Fabrication of carbon nanorods and graphene nanoribbons from a metal–organic framework

Co-etching effect to convert waste polyethylene terephthalate into hierarchical porous carbon toward excellent capacitive energy storage

With the ever-increasing consumption of polyethylene terephthalate (PET) related products, how to recycle the waste PET still remains as a great challenge for the sustainable development. Converting waste PET into porous carbon material has been emerged as a promising way to address this issue. Recently, the microporous carbon derived from waste PET has drawn considerable attention in adsorption field, but its electrochemical application is still impeded by low specific surface area (SSA <1500 m² g^-1) and small meso-/macropores volume (<0.2 cm³ g^-1). Herein, hierarchical porous carbon (HPC) is successfully prepared from waste PET. The obtained HPC possesses a high SSA (2238 m² g^-1) and a large meso-/macropores volume (0.51 cm³ g^-1). The formation mechanism of hierarchical porous structure is proposed: co-etching effect of sp²/sp³ hybridized carbon produces micropores and meso-/macropores, respectively. In a three-electrode configuration, HPC based electrode achieves an outstanding capacitance of 413 F g^-1, while the traditional microporous carbon exhibits a low capacitance of 142 F g^-1. The fabricated symmetric supercapacitor shows a high energy density of 25 Wh kg^-1. This work provides a good reference to convert waste plastics into hierarchical porous carbon.

Bimetallic organic framework derivation of three-dimensional and heterogeneous metal selenides/carbon composites as advanced anodes for lithium-ion batteries

Heterogeneous structures have been attracting increasing attention in energy storage and conversion applications due to the phase interface and synergistic effect of multiple components. Herein, bimetal organic framework analogues were introduced to construct a Zn/Co bimetallic selenide heterostructure within a 3D-porous N-doped carbon matrix by a NaCl template-assisted lyophilization and annealing process. The cross-linked 3D network can enhance the transport kinetics for both lithium ions and electrons. The stress resulting from the cycling process can be released by interconnected channels in the composite. ZnSe and CoSe₂ experience electrochemical reactions at different potentials, which can buffer volume changes mutually to effectively increase structural stability. Meanwhile, abundant active sites due to the heterostructure enhance pseudocapacitive performance and reaction kinetics, resulting in high specific capacity and good rate performance. As anode materials for lithium-ion batteries, the three-dimensional ZnSe/CoSe₂-C composite exhibits a high reversible capacity of 700 mA h g^-1 after 500 cycles at 1 A g^-1.

Magnetic Fe3O4-encapsulated VAN@MIL-101(Fe) with mixed-valence sites and mesoporous structures as efficient bifunctional water splitting photocatalysts

Fe3O4/VAN@MIL-101(Fe) with both mesoporous and mixed-valence Fe3+/Fe2+ structures was controllably synthesized in the synthesis of MIL-101(Fe), and it was used as a bifunctional photocatalyst in both oxygen evolution reactions (OERs) and hydrogen evolution reactions (HERs) of photocatalytic water splitting. By the reduction of auxiliary ligand vanillin (VAN) and the introduction of Fe3O4, the mixed-valence Fe3+/Fe2+ structure in Fe3O4/VAN@MIL-101(Fe) was obtained, which improves the band gap of the Fe3+ reactive active center and increases the separation efficiency of photogenerated carriers. Owing to the partial difference in the structure between VAN and ligand terephthalic acid (H2BDC), hierarchical porous and vacant structures were effectively improved in Fe3O4/VAN@MIL-101(Fe), which can induce more active sites to adsorb more water molecules and shorten the electron-hole migration distance to improve the transfer efficiency of photogenerated carriers. Therefore, Fe3O4/VAN@MIL-101(Fe) presents excellent photocatalytic activities for improving the O2 and H2 production rate up to 360 000 μmol g-1 h-1 and 584 μmol g-1 h-1, respectively. Meanwhile, Fe3O4/VAN@MIL-101(Fe) maintains the excellent catalytic activity in OERs and HERs after recycling for 5 times. Moreover, the introduction of magnetic Fe3O4 nanoplates into Fe3O4/VAN@MIL-101(Fe) can make it easily recyclable by magnetic separation, which can maximize its performance.

