Search

Transition metal sulfides have been widely investigated and used as efficient catalysts for hydrogen evolution reactions (HER). However, the trade-off between catalytic activity and long-term stability represents a formidable challenge and has not been extensively addressed. Herein, we proposed a facile strategy for the design of Au-MoS2 nanoparticles with abundant edge sites and regular core-shell structure through the interface engineering. The electrospun carbon nanofibers (CNFs) served as reactors and supports to control the preparation of core-shell heterostructures. Core-shell heterostructure exhibits more excellent catalytic than single component resulting from the synergistic effects at nano-interface. The obtained Au-MoS2/CNFs catalyst yield a current density of 10 mA cm−2 at the overpotential of 92 mV and a Tafel slope of 126 mV dec−1. Particularly, the durability of catalyst is relatively stable at the 50 h. The successful synthesis of core-shell nanocrystals provides a new path for designing advanced electrocatalysts.

Exploring and designing efficient non-noble catalysts formed by element doping and nanostructure modification for the hydrogen evolution reaction (HER) is of critical importance with respect to sustainable resources. Herein, we have prepared a three-dimensional binary NiCo phosphide with hierarchical architecture (HA) composed of NiCoP nanosheets and nanowires grown on carbon cloth (CC) via a facile hydrothermal method followed by oxidation and phosphorization. Due to its unique hierarchical nanostructure, the NiCoP HA/CC electrocatalyst exhibits excellent performance and good working stability for the HER in both acidic and alkaline conditions. The obtained NiCoP HA/CC shows excellent HER activity with a low potential of 74 and 89 mV at 10 mA cm−2, a small Tafel slope of 77.2 and 99.8 mV dec−1 and long-term stability up to 24 h in acidic and alkaline electrolyte, respectively. NiCoP HA/CC, a non-noble metal material, is a promising electrocatalyst to replace noble metal-based electrocatalysts for the HER.

Aerial-ground cooperative vehicular networks are envisioned as a novel paradigm in B5G/6G visions. In this letter, the challenge of optimizing the global energy-efficiency (EE) of multi-UAV-aided vehicular networks in the presence of uncertain air-to-ground (A2G) channels is addressed. Specifically, we propose a maximin paradigm to characterize the system, which aims to maximize its global EE meanwhile satisfying Quality-of-Service (QoS)-oriented data rate requirements in the worst-case situation. We theoretically derive a closed-form optimal solution for an embedded minimization subproblem under a parametric channel uncertainty set and thus develop a computationally tractable robust counterpart, which leads to a robust EE optimization design. Simulation results show that the proposed method significantly outperforms conventional EE schemes in terms of achieving higher global system performance and better robustness under random uncertain environments.

A multiscale modeling and characterization method for coupled damage-healing-plasticity occurring in granular material is proposed. The characterization is performed on the basis of multiscale modeling of granular material in the frame of concurrent second-order computational homogenization method, in which granular material is modeled as gradient-enhanced Cosserat continuum at the macroscale. The damage-healing-plasticity is characterized in terms of meso-structural evolution of discrete particle assembly within representative volume elements (RVEs) assigned to selected local material points in macroscopic continuum, with no need to specify macroscopic phenomenological constitutive models, failure criteria along with evolution laws, and associated macroscopic material parameters. The proposed modeling and characterization method for coupled damage-healing-plasticity in granular material is comprised of the following three constituents. The incremental non-linear constitutive relation for the discrete particle assembly of RVE is first established. Then the meso-mechanically informed incremental non-linear constitutive relation of macroscopic gradient-enhanced Cosserat continuum is derived from volume averages of the RVE-scale solutions. Finally the thermodynamic framework is set up to define meso-mechanically informed anisotropic damage and healing factors, anisotropic net damage factors combining both damage and healing effects, and plastic strains. Densities of damage, plastic and total dissipative energies as well as non-dissipative healing energy, as scalar internal state variables, are provided to compare the effects of damage, healing and plasticity on material failure and structural collapse. The numerical example of strain localization and softening problem is performed to demonstrate the performance and applicability of the proposed multiscale modeling and characterization method of coupled damage-healing-plasticity for granular materials.

