Compact Coupled Graphene and Porous Polyaryltriazine-Derived Frameworks as High Performance Cathodes for Lithium-Ion Batteries

Electrochemical lithium storage of a biactive organic molecule containing cyano and imine groups

With an electron-deficient rigid planar structure and excellent π-π stacking ability, hexaazatriphenylene (HAT) and its derivatives are widely used as basic building blocks for constructing covalent organic frameworks (COFs), components of organic light-emitting diodes and solar cells, and electrode materials for lithium-ion batteries (LIBs). Here, a HAT derivative, hexaazatriphenylenehexacarbonitrile, is explored as an anode material for LIBs. The HAT anode exhibited high initial reversible capacities of 672 mA h g-1 at 100 mA g-1 and 550 mA h g-1 at 400 mA g-1 and stable cycling with a capacity of 503 mA h g-1 after 1000 cycles at 400 mA g-1 corresponding to a capacity retention of 91.5%. Furthermore, the lithium storage mechanism and the cause of the first irreversible capacity loss of the HAT anode were investigated by X-ray photoelectron spectroscopy (XPS) analysis and density functional theory (DFT) calculations. We have carried out a series of analyses on the mechanism of initial capacity loss. This study provides new insight on initial capacity loss and provides valuable insights into the molecular design and the electrochemical properties of HAT-based anode materials.

Confined Synthesis of Dual-Atoms Within Pores of Covalent Organic Frameworks for Oxygen Reduction Reaction

Dual-atom catalysts exhibit higher reactivity and selectivity than the single-atom catalysts. The pyrolysis of bimetal salt precursors is the most typical method for synthesizing dual-atomic catalysts; however, the finiteness of bimetal salts limits the variety of dual-atomic catalysts. In this study, a confined synthesis strategy for synthesizing dual-atomic catalysts is developed. Owing to the in situ synthesis of zeolitic imidazolate frameworks in the pores of covalent organic frameworks (COFs), the migration and aggregation of metal atoms are suppressed adequately during the pyrolysis process. The resultant catalyst contains abundant Zn─Co dual atomic sites with 2.8 wt.% Zn and 0.5 wt.% Co. The catalyst exhibits high reactivity toward oxygen reduction reaction with a half-wave potential of 0.86 V, which is superior to that of the commercial Pt/C catalyst. Theoretical calculations reveal that the Zn atoms in the Zn─Co dual atomic sites promote the formation of intermediate OOH*, and thus contribute to high catalytic performance. This study provides new insights into the design of dual-atom catalysts using COFs.

Two Birds One Stone: Graphene Assisted Reaction Kinetics and Ionic Conductivity in Phthalocyanine-Based Covalent Organic Framework Anodes for Lithium-ion Batteries

This work reports a covalent organic framework composite structure (PMDA-NiPc-G), incorporating multiple-active carbonyls and graphene on the basis of the combination of phthalocyanine (NiPc(NH2 )4 ) containing a large π-conjugated system and pyromellitic dianhydride (PMDA) as the anode of lithium-ion batteries. Meanwhile, graphene is used as a dispersion medium to reduce the accumulation of bulk covalent organic frameworks (COFs) to obtain COFs with small-volume and few-layers, shortening the ion migration path and improving the diffusion rate of lithium ions in the two dimensional (2D) grid layered structure. PMDA-NiPc-G showed a lithium-ion diffusion coefficient (DLi + ) of 3.04 × 10-10 cm2 s-1 which is 3.6 times to that of its bulk form (0.84 × 10-10 cm2 s-1 ). Remarkably, this enables a large reversible capacity of 1290 mAh g-1 can be achieved after 300 cycles and almost no capacity fading in the next 300 cycles at 100 mA g-1 . At a high areal capacity loading of ≈3 mAh cm-2 , full batteries assembled with LiNi0.8 Co0.1 Mn0.1 O2 (NCM-811) and LiFePO4 (LFP) cathodes showed 60.2% and 74.7% capacity retention at 1 C for 200 cycles. Astonishingly, the PMDA-NiPc-G/NCM-811 full battery exhibits ≈100% capacity retention after cycling at 0.2 C. Aided by the analysis of kinetic behavior of lithium storage and theoretical calculations, the capacity-enhancing mechanism and lithium storage mechanism of covalent organic frameworks are revealed. This work may lead to more research on designable, multifunctional COFs for electrochemical energy storage.

Isometric Covalent Triazine Framework-Derived Porous Carbons as Metal-Free Electrocatalysts for the Oxygen Reduction Reaction

Covalent triazine frameworks (CTFs) and their derivative N-doped carbons have attracted much attention for application in energy conversion and storage. However, previous studies have mainly focused on developing new building blocks and optimizing synthetic conditions. The use of isometric building blocks to control the porous structure and to fundamentally understand structure-property relationships have rarely been reported. In this work, two isometric building blocks are used to produce isometric CTFs with controllable pore geometries. The as-prepared CTF with nonplanar hexagonal rings demonstrates higher surface area, larger pore volume, and richer N content than the planar CTF. After pyrolysis, nonplanar porous CTF-derived N-doped carbons exhibit admirable catalytic activity for oxygen reduction in alkaline media (half-wave potential: 0.86 V; Tafel slope: 65 mV dec^-1 ), owing to their larger pore volume and the abundance of pyridinic and graphitic N species. When assembled into a zinc-air battery, the as-made electrocatalysts show high capacities of up to 651 mAh g^-1 and excellent durability.

