Dopant-Induced Electronic Structure Modification of HOPG Surfaces: Implications for High Activity Fuel Cell Catalysts

N-doped graphite has been reported to provide enhanced catalytic properties as a support material for Pt catalysts in fuel cell applications. With use of a combined experimental and modeling approach, this work identifies the potential fundamental mechanisms for this enhancement effect. To ensure a well-defined experimental system, this work employs highly oriented pyrolitic graphite (HOPG) as a model analogue of the graphite support commonly used in fuel cell applications. Undoped, Ar-doped, and N-doped HOPG substrates have been investigated via electrochemical capacitance and X-ray photoelectron spectroscopy (XPS) measurements. The results indicate that doping, especially N-doping, induces significant modification to the electronic structure of the HOPG surface. A simplified model of the doping effects and band structures for the doped graphite surfaces are proposed to explain these results. When Pt nanoparticles are grown on top of these dopant-modified HOPG surfaces, the resulting Pt/surface-defect interactions significantly impact the Pt nanoparticle nucleation, growth, and catalytic activity.