Oxygen evolution reaction (OER) plays an important role in various renewable energy systems. Owing to its complex four-electron redox process, the OER process with sluggish kinetics often requires electrocatalysts to reduce the overpotential and promote the reaction rate. Herein, we have proposed an “all-in-one” strategy to synthesize mutil-elemental perovskite oxides nanofibers (NFs) with hollow and porous structures by using electrospinning technology and Ostwald ripening approach. The hollow La0.7Sr0.3Co0.25Mn0.75O3 nanofibers (LSCM NFs) consist of large amounts of building block La0.7Sr0.3Co0.25Mn0.75O3 nanoparticles (LSCM NPs), forming the unique architecture and the morphologies can be engineering by adjusting the calcination temperatures and the heating rates. Notably, the hollow LSCM NFs prepared at 800 °C and 10 °C min−1 demonstrated the excellent electrocatalytic performance, with overpotential of 340 mV at current density of 10 mA cm−2 and Tafel slope of 111 mV dec−1, as well as the long-term stability in alkaline electrolyte. The hollow NFs architectures exhibited a large specific surface area, a high porosity and a large inner space, which are beneficial for the OER, reducing the overpotentials and accelerating the electrode kinetics.

The appropriate catalyst model with a precisely designed interface is highly desirable for revealing the real active site at the atomic level. Herein, we report a proof-of-concept strategy for creating an exposed and embedding interface model by constructing a unique Co

Developing highly efficient electrocatalysts while revealing the active site and reaction mechanism is essential for electrocatalytic water splitting. To overcome the number and location limitations of defects in the electrocatalyst induced by conventional transition-metal atom (e.g. Fe, Co, and Ni) surface doping, we report a facile strategy of substitution with lower electronegative vanadium in the cobalt carbide, leading to larger amounts of defects in the whole lattice. The self-supported and quantitatively substituted VxCo3–xC (0 ≤ x ≤ 0.80) was one-step synthesized in the electrospun carbon nanofibers (CNFs) through the solid-state reaction. Particularly, the V0.28Co2.72C/CNFs exhibit superior hydrogen evolution reaction and oxygen evolution reaction activity and deliver a current density of 10 mA cm–2 at 1.47 V as the alkaline electrolyzer, which is lower than the values for the Pt/C–Ir/C couple (1.60 V). The operando Raman spectra and density functional theory calculations show that the enhanced electron transfer from V to the orbit of the Co atom makes Co a local negative charge center and leads to a significant increase in efficiency for overall water splitting.

The key issue in efficient electrochemical detection of trace heavy metal ions (HMIs) is to design hierarchical nanostructure electrodes with high sensitivity and low detection limit. In this study, bimetallic PtAu alloy nanoparticles (PtAuNPs) with uniform size and distribution were constructed in electrospun carbon nanofibers (CNFs) by combining an electrospinning procedure and an in situ thermal reduction process. The PtAu/CNF membrane can be directly used as a sensor electrode for simultaneous detection of trace Cd2+, Pb2+, and Cu2+ by square wave anodic stripping voltammetry (SWASV). The prepared PtAu/CNF membrane is capable of simultaneously detecting Cd2+, Pb2+, and Cu2+ with a sensitivity of 0.10 μM and correlation coefficients of 0.976, 0.993, and 0.976, respectively, indicating high sensitivity and good linear relation. The excellent sensitivity and low detection limit for HMI detection were ascribed to the high conductivity of CNFs, fast response of PtAu alloy NPs, and high specific surface area of the hybrid structure. The present research provides a convenient and efficient way to construct new sensors for simultaneous trace detection of HMIs.

Based on the meso-structured Voronoi cell model and the meso-macro homogenization procedure between the discrete particle assembly and the porous continuum for wet granular materials, meso-hydro-mechanically informed effective pressure and effective stress measures for saturated and unsaturated porous media are defined. The meso-hydro-mechanically informed generalized effective stress for saturated porous continua taking into account the volumetric deformation of solid grains due to pore liquid pressure is derived. The Biot coefficient associated to the meso-hydro- mechanically informed generalized effective stress for saturated porous media is formulated. The differences of the definitions for proposed generalized effective stress and Biot coefficient compared with those defined in the generalized Biot theory of saturated porous continua and in averaging theories are discussed. The wet meso-structured Voronoi cell model, consisting of three immiscible and interrelated (i.e. solid grains, interstitial liquid and gas) phases, at low bulk saturation (below about 30%) is proposed. A meso-structural pattern with the binary bond mode of pendular liquid bridges is assumed in particular to derive the meso-hydro- mechanically informed macroscopic anisotropic effective pressure and effective stress tensors for unsaturated porous media. As the isotropic case of the wet meso-structured Voronoi cell model is considered, the meso-hydro-mechanically informed effective pressure tensor degrades to the scalar variable in the same form as in the theory of macroscopic unsaturated porous continua. The proposed meso-hydro-mechanically informed Bishop's parameter is derived and obtained as a function of saturation, porosity, and meso-structural parameters, without need to introduce any macroscopic phenomenological assumptions for the description of hydro-mechanical constitutive behavior.