Organic Anode Materials for Lithium-Ion Batteries: Recent Progress and Challenges

In the search for novel anode materials for lithium-ion batteries (LIBs), organic electrode materials have recently attracted substantial attention and seem to be the next preferred candidates for use as high-performance anode materials in rechargeable LIBs due to their low cost, high theoretical capacity, structural diversity, environmental friendliness, and facile synthesis. Up to now, the electrochemical properties of numerous organic compounds with different functional groups (carbonyl, azo, sulfur, imine, etc.) have been thoroughly explored as anode materials for LIBs, dividing organic anode materials into four main classes: organic carbonyl compounds, covalent organic frameworks (COFs), metal-organic frameworks (MOFs), and organic compounds with nitrogen-containing groups. In this review, an overview of the recent progress in organic anodes is provided. The electrochemical performances of different organic anode materials are compared, revealing the advantages and disadvantages of each class of organic materials in both research and commercial applications. Afterward, the practical applications of some organic anode materials in full cells of LIBs are provided. Finally, some techniques to address significant issues, such as poor electronic conductivity, low discharge voltage, and undesired dissolution of active organic anode material into typical organic electrolytes, are discussed. This paper will guide the study of more efficient organic compounds that can be employed as high-performance anode materials in LIBs.

Covalent Triazine Frameworks and Porous Carbons: Perspective from an Azulene-Based Case

Covalent triazine frameworks (CTFs) are among the most valuable frameworks owing to many fantastic properties. However, molten salt-involved preparation of CTFs at 400-600 °C causes debate on whether CTFs represent organic frameworks or carbon. Herein, new CTFs based on the 1,3-dicyanoazulene monomer (CTF-Azs) are synthesized using molten ZnCl₂ at 400-600 °C. Chemical structure analysis reveals that the CTF-Az prepared at low temperature (400 °C) exhibits polymeric features, whereas those prepared at high temperatures (600 °C) exhibit typical carbon features. Even after being treated at even higher temperatures, the CTF-Azs retain their rich porosity, but the polymeric features vanish. Although structural de-conformation is a widely accepted outcome in polymer-to-carbon rearrangement processes, the study evaluates such processes in the context of CTF systems. A proof-of-concept study is performed, observing that the as-synthesized CTF-Azs exhibit promising performance as cathodes for Li- and K-ion batteries. Moreover, the as-prepared NPCs exhibit excellent catalytic oxygen reduction reaction (ORR) performance; hence, they can be used as air cathodes in Zn-air batteries. This study not only provides new building blocks for novel CTFs with controllable polymer/carbon features but also offers insights into the formation and structure transformation history of CTFs during thermal treatment.

A facile synthesis of hierarchically porous graphene for high-performance lithium storage

Hierarchically porous graphene with macro-mesopores is highly desired for enhancing lithium storage.

A template oriented one-dimensional Schiff-base polymer: towards flexible nitrogen-enriched carbonaceous electrodes with ultrahigh electrochemical capacity

Lithium-ion capacitors (LICs) have attracted much attention considering their efficient combination of high energy density and high-power density. However, to meet the increasing requirements of energy storage devices and the flexible portable electronic equipment, it is still challenging to develop flexible LIC anodes with high specific capacity and excellent rate capability. Herein, we propose a delicate bottom-up strategy to integrate unique Schiff-base-type polymers into desirable one-dimensional (1D) polymeric structures. A secondary-polymerization-induced template-oriented synthesis approach realizes the 1D integration of Schiff-base porous organic polymers with appealing characteristics of a high nitrogen-doping level and developed pore channels, and a further thermalization yields flexible nitrogen-enriched carbon nanofibers with high specific capacity and fast ion transport. Remarkably, when used as the flexible anode in LICs, the NPCNF//AC LIC demonstrates a high energy density of 154 W h kg^-1 at 500 W kg^-1 and a high power density of 12.5 kW kg^-1 at 104 W h kg^-1. This work may provide a new scenario for synthesizing 1D Schiff-base-type polymer derived nitrogen-enriched carbonaceous materials towards promising free-standing anodes in LICs.

