Long Term Testing of Solid Oxide Fuel Cell Stacks with Yttria Stabilized Zirconia Electrolyte in the H2O Electrolysis Mode

Abstract

A fairly broad experimental basis exists for solid oxide fuel cells reversibly operated as H2O electrolyser cells (SOECs), notably for classical cells with Ni based anodes, YSZ electrolytes, and LSM cathodes. High electrical-to-chemical energy conversion efficiencies are achieved at such cells. Results from the long-term SOEC testing of two 5-cell stacks are compared, stack I with (H2) electrode and stack II with electrolyte supported cells. Operation times were 2600 h and 2000 h, respectively, under current densities between -0.4 and -0.6 Acm-2, 90% feed gas humidity, and 40 to 60 % steam conversion. The voltage degradation under constant current operation amounts to 3% (stack I) and 4.6% (stack II) per 1000 h. The evaluation is complicated by instabilities arising from poor endplate contacts and also by initial passivation/activation at stack I. Faradaic efficiencies are close to 100%. Electronic conduction in the electrolyte limits the cell voltage under current flow without steam supply.