2 research outputs found
Core–Shell Compositional Fine Structures of Dealloyed Pt<sub><i>x</i></sub>Ni<sub>1–<i>x</i></sub> Nanoparticles and Their Impact on Oxygen Reduction Catalysis
Using aberration-corrected scanning transmission electron
microscopy
and electron energy loss spectroscopy line profiles with Ã…ngstrom
resolution, we uncover novel core–shell fine structures in
a series of catalytically active dealloyed Pt<sub><i>x</i></sub>Ni<sub>1–<i>x</i></sub> core–shell
nanoparticles, showing the formation of unusual near-surface Ni-enriched
inner shells. The radial location and the composition of the Ni-enriched
inner shells were sensitively dependent on the initial alloy compositions.
We further discuss how these self-organized Ni-enriched inner shells
play a key role in maintaining surface lattice strain and thus control
the surface catalytic activity for oxygen reduction
<i>In Situ</i> Study of Atomic Structure Transformations of Pt–Ni Nanoparticle Catalysts during Electrochemical Potential Cycling
When exposed to corrosive anodic electrochemical environments, Pt alloy nanoparticles (NPs) undergo selective dissolution of the less noble component, resulting in catalytically active bimetallic Pt-rich core–shell structures. Structural evolution of PtNi<sub>6</sub> and PtNi<sub>3</sub> NP catalysts during their electrochemical activation and catalysis was studied by <i>in situ</i> anomalous small-angle X-ray scattering to obtain insight in element-specific particle size evolution and time-resolved insight in the intraparticle structure evolution. <i>Ex situ</i> high-energy X-ray diffraction coupled with pair distribution function analysis was employed to obtain detailed information on the atomic-scale ordering, particle phases, structural coherence lengths, and particle segregation. Our studies reveal a spontaneous electrochemically induced formation of PtNi particles of ordered Au<sub>3</sub>Cu-type alloy structures from disordered alloy phases (solid solutions) concomitant with surface Ni dissolution, which is coupled to spontaneous residual Ni metal segregation during the activation of PtNi<sub>6</sub>. Pt-enriched core–shell structures were not formed using the studied Ni-rich nanoparticle precursors. In contrast, disordered PtNi<sub>3</sub> alloy nanoparticles lose Ni more rapidly, forming Pt-enriched core–shell structures with superior catalytic activity. Our X-ray scattering results are confirmed by STEM/EELS results on similar nanoparticles