Ageing of anode-supported solid oxide fuel cell stacks including thermal cycling, and expansion behaviour of MgO-NiO anodes

This paper reports on medium term tests of anode-supported five-cell short stacks, as well as on some separate anode development. Two stacks were operated under steady-state conditions: one with unprotected metal interconnects, H-2 fuel and 0.35 A cm(-2) (40% fuel utilisation) polarisation current showed an average cell voltage degradation of 56 mV per 1000 h for 2750 h; one with coated metal interconnects, synthetic reformate fuel and 0.5 A cm(-2) (60% fuel utilisation) polarisation current showed an averaged cell voltage degradation slope of 6.6 mV per 1000 h for 800 h before a power cut prematurely interrupted the test. A third stack was subjected to 13 complete thermal cycles over 1000 h, average cell voltage degradation was evaluated to -2 mV per cycle for operation at 0.3 A cm(-2), open circuit voltage (OCV) remained stable, whereas area specific resistance (ASR) increase amounted on average to 0.008 Omega cm(2) per cycle. To improve anode reoxidation tolerance, MgO addition was considered. (Mg, Ni)O solid solutions were synthesized from MgO and NiO powders at 1500 degrees C for 2 h in air. Samples were reduced at 1000 degrees C in 4 vol% H-2 in N-2, and their expansion behaviour was observed. XRD and SEM/EDX analysis suggested that the expansion was caused by the segregation of Ni particles between (Mg, Ni)O grains. (c) 2008 Elsevier B.V. All rights reserved.