Formation of a Porous Platinum Nanoparticle Froth for Electrochemical Applications, Produced without Templates, Surfactants, or Stabilizers

Pt nanoparticles (NPs), synthesized via the reduction of H 2 PtCl 6 by formic acid at 80 °C, formed a nanoporous froth at the upper surface of the aqueous solution in which they were produced. The NPs, brought to the surface by the escape of CO 2 bubbles produced by the reduction, partly coalesced to form a froth film with a porosity >95%. Scanning and transmission electron microscopies were used to characterize the froth morphology and the NP dimensions, and X-ray photoelectron spectroscopy was used to characterize the NP surface chemistry. The froth was found to be composed of 3−5 nm zerovalent Pt NPs. The porous froth films, which could be removed and handled, demonstrated an electroactive surface area of 168 ± 8 m 2 /g Pt, more than 4 times that of a commercial colloidal Pt black, and equivalent to that of the best Pt particle/carbon black electrocatalysts.