Non-Ionic Conduction Phenomena in Yttria Stabilised Zirconia Electrolyte in SOFC Operated in the Electrolysis Mode

摘要

Anode supported solid oxide fuel cells (SOFCs) with yttria stabilised zirconia (YSZ) electrolyte were operated at ～800°C as solid oxide H_2O electrolyser cells (SOECs). Typical operation voltages were 1.0 to 1.3 V. When operation was extended to current densities j corresponding to a steam conversion rate above 100%, or when the steam supply was interrupted under constant current conditions, cell voltages saturated at about 1.8 to 2.0 V. Cells survived long-term current polarisation with j ～ -0.3 to -0.5 Acm~(-2) without steam supply. The mechanism limiting the cell voltage is attributed to electronic conduction in the YSZ electrolyte. Electrolyte conduction in the normal SOEC mode (with reasonable steam conversion rates) remains predominantly ionic in the investigated temperature range. Depending on the cell characteristics and the operation conditions (notably the temperature), however, the ionic transfer number may be significantly lower compared to the SOFC operation.