Effect of graphene support on large Pt nanoparticles.

L G Verga,C.-K Skylaris,D Thompsett,M Sarwar,A E Russell,J Aarons

doi:10.1039/c6cp07334d

Abstract

State-of-the-art catalysts are often created via deposition of monolayers, sub-monolayers or nanoparticles of the catalytic material over supports, aiming to increase the surface area and decrease the loading of the catalytic material and therefore the overall cost. Here, we employ large-scale DFT calculations to simulate platinum clusters with up to 309 atoms interacting with single layer graphene supports with up to 880 carbon atoms. We compute the adsorption, cohesion and formation energies of two and three-dimensional Pt clusters interacting with the support, including dispersion interactions via a semi-empirical dispersion correction and a vdW functional. We find that three-dimensional Pt clusters are more stable than the two-dimensional when interacting with the support, and that the difference between their stabilities increases with the system size. Also, the dispersion interactions are more pronounced as we increase the nanoparticle size, being essential to a reliable description of larger systems. We observe inter-atomic expansion (contraction) on the closest (farthest) Pt facets from the graphene sheet and charge redistribution with overall charge being transferred from the platinum clusters to the support. The Pt-Pt expansion, which is related to the charge transfer in the system, correlates with the adsorption energy per Pt atom in contact with the graphene. These, and other electronic and structural observations show that the effect of the support cannot be neglected. Our study provides for the first time, to the best of our knowledge, quantitative results on the non-trivial combination of size and support effects for nanoparticles sizes which are relevant to catalyst design.

Highlights

During the last decades, the interest in more powerful and flexible ways to generate electricity is bringing special attention to fuel cell technology
We present our calculations in order to compare two and three dimensional Pt clusters interacting with a graphene support
We simulated our systems with the rVV10 exchange correlation functional, which is one of the so-called vdW density functionals designed to include the dispersion interactions via a fully non-local term depending on the electronic density

Summary

Introduction

The interest in more powerful and flexible ways to generate electricity is bringing special attention to fuel cell technology. EOR,[3] and the oxygen reduction reaction in the cathode, ORR.[4] Platinum and platinum based alloys, are widely studied as excellent catalysts for both reactions, but due to the high cost of Pt, its inadequate global supply, and the slow kinetics of the ORR in pure Pt catalysts, it is necessary to search for different approaches to construct Pt based catalysts Aiming to solve these problems, most of the catalyst researchers choose to disperse nanoparticles or monolayers of the catalyst material over supports as recently pointed in some review papers.[3,5,6] Another interesting approach to design efficient catalysts is the usage of Pt monolayers as the external layer of core–shell structures.[3,7,8] In both techniques, the main goal is to decrease the platinum loading, increase its surface area and decrease the overall cost of the catalyst

Methods

Results

Conclusion