Superlithiation Performance of Covalent Triazine Frameworks as Anodes in Lithium-Ion Batteries

Organics with the merit of renewability have been viewed as the promising alternative of inorganic electrode materials in lithium-ion batteries, but most of them display inferior performance due to the sluggish ion/electron diffusion and the potential dissolution in aprotic electrolytes. Here, covalent triazine frameworks (CTFs-1), full of vertical pores and layered spaces for Li⁺ transfer, have been synthesized with p-dicyanobenzene as the monomer by a facile two-step method including a prepolymerization with CF₃SO₃H as the catalyst and deep polymerization in molten ZnCl₂. CTFs-1-400, obtained at the deep polymerization temperature of 400 °C, exhibits the superlithiation property with the specific capacities of 1626 mA h g^-1 at 25 °C and 1913 mA h g^-1 at 45 °C at 100 mA g^-1, indicating the formation of Li₆C₆/Li₆C₃N₃ in the reduction process. Electrochemical analysis and density functional theory calculation indicate that the ultrahigh capacity is mainly contributed by the capacitance of micropores and the redox capacity of benzene and triazine rings. Moreover, CTFs-1-400 displays the specific capacity of 740 mA h g^-1 for 1000 cycles at 1 A g^-1 with almost no capacity fading.

Graphene Oxide-Assisted Covalent Triazine Framework for Boosting Photocatalytic H2 Evolution

Covalent triazine frameworks (CTFs) with two-dimensional structures have exhibited promising visible-light-induced H₂ evolution performance. However, it is still a challenge to improve their activity. Herein, we report π-conjugation-linked CTF-1/GO for boosting photocatalytic H₂ evolution. The CTF-1/GO hybrid material was obtained by a facile low-temperature condensation of 1,4-dicyanobenzene in the presence of GO. The results of photocatalytic H₂ evolution indicate that the optimum hybrid, CTF-1/GO-3.0, exhibited an H₂ evolution rate of 2262.4 μmol ⋅ g^-1  ⋅ h^-1 under visible light irradiation, which was 9 times that of pure CTF-1. The enhanced photocatalytic performance could be attributed to the fact that GO in CTF-1/GO hybrids not only acts as an electron collector and transporter like a "bridge" to facilitate the separation and transfer of photogenerated charges but also shortens the electron migration path due to its thin sheet layer uniformly distribution over CTF-1. This work could help future development of novel conjugated CTF-based composite materials as high-efficiency photocatalyst for photocatalysis.

Emerging trends in anion storage materials for the capacitive and hybrid energy storage and beyond

Electrochemical capacitors charge and discharge more rapidly than batteries over longer cycles, but their practical applications remain limited due to their significantly lower energy densities. Pseudocapacitors and hybrid capacitors have been developed to extend Ragone plots to higher energy density values, but they are also limited by the insufficient breadth of options for electrode materials, which require materials that store alkali metal cations such as Li⁺ and Na⁺. Herein, we report a comprehensive and systematic review of emerging anion storage materials for performance- and functionality-oriented applications in electrochemical and battery-capacitor hybrid devices. The operating principles and types of dual-ion and whole-anion storage in electrochemical and hybrid capacitors are addressed along with the classification, thermodynamic and kinetic aspects, and associated interfaces of anion storage materials in various aqueous and non-aqueous electrolytes. The charge storage mechanism, structure-property correlation, and electrochemical features of anion storage materials are comprehensively discussed. The recent progress in emerging anion storage materials is also discussed, focusing on high-performance applications, such as dual-ion- and whole-anion-storing electrochemical capacitors in a symmetric or hybrid manner, and functional applications including micro- and flexible capacitors, desalination, and salinity cells. Finally, we present our perspective on the current impediments and future directions in this field.

The Functional Chameleon of Materials Chemistry-Combining Carbon Structures into All-Carbon Hybrid Nanomaterials with Intrinsic Porosity to Overcome the "Functionality-Conductivity-Dilemma" in Electrochemical Energy Storage and Electrocatalysis

Nanoporous carbon materials can cover a remarkably wide range of physicochemical properties. They are widely applied in electrochemical energy storage and electrocatalysis. As a matter of fact, all these applications combine a chemical process at the electrode-electrolyte interface with the transport (and possibly the transfer) of electrons. This leads to multiple requirements which can hardly be fulfilled by one and the same material. This "functionality-conductivity-dilemma" can be minimized when multiple carbon-based compounds are combined into porous all-carbon hybrid nanomaterials. This article is giving a broad and general perspective on this approach from the viewpoint of materials chemists. The problem and existing solutions are first summarized. This is followed by an overview of the most important design principles for such porous materials, a chapter discussing recent examples from different fields where the formation of comparable structures has already been successfully applied, and an outlook over the future development of this field that is foreseen.

