Materials for Solid Oxide Fuel Cells

Abstract

Over the past one decade, several cell component materials and their combinations have been attempted to match with the appropriate requirements of solid oxide fuel cells (SOFCs). A large number of cell component materials with superior properties have been developed. The general observation is that most of the technological challenges associated with the development of SOFCs are related to materials science. For example, development of superior oxide-ion conductor electrolyte as well as cost-effective fabrication processes involves tremendous materials challenges. The improvements of the materials properties mostly include electrical conductivity, catalytic activity, stability and thermal expansion coefficient. Of late, significant improvements have also been made in the area of fast oxide-ion conductors. These oxide-ion conductors show extraordinarily high electrical conductivity compared to traditional zirconia-electrolyte. This helps SOFC not only to operate at lower temperature but also minimizes the polarization losses which is the key factor for a high performance cell (high power density or power per unit area). The differences between the operating cell voltage and the expected reversible voltage is termed as polarization or overpotential. More clear understanding of the fundamentals of these materials has been published by several groups through numerous articles (Steele 1993, 2000, Mogensen et al. 2000, Goodenough 2003, Singhal et al. 2003, Stover et al. 2003, Kilner 2005). Reduction of electrolyte thickness also has tremendous advantages particularly from the technological point of view. Lower the electrolyte thickness lower is the internal resistance of the electrolyte, which in turn helps the cell to operate at a considerably lower temperature. The current research trend undoubtedly is more focused towards the development of high performance SOFC at low temperature (650°C and below). For making such high performance cell, inter facial contacts between two adjacent cell components is very critical. Therefore, an excellent compatibility (connectivity) between electrolyte and electrodes, and also with the interconnect (while stacking) is absolutely necessary.