Foamlike nanostructures created from dendritic platinum sheets on liposomes

The synthesis of novel dendritic platinum sheets of 2-nm thickness by the reduction of an aqueous metal complex with ascorbic acid in the presence of liposomes is reported. Variation of the reaction conditions, including incorporation of a tin porphyrin photocatalyst within the liposomal bilayer to initiate seed-particle growth, allows access to a diverse range of platinum nanostructures, including dendritic nanosheets of uniform diameters and convoluted foamlike structures composed of interwoven dendritic nanosheets. The mechanism of formation of these nanomaterials is investigated with regard to the photocatalytic generation of platinum nanoparticle seeds, the autocatalytic dendritic growth, and the templating on liposomes. The discrete nanospheres of foamlike platinum are of particular interest, as they may have advantages over conventional platinum black in some applications. For example, they will likely exhibit improved electrical connectivity and mass-transport properties in electrocatalytic applications. Electrochemical CO-stripping measurements and N-2 adsorption experiments show that the nanospheres of foamlike platinum possess high surface areas. In addition, these platinum foam nanospheres are as active as commercial platinum black in catalyzing the four-electron oxygen reduction reaction.