Insight into the complex ammonia decomposition/oxidation kinetics in ammonia protonic ceramic fuel cells via elementary modeling

The protonic ceramic fuel cells (PCFCs) can convert the chemical energy of fuel directly into electric power, with the advantages of high efficiency and alternative fuel range at intermediate temperatures. Ammonia has been regarded as a promising fuel for PCFCs due to its carbon-free and hydrogen-rich properties, high volumetric energy density and easy storage/transportation. However, the performance of ammonia PCFCs (NH₃-PCFCs) is far inferior to the hydrogen PCFCs (H₂-PCFCs) because of the sluggish and complex kinetics at anodes. In this study, we established an elementary reaction kinetic model for NH₃-PCFCs, investigated the effect of reaction parameters, anode components and reaction partition, and explored the coupling mechanism between the ammonia decomposition and electrochemical reaction. Importantly, the ammonia decomposition and electrochemical reaction can be flexibly regulated by adjusting anode parameters, then affecting the performance ratio of NH₃-PCFCs and H₂-PCFCs. The detailed rate-determining steps were further identified by experimental and model analysis. Thus, the ammonia/hydrogen performance ratio of the cell can exceed 95% at 550°C after accelerating the ammonia decomposition reaction. Our work provides insights into the kinetics in NH₃-PCFCs for improving their performance with optimization.