Direct Use of Sulfur-Containing Coke on a Ni-Yttria-Stabilized Zirconia Anode Solid Oxide Fuel Cell

The direct use of sulfur-containing coke to generate electricity has been studied by a transient approach that involves feeding a batch of coke samples to a Ni-yttria-stabilized zirconia (YSZ) anode solid oxide fuel cell operating at 750 degrees C in flowing He, measuring the fuel cell performance, and monitoring the concentration of the exhaust gases with a mass spectrometer (MS) and a gas chromatograph (GC). Feeding coke to the fuel cell produced current densities as high as 261 mA/cm(2) at a load of 0.56 V with the concomitant evolution of CO2, giving an energy efficiency (i.e., the ratio of the electric energy produced to the enthalpy of consumed fuel) of 52.9%, nearly 3 times higher than the efficiency resulting from feeding H-2 fuel. The volumetric three-phase boundary (TPB) length available at the Ni-YSZ anode for electrochemical oxidation of H-2 was estimated to be 4.1 x 10(12) m/m(3), which is 3 orders of magnitude larger than the TPB length available for oxidation of carbon at the anode surface in direct contact with the solid fuel. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) mapping of the Ni-YSZ anode after the experiments in coke showed the absence of sulfur compounds, indicating that the sulfur-containing coke did not transfer any sulfur species that could cause poisoning to the anode surface. The fuel cell performance and energy efficiency results support the feasibility of direct power generation from coke in a Ni-YSZ anode solid oxide fuel cell.