Experimental and Modelling Study of a Segmented SOFC Operated with Methane-Steam Mixtures

Kurzfassung

Spatially inhomogeneous distributions of current density and temperature in solid oxide fuel cells (SOFC) can contribute significantly to accelerated electrode degradation, thermomechanical stresses, and reduced efficiency, especially under high fuel utilization and the use of reformate gases or methane-steam mixtures as fuel. Here, water-gas shift and reforming reactions at the anode are coupled to diffusive and convective transport processes, leading to a variation of temperature and gas-phase species along the flow channel and through the anode thickness. A combined experimental and modelling study of the spatially resolved performance of a planar segmented SOFC was performed in order to investigate and understand the spatial inhomogeneities in gas composition and temperature. A planar anode-supported SOFC single cell was locally characterized in a 44-segmented cell arrangement. The tests were performed in counter-flow operation with methane-steam mixtures. Local and global current-voltage relationship was measured as a function of gas composition and fuel utilization. A two-dimensional elementary kinetic electrochemical model representing the segmented cell along the flow path and through the thickness of membrane-electrode assembly and interconnector was developed. The coupled charge-transfer and heterogeneous chemical kinetics are represented by an elementary kinetic mechanism consisting of 24 reactions between 6 gas-phase species, 12 Ni-surface-adsorbed species, and 4 YSZ-adsorbed species. The study allows a detailed insight into gas-phase species and temperature distribution for an anode-supported SOFC fuelled with methane-steam mixtures. A good agreement between model and experiment was achieved.