Supercritical deposition (SCD) is used to prepare carbon-supported Pt nanoparticles as electrocatalysts for proton exchange membrane fuel cells (PEMFCs). Dimethyl(1,5-cyclooctadiene)platinum(II) (Pt(cod)me(2)) is adsorbed from supercritical carbon dioxide (scCO(2)) solutions onto Vulcan VX-72 at 13.2 MPa and 50 degrees C. The adsorbed metal precursor is converted to its metal form via three different routes: thermal conversion in N-2 at ambient pressure (route 1), thermal conversion in scCO(2) (route 2), or chemical conversion in H-2 at ambient pressure (route 3). Sequential SCD is used in routes 1 and 3. The mean diameters of the synthesized Pt nanoparticles are smallest for route 1 and largest for route 3. Nano-scale morphology of the electrocatalysts is characterized using transmission electron microscopy (TEM), revealing narrower Pt particle size distributions for the catalyst prepared via route 1 than for those synthesized by routes 2 and 3. Electrocatalyst prepared using route 1 showed the best performance both in specific activity (measured via cyclic voltammetry) and in PEMFC tests among electrocatalysts prepared using different routes. (C) 2014 Elsevier B.V. All rights reserved.