Palladium-copper membranes for hydrogen separation

High-Performance Hydrogen-Selective Pd-Ag Membranes Modified with Pd-Pt Nanoparticles for Use in Steam Reforming Membrane Reactors

A unique method for synthesizing a surface modifier for metallic hydrogen permeable membranes based on non-classic bimetallic pentagonally structured Pd-Pt nanoparticles was developed. It was found that nanoparticles had unique hollow structures. This significantly reduced the cost of their production due to the economical use of metal. According to the results of electrochemical studies, a synthesized bimetallic Pd-Pt/Pd-Ag modifier showed excellent catalytic activity (up to 60.72 mA cm-2), long-term stability, and resistance to COads poisoning in the alkaline oxidation reaction of methanol. The membrane with the pentagonally structured Pd-Pt/Pd-Ag modifier showed the highest hydrogen permeation flux density, up to 27.3 mmol s-1 m-2. The obtained hydrogen flux density was two times higher than that for membranes with a classic Pdblack/Pd-Ag modifier and an order of magnitude higher than that for an unmodified membrane. Since the rate of transcrystalline hydrogen transfer through a membrane increased, while the speed of transfer through defects remained unchanged, a one and a half times rise in selectivity of the developed Pd-Pt/Pd-Ag membranes was recorded, and it amounted to 3514. The achieved results were due to both the synergistic effect of the combination of Pd and Pt metals in the modifier composition and the large number of available catalytically active centers, which were present as a result of non-classic morphology with high-index facets. The specific faceting, defect structure, and unusual properties provide great opportunities for the application of nanoparticles in the areas of membrane reactors, electrocatalysis, and the petrochemical and hydrogen industries.

Compositional tuning of gas-phase synthesized Pd-Cu nanoparticles

Bimetallic nanoparticles have gained significant attention in catalysis as potential alternatives to expensive catalysts based on noble metals. In this study, we investigate the compositional tuning of Pd-Cu bimetallic nanoparticles using a physical synthesis method called spark ablation. By utilizing pure and alloyed electrodes in different configurations, we demonstrate the ability to tailor the chemical composition of nanoparticles within the range of approximately 80 : 20 at% to 40 : 60 at% (Pd : Cu), measured using X-ray fluorescence (XRF) and transmission electron microscopy energy dispersive X-ray spectroscopy (TEM-EDXS). Time-resolved XRF measurements revealed a shift in composition throughout the ablation process, potentially influenced by material transfer between electrodes. Powder X-ray diffraction confirmed the predominantly fcc phase of the nanoparticles while high-resolution TEM and scanning TEM-EDXS confirmed the mixing of Pd and Cu within individual nanoparticles. X-ray photoelectron and absorption spectroscopy were used to analyze the outermost atomic layers of the nanoparticles, which is highly important for catalytic applications. Such comprehensive analyses offer insights into the formation and structure of bimetallic nanoparticles and pave the way for the development of efficient and affordable catalysts for various applications.

Collectable Single Pure-Pd Metal Membrane with High Strength and Flexibility Prepared through Electroplating for Hydrogen Purification

Among the various film preparation methods, electroplating is one of the simplest and most economical methods. However, it is challenging to collect a dense single Pd film through plating, owing to the accumulation of stress in the film during the process. Therefore, the characteristics of a single plated film have not been clearly identified, although pure Pd is widely used in metallic-hydrogen-purification membranes. In this study, stress concentration in film during preparation was reduced by optimizing the plating process, and a dense single flat film was successfully collected. No impurities were detected. Thus, a high-purity Pd film was prepared. Its surface texture was found to be significantly different from that of the rolled film, and several approximately 5 μm sized aggregates were observed on the surface. The plated film is reported to have mechanical properties superior to those of the rolled film, with twice the displacement and four times the breaking point strength. The hydrogen permeabilities of the plated film (5.4 × 10−9–1.1 × 10−8 mol·m−1·s−1·Pa−1/2 at 250–450 °C) were comparable to those of the rolled and reported films, indicating that the surface texture does not have a strong effect on hydrogen permeability. The results of this study promote the practical use of Pd-based membranes through electroplating.

