Integrated thermal reforming and electro-oxidation in ammonia-fueled tubular solid oxide fuel cells toward autothermal operation

Ammonia has emerged as an attractive potential hydrogen carrier due to its high energy density, storage and transportation ability as a liquid, and its carbon-free nature. Direct utilization of ammonia in high-temperature solid oxide fuel cells (SOFCs) has been demonstrated over the past decade. Concurrence of integrated endothermic ammonia decomposition and exothermic electrochemical hydrogen oxidation enables efficient heat integration. In this study, the experimental analyses of axial temperature and concentration profiles along an intensified tubular SOFC (t-SOFC) fed directly with ammonia are performed to investigate spatially resolved thermal and concentration effects of the coupled ammonia decomposition and hydrogen oxidation reactions under varying electrical loads and operating conditions. Fast ammonia decomposition over the supported Ni catalyst is evident at the inlet of the t-SOFC and complete ammonia conversion is confirmed above 600 °C. It is found that the direct ammonia-fueled t-SOFC and an equivalent hydrogen-nitrogen fueled t-SOFC provide identical performances. The steady state temperature and concentration profiles validate that the efficient heat integration inside an ammonia-fueled t-SOFC is feasible if the t-SOFC is operated at the temperature of 700 °C and below. A 150-h performance test demonstrates stability and durability of the ammonia t-SOFC.