Predicting degradation in direct ammonia SOFCs: The temperature trade–off between nickel nitriding and coarsening

Ammonia is a promising carbon-free fuel for solid oxide fuel cells (SOFCs), since nickel-based anodes can crack it internally without a separate reformer. Direct-ammonia operation, however, compromises durability through nickel nitriding and coarsening. These mechanisms respond oppositely to temperature and are usually studied separately, leading to conflicting set-point guidance. This study combines both mechanisms in a reduced-order model linking operating conditions to voltage losses. The combined response reveals two effects. First, nitriding is non-monotonic, peaking at approximately 625–665 °C under the assumed kinetics; thus, a moderate increase above 600 °C may accelerate it. Second, the mechanisms cross over at 731–741 °C, with nitriding dominating below and coarsening above. From a degradation perspective, a balanced long-term window of approximately 750–780 °C is identified. Both the crossover and the high-temperature penalty remain robust in a sensitivity analysis. The joint model supports what-if analysis and remaining-useful-life estimation for maintenance planning.