Physicochemical characterization of the Pd/MWCNTs catalysts for fuel cell applications

Abstract

AbstractThe multiwall carbon nanotubes (MWCNTs) supported Pd catalyst, prepared by the polyol method and reduced in 5% of H2 in Ar atmosphere at temperature of 200 °C, exhibits high activity in electrooxidation of formic acid, whereas, the same catalyst calcinated at temperature of 250 °C in 100% of Ar is inactive. The structural and chemical properties of the catalyst surfaces after reducing and calcination treatments were investigated using electron spectroscopy. The catalytically active sample indicated smaller O content, with the same content of Pd and C at the surface. Simultaneously, the content of carbon–oxygen–hydrogen groups, i.e., carboxyl, carbonyl, ester, ether, and acid anhydride, was lower. In the surface layer of both catalysts, three chemical Pd forms were observed: Pd metallic crystallites, PdO and Pd in organic matrix. In active catalyst, similar content of Pd crystallites and smaller content of PdO were observed. The differences in activity of the investigated Pd/MWCNTs catalysts after reduction and calcination result from the amorphous carbon covering the PdO/Pd nanoparticles, where the PdO layer is of larger thickness for inactive catalyst. This overlayer is removed after reduction in 5% of H2 in Ar atmosphere at temperature of 200 °C.