In-situ transmission electron microscopy observation of particle size effect of nanoscale platinum catalysts on the formation of fullerenelike carbon shells

Drastically different catalytic behaviors of nanometer-sized platinum particles which have diverse sizes are observed using in-situ transmission electron microscopy. For small platinum catalyst particles (with diameters less than 5 nm), carbon shells form on the surfaces of the platinum catalyst particles. The formation of the carbon shells starts from the nucleation of amorphous carbon on the preferred (1 1 1) planes of platinum nanoparticles. For these small platinum catalyst particles encapsulated in graphitic shells, they are passivated by the carbon shells and their coalescence is hindered by the surrounding shells. After the platinum catalyst particles ultimately coalesce, they interact to form a compact platinum particle after breaking the encapsulating shells. For larger platinum nanoparticles (with diameters larger than 5 nm), no encapsulation of platinum nanoparticles is observed and there occurs only the coalescence of platinum nanoparticles.