To replace precious platinum (Pt)‐based electrocatalysts for cathodic oxygen reduction reaction (ORR), edge‐selectively sulfurized graphene nanoplatelets (SGnP) are synthesized as efficient ...metal‐free electrocatalysts simply by ball‐milling pristine graphite in the presence of sulfur (S8). The resultant SGnPs exhibit remarkable electrocatalytic activity toward ORR with better tolerance to methanol crossover/CO poisoning effects and longer‐term stability than those of pristine graphite and commercial Pt/C electrocatalysts. Edge‐Selectively Sulfurized Graphene Nanoplatelets as Efficient Metal‐Free Electrocatalysts for Oxygen Reduction Reaction: The Electron Spin Effect
There have been extensive efforts to synthesize crystalline covalent triazine‐based frameworks (CTFs) for practical applications and to realize their potential. The phosphorus pentoxide ...(P2O5)‐catalyzed direct condensation of aromatic amide instead of aromatic nitrile to form triazine rings. P2O5‐catalyzed condensation was applied on terephthalamide to construct a covalent triazine‐based framework (pCTF‐1). This approach yielded highly crystalline pCTF‐1 with high specific surface area (2034.1 m2 g−1). At low pressure, the pCTF‐1 showed high CO2 (21.9 wt % at 273 K) and H2 (1.75 wt % at 77 K) uptake capacities. The direct formation of a triazine‐based COF was also confirmed by model reactions, with the P2O5‐catalyzed condensation reaction of both benzamide and benzonitrile to form 1,3,5‐triphenyl‐2,4,6‐triazine in high yield.
A covalent triazine‐based framework was synthesized by phosphorus pentoxide (P2O5)‐catalyzed direct condensation of aromatic amides to form a triazine ring. Highly crystalline covalent triazine frameworks (pCTF‐1) were produced with high specific surface area (2034.1 m2 g−1). At low pressure, pCTF‐1 shows a high carbon dioxide (CO2) uptake capacity of 21.9 wt % at 273 K and a hydrogen (H2) uptake capacity of 1.75 wt % at 77 K.
Although there are a variety of methods for producing graphene, commercialization remains challenging because each method has its own pros and cons. For the wide use of graphene as a next generation ...material in diverse applications, the process by which graphene is manufactured must be robust enough to overcome barriers to commercialization, as has been experienced in commercializing carbon nanotube products. Here, a recent discovery of a new manufacturing process for efficient delamination of graphite into graphene nanoplatelets (GnPs) via mechanochemical ball‐milling is summarized. In this process, transferring sufficient kinetic energy to graphitic frameworks will crack graphitic C–C bonds, generate active carbon species (mostly carbon free radicals), introduce edge‐functional groups, and delaminate graphitic layers into edge‐functionalized GnPs (EFGnPs). While this process is a method for mass production, it does not involve hazardous chemicals (e.g., corrosive acids and toxic reducing agents) such as those used for producing graphene oxide (GO) and reduced graphene oxide (rGO). Owing to its edge‐selective functionalization, the EFGnPs have minimal basal area defects with selectivity of a variety of edge groups by forming edge C–X bonds (X = nonmetals or metalloids) that are tunable.
A method for producing edge‐selectively functionalized graphene nanoplatelets (EFGnPs) is developed by simple mechanochemical ball‐milling graphite in the presence of the desired reactant(s). Due to their advantages such as manufacturing simplicity, edge‐selectivity, eco‐friendliness, low‐cost and high‐quality over other commonly used methods, EFGnPs have potential in a broad range of applications.
Recent graphene research has triggered enormous interest in new two-dimensional ordered crystals constructed by the inclusion of elements other than carbon for bandgap opening. The design of new ...multifunctional two-dimensional materials with proper bandgap has become an important challenge. Here we report a layered two-dimensional network structure that possesses evenly distributed holes and nitrogen atoms and a C2N stoichiometry in its basal plane. The two-dimensional structure can be efficiently synthesized via a simple wet-chemical reaction and confirmed with various characterization techniques, including scanning tunnelling microscopy. Furthermore, a field-effect transistor device fabricated using the material exhibits an on/off ratio of 10(7), with calculated and experimental bandgaps of approximately 1.70 and 1.96 eV, respectively. In view of the simplicity of the production method and the advantages of the solution processability, the C2N-h2D crystal has potential for use in practical applications.
Covalent organic frameworks (COFs) have emerged as a promising platform for photocatalysts. Their crystalline porous nature allows comprehensive mechanistic studies of photocatalysis, which have ...revealed that their general photophysical parameters, such as light absorption ability, electronic band structure, and charge separation efficiency, can be conveniently tailored by structural modifications. However, further understanding of the relationship between structure‐property‐activity is required from the viewpoint of charge‐carrier transport, because the charge‐carrier property is closely related to alleviation of the excitonic effect. In the present study, COFs composed of a fixed cobalt (Co) porphyrin (Por) centered tetraamine as an acceptor unit with differently conjugated di‐carbaldehyde based donor units, such as benzodithiophene (BDT), thienothiophene (TT), or phenyl (TA), were synthesized to form Co‐Por‐BDT, Co‐Por‐TT, or Co‐Por‐TA, respectively. Their photocatalytic activity for reducing carbon dioxide into carbon monoxide was in the order of Co‐Por‐BDT>Co‐Por‐TT>Co‐Por‐TA. The results indicated that the excitonic effect, associated with their charge‐carrier densities and π‐conjugation lengths, was a significant factor in photocatalysis performance.
Cobalt‐porphyrin‐based covalent organic frameworks (Co‐Por‐COFs) were prepared with different donor building units. Their photophysical studies indicated that the Co‐Por‐COFs with higher charge‐carrier density and longer conjugation length led to a more efficient charge separation with a reduced exciton binding energy, resulting in an enhanced photocatalytic activity of CO2 reduction into CO.