Effect of Hydrogen Exposure Temperature on Hydrogen Embrittlement in the Palladium-Copper Alloy System (Copper Content 5-25 wt.%)

The yield strength, ultimate strength, and elongation/ductility properties of a series of palladium-copper alloys were characterized as a function of the temperature at which each alloy underwent absorption and desorption of hydrogen. The alloys studied ranged in copper content from 5 weight percent copper to 25 wt.% copper. Compared to alloy specimens that had been well-annealed in a vacuum and never exposed to hydrogen, alloys with copper content up to 15 wt.% showed strengthening and loss of ductility due to hydrogen exposure. In these alloys, it was found that the degree of strengthening and loss of ductility was dependent on the hydrogen exposure temperature, though this dependence decreased as the copper content of the alloy increased. For alloys with copper contents greater than 15 wt.%, hydrogen exposure had no discernible effect on the strength and ductility properties compared to the vacuum-annealed alloys, over the entire temperature range studied.

Experimental and Numerical Study of Pd/Ta and PdCu/Ta Composites for Thermocatalytic Hydrogen Permeation

The development of stable and durable hydrogen (H₂) separation technology is essential for the effective use of H₂ energy. Thus, the use of H₂ permeable membranes, made of palladium (Pd), has been extensively studied in the literature. However, Pd has considerable constraints in large-scale applications due to disadvantages such as very high cost and H₂ embrittlement. To address these shortcomings, copper (Cu) and Pd were deposited on Ta to fabricate a composite H₂ permeable membrane. To this end, first, Pd was deposited on a tantalum (Ta) support disk, yielding 7.4 × 10^-8 mol_H2 m^-1 s^-1 Pa^-0.5 of permeability. Second, a Cu-Pd alloy on a Ta support was synthesized via stepwise electroless plating and plasma sputtering to improve the durability of the membrane. The use of Cu is cost-effective compared with Pd, and the appropriate composition of the PdCu alloy is advantageous for long-term H₂ permeation. Despite the lower H₂ permeation of the PdCu/Ta membrane (than the Pd/Ta membrane), about two-fold temporal stability is achieved using the PdCu/Ta composite. The degradation process of the Ta support-based H₂ permeable membrane is examined by SEM. Moreover, thermocatalytic H₂ dissociation mechanisms on Pd and PdCu were investigated and are discussed numerically via a density functional theory study.

Development of Electrode-Supported Proton Conducting Solid Oxide Cells and their Evaluation as Electrochemical Hydrogen Pumps

Protonic ceramic solid oxide cells (P-SOCs) have gained widespread attention due to their potential for operation in the temperature range of 300-500 °C, which is not only beneficial in terms of material stability but also offers unique possibilities from a thermodynamic point of view to realize a series of reactions. For instance, they are ideal for the production of synthetic fuels by hydrogenation of carbon dioxide and nitrogen, upgradation of hydrocarbons, or dehydrogenation reactions. However, the development of P-SOC is quite challenging because it requires a multifront optimization in terms of material synthesis and fabrication procedures. Herein, we report in detail a method to overcome various fabrication challenges for the development of efficient and robust electrode-supported P-SOCs (Ni-BCZY/BCZY/Ni-BCZY) based on a BaCe_0.2Zr_0.7Y_0.1O_3-δ (BCZY271) electrolyte. We examined the effect of pore formers on the porosity of the Ni-BCZY support electrode, various electrolyte deposition techniques (spray, spin, and vacuum-assisted), and thermal treatments for developing robust and flat half-cells. Half-cells containing a thin (10-12 μm) pinhole-free electrolyte layer were completed by a screen-printed Ni-BCZY electrode and evaluated as an electrochemical hydrogen pump to access the functionality. The P-SOCs are found to show a current density ranging from 150 to 525 mA cm^-2 at 1 V over an operating temperature range of 350-450 °C. The faradaic efficiency of the P-SOCs as well as their stability were also evaluated.