Hierarchically Porous Carbons Derived from Nonporous Coordination Polymers

Hierarchically porous carbons (HPCs) with multimodal pore systems exhibit great technological potentials, especially in the fields of heterogeneous catalysis, energy storage, and conversion. Here, we establish a simple and general approach to HPCs by carbonization of nonporous coordination polymers that are produced by mixing metal salts with polytopic ligands in alkaline aqueous solutions at room temperature. The proposed approach is applicable to a wide scope of ligand molecules (18 examples), thus affording the synthesized HPCs with high diversity in porosity, morphology, and composition. In particular, the prepared HPCs exhibit high specific surface areas (up to 2647 m² g^-1) and large pore volumes (up to 2.39 cm³ g^-1). The HPCs-supported atomically dispersed Fe-N_x catalysts show much-improved fuel cell cathode performance over the micropore-dominated carbon black-supported catalysts, demonstrating the structural superiority of the HPCs for enhancing the mass transport properties.

Direct carbonization of organic solvents toward graphene quantum dots

The bottom-up synthesis of graphene quantum dots (GQDs) using solvothermal methods has attracted considerable attention because of their fewer defects and controllable size/morphology. However, the influence of organic solvents on the preparation of GQDs is still unknown. Herein, a systematic study on the carbonization of organic solvents toward GQDs is reported. The results show that organic solvents with the double bond or benzene ring or double hydrophilic groups could be directly decomposed into GQDs without the addition of catalysts or molecular precursors. The as-synthesized GQDs demonstrate ultra-small size distribution, high stability, tunable excitation wavelength and upconverted fluorescence. Both hematological and histopathological analyses show that the as-synthesized GQDs demonstrate a very good safety profile and excellent biocompatibility. The versatility of this synthesis strategy offers easy control of the surface group, composition, and optical properties of GQDs at the molecular level.

A Honeycomb-Like Bulk Superstructure of Carbon Nanosheets for Electrocatalysis and Energy Storage

Superstructures have attracted extensive attention because of their potential applications in materials science and biology. Herein, we fabricate the first centimeter-sized porous superstructure of carbon nanosheets (SCNS) by using metal-organic framework nanoparticles as a template and polyvinylpyrrolidone as an additional carbon source. The SCNS shows a honeycomb-like morphology with wall-sharing carbon cages, in each cavity of which a porous carbon sphere is encapsulated. A single piece of SCNS is directly used as the electrode for a two-electrode symmetrical supercapacitor cell without any binders and supports, benefiting from its advantage in ultra-large geometric size, and the Fe-immobilized SCNS exhibits excellent catalytic performances for oxygen reduction reaction and in a Zn-air battery. This synthetic strategy presents a facile approach for preparing functional SCNS at centimetric scale with controllable morphologies and compositions favoring the fabrication of energy devices.

Coal-based 3D hierarchical porous carbon aerogels for high performance and super-long life supercapacitors

Coal-based 3D hierarchical porous carbon aerogels (3D HPCAs) has been successfully fabricated from a freeze-drying method and with subsequent of calcination process, using coal oxide as carbon precursors, and PVA as both cross-linking agent and sacrifice template. The 3D HPCAs, using as electrode materials for supercapacitors, display outstanding electrochemical performance. The optimal sample (HPCAs-0.4-800) presents a high specific capacitance of 260 F g-1 at 1 A g-1, and exhibits considerable rate capability with the retention of 81% at 10 A g-1. Notably, HPCAs-0.4-800 shows an excellent cycling stability with 105% of the capacitance retention after 50000 cycles at 10 A g-1, attributing to its unique hierarchical porosity, high surface area up to 1303 m2 g-1, and improved conductivity. This work offers a promising route to synthesize coal-based porous carbon aerogels electrode materials for supercapacitors.

