Rationally
designing cheap and efficient electrocatalysts at the
atomic level is highly desirable for the hydrogen evolution reaction
(HER). Here, we demonstrate a metallic MoS2 electrocatalyst
decorated with platinum single atoms. When combined with electron
microscopy observations, our synchrotron X-ray characterizations and
theoretical calculations clearly reveal that the doped Pt atoms bond
to S atoms on the surface of MoS2. Notably, these Pt single
atoms serve as critical active centers for the HER through capturing
H+ from the solution. The optimized Pt-MoS2 catalysts
achieve significantly enhanced HER performance due to the single-atom
coordination effect. This finding is expected to facilitate further
realization of hybridized catalysts through the monatomic riveting
strategy.
Glasses have markedly different stability around their glass transition temperature (
T
g
), and metallic glasses (MGs) are conventionally regarded as metastable compared to other glasses such as silicate glass or amber. Here, we show an aging experiment on a Ce-based MG around its
T
g
(~0.85
T
g
) for more than 17 years. We find that the MG with strong fragility could transform into kinetic and thermodynamic hyperstable state after the long-term room temperature aging and exhibits strong resistance against crystallization. The achieved hyperstable state is closer to the ideal glass state compared with that of other MGs and similar to that of the million-year-aged amber, which is attributed to its strong fragility and strong resistance against nucleation. It is also observed through the asymmetrical approaching experiment that the hyperaged Ce-based MG can reach equilibrium liquid state below
T
g
without crystallization, which supports the idea that nucleation only occurs after the completion of enthalpy relaxation.
The structural features of the antiferromagnetic K0.8Fe1.6S2 have been studied in the temperature range from 300 K up to 700 K by means of in situ transmission electron microscopy (TEM). The superstructure with a wave vector originating from a Fe-vacancy order has been clearly observed; moreover, the structural analysis shows that K0.8Fe1.6S2 undergoes a transition from the Fe-vacancy order to disorder at about 585 K. The S substitution effect on the phase separation and superconductivity in the K0.8Fe1.75Se2−ySy materials has been systematically investigated by SEM and TEM structural analyses, as well as by electrical resistivity measurements. Our experimental results reveal that the S element adopts a homogeneous distribution in all investigated materials, and the essential phase-separation nature is very similar to what was observed in the K0.8Fe1.75Se2 superconductor. A phase-separated state formed by the coexistence of two Fe-vacancy orders with wave vectors and in K0.8Fe1.5+xS2 (0 < x < 0.1) has been briefly discussed.
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