Reactions and Transport Pathways in Syngas Fueled Ni/YSZ SOFC Anodes: Experiments and Modeling

Abstract

This paper reports a comprehensive understanding of the reactions and transport processes that determine the performance of syngas fueled Solid Oxide Fuel Cells with Ni/8YSZ anodes. With a combined electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) study the individual polarization processes for syngas operation are identified. Complex non-linear least squares (CNLS) fitting of a subsequently developed physically meaningful equivalent circuit enables quantitative analyses of the individual loss contributions. A detailed kinetic analysis of the high-frequency activation polarization processes has revealed the mechanism of the electrochemical fuel oxidation. For syngas operation, only H 2 is electrochemically oxidized at the Ni/8YSZ anode. Consequently, the syngas fuel is transported through Ni/8YSZ anodes via (i) a H 2 /H 2 O diffusion pathway and (ii) a CO/CO 2 diffusion pathway, which is activated by heterogeneous reforming chemistry. Transient numerical simulation validates this reaction-diffusion model and further helps to assign the measured low-frequency polarization processes to the identified transport pathways.