Study of the nucleation of Pd clusters on graphene

F. BANAFE; G. SOLDANO; M. M. MARISCAL

Congreso; XXII International Materials Research Congress. MRS; 2013

MRS

One of the most remarkable applications of nanoscience is the use of metallic clusters and nanoalloys to design and build ultra-sensitive hydrogen sensors. The growing interest in this area is motivated by the imminent use of hydrogen as a mean for storing energy obtained from renewable sources. Palladium and/or some of its alloys have been considered an alternative to the available commercial hydrogen sensors since it markedly increases gas selectivity and response1. Graphene is a suitable support material due to its huge surface/volume ratio and its physical properties which could lead to an increase in the versatility of sensors. A novel and simple method to build flexible hydrogen sensors using Pd nanoparticles deposited on graphene has been recently reported2. This sensor is able to detect 20 ppm of H2 at room temperature. A preliminary study on nanoparticle size and distribution has been also reported by the authors. However, a detailed study on the effect of size distribution, rugosity and defects of the support material on the nucleation of Pd nanoparticles has not reported so far. In the present work we studied the nucleation and growth of Pd clusters on graphene through ab-initio calculations and classical molecular dynamics (MD). Adsorption energy as a function of distance to the graphene surface of a single Pd atom was calculated using the Quantum Espresso3 package. A Lennard Jones potential function was fitted using the ab-initio results and later used to describe the Pd-C pairwise interaction in MD simulations. The Pd-Pd4 interaction energy was modeled with the embedded atom method (EAM) and the C-C interaction with the Airebo5 potential. All MD simulations were done using the LAMMPS6 code. We explored the diffusion of Pd atoms on the surface as well as the geometry and energy of adsorption of dimers, trimers and bigger clusters.