Solid Oxide Fuel Cells Enable Direct Oxidation of Common Liquid Fuels
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Solid Oxide Fuel Cells Enable Direct Oxidation of Common Liquid Fuels Fuel cells can produce power in the same way that combustion engines can, but with higher efficiencies and environmentally friendly and predictable by-products. However, a major difficulty in the implementation of fuel cells is the requirement that most fuels must first be converted to hydrogen. Current research in this field focuses on creating materials that electrochemically oxidize and draw power from readily available fuels, such as gasoline and diesel fuel, without first reforming these fuels to hydrogen. To this end, researchers at the University of Pennsylvania, led by Raymond J. Gorte, have revealed that Cu-cermet anodes are capable of electrochemically oxidizing toluene, n-decane, and synthetic diesel fuel directly, without first reforming them to hydrogen. As reported in the Journal of The Electrochemical Society 148 (7) (2001), model solid-oxide fuel cells were used. The fuel cells were prepared by first fabricating an yttria-stabilized zirconia (YSZ) wafer with a 400-µm porous layer and a 60-µm dense layer. After attaching the cathode material (50:50 YSZ and La0.8Sr0.2MnO2) on the dense side of the YSZ wafer, the porous side was made into a composite anode by impregnation with nitrate solutions of Cu and ceria and subsequent oxidation and reduction to form the Cu-ceria-YSZ cermet. Electrocatalytic characterization was then performed while injecting liquid hydrocarbons (toluene, n-decane, and synthetic diesel fuel) directly into the cell. A flow of dry N2 gas was included in most, but not all, of the experiments to maintain flow. Fuel conversions were less than 1%, conditions that are most likely to cause coking (i.e., the formation of tar-like substances) because insignificant amounts of water are formed. The cathode was left open to air. Results for Cu-ceria-YSZ cermets showed positive characteristics, according to the researchers. First, the fuel cell was stable. The cell was operated at 973 K and a potential of 0.5 V for 12 h in a 40 wt% hydrocarbon-N2 mixture for each of the three fuels. The anode was also stable in pure n-decane for at least 1.5 h. By comparison, the researchers reported, a fuel cell made with a traditional Ni-based anode was rapidly destroyed at 973 K in the 40% toluene-N2 mixture. Even without optimization or the use of a thin electrolyte, a reasonable power density of 0.1 W/cm2 was observed for each of the fuels with a 40 wt% hydrocarbon-N 2 feed. Analysis of the effluent gas using gas chromatography for the toluene feed showed that the fuel was completely oxi-
dized to CO2 and water. The researchers said that this report is important to the materials community in the search for cost-effective, environmentally friendly ways to use hydrocarbon fuels to produce electrical power, especially for transportation and portable power devices. MATHEW M. MAYE
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