Layer Fabrication Methods

All in such way produced clusters are small, flat and asymmetric. Upon heating to 100 to 350°C (Au up to 60G°C) the clusters as well as layers melt, resulting in round shaped well-defined nano-clusters films. 

A novel technique to produee silver clusters films dispersions is the reduction of Ag ions by N,N-dimethylformamide (DMF) [51]. Either fiin films of silver nanoparticles electrostatically attached onto surfaces are produced, or in the presence of a silane (e.g. 3-aminopropyltrimethoxysilane) stable dispersions of silver nanoparticles. 

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Numerous efforts have been made to develop in situ catalyst layer fabrication methods to lower Pt loading and increase platinum utilization without sacrificing electrode performance. 

The most important electrokinetic data pertinent to fuel cell models are the specific interfacial area in the catalyst layer, a, the exchange current density of the oxygen reduction reaction (ORR), io, and Tafel slope of ORR. The specific interfacial area is proportional to the catalyst loading and inversely proportional to the catalyst layer thickness. It is also a strong function of the catalyst layer fabrication methods and procedures. The exchange current density and Tafel slope of ORR have been well documented in refs 28—31. 

In the paste coating method, a PVC paste, which contains emulsion-polymerized PVC and additives, is appHed onto a substrate and heated to gelation before fusion to produce a coating layer. This method is employed for products with a thin layer, ie, of 0.007—0.05 mm thickness. For foamed vinyl-coated fabrics, a substrate is laminated onto a transfer paper on which a PVC paste containing a foam-blowing agent has been appHed and geUed. After removal of the transfer paper, the paste is blown. 

In recent years, there are more applications based on the layer-by-layer fabrication techniques for CNT-modified electrodes. This technique clearly provides thinner and more isolated CNTs compared with other methods such as CNT-composite and CNT coated electrodes in which CNTs are in the form of big bundles. This method should help biomolecules such as enzymes and DNA to interact more effectively with CNTs than other methods, and sensors based on this technique are expected to be more sensitive. Important biosensors such as glucose sensors have been developed using this technique, and further development of other sensors based on the layer-by-layer technique is expected. 

Once the structural support layers have been fabricated by extrusion or EPD for tubular cells or by tape casting or powder pressing for planar cells, the subsequent cell layers must be deposited to complete the cell. A wide variety of fabrication methods have been utilized for this purpose, with the choice of method or methods depending on the cell geometry (tubular or planar, and overall size) materials to be deposited and support layer material, both in terms of compatibility of the process with the layer to be deposited and with the previously deposited layers, and desired microstructure of the layer being deposited. In general, the methods can be classified into two very broad categories wet-ceramic techniques and direct-deposition techniques. 

Both wet-ceramic techniques and direct-deposition techniques require preparation of the feedstock, which can consist of dry powders, suspensions of powders in liquid, or solution precursors for the desired phases, such as nitrates of the cations from which the oxides are formed. Section 6.1.3 presented some processing methods utilized to prepare the powder precursors for use in SOFC fabrication. The component fabrication methods are presented here. An overview of the major wet-ceramic and direct-deposition techniques utilized to deposit the thinner fuel cell components onto the thicker structural support layer are presented below. 

The microstructure of a catalyst layer is mainly determined by its composition and the fabrication method. Many attempts have been made to optimize pore size, pore distribution, and pore structure for better mass transport. Liu and Wang [141] found that a CL structure with a higher porosity near the GDL was beneficial for O2 transport and water removal. A CL with a stepwise porosity distribution, a higher porosity near the GDL, and a lower porosity near the membrane could perform better than one with a uniform porosity distribution. This pore structure led to better O2 distribution in the GL and extended the reaction zone toward the GDL side. The position of macropores also played an important role in proton conduction and oxygen transport within the CL, due to favorable proton and oxygen concentration conduction profiles. 

Wang, Y.J., Tang, Y., Wang, X.D., Yang, W.L., and Gao, Z. (2000) Fabrication of hollow zeolite fibers through layer-by-layer Adsorption Method. Chem. Lett., 1344-1345. 

The PA-300 membrane was commercially developed by Riley and coworkers (15), and is similar to the NS-101 membrane in structure and fabrication method. The principal difference is the substitution of a polyetheramlne, the adduct of polyepichlorohydrin with 1,2-ethanediamine, in place of polyethylenlmine. Use of the polyetheramlne was significant improvement in that considerably higher membrane fluxes were possible at salt rejections equivalent to the NS-lOO membrane system. The actual barrier layer in the PA-300 membrane is a polyamide formed by Interfaclal reaction of Isophthaloyl chloride with the polyetheramlne. 

Figure 13.1 Depiction of the glass-based lab-on-a-chip fabrication method. Shown in the figure is (a) the photoresist and chrome-coated glass substrate, (b) the coated substrate exposed to UV light through a mask (black rectangle), (c) removal of the exposed photoresist, (d) removal of the exposed chrome layer, (e) removal of glass by wet chemical etching, (f) removal of the bulk photoresist, and (g) removal of the bulk chrome layer.

The poly(ether/amide) thin film composite membrane (PA-100) was developed by Riley et al., and is similar to the NS-101 membranes in structure and fabrication method 101 102). The membrane was prepared by depositing a thin layer of an aqueous solution of the adduct of polyepichlorohydrin with ethylenediamine, in place of an aqueous polyethyleneimine solution on the finely porous surface of a polysulfone support membrane and subsequently contacting the poly(ether/amide) layer with a water immiscible solution of isophthaloyl chloride. Water fluxes of 1400 16001/m2 xday and salt rejection greater than 98% have been attained with a 0.5% sodium chloride feed at an applied pressure of 28 kg/cm2. Limitations of this membrane include its poor chemical stability, temperature limitations, and associated flux decline due to compaction. 

An acrylic chip was fabricated by stereolithography without an assembly process such as bonding. This fabrication method is a 3D method by solidifying a photopolymerizable resin layer-by-layer via the scanning of a UV laser beam. A special double-controlled surface method was adopted in order to produce a smooth and transparent surface for high-quality optical detection [240]. 

Separation of the individual contributors can provide useful information about performance optimization for fuel cells, helping to optimize MEA components, including catalyst layers (e.g., catalyst loading, Nafion content, and PTFE content), gas diffusion layers, and membranes. It assists in the down-selection of catalysts, composite structure, and MEA fabrication methods. It also helps in selecting the most appropriate operating conditions, including humidification, temperature, back-pressure, and reactant flow rates. 

Fuel cell performance is affected by MEA composition, including catalyst loading, PTFE content in the gas diffusion layer, and Nafion content in the catalyst layer and membrane, each of which affects the performance in different ways, yielding distinct characteristics in the electrochemical impedance spectra. Even different fabrication methods may influence a cell s performance and electrochemical impedance spectra. With the help of the model described above, impedance spectra can provide us with a useful tool to probe structure-performance relationships and thereby optimize MEA structure and fabrication methods. 

Various nanoscale architecture can be designed, including solid spheres, hollow spheres, tubes, porous particles, solid particles, and branched structures (Table 2).To achieve such nanostructures, different fabrication methods are used depending on the types of material. The methods used for nanoscale assembly include molecular self-assembly, bioaggregation, nanomanipulation, photochemical patterning, molecular imprinting, layer-by-layer electrsostatic deposition, and vapor deposition. 

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