Platinum Nanoparticles Supported on Nitrogen-Doped Graphene Nanosheets as Electrocatalysts for Oxygen Reduction Reaction

This paper deals with nitrogen-doped graphene nanosheets prepared using dicyandiamide precursor as a catalyst support for oxygen reduction reaction (ORR). Platinum nanoparticles supported on N-doped graphene nanosheets (Pt/NG) were studied as electrocatalysts for ORR in acid and alkaline solutions employing the rotating disk electrode (RDE) technique. Pt/NG nanomaterials were synthesised by chemical reduction of hexachloroplatinic acid using sodium borohydride or ethylene glycol as reducing agents. Surface morphology and composition of the prepared catalysts were examined by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The TEM images showed a high dispersion of Pt nanoparticles on N-doped graphene nanosheets due to strong interaction of Pt with nitrogen functionalities. The average nitrogen content was between 6 and 7 at.% according to the XPS analysis. In acidic solution, 20 wt% Pt/NG catalyst prepared by borohydride reduction showed the highest specific activity for O2 reduction from all the Pt/NG materials studied. Pt/NG nanomaterials exhibited excellent electrocatalytic activity in alkaline media, and their half-wave potentials were similar to that of commercial Pt/C catalyst. The RDE data analysis showed that the ORR on the Pt/NG catalysts proceeded via four-electron pathway.