Despite the enormous interest in Li metal as an ideal anode material, the uncontrollable Li dendrite growth and unstable solid electrolyte interphase have plagued its practical application. These ...limitations can be attributed to the sluggish and uneven Li+ migration towards Li metal surface. Here, we report olefin‐linked covalent organic frameworks (COFs) with electronegative channels for facilitating selective Li+ transport. The triazine rings and fluorinated groups of the COFs are introduced as electron‐rich sites capable of enhancing salt dissociation and guiding uniform Li+ flux within the channels, resulting in a high Li+ transference number (0.85) and high ionic conductivity (1.78 mS cm−1). The COFs are mixed with a polymeric binder to form mixed matrix membranes. These membranes enable reliable Li plating/stripping cyclability over 700 h in Li/Li symmetric cells and stable capacity retention in Li/LiFePO4 cells, demonstrating its potential as a viable cationic highway for accelerating Li+ conduction.
Olefin‐linked covalent organic frameworks (COFs) with electronegative 1D channels are presented as a cationic highway membrane strategy for sustainable Li metal battery anodes. Introduction of triazine rings and fluorinated groups into the COF skeletons played a viable role in enhancing salt dissociation and guiding uniform Li+ flux within the channels. The resulting COF membrane exhibited reliable Li plating/stripping cyclability and stable capacity retention in the Li/LiFePO4 full cell.
The formation of 2D polyaniline (PANI) has attracted considerable interest due to its expected electronic and optoelectronic properties. Although PANIwas discovered over 150 y ago, obtaining an ...atomically well-defined 2D PANI framework has been a longstanding challenge. Here, we describe the synthesis of 2D PANI via the direct pyrolysis of hexaaminobenzene trihydrochloride single crystals in solid state. The 2D PANI consists of three phenyl rings sharing six nitrogen atoms, and its structural unit has the empirical formula of C₃N. The topological and electronic structures of the 2D PANI were revealed by scanning tunneling microscopy and scanning tunneling spectroscopy combined with a first-principle density functional theory calculation. The electronic properties of pristine 2D PANI films (undoped) showed ambipolar behaviors with a Dirac point of −37 V and an average conductivity of 0.72 S/cm. After doping with hydrochloric acid, the conductivity jumped to 1.41 × 10³ S/cm, which is the highest value for doped PANI reported to date. Although the structure of 2D PANI is analogous to graphene, it contains uniformly distributed nitrogen atoms for multifunctionality; hence, we anticipate that 2D PANI has strong potential, from wet chemistry to device applications, beyond linear PANI and other 2D materials.
Edge‐selectively halogenated graphene nanoplatelets (XGnPs, X = Cl, Br, or I) are prepared by a simple mechanochemical ball‐milling method, which allows low‐cost and scalable production of XGnPs as ...highly stable anode materials for lithium‐ion batteries.
Hierarchically structured nitrogen‐doped carbon nanotube (NCNT) composites, with copper (Cu) nanoparticles embedded uniformly within the nanotube walls and cobalt oxide (CoxOy) nanoparticles ...decorated on the nanotube surfaces, are fabricated via a combinational process. This process involves the growth of Cu embedded CNTs by low‐ and high‐temperature chemical vapor deposition, post‐treatment with ammonia for nitrogen doping of these CNTs, precipitation‐assisted separation of NCNTs from cobalt nitrate aqueous solution, and finally thermal annealing for CoxOy decoration. Theoretical calculations show that interaction of Cu nanoparticles with CNT walls can effectively decrease the work function of CNT surfaces and improve adsorption of hydroxyl ions onto the CNT surfaces. Thus, the activities of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are significantly enhanced. Because of this benefit, further nitrogen doping, and synergistic coupling between CoxOy and NCNTs, Cu@NCNT/CoxOy composites exhibit ORR activity comparable to that of commercial Pt/C catalysts and high OER activity (outperforming that of IrO2 catalysts). More importantly, the composites display superior long‐term stability for both ORR and OER. This simple but general synthesis protocol can be extended to design and synthesis of other metal/metal oxide systems for fabrication of high‐performance carbon‐based electrocatalysts with multifunctional catalytic activities.
Nitrogen‐doped carbon nanotubes (NCNTs), with copper (Cu) nanoparticles embedded uniformly within their walls and cobalt oxide (CoxOy) nanoparticles decorated on their surfaces, are controllably synthesized via a rationally designed multistep procedure. The resultant Cu@NCNT/CoxOy composites exhibit electrocatalytic activity comparable to that of commercial Pt/C catalysts for the oxygen reduction reaction and activity higher than that of IrO2 catalysts for the oxygen evolution reaction.
Porous polymer networks (PPNs) are promising candidates as photocatalysts for hydrogen production. Constructing a donor‐acceptor structure is known to be an effective approach for improving ...photocatalytic activity. However, the process of how a functional group of a monomer can ensure photoexcited charges transfer and improve the hydrogen evolution rate (HER) has not yet been studied on the molecular level. Herein, we design and synthesize two kinds of triazatruxene (TAT)‐based PPNs: TATR‐PPN with a hexyl (R) group and TAT‐PPN without the hexyl group, to understand the relationship between the presence of the functional group and charge transfer. The hexyl group on the TAT unit was found to ensure the transfer of photoexcited electrons from a donor unit to an acceptor unit and endowed the TATR‐PPN with stable hydrogen production.
Triazatruxene (TAT)‐based PPNs were synthesized to investigate how the existence of a hexyl functional group would affect charge transfer. The hexyl group on the TAT unit ensured the transfer of photoexcited electrons from a donor unit to an acceptor unit, resulting in improved photocatalytic activity and hydrogen production.
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