Uniform PtNi octahedra with different alloying composition, including Pt18Ni6, Pt12Ni12, and Pt10Ni14, are successfully prepared through fine-tuning the precursor ratio (Pt-to-Ni) in the presence of dioctyl amine (DiOL) and oleic acid (OAc). PtNi octahedra with different alloying composition have been well characterized via high-resolution transmission electron microscopy (HR-TEM) and powder x-ray diffraction (PXRD). The optimal surfactant ratio for DiOL versus OAc plays a key role in the formation of PtNi octahedral due to the specific crystal facet-surfactant bindings on the growth seed. Careful electrochemical examinations show that the oxygen reduction reaction (ORR) mass activity (MA) and specific area activity (SA) of all PtNi octahedra outperform those of commercial Pt/C catalysts. The results show that the MA of Pt18Ni6, Pt10Ni14, and Pt12Ni12 octahedra are ~1.7 folds, ~1.8 folds and ~2.1 folds, respectively, higher than that of the Pt/C catalyst. The SA of Pt18Ni6, Pt10Ni14, and Pt12Ni12 octahedra are ~2.9 folds, ~4.1 folds and ~4.3 folds, respectively, higher than that of Pt/C catalyst as well. The plot of ORR enhancements as a function of the alloying composition of PtNi octahedra reveals a volcano-shaped plot, being maximized at equal molar ratio. Also, the volcano-shaped trend of ORR enhancements proves that Pt12Ni12 octahedra have the superior ORR activities. The results are firmly supported by theoretical works, concluding that the Pt12Ni12(111) surface provides larger adsorptionenergies forH, O, O2, and OH species than those of Pt18Ni6(111) and Pt10Ni14(111) counterparts, whereas the molecularly adsorbed H2O product is calculated to be the lowest in adsorption energy on the Pt12Ni12(111) surface. Subsequently, a combination study of chemical derivation and theoretical calculations is peformed to gain in-depth insight into the ORR on PtxNi24-x(111) surfaces.

Composition-controlled and uniform PtNi octahedra in oxygen reduction reaction and their theoretical study

248th National Meeting (2014)

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