Ionic Polyimide Derived Porous Carbon Nanosheets as High-Efficiency Oxygen Reduction Catalysts for Zn-Air Batteries

Two-dimensional (2D) porous carbon nanosheets (2DPCs) have attracted great attention for their good porosity and long-distance conductivity. Factors such as templates, precursors, and carbonization-activation methods, directly determine their performance. However, rational design and preparation of porous carbon materials with controlled 2D morphology and heteroatom dopants remains a challenge. Therefore, an ionic polyimide with both sp² - and sp³ -hybridized nitrogen atoms was prepared as a precursor for fabricating N-doped hexagonal porous carbon nanosheets through a hard-template approach. Because of the large surface area and efficient charge-mass transport, the resulting activated 2D porous carbon nanosheets (2DPCs-a) displayed promising electrocatalytic properties for oxygen reduction reaction (ORR) in alkaline and acidic media, such as ultralow half-wave potential (0.83 vs. 0.84 V of Pt/C) and superior limiting current density (5.42 vs. 5.14 mA cm^-2 of Pt/C). As air cathodes in Zn-air batteries, the as-developed 2DPCs-a exhibited long stability and high capacity (up to 614 mA h g^-1 ), which are both higher than those of commercial Pt/C. This work provides a convenient method for controllable and scalable 2DPCs fabrication as well as new opportunities to develop high-efficiency electrocatalysts for ORR and Zn-air batteries.

Exfoliation of 2D Materials for Energy and Environmental Applications

The fascinating properties of single-layer graphene isolated by mechanical exfoliation have inspired extensive research efforts toward two-dimensional (2D) materials. Layered compounds serve as precursors for atomically thin 2D materials (briefly, 2D nanomaterials) owing to their strong intraplane chemical bonding but weak interplane van der Waals interactions. There are newly emerging 2D materials beyond graphene, and it is becoming increasingly important to develop cost-effective, scalable methods for producing 2D nanomaterials with controlled microstructures and properties. The variety of developed synthetic techniques can be categorized into two classes: bottom-up and top-down approaches. Of top-down approaches, the exfoliation of bulk 2D materials into single or few layers is the most common. This review highlights chemical and physical exfoliation methods that allow for the production of 2D nanomaterials in large quantities. In addition, remarkable examples of utilizing exfoliated 2D nanomaterials in energy and environmental applications are introduced.

Positively charged conjugated microporous polymers with antibiofouling activity for ultrafast and highly selective uranium extraction from seawater

Uranium high-efficiency separation from seawater still has some obstacles such as slow sorption rate, poor selectivity and biofouling. Herein, we report a strategy for ultrafast and highly selective uranium extraction from seawater by positively charged conjugated microporous polymers (CMPs). The polymers are synthesized by Sonogashira-Hagihara cross-coupling reaction of 1,3-dibromo-5,5-dimethylhydantoin and 1,3,5-triethynylbenzene, and then modified with oxime and carboxyl via click reaction. The CMPs show an ultrafast sorption (0.46 mg g^-1 day^-1) for uranium, and possess an outstanding selectivity with a high sorption capacity ratio of U/V (8.4) in real seawater. The study of adsorption process and mechanism indicate that the CMPs skeleton exhibits high affinity for uranium and can accelerate the sorption, and uranium(VI) is adsorbed on the materials by the interaction of oxime/carboxyl ligands and hydantoin. Moreover, the material can be simply loaded onto the filter membrane, and shows remarkable antibiofouling properties against E. coli and S. aureus and excellent uptake capacity for uranium with low concentration in real seawater. This work may provide a promising approach to design adsorbents with fast adsorption rate, high selectivity and antibacterial activity, and expand the thinking over the development of novel and highly efficient adsorbents for uranium extraction from seawater.

Reduced graphene oxide promoted assembly of graphene@polyimide film as a flexible cathode for high-performance lithium-ion battery

Organic carbonyl polymers have been gradually used as the cathode in lithium-ion batteries (LIB). However, there are some limits in most organic polymers, such as low reversible capacity, poor rate performance, cycle instability, etc., due to low electrochemical conductivity. To mitigate the limits, we propose a strategy based on polyimide (PI)/graphene electroactive materials coated with reduced graphene oxide to prepare a flexible film (G@PI/RGO) by solvothermal and vacuum filtration processes. As a flexible cathode for LIB, it provides a reversible capacity of 198 mA h g⁻¹ at 30 mA g⁻¹ and excellent rate performance of 100 mA h g⁻¹ at high current densities of 6000 mA g⁻¹, and even a super long cycle performance (2500 cycles, 70% capacity retention). The excellent performance results in a special layer structure in which the electroactive PI was anchored and coated by the graphene. The present synthetic method can be further applied to construct other high-performance organic electrodes in energy storage.

G@PI/RGO is prepared by a combination of solvothermal reaction and carbonization. With good mechanical flexibility and high conductivity, it shows excellent performance when directly used as the cathode for LIB.

Nitrogen-Linked Hexaazatrinaphthylene Polymer as Cathode Material in Lithium-Ion Battery

Nitrogen-linked hexaazatrinaphthylene polymer (N² -HATN) as organic cathode material with low HOMO-LOMO gap was synthesized and was observed to possess reversible high capacity and unexpected long-term cycling stability. The pre-treated N² -HATN and pRGO combination demonstrated good structure compatibility and the resultant cathode exhibited a constant increment of capacity during the redox cycles. The initial capacity at 0.05 A g^-1 was 406 mA h^-1  g^-1 , and increased to 630 mA h^-1  g^-1 after 70 cycles. At 0.5 A g^-1 discharging rate, the capacity increased from an initial value of 186 mA h^-1  g^-1 to 588 mA h^-1  g^-1 after 1600 cycles. The pseudocapacitance-type behavior is postulated to be attributed to the structure compatibility between the active material and pRGO.

