Platinum–Phosphorus Nanoparticles on Carbon Supports for Oxygen-Reduction Catalysts

Highly dispersed platinum nanoparticles on carbon supports were synthesized by electrochemical reducing platinum ions in an aqueous solution containing hypophosphite H3PO2 . Adding H3PO2 during the synthesis of the catalyst was effective for reducing platinum particle size, and the platinum particles with a mean size of 2.0–2.3 nm were obtained at a high platinum loading amount of over 50 wt %. The oxygen-reduction activity of the catalysts that added H3PO2 was higher than that of the catalyst that did not add H3PO2, which was due to the large surface area of the platinum in the former catalyst. According to the results of scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analysis, the phosphorus in the catalysts bonded with the surface of platinum particles as an oxide. The growth suppression of platinum particles was therefore attributed to the existence of a phosphorus oxide on the surface of platinum particles. But, adding H3PO2 excessively reduced the platinum surface area. © 2008 The Electrochemical Society. DOI: 10.1149/1.3005578 All rights reserved.