Alternative supports for the preparation of catalysts for low-temperature fuel cells: the use of carbon nanotubes

Noble metal catalysts in the form of nanoparticles supported on high surface area carbon exhibit characteristics which depend strongly on the nature of the support. This work presents results with noble metal catalysts supported on carbon nanotubes (MWNT and SWNT) and also on a high surface area carbon powder Vulcan XC-72, for proton exchange membrane fuel cells (PEMFC) fed with hydrogen contaminated with CO and also for the direct methanol fuel cell (DMFC). A high performance was achieved with PtRu supported on nanotubes for H2 + 100 ppm CO, although it was similar to that presented by PtRu on Vulcan XC-72 with an overpotential of 100 mV at 1 A cm−2. Results for the DMFC showed power densities exceeding 100 mW cm−2 at 90 °C and 0.3 MPa and the activity of the anodes followed the sequence: PtRu/MWNT > PtRu/Vulcan XC-72 > PtRu/SWNT. The electrocatalysts were all prepared with the same method, namely impregnation of the carbons with the precursors in ethanol and reduction under a hydrogen atmosphere. The role of Ni, Fe and other contaminants contained in the as-received carbon nanotubes is discussed.