Cyclic voltammetry and X-ray photoelectron spectroscopy studies of electrochemical stability of clean and Pt-modified tungsten and molybdenum carbide (WC and Mo2C) electrocatalysts

The electrochemical stability of tungsten carbide (WC), Pt-modified WC, molybdenum carbide (Mo2C), and Pt-modified Mo2C has been examined using an in situ electrochemical half-cell in combination with X-ray photoelectron spectroscopy (XPS). The WC surface, created via the carburization of a tungsten foil, was electrochemically stable to ∼0.8 V with respect to the normal hydrogen electrode (NHE) when exposed to dilute sulfuric acid. At higher potentials, XPS confirmed the surface oxidation of WC to form WxOy species. The deposition of submonolayer coverage of Pt on the WC surface increased the region of stability of WC, extending the onset of catalyst oxidation to ∼1.0 V (NHE). These results suggest that both WC and Pt/WC have the potential to be used as anode electrocatalysts. In contrast, both Mo2C and Pt-modified Mo2C underwent oxidation at ∼0.4 V (NHE), indicating that molybdenum carbides are not stable enough for applications as anode electrocatalysts.