| One of the major challenges in the commercialization of proton exchange membrane fuel cells (PEMFC) is the cost, and low CO tolerance of the anode electrocatalyst material. The anode typically requires a high loading of precious metal electrocatalyst (Pt or Pt–Ru) to obtain a useful amount of electrical energy from the electrooxidation of methanol (CH3OH) or ethanol (C2H5OH). The complete electro–oxidation of methanol or ethanol on these catalysts produces strongly adsorbed CO on the surface, which reduces the activity of the Pt or Pt–Ru catalysts. Another major disadvantage of these electrocatalyst components is the scarcity and consequently high price of both Pt and Ru.;Tungsten monocarbide (WC) has shown similar catalytic properties to Pt, leading to the utilization of WC and metal modified WC as replacements to Pt and Pt–Ru. In this thesis we investigated WC and Pt–modified WC as a potentially more CO–tolerant electrocatalysts as compared to pure Pt. These catalysts would reduce or remove the high loading of Pt used industrially. The binding energy of CO, estimated using temperature programmed desorption, is weaker on WC and Pt/WC than on Pt, suggesting that it should be easier to oxidize CO on WC and Pt/WC. This hypothesis was verified using cyclic voltammetry to compare the electro–oxidation of CO on WC, Pt/WC, and Pt supported on carbon substrates, which showed a lower voltage for the onset of oxidation of CO on WC and Pt/WC than on Pt.;After observing these improved properties on the Pt/WC catalysts, we decided to expand our studies to investigate Pd–modified WC as Pd is less expensive than Pt and has shown more ideal properties for alcohol electrocatalysis in alkaline media. Pd/WC showed a lower binding energy of CO than both its parent metal Pd as well as Pt. Then, density functional theory (DFT) calculations were performed to determine how the presence of Pd affected the bonding of methanol and ethanol on the WC surface. The DFT studies showed that the binding energies for methanol and methoxy as well as ethanol and ethoxy on one monolayer (ML) Pd/WC are more similar to Pd than to WC. This predicts that the ML Pd/WC surface should have catalytic properties more similar to Pd than to WC. Ultra–high vacuum (UHV) experiments were then performed to determine the reaction products and pathways for methanol and ethanol on Pd(111), WC, and Pd/WC surfaces. These studies showed that the WC surface was very active toward the O–H bond cleavage to produce a methoxy intermediate, although WC was also undesirable because it was active for C–O bond scission and less active for the C–H bond scission. Adding Pd on WC enhanced the scission of the C–H bonds of methoxy while removing the C–O bond scission reaction pathway, suggesting a synergistic effect of using Pd/WC as electrocatalysts for methanol and ethanol decomposition. Dissociation of water, which is important for CO tolerance, was also investigated using UHV techniques with the conclusion that both the WC and Pd/WC surfaces dissociated water. The predictions from UHV studies was verified in electrochemical experiments using cyclic voltammetry (CV) and chronoamperometry (CA) measurements of electro–oxidation of methanol and ethanol in an alkaline environment. These experiments showed that Pd/WC was electrochemically active towards methanol and ethanol decomposition and has greater electrochemical stability over time than pure Pd, potentially due to higher CO tolerance for Pd/WC. |
