Direct methane operation of a micro-tubular solid oxide fuel cell with a porous zirconia support

A novel micro-tubular solid oxide fuel cell (SOFC) design with an inert support was proposed for operation on direct hydrocarbon fuels with an improved stability. In this design, the inert support also serves as a diffusion barrier between the fuel stream and Ni cermet anode. The barrier effect leads to higher local steam to carbon ratios in the anode, thus inhibiting carbon deposition. To demonstrate this concept, we fabricated micro-tubular SOFCs with a porous yttria-stabilized zirconia (YSZ) support. Ni, Ni-scandia-stabilized zirconia (ScSZ), ScSZ, strontium-doped lanthanum manganite (LSM)–ScSZ, and LSM were used as the anode current collector, anode, electrolyte, cathode, and cathode current collector, respectively. Good electrochemical performance was achieved with hydrogen and methane fuels in a temperature range 600–750 °C. Continuous cell operation on direct methane fuel for >40 h at 750 °C under moderate current densities delivered stable voltage without any evident performance degradation due to carbon deposition. The absence of carbon deposition on the anode and anode current collector layers was also confirmed by scanning electron microscope images and energy-dispersive X-ray spectra. We further discuss oxidation mechanism of the direct methane fuel and removal of the carbon possibly formed in the anodic layers during stability testing.