This work reports on solid oxide fuel cells (SOFCs) based on abundant natural resources of industrial grade mixed rare-earth carbonates and composites. The materials possessed natural compositions and nano-scale particles. The electrolytes made from these materials were able to achieve excellent fuel cell performances, 300-800 mW/cm(2), at low temperatures (LT: 300-600 degrees C). Ionic transport mechanism, two-phase interface functions and composite role in electrolytes as well as resulted advanced fuel cell performances are discussed. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.