Formulation of ammonia decomposition rate in Ni-YSZ anode of solid oxide fuel cells

Abstract

Ammonia decomposition rate on a conventional porous Ni-YSZ anode of solid oxide fuel cells (SOFCs) is experimentally investigated under various temperatures and gas compositions to formulate a reaction rate equation. It is confirmed that the decomposition rate depends not only on the partial pressure of ammonia but also on that of hydrogen at the common operating conditions of SOFCs, with larger hydrogen concentration significantly reducing the decomposition rate. 3D microstructure of the tested Ni-YSZ anode is analyzed using the focused ion beam and scanning electron microscope (FIB-SEM), and microstructural parameters are quantified. By using the quantified Ni–Pore interface area density, a reaction rate model for a unit reaction area in Ni-YSZ anodes is obtained. The proposed model is then applied to a simple computational fluid dynamics (CFD) model for validation. The proposed reaction rate model can be applied to a variety of numerical analysis of ammonia decomposition on Ni-YSZ anodes having different microstructures, and expected to be useful for the analysis of ammonia-fed SOFCs.