–Ti alloys by correlating the microstructures,solidification paths and hydrogen permeability

The compositional window in Nb–Ni–Ti alloys leading to the crystallization of primary α-Nb phase and the eutectic (α-Nb + NiTi) phase is of high technical relevance due to its favorable properties with respect to hydrogen permeation. The solidification behavior of Nb–Ni–Ti alloys in the primary α-Nb phase region is investigated to reveal the potential solidification paths. The study is based on the characterization of as-cast microstructures in combination with numerical calculations of solidification paths using the CALPHAD method coupled with a microsegregation model. Four different kinds of solidification paths depending on initial composition and cooling rate are found. Correspondingly, a new compositional window appropriate for hydrogen permeation is established in the primary α-Nb phase region. The variation of the hydrogen permeability of the alloys in this window is surprisingly high. High Nb content and Ni/Ti ratio lead to a high permeability. Nb₅₅Ni₂₀Ti₂₅ shows the highest permeability at 673 K, particularly 2.9 × 10⁻⁸ mol H₂ m⁻¹ s⁻¹ Pa^−1/2. This is about 1.8 times higher than that of pure Pd.     

First-principles based modeling of hydrogen permeation through Pd–Cu alloys

The solubility and diffusivity of hydrogen in disordered fcc Pd_1−xCu_x alloys are investigated using a combination of first-principles calculations, a composition-dependent local cluster expansion (CDLCE) technique, and kinetic Monte Carlo simulations. We demonstrate that a linear CDCLE model can accurately describe interstitial H in fcc Pd_1−xCu_x alloys over the entire composition range (0 ≤ x ≤ 1) with accuracy comparable to that of direct first-principles calculations. Our predicted H solubility and permeability results are in reasonable agreement with experimental measurements. The proposed model is quite general and can be employed to rapidly and accurately screen a large number of alloy compositions for potential membrane applications. Extension to ternary or higher-order alloy systems should be straightforward. Our study also highlights the significant effect of local lattice relaxations on H energetics in size-mismatched disordered alloys, which has been largely overlooked in the literature.     

Pd–Cu alloy membrane deposited on CeO2 modified porous nickel support for hydrogen separation

In this study, the hydrogen permeation behavior of a Pd₉₃–Cu₇ alloy membrane deposited on ceria-modified porous nickel support (PNS) was evaluated. PNS, which has an average pore size of 600 nm, was modified by alumina sol. Alumina sol was prepared using precursors that had a mean particle size of 300 nm. Alumina-modified PNS was further treated with ceria sol modification to produce a smoother surface morphology and narrow surface pores. A 7 μm thick Pd₉₃–Cu₇ alloy membrane was made on an alumina-modified PNS and a ceria-finished membrane was fabricated by magnetron sputtering followed by Cu-reflow at 700 °C for 2 h. SEM analysis showed that the membrane deposited on a ceria-finished PNS contained more clear grain boundaries than the membrane deposited on the alumina-modified PNS. The membrane was mounted in a stainless steel permeation cell with a gold-plated stainless steel O-ring. Permeation tests were then conducted using pure hydrogen and helium at temperatures ranging from 673 to 773 K and feed side pressures ranging from 100 to 400 kPa. These tests showed that the membrane had a hydrogen permeation flux of 2.8 × 10⁻¹ mol m⁻² s⁻¹ with H₂/He selectivity of >50,000 at a temperature of 773 K and pressure difference of 400 kPa.     

Anti-sintering mesoporous Ni–Pd bimetallic catalysts for hydrogen production via dry reforming of methane

In this work, a series of mesoporous silica supported nickel or nickel-palladium catalysts were synthesized and performed in dry reforming of methane (DRM) reaction for producing syngas. Compared with the monometallic catalyst, the Ni–Pd bimetallic catalysts, especially synthesized by the OA-assisted route, exhibited promising yields of H₂ and CO in the catalytic DRM reaction, achieved at 63% and 69% over NiPd-SP-OA bimetallic catalyst at the reaction temperature of 700 °C, respectively. TEM image results confirmed that no obvious sintering phenomenon happened on spent NiPd-SP-OA bimetallic catalyst within 1550 min time-on-stream reaction. Based on the results of XRD, XPS and H₂-TPR, it could be known that the superior catalytic performance on NiPd-SP-OA catalyst were main ascribed to the smaller-sized Ni nanoparticles with a uniform metal dispersion and a larger fraction of exposed active sites (Ni⁰).     

