From Deposited Metal Precursors to Supported Atoms or Nanoparticles

Strong Electrostatic Adsorption is a simple method to prepare highly dispersed supported metals. However, the minimum size of nanoparticles produced with gas phase reductions after SEA is typically about 1-2 nm. Alternative methods are explored to further decrease particle size, that is, to control the agglomeration of adsorbed precursors into nanoparticles, clusters, or isolated atoms. Three alternative methods have been employed to synthesize carbon supported Pt with higher dispersion than can be prepared by a "standard" method of strong electrostatic adsorption of charged Pt precursors followed by gas phase hydrogen reductions. First, gas phase reduction is replaced by a liquid phase reduction with hydrazine. Second, carbon black surfaces are oxidized to render them more hydrophilic and decrease the degree of agglomeration of Pt precursors after drying. The third method involves a switch of solvent from water to a solvent -acetone - which wets the carbon surface. The ensuing samples comprised of isolated atoms, clusters, and nanoparticles were characterized by high sensitivity XRD and z-contrast STEM imaging.