Undercooling-directed NaCl crystallization: an approach towards nanocavity-linked graphene networks for fast lithium and sodium storage

Despite the crystallization of inorganic salt is being technologically related to the fabrication of salt-templated materials, the two key steps, nucleation and crystal growth, still lack the kinetic control to enable precise design of salt scaffolds. Here, we study how the undercooling degree controls the construction of salt scaffolds by kinetically manipulating the nucleation and growth rates in a NaCl-F127-rhodanine system. An effective approach based on undercooling-directed NaCl crystallization is further proposed to tailor the morphology and structure of the carbon materials. Under different undercooling conditions (liquid nitrogen, -55 °C and -25 °C freezing), the salt scaffold can be tuned as spheroidal particles, ellipsoidal nanocrystal aggregates and cubic nanocrystals with round corners, respectively. Correspondingly, hollow carbon nanospheres, nanocavity-linked graphene networks (CGN) and graphene nanosheets (GNS) can be fabricated through a salt template method, respectively. The Li⁺ and Na⁺ storage mechanisms of 3D CGN and 2D GNS are discussed, focusing on the ion diffusion kinetics. The enhanced Li⁺ diffusion kinetics in the 3D interconnected network endows CGN with better rate performance than GNS as lithium-ion battery anode material, and Na⁺ adsorption dominates the Na⁺ storage in CGN as sodium-ion battery anode material. Our findings provide a general idea for the construction crystallization-induced architectures and offer valuable insights to achieve fast Li⁺/Na⁺ storage by boosting the ion diffusion kinetics.

Conversion of a microwave synthesized alkali-metal MOF to a carbonaceous anode for Li-ion batteries

Hierarchical carbon-rich materials have shown immense potential for various electrochemical applications. Metal-organic frameworks (MOFs) are well suited precursors for obtaining such templated carbon matrices. Usually these conversions are carried out by energy intensive processes and lead to the presence of toxic transition metal residues. Herein, we demonstrate the green, scalable, microwave-assisted synthesis of a three-dimensional s-block metal based MOF and its efficient transformation into a carbonaceous material. The MOF-derived solid functions as a negative electrode for lithium-ion batteries having moderate low-rate capacities and cycling stability.

Physical Expansion of Layered Graphene Oxide Nanosheets by Chemical Vapor Deposition of Metal-Organic Frameworks and their Thermal Conversion into Nitrogen-Doped Porous Carbons for Supercapacitor Applications

Graphene oxide (GO) nanosheets show good electrical conductivity and corrosion resistance in electrochemical devices. However, strong van der Waals attraction between adjacent nanosheets causes GO materials to collapse, reducing the exposed surfaces and limiting electron/ion transport in porous electrodes. GO nanosheets mixed with Zn₅ (OH)₈ (NO₃ )₂ ⋅2 H₂ O (ZnON) nanoplates create a layered composite structure. Exposing the resultant GO/ZnON to 2-methylimidazole vapor leads to the conversion of ZnON into the zeolitic imidazolate framework ZIF-8. The transformation of ZnON into ZIF-8 leads to a huge physical expansion of the interlayer space between the GO sheets. Annealing the material at high temperature caused the ZIF-8 to be converted into highly porous nitrogen-doped carbon, but the GO nanosheets maintained a large separation and high surface area. The morphology and porous structure of the post-annealing carbon material was sensitive to the initial ratio of ZnON to GO. The optimized sample exhibited several favorable features, including a large surface area, high degree of graphitization, and a high amount of nitrogen doping. Using chemical vapor deposition of metal-organic frameworks to physically expand nanomaterials is a novel method to increase the surface area and porosity of materials. It enabled the synthesis of nanoporous carbon electrodes with high capacitance, good rate capability, and long cyclic stability in supercapacitor devices.

Superior Electrochemical Performance of Pristine Nickel Hexaaminobenzene MOF Supercapacitors Fabricated by Electrophoretic Deposition

2 D Metal-organic frameworks (MOFs) are promising materials for supercapacitor electrodes because of their controllable structure, tunable pore size, and high specific surface area. In this study, the fabrication of pristine MOF nickel hexaaminobenzene Ni₃ (HAB)₂ supercapacitor electrodes by electrophoretic deposition (EPD) was reported. The MOF-based symmetric supercapacitor demonstrated a superior electrochemical capacitive performance over a potential window of 0-1.0 V and displayed an areal capacitance of 13.64 mF cm^-2 and a remarkable ultra-high cycling stability with a retention of 81 % over 50 000 cycles. The supercapacitor's outstanding performance was attributed to the binder-free EPD process and to the 2 D MOF nanosheets, which facilitate ion diffusion throughout the electrodes. These promising results demonstrate the potential of using pristine MOFs as the next generation of materials for energy-storage applications.

