Catalyst nanoscale assembly from the vapor phase on corrosion resistant supports

Abstract

The synthesis process, reactive spray deposition technology (RSDT), utilized a jet-flame to produce Pt nanoparticles. The RSDT process bypasses traditional wet chemical routes by simultaneously nucleating the catalyst on a support and sequential deposition of catalyst layer via the gas phase. Pt nanoparticles were attached, in the process gas during the time-of-flight, to the surface of several supports. The supports show promising corrosion resistance under the cathode conditions of a proton exchange membrane fuel cell (PEMFC). The supported Pt catalysts were then studied in regards to structure, stability and electrochemical behavior toward the oxygen reduction reaction (ORR) in perchloric acid. Transmission electron microscopy studies showed that the average Pt particle diameter is ∼2.5nm. The average diameter and distribution of the Pt particles are independent of the support type and a high degree of catalyst dispersion has been achieved on all supports. The greatest surface area and electrochemical mass activity were obtained using Vulcan XC-72R, while a graphitized carbon support produced the highest specific activity. Based on X-ray photoelectric spectroscopy (XPS) measurements, approximately 30% of the surface of the Pt particles is comprised of Pt2+. This oxide coverage does not extend into the bulk and is below the detection limits of X-ray diffraction (XRD). The electrochemical reduction of oxygen exhibits a typical Tafel slope of −65 to −71mV/dec.