Coarsening of Pt nanoparticles on amorphous carbon film

The coarsening of Pt nanoparticles (NPs) on amorphous carbon film was studied by transmission electron microscopy (TEM) after annealing at temperatures between 200 °C and 300 °C for periods of up to 160 h. NP-size distributions were measured on the basis of TEM images which yield average sizes as a function of annealing temperature and annealing duration. A significant increase of the average particle size is observed with increasing annealing time for all investigated temperatures. An in-situ annealing experiment in a transmission electron microscope reveals two coarsening stages. During the first two hours of annealing, ripening of the NP-size distribution is dominated by Smoluchowski ripening where coalescence of mobile NPs takes place. Smoluchowski ripening can be neglected during the second coarsening stage for annealing times of more than two hours, where NP coarsening proceeds via surface Ostwald ripening. The Arrhenius-type dependence of the derived surface mass-transport coefficients yields an activation energy Ed = 0.84 ± 0.08 eV atom− 1 for the surface diffusion of Pt atoms on an amorphous carbon substrate.