Carbon-based materials, as one of the most important electrode materials for supercapacitors, have attracted tremendous attention. At present, it is highly desirable but remains challenging to ...prepare one-dimensional carbon complex hollow nanomaterials for further improving the performance of supercapacitors. Herein, we report an effective strategy for the synthesis of hollow particle-based nitrogen-doped carbon nanofibers (HPCNFs-N). By embedding ultrafine zeolitic imidazolate framework (ZIF-8) nanoparticles into electrospun polyacrylonitrile (PAN), the as-prepared composite nanofibers are carbonized into hierarchical porous nanofibers composed of interconnected nitrogen-doped carbon hollow nanoparticles. Owing to its unique structural feature and the desirable chemical composition, the derived HPCNFs-N material exhibits much enhanced electrochemical properties as an electrode material for supercapacitors with remarkable specific capacitance at various current densities, high energy/power density and long cycling stability over 10 000 cycles.
Converting MOFs into amination catalysts Chen, Li-Feng; Xu, Qiang
Science (American Association for the Advancement of Science),
10/2017, Letnik:
358, Številka:
6361
Journal Article
Recenzirano
Pyrolysis of metal-organic frameworks creates graphitic carbon–coated cobalt nanoparticles
Amines are extensively used in chemicals, pharmaceuticals, and materials (
1
). Much effort has been devoted ...to catalytic reductive amination for the synthesis of amines, but the development of cost-effective catalysts with high activity and selectivity remains an important goal for synthetic chemists (
2
). On page 326 of this issue, Jagadeesh
et al.
(
3
) report a general synthesis of amines, including primary, secondary, tertiary, and N-methylamines (>140 examples), as well as 10 existing drug molecules, by way of the reductive amination of carbonyl compounds by using a highly effective cobalt nanoparticle (Co NP) catalyst with a well-defined structure derived from the pyrolysis of a metal-organic framework (MOF) compound.
Recently, heteroatom‐doped three‐dimensional (3D) nanostructured carbon materials have attracted immense interest because of their great potential in various applications. Hence, it is highly ...desirable to exploit a simple, renewable, scalable, multifunctional, and general strategy to engineer 3D heteroatom‐doped carbon nanomaterials. Herein, a simple, eco‐friendly, general, and effective way to fabricate 3D heteroatom‐doped carbon nanofiber networks on a large scale is reported. Using this method, 3D P‐doped, N,P‐co‐doped, and B,P‐co‐doped carbon nanofiber networks are successfully fabricated by the pyrolysis of bacterial cellulose immersed in H3PO4, NH4H2PO4, and H3BO3/H3PO4 aqueous solution, respectively. Moreover, the as‐prepared N,P‐co‐doped carbon nanofibers exhibit good supercapacitive performance.
A simple, efficient, and general approach is developed for preparing cost‐effective, three‐dimensional, and large‐scale heteroatom‐doped carbon nanofibers, such as P‐doped, N,P‐co‐doped, and B,P‐co‐doped carbon nanofibers, by pyrolyzing bacterial cellulose (BC) previously immersed in H3PO4, NH4H2PO4, and H3BO3/H3PO4, respectively. Moreover, the as‐prepared N,P‐co‐doped carbon nanofibers exhibit good supercapacitive performance.
Exploring low‐cost and high‐performance nonprecious metal catalysts (NPMCs) for oxygen reduction reaction (ORR) in fuel cells and metal–air batteries is crucial for the commercialization of these ...energy conversion and storage devices. Here we report a novel NPMC consisting of Fe3C nanoparticles encapsulated in mesoporous Fe‐N‐doped carbon nanofibers, which is synthesized by a cost‐effective method using carbonaceous nanofibers, pyrrole, and FeCl3 as precursors. The electrocatalyst exhibits outstanding ORR activity (onset potential of −0.02 V and half‐wave potential of −0.140 V) closely comparable to the state‐of‐the‐art Pt/C catalyst in alkaline media, and good ORR activity in acidic media, which is among the highest reported activities of NPMCs.
Nanocomposite electrocatalyst: A high‐performance electrocatalyst for the oxygen reduction reaction (ORR) is based on Fe3C nanoparticles encapsulated in mesoporous Fe‐N‐doped carbon nanofibers. It can be synthesized from low‐cost and abundant precursors and exhibits excellent electrocatalytic performance for the ORR in both alkaline and acidic media.