Scalable and Precise Synthesis of Armchair-Edge Graphene Nanoribbon in Metal-Organic Framework

Graphene nanoribbons (GNRs), narrow and straight-edged stripes of graphene, attract a great deal of attention because of their excellent electronic and magnetic properties. As of yet, there is no fabrication method for GNRs to satisfy both precision at the atomic scale and scalability, which is critical for fundamental research and future technological development. Here, we report a methodology for bulk-scale synthesis of GNRs with atomic precision utilizing a metal-organic framework (MOF). The GNR was synthesized by the polymerization of perylene (PER) or its derivative within the nanochannels of the MOF. Molecular dynamics simulations showed that PER was uniaxially aligned along the nanochannels of the MOF through host-guest interactions, which allowed for regulated growth of the nanoribbons. A series of characterizations of the GNR, including NMR, UV/vis/NIR, and Raman spectroscopy measurements, confirmed the formation of the GNR with well-controlled edge structure and width.

Dual-mode response behavior of a graphene oxide implanted energetic system under different thermal stimuli

GO, produced by the Hummers' method and characterized by scanning electron microscopy (SEM), elemental analysis (EA), Fourier-transform infrared spectroscopy (FT-IR), Fourier-transform infrared nanospectroscopy (nano FT-IR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and simultaneous thermal analysis combined with mass spectrometry (TG-DSC-MS), was appended to boron/potassium nitrate (B/KNO₃) in different proportions, to regulate the response of B/KNO₃ to thermal stimuli. The addition of GO delayed the onset temperature of the reaction between B and KNO₃, and brought the second reaction stage forward, however, it did not change the reaction mechanism. The integral model functions, which were in good agreement with the values calculated using the Kissinger and Ozawa method, took the form of Jander equations for three-dimensional diffusion processes. Results showing the sensitivity to flame testing demonstrated that the higher the GO content, the more insensitive the system was to temperature, which was consistent with the conclusion of the previous thermal analysis on the onset temperature of the reaction between B and KNO₃. In a closed-vessel test, as the GO content increased, the pressure peak and maximum slopes of pressure–time curves increased. Under a thermal stimulus, GO was reduced to RGO, and when the stimulation was small and slow, this helped with heat dissipation and improved safety. If the stimulation was enough to ignite the energetic materials, GO contributed to the rapid attainment of the reaction temperature and sped up the reaction process.

Under two different thermal stimuli loading methods, GO embodied dual-mode response behavior in B/KNO₃ mixtures.

A Photoactivated Cu-CeO2 Catalyst with Cu-[O]-Ce Active Species Designed through MOF Crystal Engineering

Fully utilizing solar energy for catalysis requires the integration of conversion mechanisms and therefore delicate design of catalyst structures and active species. Herein, a MOF crystal engineering method was developed to controllably synthesize a copper-ceria catalyst with well-dispersed photoactive Cu-[O]-Ce species. Using the preferential oxidation of CO as a model reaction, the catalyst showed remarkably efficient and stable photoactivated catalysis, which found practical application in feed gas treatment for fuel cell gas supply. The coexistence of photochemistry and thermochemistry effects contributes to the high efficiency. Our results demonstrate a catalyst design approach with atomic or molecular precision and a combinatorial photoactivation strategy for solar energy conversion.

Scalable syntheses of three-dimensional graphene nanoribbon aerogels from bacterial cellulose for supercapacitors

