Catalytic approaches to mitigate CO poisoning in fuel cells (Selective oxidation).

摘要

Proton exchange membrane (PEM) fuel cells are efficient energy converters that convert chemical energy of fuels such as hydrogen into electricity. However, hydrogen produced from reforming hydrocarbon such as methanol contains about 1% CO, which is a poison of PEM fuel cell anode. Two catalytic approaches were studied to mitigate CO poisoning of anode catalysts in fuel cell applications. In the first approach, five carbon supported Pt/Ru-based catalysts (Pt/Ru, Pt/Ru/Os, Pt/Ru/Au, Pt/Ru/SnO_x, and Pt/Ru/WO_x) were evaluated as CO tolerant anodes. The Pt/Ru/WO_x catalyst was found more active than the others for electrooxidation of H₂ with 1% CO. It was almost twice as active as the Pt/Ru catalyst for electrooxidation of H₂ with 1% CO at practical potentials. Oxidation of pure hydrogen showed that the Pt/Ru/SnO_x catalyst was a poor anode for hydrogen and all others were more active than the Pt/Ru/SnO_x catalyst. The CO that absorbed on the Pt/Ru/WO_x catalyst was removed at a potential 20 mV lower than on the Pt/Ru catalyst.; In the second approach, six types of catalysts (Au/MnO_x, Pt/Vulcan-XC-72, Pt/SnO_x/Vulcan-XC-72, Pt/WO_x/Vulcan-XC-72, Ir/carbon, and Ir/CoO_x-Al₂O₃/carbon) were investigated as CO selective oxidation catalysts with O₂ under conditions similar to that of an operating fuel cell (76°C, High humidity). This was done to study the possibility of integration of a CO removal reactor into a fuel cell stack. The Ir/CoO_x-Al₂O₃/carbon catalyst was the superior catalyst for CO selective oxidation. It had the highest CO conversion and selectivity among the catalysts evaluated. A 100% CO conversion occurred with the Ir/CoO_x-Al₂O₃/carbon catalyst at O₂/CO = 1.5. Although the Au/MnO_x catalyst had high activity and selectivity for CO oxidation under dry condition, its activity decayed dramatically due to instability of MnO_x in the presence of water vapor and hydrogen.