Hydrogen production technologies - Membrane based separation, storage and challenges

The production of hydrogen, its separation, and storage for use as a primary source of energy is an important component of the green energy economy of the world. Hydrogen is a potential non-carbon-based energy source, which is gradually replacing the dependency on fossil fuels. It is anticipated that as the alternative fuel since hydrogen can be produced from green and clean sources. The evolution of hydrogen from renewable and non-renewable sources by various technologies has now gained tremendous research and industrial interest. The most appropriate methods for hydrogen generation involve the direct conversion of solar energy, exploitation of solar and wind energy for the electrolysis of water, besides conversion of fuel and biomass. To produce cleaner hydrogen and its separation from the chemical impurities is crucial and several methods including photobiological, photoelectrochemical, electrochemical, photocatalytic, thermochemical, thermolysis, and steam gasification have been used. The diverse types of membranes along with the pressure gas swing adsorption technique is another technique used to separate hydrogen, but the storage of hydrogen in an inexpensive, safe, compact, and environmentally friendly manner is one of the major concerns contributing to the country's economy. Apart from the countless advantages, storage and handling of hydrogen is a serious concern. Owing to its high inflammability, enough safety measures should be adopted during its production and storage as a fuel. It is necessary to provide information regarding the production technologies, storage, and separation methods of hydrogen and the present review addresses these issues.

Technoeconomic Evaluation of the Industrial Implementation of Catalytic Direct Nonoxidative Methane Coupling

This paper presents a process design for catalytic nonoxidative natural gas conversion to olefins and aromatics, highlighting the opportunities and challenges concerning industrial implementation. The optimal reactor conditions are 5 bar and 1000 °C. Heat exchange over the reactor is challenging due to the high temperature and low gas pressure. Recovery of ethylene is economically unattractive due to the low ethylene concentration in the product stream, leading to a methane-to-aromatics process, recycling ethylene. Benzene is the most valuable product at an efficiency of 0.31 kgbenzene/kgmethane with hydrogen as a major valuable byproduct. Naphthalene, with a low value, is unfortunately the dominant product, at 0.52 kgnaphthalene/kgmethane. It is suggested to hydrocrack the naphthalene to more valuable BTX products in an additional downstream process. The process is calculated to result in a 107 $ profit per ton CH4.

Strength, Hardness, and Ductility Evidence of Solid Solution Strengthening and Limited Hydrogen Embrittlement in the Alloy System Palladium-Copper (Cu wt. % 5–25)

Strength, hardness, and ductility characteristics were determined for a series of palladium-copper alloys that compositionally vary from 5 to 25 weight percent copper. Alloy specimens subjected to vacuum annealing showed clear evidence of solid solution strengthening. These specimens showed, as a function of increasing copper content, increased yield strength, ultimate strength, and Vickers microhardness, while their ductility was little affected by compositional differences. Annealed alloy specimens subsequently subjected to exposure to hydrogen at 323 K and PH2 = 1 atm showed evidence of hydrogen embrittlement up to a composition of ~15 wt. % Cu. The magnitude of the hydrogen embrittlement decreased with increasing copper content in the alloy.

High-Performance Nanostructured Palladium-Based Hydrogen Sensors-Current Limitations and Strategies for Their Mitigation

Hydrogen gas is rapidly approaching a global breakthrough as a carbon-free energy vector. In such a hydrogen economy, safety sensors for hydrogen leak detection will be an indispensable element along the entire value chain, from the site of hydrogen production to the point of consumption, due to the high flammability of hydrogen-air mixtures. To stimulate and guide the development of such sensors, industrial and governmental stakeholders have defined sets of strict performance targets, which are yet to be entirely fulfilled. In this Perspective, we summarize recent efforts and discuss research strategies for the development of hydrogen sensors that aim at meeting the set performance goals. In the first part, we describe the state-of-the-art for fast and selective hydrogen sensors at the research level, and we identify nanostructured Pd transducer materials as the common denominator in the best performing solutions. As a consequence, in the second part, we introduce the fundamentals of the Pd-hydrogen interaction to lay the foundation for a detailed discussion of key strategies and Pd-based material design rules necessary for the development of next generation high-performance nanostructured Pd-based hydrogen sensors that are on par with even the most stringent and challenging performance targets.

