Search

Assembling graphene sheets into macroscopic fibers with graphitic layers uniaxially aligned along the fiber axis is of both fundamental and technological importance. However, the optimal performance of graphene-based fibers has been far lower than what is expected based on the properties of individual graphene. Here we show that both mechanical properties and electrical conductivity of graphene-based fibers can be significantly improved if bridges are created between graphene edges through covalent conjugating aromatic amide bonds. The improved electrical conductivity is likely due to extended electron conjugation over the aromatic amide bridged graphene sheets. The larger sheets also result in improved π-π stacking, which, along with the robust aromatic amide linkage, provides high mechanical strength. In our experiments, graphene edges were bridged using the established wet-spinning technique in the presence of an aromatic amine linker, which selectively reacts to carboxyl groups at the graphene edge sites. This technique is already industrial and can be easily upscaled. Our methodology thus paves the way to the fabrication of high-performance macroscopic graphene fibers under optimal techno-economic and ecological conditions. The performance of macroscopic graphene fibers is hampered by lower bonding strength between individual graphene sheets. Authors mitigate this by creating covalent conjugating linkages at sheet edges, improving mechanical and electrical properties. [ABSTRACT FROM AUTHOR]

Graphene has demonstrated broad applications due to its prominent properties. Its molecular structure makes graphene achiral. Here, we propose a direct way to prepare chiral graphene by transferring chiral structural conformation from chiral conjugated amino acids onto graphene basal plane through π–π interaction followed by thermal fusion. Using atomic resolution transmission electron microscopy, we estimated an areal coverage of the molecular imprints (chiral regions) up to 64 % on the basal plane of graphene (grown by chemical vapor deposition). The high concentration of molecular imprints in their single layer points to a close packing of the deposited amino acid molecules prior to "thermal fusion". Such "molecular chirality‐encoded graphene" was tested as an electrode in electrochemical enantioselective recognition. The chirality‐encoded graphene might find use for other chirality‐related studies and the encoding procedure might be extended to other two‐dimensional materials. [ABSTRACT FROM AUTHOR]

Electrocatalysis is critical to the performance displayed by sulfur cathodes. However, the constituent electrocatalysts and the sulfur reactants have vastly different molecular sizes, which ultimately restrict electrocatalysis efficiency and hamper device performance. Herein, the authors report that aggregates of cobalt single‐atom catalysts (SACs) attached to graphene via porphyrins can overcome the challenges associated with the catalyst/reactant size mismatch. Atomic‐resolution transmission electron microscopy and X‐ray absorption spectroscopy measurements show that the Co atoms present in the SAC aggregates exist as single atoms with spatially resolved dimensions that are commensurate the sulfur species found in sulfur cathodes and thus fully accessible to enable 100% atomic utilization efficiency in electrocatalysis. Density functional theory calculations demonstrate that the Co SAC aggregates can interact with the sulfur species in a synergistic manner that enhances the electrocatalytic effect and promote the performance of sulfur cathodes. For example, Li–S cells prepared from the Co SAC aggregates exhibit outstanding capacity retention (i.e., 505 mA h g–1 at 0.5 C after 600 cycles) and excellent rate capability (i.e., 648 mA h g−1 at 6 C). An ultrahigh area specific capacity of 12.52 mA h cm−2 is achieved at a high sulfur loading of 11.8 mg cm–2. [ABSTRACT FROM AUTHOR]

Lithium (Li) metal is regarded as the ultimate anode material for use in Li batteries due to its high theoretical capacity (3860 mA h g−1). However, the Li dendrites that are generated during iterative Li plating/stripping cycles cause poor cycling stability and even present safety risks, and thus severely handicap the commercial utility of Li metal anodes. Herein, we describe a graphene and carbon nanotube (CNT)‐based Li host material that features vertically aligned channels with attached ZnO particles (designated ZnO@G‐CNT‐C) and show that the material effectively regulates Li plating and stripping. ZnO@G‐CNT‐C is prepared from an aqueous suspension of Zn(OAc)2, CNTs, and graphene oxide by using ice to template channel growth. ZnO@G‐CNT‐C was found to be mechanically robust and capable of guiding Li deposition on the inner walls of the channels without the formation of Li dendrites. When used as an electrode, the material exhibits relatively low polarization for Li plating, fast Li‐ion diffusion, and high Coulombic efficiency, even over hundreds of Li plating/stripping cycles. Moreover, full cells prepared with ZnO@G‐CNT‐C as Li host and LiFePO4 as cathode exhibit outstanding performance in terms of specific capacity (155.9 mA h g−1 at 0.5 C), rate performance (91.8 mA h g−1 at 4 C), cycling stability (109.4 mA h g−1 at 0.5 C after 800 cycles). The methodology described can be readily adapted to enable the use of carbon‐based electrodes with well‐defined channels in a wide range of contemporary applications that pertain to energy storage and delivery. [ABSTRACT FROM AUTHOR]