Three-dimensional (3D) carbon aerogels with well-defined structures, e.g. high specific surface area (SSA), appropriate pore size distribution, good electrical conductivity and ideal building blocks, have been regarded as promising electrode materials or substrates for incorporation with pseudocapacitive materials for energy storage and conversion applications. Herein, we report a simple and scalable sonochemical method followed by a chemical activation process to transform bacterial cellulose-derived carbon nanofiber aerogels (CNFAs) into 3D graphene nanoribbon aerogels (GNRAs) for supercapacitors. Benefiting from a high SSA, reasonable pore size distribution and good conductivity, the GNRA electrode demonstrates a long cyclability, good rate capability and high charge storage performance for supercapacitors, yielding more than 1.5 times (three-electrode cell) and 2.6 times (two-electrode cell) the gravimetric capacitance of the CNFA electrode. In addition, a hybrid Ni-Co layered double hydroxides (LDHs)@GNRAs electrode achieves an impressive gravimetric capacitance of 968 F g^-1 (based on the mass of the active material) at a current density of 1 A g^-1. Moreover, an asymmetric supercapacitor device with a remarkable energy density of 29.87 Wh kg^-1, wide working voltage windows of 1.6 V and good cycling stability (63.5% retention after 10 000 cycles) is achieved by using the GNRA as an anode and the Ni-Co LDHs@GNRAs as a cathode.

From metal-organic frameworks to porous carbon materials: recent progress and prospects from energy and environmental perspectives

Metal-organic frameworks (MOFs) have emerged as promising materials in the areas of gas storage, magnetism, luminescence, and catalysis owing to their superior property of having highly crystalline structures. However, MOF stability toward heat or humidity is considerably less as compared to carbons because they are constructed from the assembly of ligands with metal ions or clusters via coordination bonds. Transforming MOFs into carbons is bringing the novel potential for MOFs to achieve industrialization, and carbons with controlled pore sizes and surface doping are one of the most important porous materials. By selecting MOFs as a precursor or template, carbons with heteroatom doping and well-developed pores can be achieved. In this review, we discussed the state-of-art study progress made in the new development of MOF-derived metal-free porous carbons. In particular, the potential use of metal-free carbons from environmental and energy perspectives, such as adsorption, supercapacitors, and catalysts, were analyzed in detail. Moreover, an outlook for the sustainable development of MOF-derived porous carbons in the future was also presented.

Adsorptive removal of lead (II) ion from water and wastewater media using carbon-based nanomaterials as unique sorbents: A review

Carbon-based nanomaterials and its derivatives such as carbon nanotubes, graphene, reduced graphene oxide, and graphene oxide have been widely used as unique sorbents for removal of both organic and inorganic contaminants due to unique physical and chemical properties. In the review, application of the carbon-based nanomaterials or nanocomposites is considered with particular focus on the lead(II) removal from water and wastewater samples. Moreover, various procedures of synthesis and functionalization of each class of carbon-based nanomaterials were reviewed. A critical review has been given to the adsorption behavior of these nanomaterials and interaction type between the sorbent and lead(II) ion s due to changes in their surface structure and functional group modification for the removal of lead(II)ions. The adsorption capacity, the sorbent selectivity and structure, and the adsorption mechanism for lead(II) ion adsorption with these sorbents were studied and compared. Specific consideration is devoted to effecting of pH of samples as a critical factor in the adsorption of lead(II)ions on each class of carbon-based nanomaterials. Also, the advantages and disadvantages of the nanomaterials or nanocomposites for the adsorption of lead(II) ion were evaluated in detail. In this way, the paper will contribute to presenting suggestions for the preparation of new sorbents to researchers for future study, as well as the remaining research challenges in this field.

Shape and phase controlled synthesis of mesostructured carbon single crystals through mesoscale self-assembly of reactive monomicelles and their unprecedented exfoliation into single-layered carbon nanoribbons

The formation of mesostructured polymer and carbon single-crystals is very difficult due to increased complexity of the energy hypersurface and the role of slowed-down kinetics. Here we reported the synthesis of ordered mesostructured phloroglucinol-formaldehyde single crystals through mesoscale self-assembly of reactive monomicelles under acidic conditions which were traditionally thought very difficult to control the morphology because of the rapid polymerization rate. Polymeric and carbon single crystals from unusual curved hexagonal rods and spindles with two-dimensional hexagonal mesostructures, to previously unreported lozenge single-crystal sheets with lamellar mesostructures were obtained. Contrary to the literature reports, the lamellar mesostructured lozenge single-crystal sheets were successfully transformed to graphene-like layered carbons after calcination under 800 °C, and they can be further exfoliated into unprecedented high-quality single-layered carbon nanoribbons. These results unambiguously expanded our understanding about mesocrystals, and opened up new avenues for the efficient production of single-layered carbon nanoribbons which possess promising applications in electrochemical devices.

