Louis G. Carreiro

Modeling and Verification of Steady State Operational Changes on the Performance of a Solid Oxide Fuel Cell

Solid oxide fuel cells (SOFCs) offer many potential benefits as an energy conversion device. This paper addresses experimental validation of a numerical SOFC model that has been developed. Results are compared at steady state operation for temperatures ranging from 1073 K to 1173 K and for H 2 gas concentrations fuel supplies of 10-90% with a balance of N 2 . The results agree well with a maximum of 13.3% difference seen between the numerical and experimental results, which is within the limit of the experimental uncertainties and the material constants that are measured, with most comparisons well below this level. It is concluded that since the model is very sensitive to material properties and temperature that for the best results they should be as specific as possible to the experiment. These specific properties were demonstrated in this paper and a validation of a full fuel cell model, with a concentration on the anode, was presented.

Solid Oxide Fuel Cells in Unmanned Undersea Vehicle Applications

The Navy is currently investigating solid oxide fuel cells (SOFCs) for the propulsion of unmanned undersea vehicles (UUVs). SOFCs are being targeted because of their potential to carry out extended missions, which are not possible using current battery technology. In addition, they offer the advantages of being able to utilize energy-dense hydrocarbon fuels and are self-sustaining while supplying heat to reforming processes. The SOFC system evaluated in this study consisted of a Ni-YSZ-based, 6-cell stack with anode supported cells close-coupled with a micro-channel steam reformer. Various reformate gas compositions, steam to carbon ratios and flow rates were tested to gather a range of data under the expected operating conditions of UUVs. The system was operated for more than 70 hours consuming approximately 0.5 to 0.7 ml/min of fuel and producing about 100 to 230 watts of power. The integrated stack and reformer displayed stable performance with a fuel utilization of 80% and an efficiency of 50% at maximum power output.

Electrochemical Reduction of Sulfur Hexafluoride in Novel, Air-Independent Power Systems

The electrochemical reduction of sulfur hexafluoride (SF6) was investigated in cells using 1-n-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide electrolyte with additives to enhance SF6 solubility and anode activity. Magnesium was used as the counter electrode (anode) in these cells. In post run analyses, metal fluoride formations at the anode and sulfur deposits at the cathode were found. These findings are possible evidence of SF6 decomposition; however, degradation of the electrolyte may have also been the source of these reaction by-products. Output power over 1 mW was demonstrated in the cell.