Direct ammonia protonic ceramic fuel cell: A modelling study based on elementary reaction kinetics

Abstract

As an efficient energy carrier with high volumetric energy density, ammonia can be effectively utilized by protonic ceramic fuel cells (PCFCs) for power generation at an intermediate temperature (IT) (500–600 °C). The pioneering modelling studies in the literature on NH3-PCFC usually simplify the reaction processes and neglect the current leakage through the electrolyte. A NH3-PCFC model is developed to fully consider the elementary reaction kinetics in the anode and different charges’ transport including electronic holes in the electrolyte. Results suggest the operating potential to be < 0.7 V to minimize the current leakage. When the transport of electronic holes is slowed down by 10%, the Faraday efficiency increases by 11.5%. It is also found that chemical reactions can be the limiting factor for PCFC performance. By increasing inlet steam fraction, while cell performance and proton uptake are improved, electronic hole formation is enhanced by 80%. Importantly, NH3-PCFC performance at an IT is sensitive to temperature distribution. Introducing 5% H2 can occupy surface reaction sites and inhibit ammonia decomposition, thereby decreasing temperature-gradient by 22% and improving cell performance by 3%. Increasing nitrogen desorption by 20% results in a 3% decrease in cell performance due to the enhanced endothermic effect.