Direct observation of the reversible changes of the morphology of Pt nanoparticles under gas environment

Large faceted Pt particles prepared in solution were in situ observed by ETEM (Environmental Transmission Electron Microscopy) during oxidation - reduction cycles. Reversible shape transformations were observed with the increase or decrease of the ratio of (111) faces to (001) faces in H2 and O2 respectively, at pressures of a few mbars. Under Hydrogen, the shape is relatively close to the Wulff shape of an fcc crystal under vacuum, while under oxygen, the (001) faces extend and the (111) faces shrink due to a stronger adsorption of oxygen on the more open (100) faces. Going from hydrogen to oxygen, the surface energy anisotropy is inverted.