Slowing down or even trapping electromagnetic (EM) waves attract researchers’ attention for its potential applications in energy storage, optical signal processing and nonlinearity enhancement. However, conventional trapping, in fact, is not truly trapping because of the existence of strong coupling effects and reflections. In this paper, a novel metal-semiconductor-semiconductor-metal (MSSM) heterostructure is presented, and novel truly rainbow trapping of terahertz waves is demonstrated based on a tapered MSSM structure. More importantly, functional devices such as optical buffer, optical switch and optical filter are achieved in one single structure based on the truly rainbow trapping theory. Owing to the property of one-way propagation, these new types of optical devices can be high performance and are expected to be used in integrated optical circuits.
Summary
Hydrogen is considered a promising solution for energy, but the methods that are currently used in hydrogen production continue to rely on fossil fuels. Water electrolysis, a green and sustainable method for hydrogen production, is limited by the lack of nonprecious metal electrocatalysts that exhibit high performance. In this study, novel S‐substituted Ni2P nanowires with large aspect ratios were successfully grown on nickel foam (Ni2P(S)/NF) using a facile one‐step phosphating‐sulfuration heat treatment process. The as‐prepared Ni2P(S)/NF exhibited enhanced activity in the hydrogen evolution reaction (HER) performed both in alkaline and acidic media. It only required overpotentials of 171 and 208 mV to drive current densities of 100 mA cm−2 in 1.0 M KOH solution and 0.5 M H2SO4, respectively. The characterization studies and density functional theory calculations suggested that the enhanced catalytic activity can be ascribed to the in situ growth of nanowires on nickel foam, the 1D nanowires morphology with high length‐to‐diameter ratio, appropriate free energy of hydrogen adsorption, and enhanced H2O binding activity. This work will provide inspiration for the development of non‐precious metal HER catalysts.
Hydrogen is not only a promising energy, but also widely used in
inflammation treatment and sports training. The key to these
applications is to obtain purity hydrogen conveniently. Water
electrolysis provides a green and sustainable method for hydrogen
production, but the urgent problem is to develop low-cost and efficient
electrocatalysts. In this work, hierarchically porous
NiS nanostructures, which the
flocculent two-dimensional NiS is
coated on the surface of NiS
nanosheets, were successfully grown on nickel foam through a facile
two-step hydrothermal reaction. The hierarchically porous
NiS nanostructures has a large
specific surface area can expose more active sites and facilitates
desorption of bubbles. Moreover, the theoretical calculation indicated
that the dimensional confinement effect of metallic
NiS improves the carrier concentration
and conductivity. Therefore, the hierarchically porous
NiS nanostructures on nickel foam
exhibited enhanced hydrogen evolution reaction and good catalytic
stability. This work sheds some light on improving the catalytic
performance of metallic compounds.
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