Thin coatings fuel cells

It was quite recently reported that La can be electrodeposited from chloroaluminate ionic liquids [25]. Whereas only AlLa alloys can be obtained from the pure liquid, the addition of excess LiCl and small quantities of thionyl chloride (SOCI2) to a LaCl3-sat-urated melt allows the deposition of elemental La, but the electrodissolution seems to be somewhat Idnetically hindered. This result could perhaps be interesting for coating purposes, as elemental La can normally only be deposited in high-temperature molten salts, which require much more difficult experimental or technical conditions. Furthermore, La and Ce electrodeposition would be important, as their oxides have interesting catalytic activity as, for instance, oxidation catalysts. A controlled deposition of thin metal layers followed by selective oxidation could perhaps produce cat-alytically active thin layers interesting for fuel cells or waste gas treatment. 

Another key part of a PEM membrane is the thin layer of platinum-based catalyst coating that is used. It makes up about 40% of the fuel cell cost. The catalyst prepares hydrogen from the fuel and oxygen from the... 

Dr. Hui has worked on various projects, including chemical sensors, solid oxide fuel cells, magnetic materials, gas separation membranes, nanostruc-tured materials, thin film fabrication, and protective coatings for metals. He has more than 80 research publications, one worldwide patent, and one U.S. patent (pending). He is currently leading and involved in several projects for the development of metal-supported solid oxide fuel cells (SOFCs), ceramic nanomaterials as catalyst supports for high-temperature PEM fuel cells, protective ceramic coatings on metallic substrates, ceramic electrode materials for batteries, and ceramic proton conductors. Dr. Hui is also an active member of the Electrochemical Society and the American Ceramic Society. 

Unlike the RDE technique, which is quite popular for characterizing catalyst activities, the gas diffusion electrode (GDE) technique is not commonly used by fuel cell researchers in an electrochemical half-cell configuration. The fabrication of a house-made GDE is similar to the preparation of a membrane electrode assembly (MEA). In this fabrication, Nation membrane disks are first hot-washed successively in nitric acid, sulphuric acid, hydrogen peroxide, and ultra-pure water. The membranes are then coated with a very thin active layer and hot-pressed onto the gas diffusion layer (GDL) to obtain a Nation membrane assembly. The GDL (e.g., Toray paper) is very thin and porous, and thus the associated diffusion limitation is small enough to be ignored, which makes it possible to study the specific kinetic behaviour of the active layer [6],... 

The noble metals or their oxides are the most convenient substrates for most electrochemical reactions taking place in fuel cells or in industrial electrolysis, for example. Because of this, the activated electrodes are introduced, consisting of a conducting, inert support coated with a thin layer of electrocatalyst. In this way, not only the chemical nature of the electrode can be modified but also its morphology and structure in dependence on the procedure of preparation.1... 

In Chapter 4 by Popov et al., the aspects of the newest developments of the effect of surface morphology of activated electrodes on their electrochemical properties are discussed. These electrodes, consisting of conducting, inert support which is coated with a thin layer of electrocatalyst, have applications in numerous electrochemical processes such as fuel cells, industrial electrolysis, etc. The inert electrodes are activated with electrodeposited metals of different surface morphologies, for example, dendritic, spongy-like, honeycomblike, pyramid-like, cauliflower-like, etc. Importantly, the authors correlate further the quantity of a catalyst and its electrochemical behavior with the size and density of hemispherical active grain. 

S. Uhlenbruck, N. Jordan, D. Sebold, H.P. Buchkremer, V.A.C. Haanappel and D. Stover, Thin Film Coating Technologies of (Ce,Gd)02.6 Interlayers for Application in Ceramic High-Temperature Fuel Cells, Thin Solid Films, 515,4053-4060(2007). 

M. Alvisi, G. Galtieri, L. Giorgi, R. Giorgi, E. Serra, M.A. Signore, Sputter deposition of Pt nanoclusters and thin films on PEM fuel cell electrodes. Surf. Coat. Technol. 200, 1325—1329 (2005)... 

Corrosion of the plates not only detracts from their mechanical properties but also gives rise to undesirable corrosion products, namely, heavy-metal ions, which, when depositing on the catalysts, strongly depress their activity. The corrosion processes also give rise to superficial oxide films on the metal parts, and these cause contact resistance of the surfaces. For a lower contact resistance, metallic bipolar plates sometimes have a surface layer of a more stable metal. Thus, in the first polymer electrolyte membrane fuel cell, developed by General Electric for the Gemini spacecraft, the bipolar plates consisted of niobium and tantalum coated with a thin layer of gold. A bipolar plate could also be coated with a layer of carbide or nitride. 

Be familiar with the design of a representative array of nine chemical products. These products include small hemodialysis devices, solar desalinators, hand warmers, fuel cells to power automobiles, and thin silicon films that coat microelectronic devices. 

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