Nb–HfCo alloys with pronounced high hydrogen permeability: A new family of metallic hydrogen permeation membranes

Microstructures and hydrogen permeability of the Nb_xHf_(100−x)/2Co_(100−x)/2 (x = 15…40) alloys were investigated. The composition Nb₃₀Hf₃₅Co₃₅ resulted in a fully eutectic microstructure. Alloys with x (20 < x < 30) contain the primary HfCo and the eutectic {bcc-(Nb, Hf) + B_f-HfCo} phases, while those with x (x ≤ 20) additionally contain small fractions of the Hf₂Co phase that results from a ternary eutectic reaction. Alloys with x (x > 30) contain the primary bcc-(Nb, Hf) and the eutectic phases, which exhibits pronounced high hydrogen permeability and large resistance to hydrogen embrittlement. The permeability increases with increasing Nb content and increasing volume fraction of the primary bcc-(Nb, Hf) phase. Nb₄₀Hf₃₀Co₃₀ shows the highest permeability, particularly 4.96 × 10⁻⁸ mol H₂ m⁻¹ s⁻¹ Pa^−1/2 at 673 K. This is about 3.5 times higher than that of pure Pd and also the highest value among all the currently reported ones.     

Synthesis and electrocatalytic hydrogen evolution performance of Ni–Mo–Cu alloy coating electrode

Ni–Mo–Cu alloy coating electrode was prepared on copper substrate by constant current electrodeposition and characterized by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The electrochemical characterization for hydrogen evolution reaction (HER) was investigated by cyclic voltammetry (CV) curves, linear sweep voltammetry (LSV) curves and electrochemical impedance spectroscopy (EIS) techniques. Parameters affecting the electrocatalytic activity for the HER are systematically investigated. Results show the Ni–Mo–Cu coating by the introduction of Cu has a rough and cauliflower-like structure and presents a most efficient activity for HER in comparison with binary Ni–Mo electrode. Its remarkably enhanced catalytic activity is attributed to the high surface area as well as synergistic interaction between Ni, Mo and Cu.     

Improved hydrogen gas sensing performance of Pd–Ni alloy thin films

This study examined the palladium (Pd)-nickel (Ni) alloy films' ability to detect hydrogen (H₂) at various Ni concentrations. The co-sputtering method was used to make the Pd–Ni alloy sensors. The response of the Pd–Ni alloys sensor reduced linearly as Ni_8% concentration was added to Pd, and the resistance of the Pd–Ni alloys was reversible upon exposure to H₂ gas with absorption and desorption characteristics. The experimental findings demonstrated that the Pd–Ni alloy sensor response time of 11 s was much faster than that of pure Pd, with great selectivity and stability for a period of 90 days.     

Pd–Ni–Cu–P metallic glass nanowires for methanol and ethanol oxidation in alkaline media

We demonstrate that Pd₄₃Ni₁₀Cu₂₇P₂₀ bulk metallic glass (BMG) nanowires, prepared by a facile, scalable top-down nanomolding approach, can be used as high surface area electrocatalysts for alkaline alcohol fuel cell applications. These nanowires exhibit higher activity for methanol and ethanol oxidation in alkaline media compared to pure Pd, quantified by cyclic voltammetry. Furthermore, the Pd-BMG nanowire electrocatalyst has a 300 mV lower onset potential for CO oxidation suggesting improved poisoning resistance beyond pure Pd. The Pd-BMG electrocatalyst activation energies for methanol and ethanol oxidation of 22 and 17 kJ mol⁻¹ are lower than the pure Pd values of 38 and 30 kJ mol⁻¹, respectively. Unique properties of BMGs (homogeneity, viscosity, surface tension) facilitate the formability into high surface area electrocatalysts at low processing temperatures. The high electrical conductivity and chemical/physical stability suggest that these materials are ideal candidates for widespread commercial use including energy conversion/storage, hydrogen production, and sensors.     