In the framework of the second-order concurrent computation homogenization method for saturated granular material, meso-structured RVE (Representative Volume Element) is modeled as a compact assembly of saturated discrete particles. The boundary conditions imposed on the RVE are comprised of the two parts: (1) the boundary displacements and pressures prescribed by downscaled macroscopic strain variables and pore pressure, and (2) constrained fine scale fluctuations of mesoscopic hydro-mechanical variables expressed in terms of periodic boundary conditions. The present paper focuses on the estimation of effective hydro-mechanical material properties and constitutive behaviors of meso-structured RVE of saturated discrete particle assembly via a proposed homogenization procedure. To achieve this target, a novel scheme for determining and imposing periodic boundary conditions on peripheral particles contacting with the RVE boundary of saturated discrete particle assembly is proposed. Numerical results demonstrate performances and capabilities of the proposed scheme in estimating effective hydro-mechanical non-linear material properties and predicting hydro-mechanical constitutive behaviors of saturated granular materials evolving with loading histories. They also demonstrate the significance and necessity of imposing periodic boundary conditions on the RVE in proper prediction of effective hydro-mechanical material properties and constitutive behaviors.

Supercapacitors with the advantages of high power density and fast discharging rate have full applications in energy storage. However, the low energy density restricts their development. Conventional methods for improving energy density are mainly confined to doping atoms and hybridizing with other active materials. Herein, a Co3O4/g-C3N4 p-n junction with excellent capacity is developed and its application in an all-solid-state flexible device is demonstrated, whose capacity and energy density are considerably enhanced by simulated solar light irradiation. Under photoirradiation, the capacity is increased by 70.6% at the maximum current density of 26.6 mA cm-2 and a power density of 16.0 kW kg-1. The energy density is enhanced from 7.5 to 12.9 Wh kg-1 with photoirradiation. The maximum energy density reaches 16.4 Wh kg-1 at a power density of 6.4 kW kg-1. It is uncovered that the lattice distortion of Co3O4, reduces defects of g-C3N4, and the facilitated photo-generated charge separation by the Co3O4/g-C3N4 p-n junction all make contributions to the promoted electrochemical storage performance. This work may provide a new strategy to enhance the energy density of supercapacitors and expand the application range of photocatalytic materials.

A concept of experiment to tune the two-dimensional MoS2 into VMo2S4 via thermodynamic driven phase engineering by combining the facile electrospinning technology and S-vapor assisted graphitization process has been demonstrated. Compared to V doped MoS2 nanosheets, the VMo2S4 nanosheets show a superior oxygen evolution reaction (OER) activity in alkaline electrolyte, reaching a current density of 10 mA cm−2 at overpotential of 295 mV with Tafel slope of 97 mV dec−1. The VMo2S4 nanosheets also show superior water splitting activity with 10 mA cm−2 at a cell voltage of 1.65 V. The theoretical and experimental results reveal that the V introduction into interplane of MoS2 leads to the significant decrease in the energy barrier for *OOH formation (0.99 eV), thus suggesting the improved transformation from *OOH to O2.

1D hollow nanostructures combine the advantages of enhanced surface-to-volume ratio, short transport lengths, and efficient 1D electron transport, which can provide more design ideas for the preparation of highly active oxygen evolution (OER) electrocatalysts. A unique architecture of dual-phase octahedral CoMn2 O4 /carbon hollow nanofibers has been prepared via a two-step heat-treatment process including preoxidation treatment and Ostwald ripening process. The hollow and porous structures provide interior void spaces, large exposed surfaces, and high contact areas between the nanofibers and electrolyte and the morphology can be engineered by adjusting the heating conditions. Due to the intimate electrical and chemical coupling between the oxide nanocrystals and integrated carbon, the dual-phase octahedral CoMn2 O4 /carbon hollow nanofibers exhibit excellent OER activity with overpotentials of 337 mV at current density of 10 mA cm-2 and Tafel slope of 82 mV dec-1 . This approach will lead to the new perception of design issue for the nanoarchitecture with fine morphology, structures, and excellent electrocatalytic activity.