Analysis of gas phase composition in fuel and exhaust gas in Solid Oxide Fuel Cells.

摘要

Direct utilization of coal syngas in Solid Oxide Fuel Cell faces a number of challenges. One of the impediments to the implementation of SOFCs is their degradation in the presence of impurities in the fuel. Phosphine (PH 3) is present in coal syngas at ppm levels, and a number of researches have shown that the nickel anode is damaged by long term exposure to ppm levels of phosphine in various fuels. Because phosphine is exposed to high temperatures (~800°C) and varying amounts of water and oxygen in fuels, the exact nature of the phosphorus species reaching the anode is unknown. Thermodynamic calculations vary in the predicted species at equilibrium, some of which are HPO (mass 48), HPO2 (mass 64), HPO3 (mass 80), and P4O 10 (mass 288). Mass spectroscopic analyses of exhaust gases from SOFC test systems are provided, with and without Ni/YSZ anodes in the path of the gas flow. The mass spectrometer, a MKS Cirrus system, has a mass range of 1--100 amu and a detection limit of ∼0.001 torr. The mass spectrometry is applied to full-cell tests. The cell is operated in H 2 as fuel. The cell is tested with and without 10--20 torr water added, with and without 20 ppm PH3 added, and with different current applied to the cell. Degradation in cell performance is observed as expected. The water generated by the electrochemical reactions is detected. Leaks are incorporated in the tests and air impurities such as N2, O 2, Ar and CO2 signals are also detected. No new mass signals appear in all conditions, suggesting that the possible phosphine reaction products have a mass outside the 100 amu range of the mass spectrometer.