Tuning the oxygen reduction activity of the Pt-Ni nanoparticles upon specific anion adsorption by varying heat treatment atmospheres.

Heat treatment of Pt based nanoparticles under various conditions is one of the conventional ways to modify the electrocatalytic properties for enhancement of the oxygen reduction reaction (ORR). However, the effect of the heat treatment atmosphere on the ORR activity especially upon specific anion adsorption still remains unclear. This paper investigates the Pt-Ni bimetallic nanoparticles (Pt2Ni1), under various heat treatment atmospheres, as enhanced cathodic electrocatalysts for the high temperature-proton exchange membrane fuel cell (HT-PEMFC) using a phosphoric acid doped polybenzimidazole (p-PBI) membrane. The X-ray spectroscopic measurement showed the variations of the electronic structures of Pt-Ni nanoparticles under the heat treatment condition. In the half-cell measurement, the argon treated electrocatalyst demonstrated the highest catalytic activity owing to the appropriate electronic interaction between Pt and Ni. The single cell test with a p-PBI membrane, at 160 °C, also confirmed the excellent oxygen reduction reactivity and durability of the argon-treated Pt-Ni nanoparticles. This result suggested that the alteration of the electronic structure by a proper heat treatment atmosphere upon specific anion adsorption decisively influenced the ORR activity both at half-cell and single-cell scales.