The Mechanistic Details for the Growth of Palladium Nanoparticles on Graphene Oxide Support

Abstract

AbstractComposite materials, comprising metal nanoparticles (NP) on a structural support have gained significant attention as novel systems for catalysis and energy conversion. Despite the importance of these materials for practical applications, the mechanism of the NPs formation remains elusive. Here, we investigate the seeding and the growth of Pd‐NPs on graphene oxide (GO) support in the two‐step process: impregnation and annealing. During the impregnation step, Pd2+ uniformly covers GO surface due to the strong chemical bonding with the oxygen functional groups. During the thermal annealing step, the growth of Pd‐NPs occurs via the radial in‐plane migration of Pd‐NPs along the GO surface to incorporate new Pd atoms in a way, similar to the snowball effect. The exact migration path depends on the annealing temperature, and on the Pd/GO ratio. The same two factors are responsible for the size‐distribution and the lateral density of as‐grown Pd‐NPs. At high temperatures, diffusion of the growing Pd‐NPs across the GO layers complicates the picture. The annealing temperature also influences the crystallinity, or the degree of porosity of the graphenic support. Below 500°C, carbon planes remain almost intact, while above 700°C, GO decomposes into highly porous material.