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One of the key elements to the success of Pd-Ag membrane based reactor for the H2 production is the synthesis of thin and highly selective membranes using the electroless plating method. This work describes the effect of electroless plating conditions on the obtained Pd and Ag deposits properties (morphology, compactness, phase structure, compositional homogeneity and adhesion) important from synthesis of thin and H2 selective membrane viewpoint. Both sequential and co-deposition deposition methods were investigated. The conventional Pd and Ag plating conditions (NH3+EDTA based bath) produced dendritic and non-uniform sequential (multi layer) deposits, not suitable for synthesizing the thin and H2 selective Pd-Ag membranes. Ag under the conventional plating conditions deposited at high overpotential resulting in the dendritic and non-uniform sequential deposits. The modified Ag plating conditions eliminated Ag deposition at high overpotential and the sequential deposits obtained were non-dendritic and uniform. Thin (< 10 µm thick) and H2 selective Pd-Ag membranes were successfully synthesized using the modified Ag plating conditions. The membranes were then successfully annealed at 550 oC. After the annealing step, the membranes showed activation energy for the H2 permeation (4.3-11.5 kJ/mole) lower than that of the pure Pd membrane (12-16.4 kJ/mole) meaning that the Pd-Ag membranes were more effective for the H2 separation at lower temperatures than the pure Pd membrane. A Pd-Ag (20 wt%) membrane showed H2 permeance higher by a factor of 2.47 at 250 oC than the pure Pd foil. The Pd-Ag membranes also showed decline in the H2/He selectivity on exposure to the annealing and H2 permeation (300-500 oC) study conditions. The Pd-Ag co-deposits obtained (using NH3+EDTA bath) were dendritic, inhomogeneous with poor substrate adhesion, therefore not suitable for the membrane synthesis. The co-deposits were bi-metallic and required the annealing step to form the Pd-Ag alloy. There existed a large difference in the deposition potentials (600 to 650 mV) of Pd and Ag. The Ag deposition was severely controlled by its mass transfer in the solution resulting in the dendritic and inhomogeneous deposits. Among the different complexing agents investigated, KCl showed the least difference between the Pd and Ag deposition potentials. The co-deposits obtained using the KCl bath were non-dendritic, homogeneous and were Pd-Ag alloy therefore required no annealing step. Finally, the multi step plating, annealing and polishing approach was used to avoid the decline in the selectivity of the sequentially prepared Pd-Ag membranes. The membranes prepared by the plating, annealing and polishing approach showed very high selectivity (H2/He) and no decline in the selectivity was observed between 300-450 oC for the total exposure time > 550 h (> 200 h at 450 oC).

Hydrogen (H2) and fuel cells applications are central to the realization of a global hydrogen economy. In this scenario, H2 may be produced from renewable biofuels via steam reforming and by solar powered water electrolysis. The purification required for fuel cell grade H2, whether in tandem or in situ within a catalytic reformer operating at 500 oC or above, would be greatly facilitated by the availability a cheaper and more robust option to palladium (Pd) dense metal membrane, currently the leading candidate. Here we describe our results on the feasibility of a completely novel membrane for hydrogen separation: Sandwiched Liquid Metal Membrane, or SLiMM, comprising of a low-melting, non-precious metal (e.g., Sn, In, Ga) film held between two porous substrates. Gallium was selected for this feasibility study to prove of the concept of SLiMM. It is molten at essentially room temperature, is non-toxic, and is much cheaper and more abundant than Pd. Our experimental and theoretical results indicate that the Ga SLiMM at 500 oC has a permeability 35 times higher than Pd, and substantially exceeds the 2015 DOE target for dense metal membranes. For developing a fundamental understanding of the thermodynamics and transport in liquid metals, a Pauling Bond Valence-Modified Morse Potential (PBV-MMP) model was developed. Based on little input, the PBV-MPP model accurately predicts liquid metal self-diffusion, viscosity, surface tension, as well as thermodynamic and energetic properties of hydrogen solution and diffusion in a liquid metal such as heat of dissociative adsorption, heat of solution, and activation energy of diffusion. The concept of SLiMM proved here opens up avenues for development practical H2 membranes, For this, improving the physical stability of the membrane is a key goal. Consequently, a thermodynamic theory was developed to better understand the change in liquid metal surface tension and contact angle as a function of temperature, pressure and gas-phase composition.

