Disordered solid‐solution high‐entropy alloys have attracted wide research attention as robust electrocatalysts. In comparison, ordered high‐entropy intermetallics have been hardly explored and the effects of the degree of chemical ordering on catalytic activity remain unknown. In this study, a series of multicomponent intermetallic Pt4FeCoCuNi nanoparticles with tunable ordering degrees is fabricated. The transformation mechanism of the multicomponent nanoparticles from disordered structure into ordered structure is revealed at the single‐particle level, and it agrees with macroscopic analysis by selected‐area electron diffraction and X‐ray diffraction. The electrocatalytic performance of Pt4FeCoCuNi nanoparticles correlates well with their crystal structure and electronic structure. It is found that increasing the degree of ordering promotes electrocatalytic performance. The highly ordered Pt4FeCoCuNi achieves the highest mass activities toward both acidic oxygen reduction reaction (ORR) and alkaline hydrogen evolution reaction (HER) which are 18.9‐fold and 5.6‐fold higher than those of commercial Pt/C, respectively. The experiment also shows that this catalyst demonstrates better long‐term stability than both partially ordered and disordered Pt4FeCoCuNi as well as Pt/C when subject to both HER and ORR. This ordering‐dependent structure–property relationship provides insight into the rational design of catalysts and stimulates the exploration of many other multicomponent intermetallic alloys.
Recent theoretical studies suggest none
or minor changes in the band gap of two-dimensional (2D) α-MoO3 nanosheets as compared with that of the bulk because of the
weak interlayer electronic interactions. Unfortunately, this suggestion
is lacking positive support in the literature. Herein, we report experimental
observations of huge blue shifts in the absorption edge of layered
α-MoO3 as its thickness t is reduced
approaching atomic layers. When t > 10 nm, every
order of magnitude of thickness reduction gives rise to a blue shift
of ∼0.29 eV without causing any Raman mode shifts. This blue
shift, in terms of finite difference time domain calculations, is
attributable to optical interferences at the crystal surfaces. However,
when t is further reduced below ∼10 nm, an
even larger blue shift, accompanied by a mode softening of the most
strengthened Mo–O–Mo stretching phonon (Ag), has been observed. This observation is consistent with those of
2D α-MoO3 nanosheets produced by aqueous exfoliations
and, based on our calculations of the electronic structures, can be
explained as anisotropic in-plane strain relaxations/redistributions.
A gas-phase layer-by-layer etching of the layered α-MoO3 single crystals has also been demonstrated for consequent
fabrications of novel electronic devices, as well as their integrations,
based on α-MoO3 and other 2D nanosheets.
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