A present challenge in electrocatalysis is to identify highly active catalysts. Therefore it is of fundamental importance to achieve a better understanding of the activity of catalyst materials in dependence of morphology and supporting material. Here, we used platinum nanoparticles supported on highly oriented pyrolytic graphite (HOPG) to investigate catalytic properties for hydrogen related reactions. The activity of Pt nanoparticles supported on carbon for application in fuel cells and platinum on glassy carbon has been investigated extensively for hydrogen related reactions in the past. However, there are only few experimental investigations on the activity of Pt nanoparticles supported on a HOPG basal plane, a well-defined support regarding geometric and electronic structure. Platinum was deposited electrochemically from solution containing K(2)PtCl(6) by means of potentiostatic single pulse method to produce nanostructured HOPG surfaces with different particle sizes (in the range between <10 nm and 50 nm) and particle densities. The samples were characterized electrochemically and via SPM techniques with respect to morphology, size and distribution of the platinum nanoparticles. The results on the catalytic activity of Pt/HOPG regarding HER show no pronounced dependence on the particle size or coverage of the substrate. This differs from results obtained for the nanostructured systems Pt/Au(1 1 1) and Pd/Au(1 1 1) reported in literature, which show a strong enhancement in HER activity for decreasing Pt or Pd coverage. We therefore conclude that the support can strongly influence the activity of platinum nanoparticles. (C) 2009 Elsevier B.V. All rights reserved.