Organic Electrode Materials for Metal Ion Batteries

Organic and polymer materials have been extensively investigated as electrode materials for rechargeable batteries because of the low cost, abundance, environmental benignity, and high sustainability. To date, organic electrode materials have been applied in a large variety of energy storage devices, including nonaqueous Li-ion, Na-ion, K-ion, dual-ion, multivalent-metal, aqueous, all-solid-state, and redox flow batteries, because of the universal properties of organic electrode materials. Moreover, some organic materials enable the batteries to be operated in the extreme conditions, such as a wide temperature range (-70 to 150 °C), a wide pH range, and in the presence of O₂. As a guidance for the research in organic batteries, this Review focuses on the reaction mechanisms and applications of organic electrode materials. Six categories of reaction mechanisms and the applications of organic and polymer materials in various rechargeable batteries are discussed to provide an overview of the state-of-the-art organic batteries.

Highly Exfoliated and Functionalized Single-Walled Carbon Nanotubes as Fast-Charging, High-Capacity Cathodes for Rechargeable Lithium-Ion Batteries

Compared with traditional metal-oxide lithium-ion battery (LIB) cathodes, nanocarbon-based cathode materials have received much attention for potential application in LIBs because of their superior power density and long-term cyclability. However, their lithium-ion storage capacity needs further improvement for practical applications, and the trade-off between capacity and conductivity, when oxygen functional groups as lithium-ion storage sites are introduced to the nanocarbon materials, needs to be addressed. Here, we report a sequential oxidation-reduction process for the synthesis of single-walled carbon nanotubes (SWCNTs) for LIB cathodes with fast charging, long-term cyclability, and high gravimetric capacity. A LIB cathode based on highly exfoliated (d_bundle < 10 nm) and oxygen-functionalized single-walled carbon nanotubes is obtained via the modified Brodie's method using fuming nitric acid and a mild oxidant (B-SWCNTs). Post treatment including horn sonication and hydrogen thermal reduction developed surface defects and removed the unnecessary C-O groups, resulting in an increase in the Li-ion storage capacity. The B-SWCNTs exhibit a high reversible gravimetric capacity of 344 mA h g^-1 at 0.1 A g^-1 without noticeable capacity fading after 1000 cycles. Furthermore, it delivers a high gravimetric energy density of 797 W h kg_electrode^-1 at a low gravimetric power density of 300 W kg_electrode^-1 and retains its high gravimetric energy density of ∼100 W h kg_electrode^-1 at a high gravimetric power of 10⁵ W kg_electrode^-1. These results suggest that the highly exfoliated, oxygen-functionalized single-walled carbon nanotubes can be applied to LIBs designed for high-rate operations and long cycling.

MOF-derived hollow NiCo2O4 nanowires as stable Li-ion battery anodes

Although binary metal oxides with high theoretical specific capacities and power densities are widely investigated as promising anode materials for lithium-ion batteries (LIBs), their poor cycling stability and huge volume expansion largely limit their extensive application in practical electrode materials. Herein, we report a facile strategy to synthesize hollow NiCo2O4 nanowires through direct calcination of binary metal-organic frameworks (MOFs) in air. When evaluated as an anode material for LIBs, NiCo2O4 nanowires deliver a reversible capacity of 1310 mA h g-1 at a current density of 100 mA g-1 after 100 cycles. Even at a high current density of 1 A g-1, NiCo2O4 nanowires exhibit long-term cycling stability with a capacity of 720 mA h g-1 after 1000 cycles. The outstanding lithium-storage performance can be attributed to the unique structures with 1D porous channels, which are beneficial for the fast transfer of Li+ ions and electrolyte and alleviate the strain caused by the volume expansion during cycling processes.

Porous CuO@C composite as high-performance anode materials for lithium-ion batteries

The in situ formation of a carbon matrix can confine the growth of CuO nanoparticles, which can provide more exposed active sites for electrochemical reactions.

Rational Design of Carbon-Rich Materials for Energy Storage and Conversion

Carbon-rich materials have drawn tremendous attention toward a wide spectrum of energy applications due to their superior electronic mobility, good mechanical strength, ultrahigh surface area, and more importantly, abundant diversity in structure and components. Herein, rationally designed and bottom-up constructed carbon-rich materials for energy storage and conversion are discussed. The fundamental design principles are itemized for the targeted preparation of carbon-rich materials and the latest remarkable advances are summarized in terms of emerging dimensions including sp² carbon fragment manipulation, pore structure modulation, topological defect engineering, heteroatom incorporation, and edge chemical regulation. In this respect, the corresponding structure-property relationships of the resultant carbon-rich materials are comprehensively discussed. Finally, critical perspectives on future challenges of carbon-rich materials are presented. The progress highlighted here will provide meaningful guidance on the precise design and targeted synthesis of carbon-rich materials, which are of critical importance for the achievement of performance characteristics highly desirable for urgent energy deployment.

