Pulsed-Flow Near-Critical and Supercritical Synthesis of Carbon-Supported Platinum Nanoparticles and In Situ X-ray Diffraction Study of Their Formation and Growth

The formation and growth of carbon (C)-supported platinum (Pt) nanoparticles in a high-temperature, high-pressure ethanol solution have been studied by in situ synchrotron radiation powder X-ray diffraction (PXRD). Supercritical synthesis is shown to be an efficient way to prepare Pt nanoparticles, and the crystallite size of Pt nanoparticles is much smaller when formed with supporting C material compared with synthesis without C. On the basis of the time-resolved in situ PXRD data, a surface stress of 2.65 N/m is derived from the size dependence of the cell parameters. As proof of concept, C-supported Pt nanoparticles were subsequently synthesized in a pulsed-flow supercritical reactor, which offers complete control of the reaction temperature, pressure, and residence time. Well-dispersed Pt nanoparticles decorated on the supporting C material can be obtained by adjusting the reaction conditions, and the electrocatalytic activity of the samples is explored. A mass activity of 0.1209 A/mg(Pt) at a potential of 0.9 V is obtained for the products prepared at 400 degrees C for a residence time of 20 s. The pulsed-flow supercritical method is a facile method to synthesize ligand-free C-supported Pt nanoparticles with high electrocatalytic activity.