Anode-supported cells fabrication

To solve the problem in the electrolyte-supporting cell, anode-supported cells have been developed. Since a thin electrolyte is fabricated on a thick anode, the ohmic resistance of the electrolyte can be reduced. The low resistance of the electrolyte implies that the anode-supported cell can be operated at a low temperature below 800°C. As a result, commercial alloys can be used as the interconnectors and auxiliaries. Using the alloys improves the mechanical reliability of the cell stack. For several years, Versa Power Systems have developed several kW systems with anode-supported cells and have demonstrated the performance of such systems [5],... 

Self-supported SOFC can be classified into anode-supported and cathode-supported fuel cells. The SOFC assembly for laboratory testing has a shape of button with 1 - 2 cm in diameter and less than 500 im in thickness. The majority of these button cells are anode-supported cells due to the easy of their fabrication as compared with that of the cathode-supported cell. These self-supported fuel cell usually possess thin (5-20 p,m) electrolyte and can operate at reduced temperatures (< 800 °C). The low temperature operation is the key to decrease... 

Metal Supported-Solid Oxide Fuel Cells (MS-SOFC) represent a promising new design for fuel cells which may overcome the limitations of anode-supported cells (such as poor thermal cycling resistance and brittleness. Nickel phase re-oxidation upon exposure to transient uncontrolled conditions) due to the much better mechanical properties of the support that is represented by a porous thick metal substrate, the thickness of the ceramic layers (anode/electrolyte/cathode) being in the order of 10-50 pm, only. In addition, in this design (Fig. 1), the replacement of the thick Ni/YSZ cermet with ferritic stainless steel leads to several benefits in term of fabrication cost and safety. 

In many cases, achievement of reliability is in trade-off relation to cost reduction. To overcome this, it is required to make breakthroughs in the fabrication technologies. Cells to be operated in the temperature region of around 800°C. Metal intercoruiects are used together with anode-support cells and sealing materials. The active cathode such as LSCF (lanthanum strontium cobaltite ferrites) is used so that the durability is one of the main issues. 

Metal support cells are proposed to realize cost reduction from the materials cost and fabrication cost simultaneously. Compared with nickel which is the major component in the anode support cells, the metal support cells aim at using cheaper Fe-Cr alloy as supporting materials [19]. Instead, the fabrication process becomes rather difficult compared with other cell design. 

These features have been found to be highly correlated with the fabrication method/sequence as well as materials selected. For example, anode support cells have stable anodes but there remain several points to be optimized for a cathode-complex-layer structure. On contrary, cathode-support cells have the stable performance for cathodes, but anodes may have some changed in microstructure because of nickel sintering [63]. 

There can be seen one interesting feature in the low-temperature SOFC, that is, the cell performance of the anode support cells has been much improved compared with electrolyte self support cells. This is apparently due to the lowering of the ohmic resistance inside electrolyte. Furthermore, the electrode performance is also improved very much. This can be ascribed to better fabrication procedure. When... 

TOTO attempted to fabricate micro tubes in various types. Eventually, they adopted the anode-supported tubular cells with the LSGM electrolyte. The adoption of anode-supported cells much thinner LSGM electrolyte can be used, leading to higher benefits in performance. On the other hand, technological difficulty in the fabrication process becomes more visible to avoid interdiffusion between cell components. Details are also described in a separate chapter of this book. 

Empirical development of the nickel-zirconia anode over several decades has led to solid oxide fuel cells with adequate service life and performance, but fuel reforming is still required to operate with commercially available hydrocarbon fuels. It has become evident that the anode reactions are dominated by the three-phase boundary and that the microstructure of the composite cermet anodes is pivotal. Consequently, the processing methods used for making the anode powders, and the fabrication techniques used for deposition on the electrolyte are critical in making high performance anodes. Anode-supported cells with very thin electrolyte films are becoming interesting for operation at lower temperatures. 

Besides corrosion issues of metal substrates, the use of alloys as mechanical supports of the cells is subject to interdiflfusion of iron, chromium, and nickel between ferritic steel and nickel-containing anodes during cells fabrication and operation. Diffusion of nickel into FSS substrates may cause austenitization of steels, which would result in TEC mismatch with other cell components. Diffusion of iron and chromium into Ni-based anodes may cause formation of oxide scales on nickel particles. This would result in fast degradation of cell performance during operation, as the electrochemically active surface is passivated. In order to overcome these issues, one possibility investigated by MS-SOFC developers is to use protective coatings [1-6, 13]. 

In the present work, we report results on the fabrication and performance of anode-supported, thin SDC el trolyte fuel cells operated in a single chamber configuration where methane and oxygen served as the gas mixture. 

Basu RN, Blafi G, Buchkremer HP, Stover D, Tietz F, Wessel E, et al. Fabrication of simplified anode supported planar SOFCs—a recent attempt. In Yokokawa H, Singhal SC, editors. Proceedings of the Seventh International Symposium on Solid Oxide Fuel Cells (SOFC-VII), Pennington, NJ The Electrochemical Society, 2001 2001(16) 995-1001. 

Cho et al. [140] examined the performance of PEM fuel cells fabricated using different catalyst loadings (20, 40, and 60 wt% on a carbon support). The best performance—742 mA/cm at a cell voltage of 0.6 V— was achieved using 40 wt% Pt/C in both anode and cathode. Antonie et al. [28] studied the effect of catalyst gradients on CL performances using both experimental and modeling approaches. Optimal catalyst utilization could also be achieved when a preferential location of Pt nanoparticles was close to the PEM side ... 

Du Y. and Sammes N.M., 2004. Fabrication and properties of anode-supported tubular solid oxide fuel cells. Journal of Power Sources 136, 66-71. 

R.J. Yang, M.C. Lee, J.C. Chang, T.N. Lin, Y.C. Chang, W.X. Kao, L.S. Lee, and S.W. Cheng, Fabrication and characterization of a Smo aCeo gOi.9 electrolyte film by the spin-coating method for low-temperature anode-supported solid oxide fuel cells. Journal of Power sources, 206, 111-118(2012). 

W.X. Kao, M.C, Lee, T.N. Lin, C.H. Wang, and Y.C. Chang, Fabrication and Characterization of a Bao5Sro5Coo.8Feo203. -gadolinia-doped Ceria Cathode for an Anode-supported Solid-oxide Fuel Cell, J. Power Sources, 195, 2220-2223 (2010). 

Oishi N, Atkinson A, Brandon NP, Kilner JA, Steele BCH (2005) Fabrication of an anode-supported gadolinium-doped ceria solid oxide fuel cell and its operation at 550°C. J Am Ceram Soc 88(6) 1394-1396... 

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