Potential application of tungsten carbides as electrocatalysts: III. Reactions of methanol, water, and hydrogen on Pt-modified C/W(111) surfaces

The bonding and dissociation of methanol, water, and hydrogen on Pt-modified C/W(111) surfaces have been studied using high-resolution electron energy loss spectroscopy and temperature-programmed desorption. The decomposition pathways of methanol on C/W(111) are significantly modified by the presence of submonolayer coverages of Pt. For example, on the unmodified C/W(111) surface, the decomposition of methanol occurs via three pathways: (i) partial decomposition to produce carbon monoxide and hydrogen (∼31% selectivity), (ii) partial decomposition to form methane and atomic oxygen (∼14% selectivity), and (iii) complete decomposition to produce hydrogen, atomic carbon, and atomic oxygen (∼55% selectivity). In contrast, on the 0.6 monolayer (ML) Pt-modified C/W(111) surface, ∼49% of methanol partially dissociates to carbon monoxide and hydrogen, and the other ∼51% of methanol molecules undergo complete decomposition to hydrogen, atomic carbon, and atomic oxygen. The presence of submonolayer coverages of Pt prohibits the production of methane, which is an undesirable side product in direct methanol fuel cells. Furthermore, both the C/W(111) and the Pt-modified C/W(111) surfaces are active toward the dissociation of water. However, the amount of adsorbed water that undergoes dissociation is reduced from 0.18 H2O per W atom on C/W(111) to 0.056 H2O per W on the 0.6 ML Pt-modified C/W(111) surface. Finally, both C/W(111) and 0.6 ML Pt/C/W(111) surfaces are active toward the dissociation of hydrogen. These results demonstrated the possible synergistic effects by supporting low loading of Pt onto tungsten carbides for potential applications in methanol or hydrogen fuel cells.