Recent Progress on Organic Electrodes Materials for Rechargeable Batteries and Supercapacitors

Rechargeable batteries are essential elements for many applications, ranging from portable use up to electric vehicles. Among them, lithium-ion batteries have taken an increasing importance in the day life. However, they suffer of several limitations: safety concerns and risks of thermal runaway, cost, and high carbon footprint, starting with the extraction of the transition metals in ores with low metal content. These limitations were the motivation for an intensive research to replace the inorganic electrodes by organic electrodes. Subsequently, the disadvantages that are mentioned above are overcome, but are replaced by new ones, including the solubility of the organic molecules in the electrolytes and lower operational voltage. However, recent progress has been made. The lower voltage, even though it is partly compensated by a larger capacity density, may preclude the use of organic electrodes for electric vehicles, but the very long cycling lives and the fast kinetics reached recently suggest their use in grid storage and regulation, and possibly in hybrid electric vehicles (HEVs). The purpose of this work is to review the different results and strategies that are currently being used to obtain organic electrodes that make them competitive with lithium-ion batteries for such applications.

Fused Aromatic Network Structures as a Platform for Efficient Electrocatalysis

Fused aromatic network (FAN) structures are a category of ordered porous polymers that permit the specific fusion of building blocks into extended porous network structures with designed skeletons and pores. One significant feature of FANs is that their structures can be tailorable with fused aromatic rings without rotatable single-bond connectivity. As a result, the geometry and space orientation of the building blocks are easily incorporated to guide the topological expansion of the architectural periodicity. The variety of building units and fused linkages make FANs a promising materials platform for constitutional outline and functional design. The stably confined spaces of FAN architectures can be extended for the exchange of photons, ions, electrons, holes, and guest molecules, and exhibit customized chemical, electrochemical and optical properties. Herein, the main progress and advances in the field of 2D and 3D FANs and their utilization as a platform to develop efficient electrocatalysts for energy conversion and storage applications are summarized.

New Platinum(IV) and Palladium(II) Transition Metal Complexes of s-Triazine Derivative: Synthesis, Spectral, and Anticancer Agents Studies

New Pd(II) and Pt(IV) triazine complexes [Pt3(L 1 )2(Cl)9(H2O)3].3Cl.3H2O (1), [Pt3(L 2 )2(Cl)9(H2O)3].3Cl (2), [Pt3(L 3 )2(Cl)9(H2O)3].3Cl (3), [Pt2(L 4 )2(Cl)6(H2O)2] .2Cl.4H2O (4), [Pd3(L 1 )2(H2O)6] .3Cl2 (5), [Pd3(L 2 )2(H2O)6].3Cl2 (6), [Pd3(L 3 )2(H2O)6].3Cl2 (7), and [Pd2(L 4 )2(H2O)4].2Cl2 (8) were synthesized and well characterized using elemental analyses, molar conductance, IR, UV-Vis, magnetic susceptibility, 1H, 13C-NMR spectra, and thermal analyses. These analyses deduced that the L 1 , L 2 , and L 3 ligands act as tridentate forming octahedral geometry with Pt(IV) metal ions and square planar geometry in case of Pd(II) complexes but the L 4 ligand acts as bidentate chelate. The molar conductance values refer to the fact that all the prepared s-triazine complexes have electrolyte properties which are investigated in DMSO solvent. Surface morphology behaviors of prepared complexes have been scanned using TEM. The crystalline behavior of triazine complexes has been checked based on X-ray powder diffraction patterns. The antimicrobial activity of the free ligands and their platinum(IV) and palladium(II) complexes against the species Staphylococcus aureus (G+), Escherichia coli (G-), Aspergillus flavus, and Candida albicans has been carried out and compared with the standard one. The coordination of ligands towards metal ions makes them stronger bacteriostatic agents, thus inhibiting the growth of bacteria and fungi more than the free ligands. The cytotoxic assessment IC50 of the free ligands and its platinum(IV) complexes in vitro against human colon and lung cancer cell lines introduced a promising efficiency.

