Development of processes for manufacturing of metal supported solid oxide fuel cells

Metal supports were tape casted and the rest of the half-cell components (anode and electrolyte) were fabricated using tape casting or screen printing. The metal support, anode and electrolyte were integrated together either by laminating tapes or by screen printing of anode and electrolyte inks on the metal tapes. Results from earlier projects, including PSO-FU-5849, were used as the starting point. Cathode and cathode barrier layers were developed in other projects and integrated with the half-cells developed in this project. Composition of metal supports and its production were determined by corrosion testing. Metal powders were produced by atomizing Fe-Cr alloys with different additives using Nitrogen or Argon gas. The porosity and the pore size distribution of the metal supports were controlled by addition of poreformers. The metal supports were tape casted. Diffusion of Fe and Cr into the anode and subsequent reaction with Ni was discovered. This reaction led to a catastrophic failure of the half-cell during electrochemical testing. In order to avoid this reaction, three different strategies were adopted. For screen printing of anode and electrolyte layers, Ni – stabilized Zirconia and stabilized Zirconia were inks were developed and optimized. The composition of the inks (amount of powders, poreformers etc) were optimized to obtain required anode microstructure and lower the sintering temperature of the electrolyte. Porous impregnation layers were prepared by addition of poreformers to stabilized Zirconia inks or suspensions. By addition of optimal amounts of poreformers and heat treated powders, microstructures with controlled porosity were produced. Ni was introduced into the pores by impregnation. Repeated impregnation resulted in percolation of Ni and highly conductive impregnation layers. Half-cells were also fabricated by laminating metal, anode/impregnation layer and electrolyte tapes. This processing technique for half-cells was developed and optimized in this project. Tapes with optimal amount of solids, binder and poreformers were prepared and laminated by passing the tapes together under heated rolls. Sintering temperature of the half-cells to produce gas tight electrolyte was decreased by over 100 degrees C during the project. This was achieved by optimizing the processing parameters and by adding sintering additives. Cathode was applied on the half-cell and sintered in-situ during electro-chemical testing. Lowering the sintering temperature and time of half-cells resulted in a lowering of their area specific resistance (ASR). Most of the losses occurred in the anode, with the oxidation of the Ni-Cr-Fe alloy causing electrolyte to crack in half-cells sintered at high temperatures. Lowering the sintering temperature avoided this problem. The strength of the electrolyte in the metal supported SOFC was similar to that in the anode supported SOFC. The half-cells corroded in fuel in-let conditions, occasionally leading to cracked electrolyte. However, the extent of corrosion was minimized by optimizing the composition of metal alloy, fabrication parameters, poreformers and porosity of half-cells.