Probing the correlation between Pt-support interaction and oxygen reduction reaction activity in mesoporous carbon materials modified with Pt-N active sites

Abstract

Pt nanoparticles (NPs) on nitrogen-functionalized mesoporous carbon have proved to be interesting materials for oxygen reduction reaction. In this paper, we employed a new synthetic route to simultaneously deposit Pt NPs and introduce N-doping in the carbon support, by using dichloro(1,10-phenanthroline)platinum(II) or dichloro(2,2′-bipyridyl)platinum(II) as a precursor of both platinum and nitrogen. Pt NPs (average size 2.5 nm) were successfully synthesized by solid state reduction of Pt(II) under N2/H2 flow at 650 °C on a commercial mesoporous carbon. The synthesis was also carried out by employing PtCl2 or Pt(acac)2 as platinum precursors and 1,10-phenanthroline or 2,2′-bipyridyl as nitrogen dopant agents and the resulting materials were taken for comparison. XPS analysis confirmed that during the thermal treatment the ligand degrades and the nitrogen is embedded in the mesoporous carbon structure, resulting in a surface modification of the carbon support with preservation of bulk conductivity and thermal stability. Electrochemical characterization at a rotating disk electrode in O2-saturated 0.1 M HClO4 revealed a superior catalytic activity for ORR, in terms of E1/2 and mass activity, in those catalysts showing higher PtN interaction, expressed as binding energy shift of nitrogen components. Furthermore, cyclic voltammetry analysis in Ar purged 0.1 M HClO4 electrolyte showed that nitrogen doping appears to inhibit PtO formation. The influence of nitrogen incorporation in the carbon matrix on Pt NPs/support interaction was also rationalized on the basis of density functional theory simulations.