Core–shell structured ZIF-8@ZIF-67 crystals are well-designed and prepared through a seed-mediated growth method. After thermal treatment of ZIF-8@ZIF-67 crystals, we obtain selectively ...functionalized nanoporous hybrid carbon materials consisting of nitrogen-doped carbon (NC) as the cores and highly graphitic carbon (GC) as the shells. This is the first example of the integration of NC and GC in one particle at the nanometer level. Electrochemical data strongly demonstrate that this nanoporous hybrid carbon material integrates the advantageous properties of the individual NC and GC, exhibiting a distinguished specific capacitance (270 F·g–1) calculated from the galvanostatic charge–discharge curves at a current density of 2 A·g–1. Our study not only bridges diverse carbon-based materials with infinite metal–organic frameworks but also opens a new avenue for artificially designed nanoarchitectures with target functionalities.
•We introduce recent developments of synthesis of functional nanoporous carbon materials toward fuel cell applications.•The ideal catalyst support of fuel cells should possess large surface area, ...accessible porosity, high electrical conductivity and electrochemical stability.•We focus on fine controls of pore size and graphitization degree.•Surface modification, heteroatom-doping, and encapsulation of nanoparticles are effective to promote the application of nanoporous carbon in fuel cells.
The ideal catalyst support toward development of high-performance electrodes for fuel cells should possess advantageous structural and chemical features concerning accessibility to framework surfaces and electrochemical stability of conducting frameworks. In order to satisfy these requirements for the design of fuel cells by using nanoporous carbon electrodes, a great deal of efforts has been devoted to the functionalization of nanoporous carbon electrodes. In this review, the recent developments of nanoporous carbon materials synthesis are summarized with introduction of their potentials in fuel cells. The focuses are placed on precise controls of porosity, crystallinity, and morphology, combined with the designs of surface structure, framework composition, and encapsulation of metal and metal oxide nanoparticles. Finally, some perspectives are provided for future developments and directions of the synthesis and functionalization of nanoporous carbon materials for fuel cell design.
Nanoporous carbon (NPC) is prepared by direct carbonization of Al-based porous coordination polymers (Al-PCP). By applying the appropriate carbonization temperature, both high surface area and large ...pore volume are realized for the first time. Our NPC shows much higher porosity than other carbon materials (such as activated carbons and mesoporous carbons). This new type of carbon material exhibits superior sensing capabilities toward toxic aromatic substances.
Nanoporous carbon–cobalt‐oxide hybrid materials are prepared by a simple, two‐step, thermal conversion of a cobalt‐based metal–organic framework (zeolitic imidazolate framework‐9, ZIF‐9). ZIF‐9 is ...carbonized in an inert atmosphere to form nanoporous carbon–metallic‐cobalt materials, followed by the subsequent thermal oxidation in air, yielding nanoporous carbon–cobalt‐oxide hybrids. The resulting hybrid materials are evaluated as electrocatalysts for the oxygen‐reduction reaction (ORR) and the oxygen‐evolution reaction (OER) in a KOH electrolyte solution. The hybrid materials exhibit similar catalytic activity in the ORR to the benchmark, commercial, Pt/carbon black catalyst, and show better catalytic activity for the OER than the Pt‐based catalyst.
Hybrid‐material transformers: Thermal conversion of a cobalt‐based metal–organic framework (ZIF‐9) yields nanoporous carbon–cobalt‐oxide hybrid electrocatalysts (see figure). The resulting hybrid materials exhibit excellent catalytic activities comparable to the benchmark catalysts for both oxygen reduction and evolution reactions, and accordingly may be candidate catalysts for fuel‐cell applications.
Nanoporous carbon particles with different particle sizes are synthesized by simple carbonization of monodispersed zeolitic imidazolate framework-8 (ZIF-8) crystals. Quartz crystal microbalance (QCM) ...study proves that the use of small-sized nanoporous carbon can lead to both a large adsorption uptake and a faster sensor response for toxic toluene molecules.
Nanoporous carbons (NPCs) have large specific surface areas, good electrical and thermal conductivity, and both chemical and mechanical stability, which facilitate their use in energy storage device ...applications. In the present study, highly graphitized NPCs are synthesized by one‐step direct carbonization of cobalt‐containing zeolitic imidazolate framework‐67 (ZIF‐67). After chemical etching, the deposited Co content can be completely removed to prepare pure NPCs with high specific surface area, large pore volume, and intrinsic electrical conductivity (high content of sp2‐bonded carbons). A detailed electrochemical study is performed using cyclic voltammetry and galvanostatic charge–discharge measurements. Our NPC is very promising for efficient electrodes for high‐performance supercapacitor applications. A maximum specific capacitance of 238 F g−1 is observed at a scan rate of 20 mV s−1. This value is very high compared to previous works on carbon‐based electric double layer capacitors.