Synthesis of a Macroporous Conjugated Polymer Framework: Iron Doping for Highly Stable, Highly Efficient Lithium-Sulfur Batteries

Porous conjugated polymers offer enormous potential for energy storage because of the combined features of pores and extended π-conjugated structures. However, the drawbacks such as low pore volumes and insolubilities of micro- and mesoporous conjugated polymers restrict the loading of electroactive materials and thus energy storage performance. Herein, we report the synthesis of iron-doped macroporous conjugated polymers for hosting sulfur as the cathode of high-performance lithium-sulfur (Li-S) batteries. The macroporous conjugated polymers are synthesized via in situ growth of poly(3-hexylthiophene) (P3HT) from reduced graphene oxide (RGO) sheets, followed by gelation of the composite (RGO- g-P3HT) in p-xylene and freeze-drying. The network structures of the macroporous materials can be readily tuned by controlling the chain length of P3HT grafted to RGO sheets. The large pore volumes of the macroporous RGO- g-P3HT materials (ca. 34 cm³ g^-1) make them excellent frameworks for hosting sulfur as cathodes of Li-S batteries. Furthermore, incorporation of Fe into the macroporous RGO- g-P3HT cathode results in reduced polarization, enhanced specific capacity (1,288, 1,103, and 907 mA h g^-1 at 0.05, 0.1, and 0.2 C, respectively), and improved cycling stability (765 mA h g^-1 after 100 cycles at 0.2 C). Density functional theory calculations and in situ characterizations suggest that incorporation of Fe enhances the interactions between lithium polysulfides and the P3HT framework.

Conjugated Microporous Polymers with Tunable Electronic Structure for High-Performance Potassium-Ion Batteries

Conjugated microporous polymers (CMPs) with π-conjugated skeletons show great potential as energy storage materials due to their porous structure and tunable redox nature. However, CMPs and the structure-performance relationships have not been well explored for potassium-ion batteries (KIBs). Here, we report the structure-engineered CMP anodes with tunable electronic structures for high-performance KIBs. The results demonstrate that the electronic structure of the CMPs plays an important role in enhancing potassium storage capability, including the lowest unoccupied molecular orbital (LUMO) distribution, LUMO energy level, and band gap, which can be finely tuned by synthetic control. It was revealed that the poly(pyrene- co-benzothiadiazole) (PyBT) with optimized structure delivers a high reversible capacity of 428 mAh g^-1 and shows an excellent cycling stability over 500 cycles. Our findings provide a fundamental understanding in the design of CMP anode materials for high-performance potassium-organic energy storage devices.

Preparation of triazine containing porous organic polymer for high performance supercapacitor applications

By condensing M and TFP under solvothermal conditions, a new porous organic polymer POPM-TFP was obtained. The electrode modified with triazine containing POPM-TFP exhibits well-defined rapid redox processes and showed a high specific capacitance of 130.5 F g-1 at 2 A g-1, suggesting well electrochemical performance.

Pyrolyzed Triazine-Based Nanoporous Frameworks Enable Electrochemical CO2 Reduction in Water

The first study of rational synthesis of triazine-based nanoporous frameworks as electrocatalysts for CO₂ reduction reaction (CO₂RR) was presented. The resulting optimized framework with rich pyridinic nitrogen-containing sites can selectively reduce CO₂ to CO in water with a high Faradic efficiency of ca. 82% under a moderate overpotential of 560 mV. The key of our success lies in the use of pyridine-based backbones as sacrificial groups inside the triazine framework for in situ generation of CO₂RR-active pyridinic N-doped sites during the high-temperature ZnCl₂-promoted polymerization process. We anticipate that this study may facilitate new possibilities for the development of porous organic polymers for electrochemical conversion of CO₂.

Polyanthraquinone-Triazine-A Promising Anode Material for High-Energy Lithium-Ion Batteries

A novel covalent organic framework polymer material that bears conjugated anthraquinone and triazine units in its skeleton has been prepared via a facile one-pot condensation reaction and employed as an anode material for Li-ion batteries. The conjugated units consist of C═N groups, C═O groups, and benzene groups, which enable a 17-electron redox reaction with Li per repeating unit and bring a theoretical specific capacity of 1450 mA h g^-1. The polymer also shows a large specific surface area and a hierarchically porous structure to trigger interfacial Li storage and contribute to an additional capacity. The highly conductive conjugated polymer skeleton enables fast electron transport to facilitate the Li storage. In this way, the polymer electrode shows a large specific capacity and favorable cycling and rate performance, making it an appealing anode choice for the next-generation high-energy batteries.

Nitrogen and Phosphorus Codoped Porous Carbon Framework as Anode Material for High Rate Lithium-Ion Batteries

Slow kinetics and low specific capacity of graphite anode significantly limit its applications in the rapidly developing lithium-ion battery (LIB) markets. Herein, we report a carbon framework anode with ultrafast rate and cycling stability for LIBs by nitrogen and phosphorus doping. The electrode structure is constructed of a 3D framework built from 2D heteroatom-doped graphene layers via pyrolysis of self-assembled supramolecular aggregates. The synergistic effect from the nanostructured 3D framework and chemical doping (i.e., N- and P-doping) enables fast kinetics in charge storage and transport. A high reversible capacity of 946 mAh g^-1 is delivered at a current rate of 0.5 A g^-1, and excellent rate capability (e.g., a capacity of 595 mAh g^-1 at 10 A g^-1) of the electrode is shown. Moreover, a moderate surface area from the 3D porous structure contributes to a relatively high initial Coulombic efficiency of 74%, compared to other graphene-based anode materials. The electrode also demonstrates excellent cycling stability at a current rate of 2 A g^-1 for 2000 cycles. The synthetic strategy proposed here is highly efficient and green, which can provide guidance for large-scale controllable fabrication of carbon-based anode materials.

