Catalytic approaches to mitigate CO poisoning in fuel cells

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/SnOx, and Pt/Ru/WOx) were evaluated as CO tolerant anodes. The Pt/Ru/WOx 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/SnOx catalyst was a poor anode for hydrogen and all others were more active than the Pt/Ru/SnOx catalyst. The CO that absorbed on the Pt/Ru/WOx catalyst was removed at a potential 20 mV lower than on the Pt/Ru catalyst. ^ In the second approach, six types of catalysts (Au/MnOx, Pt/Vulcan-XC-72, Pt/SnOx/Vulcan-XC-72, Pt/WOx/Vulcan-XC-72, Ir/carbon, and Ir/CoOx-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/CoOx-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/CoOx-Al2O3/carbon catalyst at O2/CO = 1.5. Although the Au/MnOx catalyst had high activity and selectivity for CO oxidation under dry condition, its activity decayed dramatically due to instability of MnOx in the presence of water vapor and hydrogen.