Nine Thousand Hours of Operation of a Solid Oxide Cell in Steam Electrolysis Mode

An anode-supported solid oxide fuel cell of 45 cm(2) area was operated during 9000 h as electrolyser cell at about 780 degrees C and -1 Acm(-2) current density. The cell consisted of yttria-stabilised zircona (YSZ) as electrolyte, the hydrogen electrode of a nickel-YSZ cermet, and the oxygen electrode of strontium-substituted lanthanum ferrite/cobaltite (LSCF). The voltage loss under constant current operation over the entire experiment was 3.8% (40 mV)/1000 h. This value also accounts for experimental incidents, e.g. contact deterioration due to mechanical shocks or a supply failure of feed gas. Degradation during the initial 5600 h was 2.5% /1000 h. It was even lower during the incident-free period of the experiment, i.e. 1.7%/1000 h from 2000 to 5600 h, close to the technical target for an electrolyser system. The low cell voltage (initial U-cell = 1.06 V) together with the known nearly ideal faradaic efficiency mean an (electrical-to-chemical) energy-conversion efficiency eta(el) above the one achieved with electrolysis at low temperature, with eta(el) > 100% up to 7600 h (with heat supply). Impedance spectroscopic results indicate that degradation results from an increase in ohmic electrolyte resistance as well as in the reaction overpotential of at least one electrode. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.076202jes] All rights reserved.