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

Abstract

An anode-supported solid oxide fuel cell of 45 cm2 area was operated during 9000 h as electrolyser cell at about 780°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 Ucell = 1.06 V) together with the known nearly ideal faradaic efficiency mean an (electrical-to-chemical) energy-conversion efficiency ηel above the one achieved with electrolysis at low temperature, with ηel > 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.