Long Term Testing of Solid Oxide Fuel Cell Stacks with Yttria Stabilised Zirconia Electrolyte in the H-2O Electrolysis Mode

摘要

A fairly broad experimental basis exists for solid oxide fuel cells reversibly operated as H-2O 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 (H-2) 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.