Highly Efficient Porous Carbon Electrocatalyst with Controllable N-Species Content for Selective CO2 Reduction

We report a straightforward strategy to design efficient N doped porous carbon (NPC) electrocatalyst that has a high concentration of easily accessible active sites for the CO₂ reduction reaction (CO₂ RR). The NPC with large amounts of active N (pyridinic and graphitic N) and highly porous structure is prepared by using an oxygen-rich metal-organic framework (Zn-MOF-74) precursor. The amount of active N species can be tuned by optimizing the calcination temperature and time. Owing to the large pore sizes, the active sites are well exposed to electrolyte for CO₂ RR. The NPC exhibits superior CO₂ RR activity with a small onset potential of -0.35 V and a high faradaic efficiency (FE) of 98.4 % towards CO at -0.55 V vs. RHE, one of the highest values among NPC-based CO₂ RR electrocatalysts. This work advances an effective and facile way towards highly active and cost-effective alternatives to noble-metal CO₂ RR electrocatalysts for practical applications.

Heteroatom-doped highly porous carbons prepared by in situ activation for efficient adsorptive removal of sulfamethoxazole

Porous carbons obtained by in situ activation of organic salts for highly efficient sulfamethoxazole adsorption.

Five naphthalene-amide-bridged Ni(ii) complexes: electrochemistry, bifunctional fluorescence responses, removal of contaminants and optimization by CVD

Five multifunctional Ni-CPs based on a new naphthalene-amide and different carboxylates were obtained and exhibited various properties. CNTs were synthesized from the precursors of CPs, showing selective removal of contaminants in water.

MOF-derived electrocatalysts for oxygen reduction, oxygen evolution and hydrogen evolution reactions

The morphology and composition design of MOF-derived carbon-based materials and their applications for electrocatalytic ORR, OER and HER are reviewed.

A review of recent work on using metal–organic frameworks to grow carbon nanotubes

In this review, we summarize catalysts and synthetic strategies for the synthesis of MOF-derived CNT-based composite materials.

Controlling the morphology of metal–organic frameworks and porous carbon materials: metal oxides as primary architecture-directing agents

We give a comprehensive overview of how the morphology control is an effective and versatile way to control the physicochemical properties of metal oxides that can be transferred to metal–organic frameworks and porous carbon materials.

Synthesis of micro/nanoscaled metal–organic frameworks and their direct electrochemical applications

Developing strategies to control the morphology and size of MOFs is important for their applications in batteries, supercapacitors and electrocatalysis. This review focuses on the design and fabrication of MOFs at the micro/nanoscale.

Low-temperature synthesis of sp2 carbon nanomaterials

sp² carbon nanomaterials are mainly composed of sp²-hybridized carbon atoms in the form of a hexagonal network. Due to the π bonds formed by unpaired electrons, sp² carbon nanomaterials possess excellent electronic, mechanical, and optical properties, which have attracted great attention in recent years. As the advanced sp² carbon nanomaterials, graphene and carbon nanotubes (CNTs) have great potential in electronics, sensors, energy storage and conversion devices, etc. The low-temperature synthesis of graphene and CNTs are indispensable to promote the practical industrial application. Furthermore, graphene and CNTs can even be expected to directly grow on the flexible plastic that cannot bear high temperature, expanding bright prospects for applications in emerging flexible nanotechnology. An in-depth understanding of the formation mechanism of sp² carbon nanomaterials is beneficial for reducing the growth temperature and satisfying the demands of industrial production in an economical and low-cost way. In this review, we discuss the main strategies and the related mechanisms in low-temperature synthesis of graphene and CNTs, including the selection of precursors with high reactivity, the design of catalyst, and the introduction of additional energy for the pre-decomposition of precursors. Furthermore, challenges and outlooks are highlighted for further progress in the practical industrial application.

