Characterization of the electrochemical performance of micro-tubular SOFC in partial reduction and oxidation conditions

During solid oxide fuel cell operation, re-oxidation of the nickel anode can occur due to a disruption in fuel supply, emergency system shutdown or leakages in the fuel delivery channel. Once oxidation occurs, the anode has to be reduced again in order to be ready for use. Cyclic reduction and oxidation (redox) is known to cause severe expansion and contraction in the anode causing significant changes to the integrity of the material interfaces leading to performance degradation and eventual failure. The redox tolerance of Ni/YSZ anode supported solid oxide fuel cell is investigated at 800 degrees C in partial oxidation and reduction conditions and a total of 52 redox cycles is performed. Partial oxidation is performed by shutting-off the hydrogen supply for 3 min to allow atmospheric air to oxidize the anode, while partial reduction proceeded by a flow of 20 ml min(-1) hydrogen for 5 min. The electrochemical performance of the cell decreased slightly after each redox cycle. An average degradation rate of 0.3% per cycle was calculated. The micro-structural changes that occurred after redox cycling is characterized by both dilatometry and scanning electron microscopy (SEM). The theory that damage was caused by defect growth in the anode was confirmed. (c) 2007 Elsevier B.V. All rights reserved.