Electrode materials systems for planar solid oxide fuel cells with high electrochemical performance including anode materials that provide exceptional long-term durability when used in reducing gases and cathode materials that provide exceptional long-term durability when used in oxygen-containing gases. The anode materials may comprise a cermet in which the metal component is a cobalt-nickel alloy. These anode materials provide exceptional long-term durability when used in reducing gases, e.g., in SOFCs with sulfur contaminated fuels. The cermet also may comprise a mixed-conducting ceria-based electrolyte material. The anode may have a bi-layer structure. A cerium oxide-based interfacial layer with mixed electronic and ionic conduction may be provided at the electrolyte/anode interface.