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, H2 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 Ω cm2 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 °C for 2 h in air. Samples were reduced at 1000 °C in 4 vol% H2 in N2, 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.