High-Performance Nitrogen-Doped Intermetallic PtNi Catalyst for the Oxygen Reduction Reaction

Abstract

PtM (M = transition metals) nanomaterials have been recognized as promising catalysts for the oxygen reduction reaction (ORR) in fuel cells, with a much higher performance than pure Pt. However, the insufficient durability issue of PtM is often raised because of the fast dissolution of M in acid, impeding their commercialization. Herein, we report on a Ketjenblack (KB)-supported, nitrogen (N)-doped intermetallic PtNiN (Int-PtNiN/KB) catalyst that exhibits remarkably enhanced ORR activity and stability in an acidic electrolyte, superior to those of disordered PtNi/KB, disordered PtNiN/KB, and commercial Pt/C. The experimental results show that Int-PtNiN/KB has a distinctive ordering structure of alternating Ni4-N and Pt planes; we attribute the origin of the superior stability of this catalyst to the combined effect of the Ni4-N formation and the unique intermetallic structure, which effectively precludes Ni dissolution from the core. The density functional theory calculations suggest that the tensile strain introduced by the formation of an intermetallic phase and N-doping optimizes the binding of oxygenated species on the Pt surface and enable highly efficient electron transfer, leading to the enhanced ORR performance. This study offers an appropriate route for further enhancing both the activity and durability of PtM catalysts through a facile synthesis method by annealing in an NH3 gas under appropriate conditions.