The development of a non-Pt electrocatalyst with a high performance for the oxygen reduction reaction (ORR) is one of the central issues in polymer electrolyte fuel cells science. Au-nanoparticles (Au-NPs) with a diameter of < 2 nm are one of the promising substitutes of Pt-NPs; however, it is still a challenge to synthesize such a small-sized Au-NPs with a narrow diameter distribution on a carbon support without using capping agents. We here describe a facile method to deposit uniform Au-NPs (diameter = 1.6 nm and 3.3 nm) on the stacked-graphene (< 10 layers) coated with poly[2,2'-(2,6-pyridine)-5,5'-bibenzimidazole] without using any capping agents. The obtained Au-NPs exhibit an excellent ORR activity with the onset potential at-0.11 V and-0.09 V (vs. Ag/AgCl) for 1.6 nm and 3.3 nm, respectively. On the other hand, inhomogeneous Au-NPs with 4.6 nm in average diameter shows the onset potential at-0.15 V (vs. Ag/AgCl).
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