Structural, Chemical, and Electronic Properties of Pt/Ni Thin Film Electrodes for Methanol Electrooxidation

Pt/Ni thin-film electrodes were fabricated by e-beam evaporation of metal layers and rapid thermal annealing (RTA), to achieve alloy formation between the Pt and Ni layers. The structural, chemical, and electronic properties of thin-film electrodes annealed at 200, 300, and 500 °C were classified as follows: Pt-dominant (as-Pt/Ni or 200 °C Pt/Ni), Pt-based (300 °C Pt/Ni), and Ni-dominant (500 °C Pt/Ni). These Pt/Ni thin-film electrodes were matched well with Pt/Ni(3:1), -(1:1), and -(1:3) nanoparticles synthesized by borohydride reduction, for use in methanol electrooxidation in a direct methanol fuel cell. The characteristics of the thin-films and nanoparticles were correlated using X-ray diffraction analysis, Auger electron spectroscopy, X-ray photoelectron spectroscopy, and electrochemical measurements. The modified electronic properties of platinum in Pt/Ni alloy electrodes as well as a higher catalytic activity for methanol electrooxidation could be attributed to the surface and bulk structure of Pt/Ni alloys with a proper composition such as 300 °C Pt/Ni thin-film electrode and Pt/Ni(1:1) nanoparticle. The possibility that electrodes designed by thin-film processing such as by means of an e-beam evaporator and RTA system could be used in a systematic approach to the characterization of alloy nanoparticles is discussed.