Adhesion and Percolation Parameters in Two Dimensional Pd-LSCM Composites for SOFC Anode Current Collection

This paper is concerned with palladium-(La0.75Sr0.25)(0.97)Cr0.5Mn0.5O3 (LSCM) composite current collectors for solid oxide fuel cells (SOFCs); the composites, which are in a 2D configuration (thickness of about 8-10 mu m) are deposited upon an LSCM electrode layer on top of an yttria zirconia electrolyte substrate. The influence of the LSCM particle size on the adhesion between palladium and LSCM are reported and discussed. Compositions using four different LSCM particle sizes (0.21, 0.49, 0.64, and 0.81 mu m) with sintered Pd particle sizes approaching 10 mu m are investigated. The best bonding is obtained when smaller particles are used. The electrical dc conductivity of the composite is reported as a function of the palladium volume fraction for all used LSCM particle sizes. The measured experimental values present typical insulating-conductive percolation. However, the transition occurs at similar to 33% of the conductive phase, that is, a lower percentage than for 2D ideal systems and a higher percentage than for 3D ideal systems. This is consistent with lower-dimension percolation for a system of large-grained conductors and small-grained insulators. The general effective media (GEM) equation is used to fit the experimental data, and the two main parameters (the threshold point phi(c) and the exponent t) are defined.