Thermodynamic Insights for Electrochemical Hydrogen Compression with Proton-Conducting Membranes

Membrane electrode assemblies (MEA) based on proton-conducting electrolyte membranes offer opportunities for the electrochemical compression of hydrogen. Mechanical hydrogen compression, which is more-mature technology, can suffer from low reliability, noise, and maintenance costs. Proton-conducting electrolyte membranes may be polymers (e.g., Nafion) or protonic-ceramics (e.g., yttrium-doped barium zirconates). Using a thermodynamics-based analysis, the paper explores technology implications for these two membrane types. The operating temperature has a dominant influence on the technology, with polymers needing low-temperature and protonic-ceramics needing elevated temperatures. Polymer membranes usually require pure hydrogen feed streams, but can compress H2 efficiently. Reactors based on protonic-ceramics can effectively integrate steam reforming, hydrogen separation, and electrochemical compression. However, because of the high temperature (e.g., 600 °C) needed to enable viable proton conductivity, the efficiency of protonic-ceramic compression is significantly lower than that of polymer-membrane compression. The thermodynamics analysis suggests significant benefits associated with systems that combine protonic-ceramic reactors to reform fuels and deliver lightly compressed H2 (e.g., 5 bar) to an electrochemical compressor using a polymer electrolyte to compress to very high pressure.

Recent advances in membrane reactors for hydrogen production by steam reforming of ethanol as a renewable resource

During the last decade, hydrogen has attracted lots of interest due to its potential as an energy carrier. Ethanol is one of the renewable resources that can be considered as a sustainable candidate for hydrogen generation. In this regard, producing hydrogen from ethanol steam reforming (ESR) would be an environmentally friendly process. Commonly, ESR is performed in packed bed reactors; however, this process needs several stages for hydrogen separation with desired purity. Recently, the concept of a membrane reactor, an attractive device integrating catalytic reactions and separation processes in a single unit, has allowed obtaining a smaller reactor volume, higher conversion degrees, and higher hydrogen yield in comparison to conventional reactors. This paper deals with recent advances in ESR in terms of catalyst utilization and the fundamental of membranes. The main part of this paper discusses the performance of different membrane reactor configurations, mainly packed bed membrane reactors, fluidized bed membrane reactors, and micro-membrane reactors. In addition, a short overview is given about the impact of ESR via different catalysts such as noble metal, non-noble metal, and bi-metallic catalysts.

Review of Supported Pd-Based Membranes Preparation by Electroless Plating for Ultra-Pure Hydrogen Production

In the last years, hydrogen has been considered as a promising energy vector for the oncoming modification of the current energy sector, mainly based on fossil fuels. Hydrogen can be produced from water with no significant pollutant emissions but in the nearest future its production from different hydrocarbon raw materials by thermochemical processes seems to be more feasible. In any case, a mixture of gaseous compounds containing hydrogen is produced, so a further purification step is needed to purify the hydrogen up to required levels accordingly to the final application, i.e., PEM fuel cells. In this mean, membrane technology is one of the available separation options, providing an efficient solution at reasonable cost. Particularly, dense palladium-based membranes have been proposed as an ideal chance in hydrogen purification due to the nearly complete hydrogen selectivity (ideally 100%), high thermal stability and mechanical resistance. Moreover, these membranes can be used in a membrane reactor, offering the possibility to combine both the chemical reaction for hydrogen production and the purification step in a unique device. There are many papers in the literature regarding the preparation of Pd-based membranes, trying to improve the properties of these materials in terms of permeability, thermal and mechanical resistance, poisoning and cost-efficiency. In this review, the most relevant advances in the preparation of supported Pd-based membranes for hydrogen production in recent years are presented. The work is mainly focused in the incorporation of the hydrogen selective layer (palladium or palladium-based alloy) by the electroless plating, since it is one of the most promising alternatives for a real industrial application of these membranes. The information is organized in different sections including: (i) a general introduction; (ii) raw commercial and modified membrane supports; (iii) metal deposition insights by electroless-plating; (iv) trends in preparation of Pd-based alloys, and, finally; (v) some essential concluding remarks in addition to futures perspectives.