Hysteresis in the solid oxide fuel cell cathode reaction

The oxygen electrode reaction at the Pt/yttria-stabilised zirconia (YSZ) in terface is investigated at 1000 degreesC on Pt point electrodes on YSZ and YSZ point contacts on Pt. Linear potential sweeps show a pronounced non-lin ear current-voltage relation and inductive hysteresis, in particular at low sweep rates (similar to 1 muV S-1). Correspondingly, an inductive behaviou r is observed at low frequency by impedance measurements on polarised elect rodes. The behaviour is attributed to a current-induced activation mechanis m and subsequent deactivation at equilibrium conditions. Several mechanisms are discussed and rejected as responsible for the phenomena. Finally, the stability of the triple phase boundary is questioned and a current-sensitiv e reaction zone geometry is suggested as an explanation for the behaviour. (C) 2001 Elsevier Science Ltd. All rights reserved.