Modulating the Charge-Transfer Step of a p-n Heterojunction with Nitrogen-Doped Carbon: A Promising Strategy To Improve Photocatalytic Performance

Engineering p-n heterojunctions among metal oxide semiconductors to provide a built-in electric field is an efficient strategy to facilitate the separation of photogenerated electrons and holes and improve their photocatalytic activities. However, the inherent poor conductivity of p-n heterojunctions still limits the charge-transfer step and thus hampers their practical application in photocatalysis. In this work, a nitrogen-doped carbon-coated NiO/TiO₂ p-n (NCNT) heterojunction with hierarchical mesoporous sphere morphology was synthesized by in situ pyrolytic decomposition of nickel-titanium complexes. The NiO/TiO₂ p-n heterojunction in NCNT was fully characterized by several techniques, supported by theoretical calculations and Mott-Schottky plots. On coating with a thin nitrogen-doped carbon layer, the electron transfer of the obtained p-n heterojunction could be significantly enhanced. On account of the favorable structural features of the p-n heterojunction with nitrogen-doped carbon coating and hierarchical mesoporous structure, NCNT exhibited excellent photocatalytic activity toward various reaction systems, including the hydrogen evolution reaction and the visible-light-induced hydroxylation of phenylboronic acids.

Macromolecular Polyethynylbenzonitrile Precursor-Based Porous Covalent Triazine Frameworks for Superior High-Rate High-Energy Supercapacitors

Porous covalent triazine framework (CTF)-based carbon materials have gained increasing attention in energy-storage applications because of their tunable structure, high chemical stability, and rich heteroatom contents. However, CTFs have thus far been exclusively synthesized from small-molecular precursors and generally show unsatisfactory supercapacitive performance. We report herein the construction of a novel range of CTFs of significantly improved supercapacitive performance from polyethynylbenzonitrile (PEBN) as a unique macromolecular precursor for the first time by ionothermal synthesis. CTF-800 synthesized at the optimized condition (800 °C; ZnCl₂/PEBN mass ratio of 3:1) shows a nanosheet-like morphology with a high yield (∼90%), high nitrogen content (>5.8%), high specific surface area (1954 m² g^-1), and optimized micropore to meso/macropore surface area ratio (42:58). As the electrode material for supercapacitor application, CTF-800 exhibits a high specific capacitance of 628 F g^-1 at 0.5 A g^-1, high-rate performance (71% of capacitance retention at 50 A g^-1), and excellent cyclic stability (96% of capacitance retention over 20 000 cycles) in a three-electrode system with aqueous 1 M H₂SO₄ electrolyte. Symmetric supercapacitor devices have been further fabricated with CTF-800 in aqueous 1 M H₂SO₄, [EMIM][BF₄], and LiPF₆ electrolytes separately. The device with the aqueous electrolyte shows the highest capacitance of 448 F g^-1 (at 0.5 A g^-1) and a high energy density of 15.5 W h kg^-1. The devices with [EMIM][BF₄] and LiPF₆ electrolytes exhibit exceptional energy densities of 70 and 78 W h kg^-1, respectively, and retain energy densities of 41 and 45 W h kg^-1, respectively, even at the high power density of 15 000 W kg^-1, confirming their high-rate high-energy performance. Meanwhile, the device with [EMIM][BF₄] electrolyte has also been demonstrated to operate well at various temperatures ranging from -20 to 60 °C with remarkable energy-storage performance.

Thermally reduced fluorographenes as efficient electrode materials for supercapacitors

There is an urgent need for a simple and up-scalable method for the preparation of supercapacitor electrode materials due to increasing global energy consumption worldwide. We have discovered that fluorographene exhibits great potential for the development of new kinds of supercapacitors aimed at practical applications. We have shown that time control of isothermal reduction of fluorographite at 450 °C under a hydrogen atmosphere led to the fine-tuning of fluorine content and electronic properties of the resulting fluorographene derivatives. Charge transfer resistances (R_ct) of the thermally reduced fluorographenes (TRFGs) were decreased with respect to the pristine fluorographene; however, the R_ctvs. time-of-reduction plot showed a v-shaped profile. The specific capacitance vs. time-of-reduction of TRFG followed the v-shaped trend, which could be the result of the decreasing content of sp³ carbons and increasing content of structural defects. An optimized material exhibited values of specific capacitance up to 539 F g^-1 recorded at a current density of 0.25 A g^-1 and excellent cycling durability with 100% specific capacitance retention after 1500 cycles in a three-electrode configuration and 96.7% of specific capacitance after 30 000 cycles in a two-electrode setup.