Design considerations for segmented-in-series fuel cells

This paper describes calculations of the electrical losses in patterned series-connected solid oxide fuel cells (SOFCs), i.e. the “segmented-in-series” configuration. Losses due to cell resistances, electrode ohmic resistances, interconnect resistance, and shunting by a weakly-conductive support material were considered. For any given set of cell dimensions and characteristics, power density was maximized at an optimal cell length - the power decreased at larger cell lengths due to electrode lateral resistance loss and decreased at smaller cell lengths due to a decreasing fraction of cell active area. For cell lengths well above the optimal value, electrolyte current was often confined to the portion of the cell nearest to where the less conductive electrode (i.e. the cathode) connected to the interconnect. Assuming dimensions expected for screen printing, i.e. ≈20 μm thick electrodes and lateral print accuracy of ≈100 μm, and area specific resistance values typical of SOFCs, optimal cell lengths typically ranged from 1 to 3 mm. Shunting currents increased with decreasing cell lengths, but were found to have little effect on power density assuming partially-stabilized zirconia supports and temperatures ≤ 800 °C.