Material characterization in support of the development of an anode substrate for solid oxide fuel cells

A new design for solid oxide fuel cells (SOFC's) was developed aiming at the reduction of the total electrical resistance of the cell. The thickness of the electrolyte was decreased, while the anode took on the role of the substrate. The pore structure with respect to gas permeability of this component has to be optimized for the proper operation of this design. Anode substrates, consisting of a cermet (yttrium-stabilized ZrO₂ and metallic Ni) and produced by two different processes, coat mix and tape casting, were characterized with respect to pore structure (shape and mean radius), porosity (total, open and permeable), pore size distribution and air permeability. The following methods were used: (i) optical and electron scanning microscopy in combination with image analysis, (ii) mercury porosity, and (iii) air permeability. Correlations between air permeability and porosity and also the percentage of permeable pores in anodes show the superiority of coat mix samples to tape-cast ones. It has been observed that the coat mix process can produce anode substrates with interconnecting porosity, while tape casting, as used in this study, needs some modifications in order to be appropriate for this purpose.