Miniaturization limits for single-chamber micro-solid oxide fuel cells with coplanar electrodes

Single-chamber solid oxide fuel cells with coplanar microelectrodes were operated in methane-air mixtures (Rmix = 2) at 700°C. The performance of cells with one pair of NiO-YSZ (yttria stabilized zirconia) anode and (La0.8Sr0.2)0.98MnO3-YSZ cathode, arranged parallel on a YSZ electrolyte substrate, was found to be significantly dependent on the electrode width. For an interelectrode gap of ~250m, cells with average electrode widths exceeding ~850m could establish a stable open circuit voltage (OCV) of ~0.8 V, while those with widths less than ~550 µm could not establish any OCV. In the intermediate range, the cells exhibited significant fluctuations in voltage and power under our testing conditions. This behavior suggests that a lower limit to electrode dimensions exists for cells with single electrode pairs, below which neither a stable difference in oxygen partial pressure, nor an OCV, can be established. Conversely, increasing the electrode width imposes a penalty in the form of an increase in the ohmic resistance. However, both size limits can be circumvented by employing multiple pairs of microscale electrodes in an interdigitated configuration.