Surface science and electrochemical studies of WC and W 2C PVD films as potential electrocatalysts

Abstract

The stability of WC and W 2C in an electrochemical environment has been examined using an electrochemical half-cell in combination with X-ray photoelectron spectroscopy (XPS) to monitor changes in surface composition. The W 2C film is not stable in the electrochemical environment, immediately oxidizing to form surface W x O y species. In contrast, the WC film is stable at the anode potential below 0.6 V, demonstrating the potential to be used as an electrocatalyst. In order to determine the feasibility of using WC as an electrocatalyst for direct methanol fuel cells (DMFC), the reaction of methanol on the PVD WC film has been studied using ultrahigh vacuum (UHV) surface techniques, including high-resolution electron energy loss spectroscopy (HREELS) and Auger electron spectroscopy (AES). Methanol dissociates on the WC film to produce the methoxy intermediate (CH 3O), which is stable on the WC surface to 500 K. The reaction of methanol has also been investigated on WC films modified by low coverages of Pt, which shows a promoting effect of Pt for the dissociation of methoxy in the temperature range of 400–500 K. The surface science results suggest a synergistic effect for supporting low coverages of Pt on WC films for the potential application as electrocatalysts.