Abstract
Studies aiming at improving the activity and stability of dispersed W and Mo containing Pt catalysts for the CO tolerance in proton exchange membrane fuel cell (PEMFC) anodes are revised for the following catalyst systems: (1) a carbon supported PtMo electrocatalyst submitted to heat treatments; (2) Pt and PtMo nanoparticles deposited on carbon-supported molybdenum carbides (Mo2C/C); (3) ternary and quaternary materials formed by PtMoFe/C, PtMoRu/C and PtMoRuFe/C and; (4) Pt nanoparticles supported on tungsten carbide/carbon catalysts and its parallel evaluation with carbon supported PtW catalyst. The heat-treated (600 oC) Pt-Mo/C catalyst showed higher hydrogen oxidation activity in the absence and in the presence of CO and better stability, compared to all other Mo-containing catalysts. PtMoRuFe, PtMoFe, PtMoRu supported on carbon and Pt supported on Mo2C/C exhibited similar CO tolerances but better stability, as compared to as-prepared PtMo supported on carbon. Among the tungsten-based catalysts, tungsten carbide supported Pt catalyst showed reasonable performance and reliable stability in comparison to simple carbon supported PtW catalyst, though an uneven level of catalytic activity towards H2 oxidation in presence of CO is observed for the former as compared to Mo containing catalyst. However, a small dissolution of Mo, Ru, Fe and W from the anodes and their migration toward cathodes during the cell operation is observed. These results indicate that the fuel cell performance and stability has been improved but not yet totally resolved.
Highlights
Nowadays different varieties of fuel cells are in use for different applications, but the proton exchange membrane fuel cells (PEMFCs) have gained considerable attention among them due to characteristics properties, such as low operating temperature, high power density, high efficiency in energy conversion etc
Due to the very low anode overpotential of the hydrogen oxidation reaction (HOR) on PtMo/C catalyst (Pt), in acid media, H2 is supposed to be the best fuel, which can be used in the anode of PEMFC for obtaining sufficient high performance in these cells, but the use of pure H2 in these system is highly unfavorable dueto the lack of required infrastructure for i t s production
Several methods have been reported in the literature for overcoming the CO poisoning effect, the most common being the physicochemical changes in Pt electrocatalyst by adding a second or third transition metal or with the formation of oxide or carbide phase employing as the catalyst support (Chung et al 2007, Leng et al 2002)
Summary
Nowadays different varieties of fuel cells are in use for different applications, but the proton exchange membrane fuel cells (PEMFCs) have gained considerable attention among them due to characteristics properties, such as low operating temperature, high power density, high efficiency in energy conversion etc. The CO concentration in the resultant gas mixture can be further reduced through succeeding clean up steps to sufficient low levels (10-100 ppm), even such a l o w concentration of CO in the anode feed stream can poison the Pt catalyst deployed in the anode. This blocks the active sites of the electrocatalyst available for H2 chemisorption and subsequent electro-oxidation, considerably decreasing the catalyst activity, especially inlow temperatures operation systems (70-150 °C) (Manasilp and Gulari 2002, Urian et al 2003, Wee and Lee 2006, Ticianelli et al 2005). Several methods have been reported in the literature for overcoming the CO poisoning effect, the most common being the physicochemical changes in Pt electrocatalyst by adding a second or third transition metal or with the formation of oxide or carbide phase employing as the catalyst support (Chung et al 2007, Leng et al 2002)
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