Calcination of metal–organic frameworks (MOFs)
to prepare
porous-carbon-based nanocomposites has emerged as a facile and viable
method for various applications. Here, the Cu-based HKUST-1 MOF is
chosen as the synthesis precursor and growth template owing to its
large surface area, high pore volume, as well as facile and large-scale
preparation. Through the direct phosphorization at elevated temperatures,
a hierarchical porous matrix consisting of HKUST-1 MOF-derived zero-dimensional
(0D) Cu3P nanoparticles embedded on the surface of conductive
carbon matrices is produced in a single step, in which its hydrogen
evolving electrocatalytic performances are assessed as a representative
application. The Cu3P/C-300 composite, at a loading mass
as small as 0.1 mg cm–2, demonstrates an overpotential
of 233 mV at 10 mA cm–2 and a Tafel slope of 91
mV dec–1 for hydrogen evolution with robust durability
in a 1 M KOH solution, which are both lower than other metal phosphides
directly dropcasted onto the conductive substrates (overpotentials
mainly >250 mV at 10 mA cm–2 and Tafel slopes
mainly
>100 mV dec–1). Such an improved hydrogen evolution
reaction performance is attributed to high specific surface area,
improved interfacial contact with the conductive substrate, and the
synergistic effects of the intrinsically active Cu3P nanoparticles
of ultrasmall sizes with carbon matrices. The synthesis strategy may
shed light on the development of cost-effective and stable electrocatalysts
with excellent electrochemical performances in energy-conversion fields.
At present, double expansion chamber structures are widely used in the field of acoustic attenuation, and two kinds of double-chamber compound structures for hydraulic attenuators are proposed in this paper. A one-dimensional analytical approach was developed to predict the pressure pulsation attenuation performance of these two structures, and comparisons of insertion loss predictions with experimental results illustrated that the one-dimensional approach is suitable for accurate prediction among the research frequency band. This approach was then used to investigate the effects of porosity and geometrical parameters on the pressure pulsation performance of these two double-chamber compound hydraulic attenuators. To optimize the pressure pulsation attenuation performance at the backwash frequency, parameter optimization was performed for these double-chamber compound structures, and a genetic algorithm based on double-precision floating-point encoding was proposed. The results showed that the range of attenuation frequency bands was widened; however, the effect on low frequency filtering characteristics was limited. The insertion loss of the second structure, which had a partially perforated tube, exhibits a superposition of dome attenuation and axial resonance in the plane wave region. By choosing the length and location of the perforated section to match resonances with the troughs of the pulsation attenuator, a desirable broadband pressure pulsation attenuation can be obtained.
In this article, we prepare the physical model with the high density epoxy resin and different sizes of coin shaped silicone pieces which can simulate the directional arrangement of fracture medium. On the basis of this, we analyze the influences of fracture angle on the ultrasonic compressional wave velocity using the pulse transmission method and compare the experimental results with the Hudson effective medium model. The experimental results show that, velocity decreases linearly with the increase of fracture angle within the interval of [0°~90°]. In a similar aspect ratio and same angle case, the increase of fracture porosity will result in the decrease of the velocity which is weakened by the increase of fracture porosity. At high fracture porosity, fracture angle becomes the important influence factor on the velocity changing. The calculation results of the Hudson model have a small deviation which is less than 5% compared with the experimental results but show a difference in different angle interval. The combination of the two methods will provide a certain basis for the indoor experiment and the measurement of the velocity in field.
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