Sunday, November 22, 2009

Nanomaterials Make SOFC Manufacturing Easier and Products More Durable

Risø Technical University of Denmark (Kgs. Lungby, DK)  researcher Peter Halvor Larsen has designed a simpler reversible solid oxide fuel cell (SOFC) using nanomaterials.  Advantageously, the impregnation of nanoparticles allows more freedom in design and material selection of the SOFC, thus allowing manufacturers to fine tune the SOFC design according to the desired application. Furthermore, the impregnation of the electrode layers results in finely distributed catalyst particles on the surface of the pores, which in turn leads to an improved cell performance. The size range of nanoparticles makes the electrode performances even more effective. Moreover, less catalytic material is needed since all material is applied to the surface of the layer structure, where it can contribute to the electrode reaction, according to U.S. Patent  7,601,183.

The reversible solid oxide fuel cell provides the following advantages: a) The method is less complicated than methods suggested in the prior art, since no cathode/metal support barrier layer is required; b) The life time of the metallic support will be increased; during operation of SOFCs having the anode on the metallic support, the relatively high pH.sub.2O (>0.5 atm.) on the anode side may result in severe corrosion of the metal support. Having the cathode on the support side, the metal will only be exposed to air, which is less corrosive; c) If the anode and cathode are impregnated after sintering, only one sintering step is required and the method can thus be made more cost effective; d) The sintering step may be carried out without the presence of anode or cathode materials, hence negative reactions, such as coarsening, during sintering is not an issue; e) Chemical reaction between electrode materials and the other cell materials can be prevented because the operational temperature of the final cell is lower than the sintering temperature; f) Due to impregnation of the electrodes, the electrodes have high surface areas; g) The composite structure of the impregnation layer(s) ensures a good mechanical bonding between electrolyte and metal support as well as good conductivity across the interfaces.

The method for producing a reversible solid oxide fuel cell, is comprised of the following steps: (a) forming a multilayer structure by (i) forming a cathode precursor layer on a metallic support layer; (ii) forming an electrolyte layer on the cathode precursor layer; and (iii) forming an anode precursor layer on the electrolyte layer; (b) sintering the multilayer structure; (c) impregnating the cathode precursor layer and the anode precursor layer in the sintered multilayer structure of step (b) so as to form a cathode layer and an anode layer.

The metallic support is Fe22C  or an FeCrMx alloy, wherein Mx is selected from the group consisting of Ni, Ti, Ce, Mn, Mo, W, Co, La, Y, Al, or mixtures of the metals. The electrode precursor layers are formed from doped zirconia and/or doped ceria and/or a FeCrMx alloy, and in the case of a cathode precursor layer the materials are selected from the group consisting of lanthanum strontium manganate, lanthanide strontium manganate, lanthanide strontium iron cobalt oxide. The addition of the oxides furthermore  results in a decrease of the thermal extension coefficient of the redox stable anode layer, which in turn strengthens the overall mechanical stability of the layers and the resulting cell. Preferred oxides are Cr2O3, TiO2, Al2O3, and Sc2O3.

The Consortium of Haldor Topsøe A/S and Risø National Laboratory continues to focus on the development of cost effective anode-supported cells and SOFC stacks for operation at intermediate temperatures. A cell production pilot plant with a capacity of more than 1 MW per year has been in operation since 2002. A fully up-scaled production process for the anode-supported cells was established and uniform cells have been produced routinely for test and stack development.

A comprehensive report FUEL CELLS, HYDROGEN ENERGY AND RELATED NANOTECHNOLOGY – A GLOBAL INDUSTRY AND MARKET ANALYSIS  details the use of nanomaterials in fuel cell production as well as hydrogen manufacturing,  purification and storage and is available from Innovative Research and Products.  

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