The development of cost-effective heterogeneous catalysts for the dehydrogenation of formic acid (FA) is the key challenge for the commercialization of FA as a hydrogen-storage medium. Herein, PdCoNi nanoparticles (NPs) with different element ratios supported on N-doped carbon nanosheets (N-CN) were designed, which exhibit excellent catalytic dehydrogenation performance for FA. Compared with PdCoNi NPs loaded on the carbon nanosheets (CN), the introduction of pyrrolic N to CN induces the formation of ultrafine, monodispersed and amorphous Pd0.6Co0.2Ni0.2 NPs with a size of 1.60 nm, which significantly increases the number of active sites and the instant contact between FA and catalysts. The as-prepared Pd0.6Co0.2Ni0.2/N-CN catalyst shows more than 99% conversion and 100% H2 selectivity at room temperature, with a record-high initial turnover frequency (TOFinitial) of 1249.0 h−1 among non-noble containing Pd-based catalysts, which demonstrates the high potential of Pd0.6Co0.2Ni0.2/N-CN as a practical catalyst for the hydrogen generation from FA. 相似文献
As a promising graphene analogue, two-dimensional (2D) polymer nanosheets with unique 2D features, diversified topological structures and as well as tunable electronic properties, have received extensive attention in recent years. Here in this review, we summarized the recent research progress in the preparation methods of 2D polymer nanosheets, mainly including interfacial polymerization and solution polymerization. We also discussed the recent research advancements of 2D polymer nanosheets in the fields of energy storage and conversion applications, such as batteries, supercapacitors, electrocatalysis and photocatalysis. Finally, on the basis of their current development, we put forward the existing challenges and some personal perspectives.
The Mn-modified 0.75BiFeO3-0.25BaTiO3 (75BFBTMn) piezoelectric ceramic possesses a high depolarization temperature of 500 °C and a large piezoelectric coefficient of 110 pC/N, showing the potential for high temperature piezoelectric sensors. However, 75BFBTMn ceramic usually suffers dielectric degradation and abrupt drop of piezoelectric coefficient in the range of 300 °C to 500 °C. Combined the high-energy synchrotron X-ray diffraction analysis with Backscatter-SEM results, it is demonstrated that the electrical thermal instability is owing to the existence of chemical inhomogeneity. The Air-annealing treatment is able to decrease the volume fraction of pseudo-cubic phase and the lattice distortion, removes the chemical inhomogeneity in the grain and free Bi2O3 at grain boundary, and then eliminates dielectric anomalies and piezoelectric degradation with temperature. These results indicate that air-annealing is a simple but effective method to eliminate the chemical inhomogeneity in 75BFBTMn ceramics, thereby improving the property thermal stability for high temperature piezoelectric sensor applications. 相似文献
Molybdenum diboride is unique among transition metal diborides because it exists in both hexagonal (AlB2-type) and rhombohedral structures. However, it is difficult to stabilize the superconducting AlB2-type phase, which requires either extreme synthesis condition or suitable chemical doping. Here we report the structural and physical properties of Sc-doped nonstoichiometric molybdenum diborides (Mo0.95Sc0.05)1-xB2 and (Mo1-yScy)0.71B2 prepared by the common arc melting method. The AlB2-type phase is found to form over wide ranges of 0 ≤ x ≤ 0.29 and 0.025 ≤ y ≤ 0.30 for the first time, and bulk superconductivity with Tc up to 7.9 K is observed. Tc increases with increasing x in the (Mo0.95Sc0.05)1-xB2 series, but evolves nonmonotonically with varying y in the (Mo1-yScy)0.71B2 series. Despite this contrast, Tc of both borides follows nearly the same linear dependence on the electron-phonon coupling constant, suggesting that it is mainly controlled by the electron-phonon interaction. In addition, the stabilization of AlB2-type structure is attributed to the decrease in the number of d electrons as a consequence of Sc doping, which suggests that a similar effect may be achieved by substituting Mo with other d electron-poorer metal elements. 相似文献
While experimental designs developed in recent decades have contributed to research on dynamic nonequilibrium effects in transient two-phase flow in porous media, this problem has been seldom investigated using direct numerical simulation (DNS). Only a few studies have sought to numerically solve Navier–Stokes equations with level-set (LS) or volume-of-fluid (VoF) methods, each of which has constraints in terms of meniscus dynamics for various flow velocities in the control volume (CV) domain. The Shan–Chen multiphase multicomponent lattice Boltzmann method (SC-LBM) has a fundamental mechanism to separate immiscible fluid phases in the density domain without these limitations. Therefore, this study applied it to explore two-phase displacement in a single representative elementary volume (REV) of two-dimensional (2D) porous media. As a continuation of a previous investigation into one-step inflow/outflow in 2D porous media, this work seeks to identify dynamic nonequilibrium effects on capillary pressure–saturation relationship (Pc–S) for quasi-steady-state flow and multistep inflow/outflow under various pressure boundary conditions. The simulation outcomes show that Pc, S and specific interfacial area (anw) had multistep-wise dynamic effects corresponding to the multistep-wise pressure boundary conditions. With finer adjustments to the increase in pressure over more steps, dynamic nonequilibrium effects were significantly alleviated and even finally disappeared to achieve quasi-steady-state inflow/outflow conditions. Furthermore, triangular wave-formed pressure boundary conditions were applied in different periods to investigate dynamic nonequilibrium effects for hysteretical Pc–S. The results showed overshoot and undershoot of Pc to S in loops of the nonequilibrium hysteresis. In addition, the flow regimes of multistep-wise dynamic effects were analyzed in terms of Reynolds and capillary numbers (Re and Ca). The analysis of REV-scale flow regimes showed higher Re (1 < Re < 10) for more significant dynamic nonequilibrium effects. This indicates that inertia is critical for transient two-phase flow in porous media under dynamic nonequilibrium conditions. 相似文献