Mathematical modeling of Ni/GDC and Au–Ni/GDC SOFC anodes performance under internal methane steam reforming conditions

Model assumed catalytic (left) and electrocatalytic (right) reactions, the latter for high (top) and low (bottom) steam-to-carbon ratios. [Display omitted] •Under high S/C ratios, H2 and CO are electrochemically oxidized.•Under low S/C ratios, CH4 is partially electrochemically oxidized to CO and H2.•Under high S/C ratios, non-faradaic poisoning in the steam reforming rate occurs.•Carbonaceous adsorbate coverage of catalyst surface coincides with that at tpb. A simple kinetic model has been developed to describe the catalytic and electrocatalytic performance of Ni/GDC and Au–Ni/GDC anodes of SOFCs operating under internal methane-steam reforming reaction conditions, at low and high steam-to-carbon ratio values. The model accounts for the surface dissociation of CH4 to form methyl species which then react with H2O to form CO and H2. Under fuel cell operation conditions, two cases have been distinguished according to the observed electrochemical behavior; the high and the low steam-to-carbon ratio feed conditions. The former is characterized by electrochemical consumption of H2 and CO, produced by internal CH4 steam reforming, while the latter by electrochemical partial oxidation of CH4, to form H2 and CO, and oxidation of H2. Interestingly, the coverage of methyl-type species of the catalyst surface, as extracted from the model and the catalytic kinetic data, was found to coincide with the methyl species coverage at the three-phase boundaries, as extracted from the electrocatalytic experiments. The model is in good agreement with experiment under both open-circuit and fuel cell operation conditions.