Spontaneous formation of gold and platinum nanostructures on Highly Oriented Pyrolytic Graphite: an ab-initio and experimental study

M.F. JUAREZ; S. FUENTES; G.J. SOLDANO; L. AVALLE; E. SANTOS

Congreso; Carbon in Electrochemistry: Faraday Discussion 172; 2014

Nanostructures have been widely studied due to their unique properties that differsubstantially from the bulk properties. They are also promising materials because ofthe capability to tune their properties by changing their morphology. One of the mostinteresting methods for the synthesis is the deposition on highly oriented pyrolyticgraphite (HOPG) [1,2]. In this case, the structure of the substrate plays an importantrole in the formation of the nanostructures. Nanomaterials of noble metals, asplatinum on HOPG, have been prepared successfully by different methods [3,4], andit has been found that the steps act as a pattern for the growth of the nanoparticles.In this paper we present theoretical and experimental results of the spontaneousdeposition of gold and platinum on HOPG. We have obtained metallic deposits byimmersion of the electrodes in acidic solutions containing the metal cations. Themorphology, shape, size and abundance were evaluated ex situ by SEM and EDS.Based on the morphology of thenanostructures, there are two differentscenarios for the formation of the metallicdeposits. In one case, gold atoms tend toform linear structures adsorbed on theHOPG edges. And in the opposite side,platinum atoms agglomerates and producenanostructures of bigger sizes.There are several forces driving the shapeand size of the nanoparticles synthetized.The metal/metal bond and the adsorbate/metal interactions are the main ones, andthe final morphology is a compromise between them. In order to understand theseforces we have studied the thermodynamics of the adsorption process at standardambient pressure and temperature conditions. On an earlier work, we have foundthat in O2/H2 atmosphere, the graphene edges are mainly oxidized. On the armchairedges, the terminal carbons are carboxyl groups, but on the zigzag edges, we havefound stable ketones and aldehyde groups [5]. Our calculations in the present workare focused on disentangle the metal/metal and metal/substrate interactions onperfectly hydrogenated and oxidized edges. We have also compared the stability ofnanowires and small clusters on the HOPG edges.Finally, we have studied the electrocatalytic activity of the modified electrodes bymeasuring the hydrogen evolution reaction (HER) in acid media. The cathodiccurrent per specific Pt area was higher than for Pt polycrystalline electrodes. Theresults were correlated with the nanostructures of the deposits.Bibliography1. C. Delerue and M. Lannoo. Nanostructures, Springer Ed.: Germany, 2004.2. L.J. Blomen and M.N. Mugerwa. Fuel Cell Systems, Plenum Press: New York, 1993.3. M. Aktary, C.E. Lee, Y. Xing, S.H. Bergens, and M.T. Mc Dermott. Langmuir 2000, 16, 5837.4. E.C. Walter, M.P. Zach, F. Favier, B.J. Murray, K. Inazu, J.C. Hemminger, and R.N. Penner. Chem.Phys. Chem. 2003, 4, 131.5. G.J. Soldano, M.F. Juarez, B. Teo, and E. Santos. Stability and structure of oxidized graphene edgesin an O2 and H2 environment from ab initio thermodynamics (submitted).