Graphene sheets have been demonstrated to be the building blocks for various assembly structures, which eventually determine the macroscopic properties of graphene materials. As a new assembly structure, transparent macroporous graphene thin films (MGTFs) are not readily prepared due to the restacking tendency of graphene sheets during processing. Here, an ice crystal-induced phase separation process is proposed for preparation of transparent MGTFs. The ice crystal-induced phase separation process exhibits several unique features, including efficient prevention of graphene oxide restacking, easy control on the transparency of the MGTFs, and wide applicability to substrates. It is shown that the MGTFs can be used as porous scaffold with high conductivity for electrochemical deposition of various semiconductors and rare metal nanoparticles such as CdSe, ZnO, and Pt, as well as successive deposition of different materials. Notably, the macroporous structures bestow the MGTFs and the nanoparticle-decorated MGTFs (i.e., Pt@MGTF and CdSe@MGTF) enhanced performance as electrode for oxygen reduction reaction and photoelectrochemical H2 generation. [ABSTRACT FROM AUTHOR]

Composite films of chemically converted graphene (CCG) and water-soluble polythiophenes (P3TOPS and P3TOPA) were prepared by a LBL method using a suspension of negatively charged CCG–P3TOPS sheets and a solution of positively charged P3TOPA. The composite films show enhanced photoresponse due to photoinduced electron transfer from the polythiophenes to CCG. [ABSTRACT FROM AUTHOR]

A new method for the preparation of graphene has been developed viaporphyrin exfoliation of graphite in NMP. The exfoliation, which follows the intercalation of organic ammonium ions, is based on the π–π interaction between graphene and porphyrins. The graphene sheets prepared by this method show undisturbed sp2carbon networks. [ABSTRACT FROM AUTHOR]

Layer-by-layer films comprised of alternating graphene and gold nanoparticle layers are readily produced by the two-step procedure involving the use of vacuum filtration of a reduced graphene oxide solution to fabricate the graphene thin film on the quartz substrate, followed by gold nanoparticle formation by spontaneous reduction of gold ions in a gold salt solution on the graphene films. [ABSTRACT FROM AUTHOR]

[Display omitted] • SACs with lower Fermi levels exhibit higher binding affinities towards sulfur species. • SAC Fermi level correlates with the electrocatalytic activity in Li−S batteries. • Ni SACs feature the lowest Fermi levels among the catalysts tested and show the highest electrocatalytic activities. Single-atom catalysts (SACs) have emerged as promising candidates for promoting sulfur cathode kinetics. Despite the growing popularity, the literature is devoid of general guidelines for predicting the electrocatalytic effects exerted by novel SACs. Herein, a series of SACs immobilized on N-doped graphene were prepared from metal (Mn, Ni, Cu, or Zn) porphyrins. The Fermi levels of the catalysts were found to be inversely correlated with their electrocatalytic effects. For example, the Ni-based SACs exhibited the lowest Fermi level but showed the strongest binding affinity to sulfur. As a result, Li−S cells containing Ni SACs exhibited a high specific capacity (10.0 mA h cm−2 at 0.05 C), excellent cycling stability (6.7 mA h cm−2 at 0.1 C after 100 cycles) and other remarkable performance metrics even at a high sulfur loading of 9.6 mg cm−2. The methodology offers a way to evaluate the catalytic activities of SACs rapidly and efficiently, particularly in electrocatalytic systems. [ABSTRACT FROM AUTHOR]

Scalable and sustainable preparation of graphene is urgently needed to address its increasing demands in basic research and practical applications. Here, we present a simple preparation of surface-functionalized graphene by ball milling graphite in the presence of an aryl diazonium salt. The efficient exfoliation of graphite is achieved through the tandem surface reaction of graphite with aryl diazonium salt and mechanical shear by ball milling. Moreover, the surface functionalities of the resultant graphene platelets are readily tuned using various aryl diazonium salts, which also provide routes for the further modification of the graphene platelets. More importantly, with 93% of the graphene platelets having layers less than 5, they contain a low quantity of structural defects (I D /I G ratio = 0.30) and a low oxygen content (10.1 atom%). Such features not only facilitate the restoration of the π-conjugated structure of graphene by thermal reduction, with the I D /I G ratio reduced to 0.11 comparable to the value of graphite, but also enhance the structural stability of the graphene platelets at low temperature. This method is ideal for scaling up, since the techniques used are industrially compatible, the chemicals employed are commercially available, and no highly polluting wastes are produced in the synthesis. Image 1 [ABSTRACT FROM AUTHOR]