Edge functionalization by selectively attaching chemical moieties at the edge of graphene sheets with minimal damage of the carbon basal plane can impart solubility, film-forming capability, and electrocatalytic activity, while largely retaining the physicochemical properties of the pristine graphene. The resultant edge-functionalized graphene materials (EFGs) are attractive for various potential applications. Here, a focused, concise review on the synthesis of EFGs is presented, along with their 2D covalent organic polymer (2D COP) analogues, as energy materials. The versatility of edge-functionalization is revealed for producing tailor-made graphene and COP materials for efficient energy conversion and storage.

Polymers are important precursors for the fabrication of carbon materials. Herein, halogenated polymers are explored as precursors for the synthesis of high-quality carbon materials via alkaline dehalogenation. It is found that the halogen elements (F, Cl) connecting to vinylidene units are highly reactive so that dehalogenation can take place a few seconds at room temperature by simple hand grinding in the presence of strong inorganic alkaline. Furthermore, the halogen element-leaving sites are shown to be susceptible to heteroatom doping (e.g., N doping) to become stable capacitive sites for charge storage (e.g., ions). By using a mixture of NaOEt and KOH as dehalogenation reagents, abundant hierarchical pores (macro/meso/micropores) in the resultant doped carbon matrix for fast mass transportation can be created. Very high capacitance (328 F g⁻¹ at 0.5 A g⁻¹) and rate capability (75.3% retention at 50 A g⁻¹ and 62.5% retention at 100 A g⁻¹) are observed for the newly developed halogenated polymer-derived doped carbon materials.

The high cost and scarcity of noble metal catalysts, such as Pt, have hindered the hydrogen production from electrochemical water splitting, the oxygen reduction in fuel cells and batteries. Herein, we developed a simple template-free approach to three-dimensional porous carbon networks codoped with nitrogen and phosphorus by pyrolysis of a supermolecular aggregate of self-assembled melamine, phytic acid, and graphene oxide (MPSA/GO). The pyrolyzed MPSA/GO acted as the first metal-free bifunctional catalyst with high activities for both oxygen reduction and hydrogen evolution. Zn–air batteries with the pyrolyzed MPSA/GO air electrode showed a high peak power density (310 W g⁻¹) and an excellent durability. Thus, the pyrolyzed MPSA/GO is a promising bifunctional catalyst for renewable energy technologies, particularly regenerative fuel cells.

The high cost and scarcity of noble metal catalysts, such as Pt, have hindered the hydrogen production from electrochemical water splitting, the oxygen reduction in fuel cells and batteries. Herein, we developed a simple template-free approach to three-dimensional porous carbon networks codoped with nitrogen and phosphorus by pyrolysis of a supermolecular aggregate of self-assembled melamine, phytic acid, and graphene oxide (MPSA/GO). The pyrolyzed MPSA/GO acted as the first metal-free bifunctional catalyst with high activities for both oxygen reduction and hydrogen evolution. Zn–air batteries with the pyrolyzed MPSA/GO air electrode showed a high peak power density (310 W g⁻¹) and an excellent durability. Thus, the pyrolyzed MPSA/GO is a promising bifunctional catalyst for renewable energy technologies, particularly regenerative fuel cells.

Edge-selectively fluorinated graphene nanoplatelets (FGnPs) are prepared by mechanochemically driven reaction between fluorine gas (20 vol% in argon) and activated carbon species from graphitic C–C bonds unzipped by high-speed stainless steel balls with a high kinetic energy. The fluorination at edges of the unzipped graphene nanoplatelets (GnPs) is confirmed by various analytical techniques while the content of fluorine in FGnPs is determined to be 3.0 and 3.4 at% by X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy, respectively. Because of the large difference in electronegativity between carbon (χ = 2.55) and fluorine (χ = 3.98) and the strong C–F bond, the edge-fluorination of GnPs can provide the maximized charge polarization with an enhanced chemical stability. Thus, electrodes based on the resultant FGnPs demonstrate superb electrochemical performance with excellent stability/cycle life in dye-sensitized solar cells (FF: 71.5%; J_sc: 14.44 mA cm⁻²; V_oc: 970 mV; PCE: 10.01%) and lithium ion batteries (650.3 mA h g⁻¹ at 0.5 C, charge retention of 76.6% after 500 cycles).

It is important to detect reactive oxygen species (ROS) in situ for investigation of various critical biological processes, and this is however very challenging because of the limited sensitivity or/and selectivity of existing methods that are mainly based on sensing ROS released by cells with short lifetimes and low concentrations in a culture medium. Here, a new approach is reported to directly grow living cells on DNA/Mn₃(PO₄)₂-immobilized and vertically aligned carbon nanotube (VACNT) array nanostructure as a smart free-standing hybrid film, of which the DNA/Mn₃(PO₄)₂ and VACNT provide high electroactivity and excellent electron transport, respectively, while the directly grown cell on the nanostructure offers short diffusion distance to reaction sites, thus constructing a highly sensitive in situ method for detection of cancer-cell-released ROS under drug stimulations. Compared to the measured ROS released by cells in a culture medium, the detection sensitivity with this constructed hybrid film increases by more than six times, which implies that ROS molecules (superoxide anions) secreted from living cells are immediately captured by this smart structure without diffusion process or with extremely short diffusion distance. This design considerably reduces the time from release to detection of the target molecules, minimizing the potential molecular decay due to the short lifetime or high reactivity.