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" This work investigated the long-term stability of sulfur tolerant Pd/Cu alloy membranes for hydrogen separation by performing characterizations lasting several thousand hours in H2, He and H2S/H2 atmospheres ranging in concentration from 0.2 – 50 ppm and temperatures ranging from 250 - 500ºC. Two methods were used for fabricating the Pd/Cu membranes so that the sulfur tolerant fcc alloy would remain on the surface and minimize the decrease in hydrogen permeance inherent with fcc Pd/Cu alloys. The first method consisted of annealing a Pd/Cu bi-layer at high-temperatures and the second consisted of depositing a Pd/Cu/Pd tri-layer with an ultra-thin surface alloy. High temperature X-ray diffraction (HT-XRD) was employed to study the kinetics of the annealing process and atomic adsorption spectroscopy (AAS) was used to investigate the kinetics of the Cu deposition and Pd displacement of Cu. Upon the introduction of H2S, the permeance decrease observed was dependent upon the H2S feed concentration, and not the time of poisoning. However, after the recovery in pure H2 there was a portion of the permeance which could not be recovered due to adsorbed sulfur blocking H2 adsorption sites. The amount of recoverable permeance was dependent on the time of exposure to H2S and reached a limiting value which decreased with temperature. X-ray photoemission spectroscopy (XPS) was used to investigate poisoned samples and it was observed that the permeance not recovered at a given temperature in H2 was caused mostly by Cu sulfides. Both bi-layer and tri-layer membranes had hydrogen permeances which were higher than homogeneous Pd/Cu membranes of the same surface concentration. However, the tri-layer membranes performed as well as Pd membranes thus eliminating the disadvantage of alloying Pd with Cu without sacrificing sulfur tolerance. "

Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Fedorov, Andrei; Committee Co-Chair: Degertekin, Levent; Committee Member: Koros, William; Committee Member: Liu, Meilin; Committee Member: Mayor, J. Rhett. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Magister Scientiae - MSc / South Africa s coal and platinum mineral resources are crucial resources towards creating an alternative and environmentally sustainable energy system. The beneficiation of these natural resources can help to enhance a sustainable and effective clean energy base infrastructure and further promote their exploration and exportation for economics gains. By diversification of these resources, coal and the platinum group metals (PGMs) especially palladium market can be further harnessed in the foreseeable future hence SA energy security can be guaranteed from the technological point of view. The South Africa power industry is a critical sector, and has served as a major platform in the South African socio-economic development. This sector has also been identified as a route towards an independent energy base, with global relevance through the development of membrane technologies to effectively and economically separate and purify hydrogen from the gas mixtures released during coal gasification. The South Africa power industry is a critical sector, and has served as a major platform in the SA's socio-economic development. This sector has also been identified as a route towards an independent energy base, with global relevance through the development of membrane technologies to effectively and economically separate and purify hydrogen from the gas mixtures released during coal gasification. Coal gasification is considered as a source of hydrogen gas and the effluent gases released during this process include hydrogen sulphide, oxides of carbon and nitrogen, hydrogen and other particulates. In developing an alternative hydrogen gas separating method, composite membrane based on organic-inorganic system is being considered since the other available methods of hydrogen separation are relatively expensive. The scientific approach of this study involves the use of palladium modified polyimide composite membrane. Palladium metal serves as hydrogen sorption material, deposited on polyimide substrates (composite film) by electroless technique. Polyimide is a class of polymer with excellent physico-chemical properties such as good mechanical strength, superior thermal stability and high resistance to chemical attack. In this study, a composite polymer-palladium membrane was developed and investigated to determine the prospect of using this membrane as a cheap, accessible, reliable and efficient system to separate and purify hydrogen gas. Prior to the palladium metal plating, the challenge of metal adhesion on glassy polymer such as polyimide film was addressed by chemical etching and unirradiated and irradiated polyimide film surface using NaOH, NaOCl and a mixture of NaOH/NaOCl solutions. The time of etching was varied and the overall effect of this surface treatment was deeply investigated using Fourier transform infrared (FTIR) spectroscopy. The FTIR study focused on the structural deformation of the polyimide functional group units and the emergence of ‘active sites’ along the polyimide backbone structures that have been identified to allow the Pd metal exchange on the functionalised polyimide film. The detailed use of FTIR spectroscopic technique in this study on the etched unirradiated and irradiated polyimide film was to understand the chemical interaction between the polyimide functional group units and the chemical etchants. The surface morphology of unirradiated and irradiated polyimide samples was studied using SEM, the depth profile (penetration) of palladium particles after electroless deposition on the polyimide matrix was investigated by SEM and TEM analysis. As for the alkaline etched irradiated polyimide, pore distribution, shape and size depended on the etching time and solution. In the XRD analysis, the palladium modified unirradiated polyimide film indicated the diffraction peaks of palladium metal in the (1,1,1), (2,2,0) and (2,0,0) planes present in the polyimide surface, and the peel test showed that the strength of adhesion of palladium on unirradiated surface was low compared to the palladium modified irradiated polyimide. The NaOH solution showed the best etchant at 20 minutes for the unirradiated palladium modified polyimide. The hallmark of this study was the design, fabrication and assemblage of home-built hydrogen diffusion reactor unit used to measure rate of hydrogen diffusion property of unirradiated and irradiated polyimide films from 25 °C to 325 °C. The rate of hydrogen diffusion was observed to depend on the etching time of polyimide surface before and after the polyimide surface irradiation treatment. / South Africa

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23578号 / 工博第4933号 / 新制||工||1770(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 江口 浩一, 教授 陰山 洋, 教授 阿部 竜 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

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