Nitridation of Solid Oxide Fuel Cell Interconnects in Ammonia: Effect of Protective Coatings and Pre-Oxidation

Direct fuelling of solid oxide fuel cells with ammonia is attractive but can lead to reduced stack durability due to nitridation of the metallic interconnect material. This works investigates the stability of the interconnect material Crofer 22 APU in ammonia-containing atmosphere and evaluates the effects of pre-oxidation and the application of nickel or yttrium coatings to mitigate nitridation. Exposures were conducted in dry and wet NH 3 -H 2 -N 2 mixtures at 650 °C and 750 °C and 20 bar for up to 800 h. Bare Crofer 22 APU suffered from nitridation under all exposure conditions with more severe degradation observed at 650 °C compared to 750 °C and in dry conditions. At 750 °C, pre-oxidation and Y coating both provided excellent resistance against nitridation in wet conditions, while these treatments had no effect in dry conditions. A Ni coating provided best protection in dry conditions and at 650 °C although it did not completely supress nitridation.