Non-noble Ni–Cu/ACC bimetallic catalyst for dehydrogenation of liquid organic hydrides for hydrogen storage

The effect of Cu on dehydrogenation activity of Ni has been observed when dehydrogenation of methyl cyclohexane (MCH) was carried out by using bimetallic Ni–Cu supported on activated carbon cloth (ACC) catalysts with various Ni to Cu ratios and constant total metal content of about 10 wt%. The dehydrogenation of MCH was studied for delivery of clean hydrogen to hydrogen fueling station. Catalysts have been synthesized by adsorption method and characterized by atomic absorption spectroscopy (AAS), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Among all combinations of this study 8 wt% Ni + 2 wt% Cu/ACC was found to show strong synergetic effect. This catalyst exhibited relatively high H₂ evolution rate 39.4 mmol/g_met/min during the dehydrogenation of MCH. At the same time methane evolution rate was relatively low which indicated insignificant side reaction of hydrogenolysis. The study reveals that presence of specific amount of Cu enhances the dehydrogenation activity of Ni and suppresses the hydrogenolysis activity for the same. The Ni–Cu/ACC catalyst may be a potential non-noble metal catalyst for dehydrogenation reaction.     

Renewable hydrogen production from steam reforming of glycerol by Ni–Cu–Al,Ni–Cu–Mg,Ni–Mg catalysts

H₂ production from glycerol steam reforming by the Ni–Cu–Al, Ni–Cu–Mg, Ni–Mg catalysts was evaluated experimentally in a continuous flow fixed-bed reactor under atmospheric pressure within a temperature range from 450 to 650 °C. The catalysts were synthesized by the co-precipitation methods, and characterized by the elemental analysis, BET, XRD and SEM. The GC and FTIR were applied to analyze the products from steam reforming of glycerol. The coke deposited on the catalysts was measured by TGA experiments during medium temperature oxidation. The results showed that glycerol conversion and H₂ production were increased with increasing temperatures, and glycerol decomposition was favored over its steam reforming at low temperatures. The Ni–Cu–Al catalyst containing NiO of 29.2 wt%, CuO of 31.1 wt%, Al₂O₃ of 39.7 wt% performed high catalytic activity, and the H₂ selectivity was found to be 92.9% and conversion of glycerol was up to 90.9% at 650 °C. The deactivation of catalysts due to the formation and deposition of coke was observed. An improved iterative Coats–Redfern method was used to evaluate the non-isothermal kinetic parameters of coke removal from catalysts, and the results showed the reaction order of n = 1 and 2 in the Fn nth order reaction model predicted accurately the main phase in the coke removal for the regeneration of Ni–Mg and Ni–Cu–Al catalysts, respectively.     

Nanostructured C–Pd films for hydrogen applications

We propose nanostructured carbonaceous-palladium (C–Pd) films as promising material for covering different, big surfaces as improving hydrogen storing properties material. The C–Pd films were obtained by annealing of samples prepared by physical vapor deposition on fused silica substrates. Palladium nanocrystallites placed within the film volume and also on its surface enhanced absorption of hydrogen due to dissolution of H₂ molecules in the nanocrystallites. We studied structure, morphology and topography of these films by different methods (XRD, GIXRD, SEM and EDS). XRD measurements performed in situ under H₂/N₂ atmosphere showed that α phase and β phase of palladium hydride were formed.     

Structure and hydrogen storage performances of La–Mg–Ni–Cu alloys prepared by melt spinning

The (Mg₂₄Ni₁₀Cu₂)_100-xLa_x(x = 0, 5, 10, 15, 20) alloys were prepared adopting the method of melt spinning technology. Adding La brings on the formation of secondary phases of La₂Mg₁₇ and LaMg₃, while it does not change the major phase of Mg₂Ni. Originally, there already have nanocrystals and amorphous structures in the experimental alloys, and the addition of La is more conducive to the formation of glass. With adding La in as-spun alloys, the gaseous hydrogen absorption capacity was significantly reduced, but it markedly improved their hydriding rates. Adding La and melt spinning considerably enhanced the dehydriding rate, the reason for which is the decrease of activation energy incurred by adding La and melt spinning. In addition, the discharge capacity of the alloys were able to reach a maximum value during La content varying, and it obviously increased with spinning rate rising.     

Hydrophobic platinum–polytetrafluoroethylene catalyst for hydrogen isotope separation

A composite catalyst, platinum supported on polytetrafluoroethylene (Pt/PTFE), has been successfully prepared by compression moulding forming and used for hydrogen isotope separation by hydrogen–water isotope exchange. The as-prepared Pt/PTFE was characterized by nitrogen adsorption. The results of the catalytic activity for hydrogen–water isotope exchange show that Pt/PTFE has high catalytic activity. The effects of different factors, such as flow rate, temperature, molar flow ratio of hydrogen gas to feed water and time have also been investigated. The present study shows a promising choice of Pt/PTFE as a composite catalyst for hydrogen isotope separation.