A stepwise crosslinking strategy toward lamellar carbon frameworks with covalently connected alternate layers of porous carbon nanosheets and porous carbon spacers

Lamellar carbon frameworks with covalently connected alternate layers of porous carbon nanosheets (PCNs) and porous carbon spacers (PCSs) were successfully fabricated based on the stepwise crosslinking of self-assembled lamellar block copolymers. The intrinsic porous structure of PCSs can maximize the utilization of well-developed surfaces/interfaces of the PCNs.

In Situ Polymerization of Dopamine on Graphene Framework for Charge Storage Applications

Polydopamine, a functional coating material, is redox active as cathode materials for both Li- and Na-ion batteries or hybrid capacitors. Here, a polydopamine coating onto 3D graphene framework is introduced through a simple hydrothermal process, during which graphene oxide serves not only as an oxidant for assisting the polymerization of dopamine, but also as a template for the conformal growth of polydopamine. High-density films are fabricated by compressing the polydopamine-coated graphene aerogels, which can be directly used as free-standing and flexible cathodes in both Li- and Na-cells. The compact electrodes deliver high capacities of ≈230 mAh g^-1 in Li-cells and ≈211 mAh g^-1 in Na-cells based on the total mass of electrodes. These compact electrodes also exhibit exceptional cycling stability and high rate performance due to the unique structure in which polydopamine is uniformly coated on the 3D structured graphene.

A facile and processable integration strategy towards Schiff-base polymer-derived carbonaceous materials with high lithium storage performance

Herein, a novel in situ concentrated-solution-induced polymerization strategy is developed towards the integration of Schiff-base networks into graphene foam with processable and moldable characteristics. This bottom-up design process endows the resultant composites with a high nitrogen content (9.6 at%) and abundant porosity and accordingly demonstrates high lithium storage properties.

Rational Design of Porous Covalent Triazine-Based Framework Composites as Advanced Organic Lithium-Ion Battery Cathodes

In an effort to explore the use of organic high-performance lithium ion battery cathodes as an alternative to resolve the current bottleneck hampering the development of their inorganic counterparts, a rational strategy focusing on the optimal composition of covalent triazine-based frameworks (CTFs) with carbon-based materials of varied dimensionalities is delineated. Two-dimensional reduced graphene oxide (rGO) with a compatible structural conformation with the layered CTF is the most suitable scaffold for the tailored mesopores in the polymeric framework, providing outstanding energy storage ability. Through facile ionothermal synthesis and structure engineering, the obtained CTF-rGO composite possesses a high specific surface area of 1357.27 m²/g, and when used as a lithium ion battery cathode it delivers a large capacity of 235 mAh/g in 80 cycles at 0.1 A/g along with a stable capacity of 127 mAh/g over 2500 cycles at 5 A/g. The composite with modified pore structure shows drastically improved performance compared to a pristine CTF, especially at large discharge currents. The CTF-rGO composite with excellent capacity, stability, and rate performance shows great promise as an emerging high-performance cathode that could revolutionize the conventional lithium-ion battery industry.

High Capacitive Storage Performance of Sulfur and Nitrogen Codoped Mesoporous Graphene

Mesoporous graphene is synthesized based on the chemical vapor deposition methodology by using heavy MgO flakes as substrates in a fluidized-bed reactor. Subsequently, sulfur and nitrogen coincorporation into graphene frameworks is realized by the reaction between carbon atoms and thiourea molecules. The as-obtained sulfur and nitrogen codoped mesoporous graphene (SNMG) exhibits remarkable capacitive energy-storage behavior, as a result of well-developed pore channels, in terms of that in a symmetric supercapacitor and lithium-ion hybrid capacitor (LIHC). The ultrahigh durability of the SNMG/SNMG symmetric supercapacitor is demonstrated by long-term cycling, for which no capacitance decay is found after 20 000 cycles. A LIHC constructed from commercial Li₄ Ti₅ O₁₂ (LTO) as the anode and SNMG as the cathode is capable of delivering much enhanced lithium-storage ability and better rate capability than that of activated carbon (AC)/LTO LIHC. Moreover, SNMG/LTO LIHC exhibits maximum energy and power densities of 86.2 Wh kg^-1 and 7443 W kg^-1 and maintains 87 % capacitance retention after 2000 cycles.

Fast tuning of covalent triazine frameworks for photocatalytic hydrogen evolution

A fast and facile route for the optimization of covalent triazine frameworks (CTFs) for photocatalytic hydrogen production is presented. Within 10 minutes a CTF with low photocatalytic activity can be converted into a highly active photocatalyst. Optimized CTF catalysts show an average hydrogen evolution rate of 1072 μmol h^-1 g^-1 under visible light (>420 nm).