Effects of regulating the cathode gas properties on the ammonia-fueled solid oxide fuel cell. Part I. Parasitic power consumption and electrical efficiency after increasing O2 and H2O

This study designed and simulated a kW-scale SOFC system equipped with liquified O-2 and NH3 tanks for unmanned underwater vehicles (UUVs). Optimizing the parasitic power consumption and electrical efficiency was performed via using oxygen-enriched cathode gas, in-cell cracking of ammonia and adding steam into cathode gas coupled with phase change of recycle steam. The results show increasing O-2 concentration helps improve the net system electrical efficiency from 47.9% at simulate air to 51.7% at pure O-2. The use of in-cell cracking increases the net system electrical efficiency by 1.3% on this basis. Interestingly, substitution of O-2 to H2O would slightly reduce the net electrical efficiency of the system with O-2-enriched cathode gas (e.g., decreased by 0.2% when using 40% H2O); however, substitution of N-2 to H2O would help improve the net electrical efficiency of the system with simulated air as cathode gas (e.g., increased by 1.2% when using 40% H2O).