Composition-Dependent Oxygen Reduction Reaction Activity of Pt-Surfaced PtNi Dodecahedral Nanoframes

Abstract

Pt-based bimetallic nanoframes have been demonstrated to have high activity for a number of electrocatalytic reactions. Their morphology, crystal facets, and compositions are important factors that regulate their catalytic activities. Herein, we synthesized a series of Pt-surfaced PtNi dodecahedral nanoframes with variable Pt/Ni ratios. The nanoframes were prepared by oxidative etching of presynthesized PtNi rhombic dodecahedron nanoparticles. The Pt ratio in the PtNi nanoframes have been tuned from 28% to 65% by changing the duration of oxidative etching. In terms of catalytic performance, the PtNi nanoframes display a volcano-type behavior in specific oxygen reduction reaction (ORR) activity as a function of Pt ratio with a maximum ORR specific activity of 1.9 mA cm–2 observed with 47% Pt. The mass activity of the particles ranges from 0.72 to 0.92 A mg–1, which significantly exceeds the mass activity of 0.19 A mg–1 measured for commercial Pt NP/C. Density functional theory calculations reveal that the Pt ratio underneath the Pt skin in the nanoframes affects the binding energy of oxygenate species and thus the ORR activity. The trend of OH binding energy versus PtNi composition from the computational results qualitatively agrees with the trend of ORR activity from the experiments.