Iridium single-atoms anchored on a TiO2 support as an efficient catalyst for the hydrogen evolution reaction.

Single-atom catalysts (SACs) play a vital role in the hydrogen evolution reaction (HER) owing to the highly desirable atom efficiency and the minimal amount of precious metals. Herein, we use TiO2 nanosheets to anchor stable atomically dispersed iridium (Ir) to be used as a catalyst (Ir@TiO2) for the HER. The atomic dispersion of Ir on the TiO2 substrate is confirmed by aberration-corrected scanning transmission electron microscopy and it is anchored by numerous surface functional groups on abundantly exposed basal planes in TiO2. In acidic media, the Ir@TiO2 catalyst (1.35 wt% Ir) shows a low overpotential (41 mV at 10 mA cm-2), a small Tafel slope of 42 mV dec-1, and a decent durability for 1000 cycles of the HER with the polarization curve having only a 1 mV shift, which are comparable with those of a commercial Pt/C catalyst with 20 wt% Pt. This work paves a way to design Ir atomically anchored catalysts with low cost and high activity.

Bimetal Metal-Organic Framework-Derived Ni-Mn@Carbon/Reduced Graphene Oxide as a Cathode for an Asymmetric Supercapacitor with High Energy Density.

As is known, metal-organic frameworks (MOFs) are a versatile class of materials in energy storage applications including supercapacitors. However, the individual kind of metal nodes connected by organic ligands to form a topological structure still limits the potential storage capacity of MOFs. Herein, a bimetal-based Ni-Mn MOF composite is configured with a one-pot hydrothermal method to derive a composite with a synergic effect to maximize the properties. Moreover, reduced graphene oxide (rGO) sheets are added as a conductive network to anchor the MOF-derived composite of Ni-Mn@C/rGO, which is expected to increase the conductivity of the materials system. The resulting composite exhibited a high specific capacitance of 1674 F g-1 at a current density of 0.3 A g-1, suggesting excellent energy storage performance. The composite was then integrated as the cathode in an asymmetrical supercapacitor with a 3D rGO aerogel anode, resulting in energy densities of 24.1 and 17.5 W h kg-1 at power densities of 88.9 and 444.4 W kg-1, respectively. Additionally, the device demonstrated remarkable long-term stability, with 90% capacitance retention after 10 000 charge-discharge cycles at 10 A g-1.

Research Based on Optical Non-Destructive Testing of Pigment Identification.

Optical Non-Destructive Testing (ONDT) can be applied as penetrating elemental and structure analysis technology in the Pigments identification field. Three-dimensional video microscopy, Raman microscopy and energy dispersive X-ray fluorescence spectroscopy are employed to measure the materials based on a Qing Dynasty meticulous painting. The results revealed that the dark yellow area within the decorative patterns was presented due to the interaction of Emerald green and hematite, and the bright yellow edge area was delineated by Cu-Zn-Pb composition. The interesting thing is that an artificial synthetic ultramarine blue was checked in the painting. According to the first synthesized time of ultramarine blue and Paris green, the time limit of the painting completion can be identified. The principle of Pigment subtractive colorant and nitikaset method were employed to interpreting the results. Optical testing combined with the area of cultural relic identification can be a potential method to build an expert identification system successfully. This work also help lay the optical method groundwork for further cultural relic identification, sterilization, and preservation.

[Study of Paints and Drawing Techniques of Fine Brushwork Yunlong Ripples Painting in Qing Dynasty].

In order to study the paints and techniques of decorative patterns of dragon among clouds and water waves, the materials based on a Qing Dynasty meticulous painting were measured by three-dimensional video microscopy, Raman microscopy and energy dispersive X-ray fluorescence spectroscopy. The results showed that the green clothes was firstly colored by Paris green, the decorative patterns of dragon among clouds and water waves were then painted by hematite, the edge was delineated by brass powder at last. The dark yellow area within the decorative patterns was presented due to the interaction of green and red paints. In addition, ultramarine blue was checked in the painting. According to the first synthesized time of ultramarine blue and Paris green, we can make sure the time limit of the painting finished.

Dynamics of charge-transfer excitons in a transition metal dichalcogenide heterostructure.

Charge-transfer excitons are formed by photoexcited electrons and holes following charge transfer across a heterojunction. They are important quasiparticles for optoelectronic applications of semiconducting heterostructures. The newly developed two-dimensional heterostructures provide a new platform to study these excitons. We report spatially and temporally resolved transient absorption measurements on the dynamics of charge-transfer excitons in a MoS2/WS2/MoSe2 trilayer heterostructure. We observed a non-classical lateral diffusion process of charge-transfer excitons with a decreasing diffusion coefficient. This feature suggests that hot charge-transfer excitons with large kinetic energies are formed and their cooling process persists for about 100 ps. The long energy relaxation time of excitons in the trilayer compared to its monolayer components is attributed to the reduced carrier and phonon scattering due to the dielectric screening effect in the trilayer. Our results help develop an in-depth understanding of the dynamics of charge-transfer excitons in two-dimensional heterostructures.