This work proposes a penalty 20‐node hexahedral element for size‐dependent electromechanical analysis based on the consistent couple stress theory. The nodal rotation degrees of freedom (DOFs) are ...used to approximate the mechanical rotation, meeting the C1 requirement in a weak sense by using the penalty function method, and to effectively enhance the standard isoparametric interpolation for determining the displacement test function. The normalized stress functions that satisfy the relevant equilibrium equation and strain compatibility equation a priori are employed to formulate the stress trial function. Since the element has only three displacement, three rotation and the electric potential DOFs per node, it has relatively simple formulation and can be readily incorporated into the existing finite element program. Several benchmarks are examined and the results demonstrate that the new element has good numerical accuracy and captures the size dependence effectively. In addition, the influence of the micro‐inertia on electromechanical dynamic responses of flexoelectric solids at small scale are analyzed using the proposed element. It is shown that the nature frequency decreases with the increase of micro‐inertia and in general, the influences are more obvious on higher order modes.
Summary
A locking‐free unsymmetric 8‐node solid‐shell element with high distortion tolerance is proposed for general shell analysis, which is equipped with translational degrees of freedom only. The ...prototype of this new model is a recent solid element US‐ATFH8 developed by combining the unsymmetric finite element method and the analytical solutions in three‐dimensional local oblique coordinates. By introducing proper shell assumptions and assumed natural strain modifications for transverse strains, the new solid‐shell element US‐ATFHS8 is successfully formulated. This element is able to give highly accurate predictions for shells with different geometric features and loading conditions and is quite insensitive to mesh distortions. In particular, the excellent performance of US‐ATFH8 under membrane load is well inherited, which is an outstanding advantage over other shell elements.
The development of high‐performance electrochemical energy storage devices is critical for addressing energy crises and environmental pollution. Hence, the design and preparation of next‐generation ...electrode materials have been gaining increasing attention. Recent progress has demonstrated that three‐dimensional (3D) carbon nanomaterials are extremely promising candidates for the electrodes of electrochemical energy storage devices due to their unique structural advantages of interlinked architecture. Herein, recent advances in the scalable fabrication of 3D carbon nanofiber (CNF)‐based materials and their applications for electrochemical energy storage devices are summarized. Some representational 3D CNF architectures, such as CNF gels, 3D CNF films, 3D CNF arrays, and their nanocomposites, are highlighted with regard to various applications, including supercapacitors, lithium‐ion batteries (LIBs), sodium‐ion batteries (SIBs), lithium–sulfur (Li–S), lithium–selenium (Li–Se), and metal–O2 batteries, as well as other new battery systems. Finally, contemporary challenges in the scalable fabrication of 3D CNF architectures are outlined and a brief outlook to future studies is given. This review illustrates significant opportunities for the macroscopic fabrication of 3D CNF architectures, and therefore inspires new discoveries to promote the practical applications of 3D CNF architectures in electrochemical energy storage fields.
High‐performance electrochemical energy storage devices are essential; therefore, the design and preparation of next‐generation electrode materials have gained increasing attention. Three‐dimensional (3D) carbon nanofiber (CNF)‐based materials are promising electrode materials, and thus their scalable fabrication and application in electrochemical energy storage devices are summarized, alongside current challenges and future studies.
An effective updated Lagrangian (UL) algorithm is designed for extending the recent distortion‐tolerant unsymmetric 8‐node, 24‐DOF hexahedral solid‐shell element, US‐ATFHS8, to finite deformation ...analysis of hyper‐elastic shell structures. The distinguishing feature of this unsymmetric element is that two different interpolation schemes are employed for virtual displacement and real stress calculations, respectively. The assumed natural strain (ANS) method with shell assumptions, referring to the current configuration, is introduced to modify the strain tensors derived from the assumed virtual displacement fields in terms of isoparametric coordinates, thereby mitigating shear locking and trapezoidal locking. On the other hand, the analytical trial functions (ATFs) derived from the general solutions of homogenous governing equations for linear elasticity are updated in each increment step to obtain the incremental deformation gradient, which is then utilized for calculating the real stresses for curing the numerical difficulties in large deformation problems. Numerical examples show that the proposed algorithm enables the hyper‐elastic solid‐shell element US‐ATFHS8 to exhibit excellent performance in both regular and distorted meshes and yield considerable results even when other models cannot work.
Summary
A recent unsymmetric 4‐node, 8‐DOF plane finite element US‐ATFQ4 is generalized to hyperelastic finite deformation analysis. Since the trial functions of US‐ATFQ4 contain the homogenous ...closed analytical solutions of governing equations for linear elasticity, the key of the proposed strategy is how to deal with these linear analytical trial functions (ATFs) during the hyperelastic finite deformation analysis. Assuming that the ATFs can properly work in each increment, an algorithm for updating the deformation gradient interpolated by ATFs is designed. Furthermore, the update of the corresponding ATFs referred to current configuration is discussed with regard to the hyperelastic material model, and a specified model, neo‐Hookean model, is employed to verify the present formulation of US‐ATFQ4 for hyperelastic finite deformation analysis. Various examples show that the present formulation not only remain the high accuracy and mesh distortion tolerance in the geometrically nonlinear problems, but also possess excellent performance in the compressible or quasi‐incompressible hyperelastic finite deformation problems where the strain is large.
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