Synthesis of Pt-Mo-N Thin Film and Catalytic Activity for Fuel Cells

Although platinum and platinum-based intermetallic alloys have been extensively studied as catalysts for proton exchange membrane fuel cells, platinum-based nitride catalysts have been relatively unexplored. We report the synthesis and characterization of a platinum-based nitride, Pt2Mo3N, using a composition spread thin-film deposition technique. The Pt2Mo3N thin film was generated by codeposition of platinum and molybdenum and subsequent heat treatment in an ammonia flow at 800 degrees C for 6 h. The thin film was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electrochemical tests, including the assessment of catalytic activity toward the oxidation of methanol and formic acid and the reduction of oxygen. The nitride film was smooth and contained single-phase, nearly stoichiometric Pt2Mo3N. Cyclic voltammograms of Pt2Mo3N in 0.1 M H2SO4 demonstrated electrochemical stability far greater than that of a PtMo alloy with the same Pt:Mo ratio, indicating that the formation of the nitride phase enhances electrochemical stability. The ternary nitride exhibited oxidation currents in formic acid and methanol solutions above approximately 0.0 and 0.4 V vs an Ag/AgCl reference electrode, respectively. These are above the expected equilibrium oxidation potentials of approximately -0.2 V. The onset potential for oxygen reduction was estimated to be similar to 0.2 V vs Ag/AgCl, well below the equilibrium value of 1.0 V.