Transmission electron microscopy (TEM) image, associated particle size
distribution (upper right insert) and scanning electron transmission microscopy
coupled with X-ray energy dispersive spectroscopy (STEM/X-EDS) elemental map
(lower right insert) of a) Sphere PtNi/C, b) Cube PtNi/C, c) Octahedron PtNi/C,
d) Hollow PtNi/C, e) Aerogel PtNi and f) Sponge PtNi/C. High-angle annular
dark-field-high resolution scanning transmission electron microscopy
(HAADF-HRSTEM) image with insertion of its associated fast Fourier transform
pattern of g) Cube Pt/C and h) Hollow PtNi/C. The HAADF-HRSTEM images highlight
the monocrystalline nature of the ‘structurally-ordered’ catalyst
family (Sphere PtNi/C, Cube PtNi/C and Octahedron PtNi/C) whereas the
‘structurally-disordered’ family (Hollow PtNi/C, Aerogel PtNi and
Sponge PtNi/C) features highly polycrystalline nanoparticles. For the Sponge
PtNi/C catalyst, the particle size distribution in f) reflects the size of the
overall aggregates.