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The potential of the wet powder spraying (WPS) process for the depositon of thin dense films for solid oxide fuel cell electrolytes is demonstrated. In contrast to many other production methods the process allows high deposition rates. Economical aspects such as good up‐scaling, low investment costs for the equipment and short sintering times for the layers make the WPS process an interesting alternative to other deposition techniques.

we used. If one phase would stay or become disconnected, one would either obtain a loose powder or the etching process would stop after the particles connected to the specimen surface have been leeched out.A section through the nanoporous metal is also shown in Figure 2d. It demonstrates that the porosity is not confined to the surface but penetrates the entire specimen thickness. This result suggests, but does not prove gas permeability. Thus, gas permeability tests using hydrogen were also performed. The set up consists of a vacuum tight holder with inlet and outlet, a vacuum pump, a gas supply and a gas chromatograph. The nanoporous sheets, approximately 6 mm 20 mm wide and 0.1 mm to 0.25 mm thick, were placed in the holder. The whole system was evacuated prior to testing to a pressure of less than 1 Pa. Constant hydrogen pressure was then applied on one side of the porous membrane for 300 seconds and the permeated gas was collected at the other side. The pressure on the inlet side was varied between 20 Pa and 102 kPa. The volume of the recipient was selected such, that the pressure increase at the outlet side was always less than a tenth of the inlet pressure. In other words, the pressure difference was essentially equal to the applied pressure at the inlet. The permeated gas content was then measured by the gas chromatograph.The test results are shown in Figure 3, whereby the flow rate is related to standard conditions. They confirm gas permeability of the nanoporous material and a linear relation between pressure drop and flow rate. At Dp = 102 kPa a column of hydrogen gas, approximately 1 mm high, permeates through a given filter area per second. It should be noted that no attempts to degas the filters prior to testing were made so far. Probably this will further improve permeability as some of the aqueous electrolyte is likely to remain in the porous structure due to capillary forces. Furthermore, it is anticipated that the permeability can be widely varied, as volume fraction and size of the open channels can be influenced by chemical composition of the alloy and processing conditions. We anticipate use of the new nanoporous Ni-alloys in such diverse fields of application as medicine, mechanical engineering and chemical engineering. Filtration of bacteria is one example, where the ability to sterilize the microorganisms by resistance heating of the metallic filter is an added advantage not amenable to ceramic filters or polymer membranes. Solid oxide fuel cells are another example, where nanoporous metals exhibiting gas permeability would be highly beneficial as they would enable thin film deposition of the electrode and membrane materials, thus reducing the electrical resistance of the cell. Nanoporous metals could also aid the development of miniaturized low temperature fuel cells, believed to power laptops and cellular phones in the future, [6] as further miniaturization of the fuel processing system, requiring micro heat exchangers and reactors, becomes possible. This is just a small selection of po...

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