A novel heterogeneous precipitation method for the synthesis of highly percolated fine NiO/Ni particles in 8YSZ matrix for IT-SOFC application

Abstract

Solid oxide fuel cells (SOFCs) have attracted much more attention as a power generating device owing to its higher energy conversion efficiency and environment friendly behavior. But its high operating temperature (800-1000°C) has imposed several constraints on the material selection, their synthesis and fabrication. There has been continuous effort to bring down its operating temperature into intermediate (600-800°C) range. In this perspective the anode of an SOFC, generally a cermet of NiO/Ni-8YSZ, needs special consideration as it plays the major role for the oxidation of fuel to generate electricity. As a composite material, its properties entirely depend upon its synthesis procedure, composition and microstructure. In this work, a cost effective heterogeneous precipitation method was followed in two different ways namely direct and reverse strike techniques to develop NiO/Ni-8YSZ nanopowders with varying NiO/Ni concentration. The reverse strike technique was found to be more effective in synthesizing Ni particles directly from the solution in contrast to the direct process. On the other hand, the direct process was found to be more suitable for the fabrication of a dense NiO/Ni-8YSZ cermet at a temperature as low as 1300°C. The thermal expansion coefficients of Ni-8YSZ cermets were comparable in both the techniques. The presence of uniformly distributed fine grains was observed from the SEM micrographs. The electrical conductivity was found to exihibit metallic behavior at lower Ni concentration due to the percolation of fine Ni particles through the 8YSZ matrix. Hence, both the ways are effective in synthesizing NiO/Ni-8YSZ composites for IT-SOFC application.