Highly graphitized nanoporous carbons (NPCs) are synthesized by one‐step direct carbonization of cobalt‐containing zeolitic imidazolate framework‐67 (ZIF‐67). After chemical etching, the deposited Co nanoparticles are completely removed to prepare pure NPCs with high specific surface area, large pore volume, and intrinsic electrical conductivity. The specific energy of the NPC‐based supercapacitor reached 19.6 W h kg−1 at a specific power of 700 W kg−1 (see figure).
Subsidies initially installed to stimulate green capacity investments tend to be withdrawn after some time. This paper analyzes the effect on investment of this phenomenon in a dynamic framework with ...demand uncertainty. We find that increasing the probability of subsidy withdrawal incentivizes the firm to accelerate investment at the expense of a smaller investment size. A similar effect is found when subsidy size as such is increased. When subsidy withdrawal risk is zero or very limited, installing a subsidy could increase welfare. In general we get that the larger the subsidy withdrawal probability, the smaller the welfare maximizing subsidy rate is. Therefore, a policy maker aiming to maximize welfare should try to reduce subsidy withdrawal risk.
•Firms accelerate investment if the withdrawal probability of a lumpsum subsidy is larger, but the investment size is smaller.•Firms accelerate investment and decrease investment size when the subsidy size is increased.•When subsidy withdrawal risk is zero or very limited, installing a subsidy can increase welfare.•A policy maker aiming to maximize welfare should try to reduce subsidy withdrawal risk.
In Alzheimer’s disease (AD) brain, exposure of axons to Aβ causes pathogenic changes that spread retrogradely by unknown mechanisms, affecting the entire neuron. We found that locally applied Aβ1-42 ...initiates axonal synthesis of a defined set of proteins including the transcription factor ATF4. Inhibition of local translation and retrograde transport or knockdown of axonal Atf4 mRNA abolished Aβ-induced ATF4 transcriptional activity and cell loss. Aβ1-42 injection into the dentate gyrus (DG) of mice caused loss of forebrain neurons whose axons project to the DG. Protein synthesis and Atf4 mRNA were upregulated in these axons, and coinjection of Atf4 siRNA into the DG reduced the effects of Aβ1-42 in the forebrain. ATF4 protein and transcripts were found with greater frequency in axons in the brain of AD patients. These results reveal an active role for intra-axonal translation in neurodegeneration and identify ATF4 as a mediator for the spread of AD pathology.
Display omitted
•Locally applied Aβ1-42 triggers recruitment of mRNAs into axons and local translation•ATF4 is locally synthesized and retrogradely transported in response to Aβ1-42•Knockdown of axonal Atf4 mRNA reduces Aβ1-42-induced neurodegeneration in vivo•ATF4 transcript and protein levels are increased in axons in the brain of AD patients
Axonal exposure to β-amyloid elicits the local synthesis of the transcription factor ATF, which is retrogradely transported to the neuron cell bodies where it triggers a transcriptional response leading to cell death.
Nanoporous carbon particles with magnetic Co nanoparticles (Co/NPC particles) are synthesized by one‐step carbonization of zeolitic imidazolate framework‐67 (ZIF‐67) crystals. After the ...carbonization, the original ZIF‐67 shapes are preserved well. Fine magnetic Co nanoparticles are well dispersed in the nanoporous carbon matrix, with the result that the Co/NPC particles show a strong magnetic response. The obtained nanoporous carbons show a high surface area and well‐developed graphitized wall, thereby realizing fast molecular diffusion of methylene blue (MB) molecules with excellent adsorption performance. The Co/NPC possesses an impressive saturation capacity for MB dye compared with the commercial activated carbon. Also, the dispersed magnetic Co nanoparticles facilitate easy magnetic separation.
Nanoporous carbon particles with magnetic Co nanoparticles are synthesized by one‐step carbonization of zeolitic imidazolate framework‐67 (ZIF‐67) crystals. The obtained nanoporous carbons show a high surface area and well‐developed graphitized wall, thereby realizing fast molecular diffusion of methylene blue molecules with excellent adsorption performance. Also, the dispersed magnetic Co nanoparticles facilitate easy magnetic separation.
To increase chemical reaction rates, general solutions include increasing the concentration/temperature and introducing catalysts. In this study, the rate constant of an electrophilic metal ...coordination reaction is accelerated 23‐fold on the surface of layered aluminosilicate (LAS), where the reaction substrate (ligand molecule) induces dielectric polarization owing to the polar and anionic surface. According to the Arrhenius plot, the frequency factor (A) is increased by almost three orders of magnitude on the surface. This leads to the conclusion that the collision efficiency between the ligands and metal ions is enhanced on the surface due to the dielectric polarization. This is surprising because one side of the ligand is obscured by the surface, so the collision efficiency is expected to be decreased. This unique method to accelerate the chemical reaction is expected to expand the range of utilization of LASs, which are chemically inert, abundant, and environmentally friendly. The concept is also applicable to other metal oxides which have polar surfaces, which will be useful for various chemical reactions in the future.
Dielectric polarization is induced on the anionic surface. Rate constant for metal coordination reaction increases 23‐fold and frequency factor increases by almost three orders of magnitude.
PDF