Heteroatom-doped carbon materials have been extensively investigated as metal-free electrocatalysts to replace commercial Pt/C catalysts in oxygen reduction reactions in fuel cells and Li–air batteries. However, the synthesis of such materials usually involves high temperature or complicated equipment. Graphene-based sulfur composites have been recently developed to prolong the cycling life of Li–S batteries, one of the most attractive energy-storage devices. Given the high cost of graphene, there is significant demand to recycle and reuse graphene from Li–S batteries. Herein, we report a green and cost-effective method to prepare sulfur-doped graphene, achieved by the continuous charge/discharge cycling of graphene–sulfur composites in Li–S batteries. This material was used as a metal-free electrocatalyst for the oxygen reduction reaction and shows better electrocatalytic activity than pristine graphene and better methanol tolerance durability than Pt/C.

A general approach toward extremely stretchable and highly conductive electrodes was developed. The method involves wrapping a continuous carbon nanotube (CNT) thin film around pre-stretched elastic wires, from which high-performance, stretchable wire-shaped supercapacitors were fabricated. The supercapacitors were made by twisting two such CNT-wrapped elastic wires, pre-coated with poly(vinyl alcohol)/H₃PO₄ hydrogel, as the electrolyte and separator. The resultant wire-shaped supercapacitors exhibited an extremely high elasticity of up to 350 % strain with a high device capacitance up to 30.7 F g⁻¹, which is two times that of the state-of-the-art stretchable supercapacitor under only 100 % strain. The wire-shaped structure facilitated the integration of multiple supercapacitors into a single wire device to meet specific energy and power needs for various potential applications. These supercapacitors can be repeatedly stretched from 0 to 200 % strain for hundreds of cycles with no change in performance, thus outperforming all the reported state-of-the-art stretchable electronics.

Using a copper wire as the substrate for the CVD growth of a hollow multilayer graphene tube, we prepared a macroscopic porous graphene fiber by removing the copper in an aqueous mixture solution of iron chloride (FeCl₃, 1 M) and hydrochloric acid (HCl, 3 M) and continuously drawing the newly released graphene tube out of the liquid. The length of the macroscopic graphene fiber thus produced is determined mainly by the length of the copper wire used. The resultant macroscopic graphene fiber with the integrated graphene structure exhibited a high electrical conductivity (127.3 S cm⁻¹) and good flexibility over thousands bending cycles, showing great promise as flexible electrodes for wearable optoelectronics and energy devices—exemplified by its use as a flexible conductive wire for lighting a LED and a cathode in a fiber-shaped dye-sensitized solar cell (DSSC) with one of the highest energy conversion efficiencies (3.25 %) among fiber-shaped DSSCs.

A general approach toward extremely stretchable and highly conductive electrodes was developed. The method involves wrapping a continuous carbon nanotube (CNT) thin film around pre-stretched elastic wires, from which high-performance, stretchable wire-shaped supercapacitors were fabricated. The supercapacitors were made by twisting two such CNT-wrapped elastic wires, pre-coated with poly(vinyl alcohol)/H₃PO₄ hydrogel, as the electrolyte and separator. The resultant wire-shaped supercapacitors exhibited an extremely high elasticity of up to 350 % strain with a high device capacitance up to 30.7 F g⁻¹, which is two times that of the state-of-the-art stretchable supercapacitor under only 100 % strain. The wire-shaped structure facilitated the integration of multiple supercapacitors into a single wire device to meet specific energy and power needs for various potential applications. These supercapacitors can be repeatedly stretched from 0 to 200 % strain for hundreds of cycles with no change in performance, thus outperforming all the reported state-of-the-art stretchable electronics.

Heteroatom-doped carbon materials have been extensively investigated as metal-free electrocatalysts to replace commercial Pt/C catalysts in oxygen reduction reactions in fuel cells and Li–air batteries. However, the synthesis of such materials usually involves high temperature or complicated equipment. Graphene-based sulfur composites have been recently developed to prolong the cycling life of Li–S batteries, one of the most attractive energy-storage devices. Given the high cost of graphene, there is significant demand to recycle and reuse graphene from Li–S batteries. Herein, we report a green and cost-effective method to prepare sulfur-doped graphene, achieved by the continuous charge/discharge cycling of graphene–sulfur composites in Li–S batteries. This material was used as a metal-free electrocatalyst for the oxygen reduction reaction and shows better electrocatalytic activity than pristine graphene and better methanol tolerance durability than Pt/C.

Using a copper wire as the substrate for the CVD growth of a hollow multilayer graphene tube, we prepared a macroscopic porous graphene fiber by removing the copper in an aqueous mixture solution of iron chloride (FeCl₃, 1 M) and hydrochloric acid (HCl, 3 M) and continuously drawing the newly released graphene tube out of the liquid. The length of the macroscopic graphene fiber thus produced is determined mainly by the length of the copper wire used. The resultant macroscopic graphene fiber with the integrated graphene structure exhibited a high electrical conductivity (127.3 S cm⁻¹) and good flexibility over thousands bending cycles, showing great promise as flexible electrodes for wearable optoelectronics and energy devices—exemplified by its use as a flexible conductive wire for lighting a LED and a cathode in a fiber-shaped dye-sensitized solar cell (DSSC) with one of the highest energy conversion efficiencies (3.25 %) among fiber-shaped DSSCs.

Carbon-based metal-free electrocatalysts for the oxygen reduction reaction (ORR) in alkaline medium have been extensively investigated with the aim of replacing the commercially available, but precious platinum-based catalysts. For the proper design of carbon-based metal-free electrocatalysts for the ORR, it would be interesting to identify the active sites of the electrocatalyst. The ORR was now studied with an air-saturated electrolyte solution droplet (diameter ca. 15 μm), which was deposited at a specified position either on the edge or on the basal plane of highly oriented pyrolytic graphite. Electrochemical measurements suggest that the edge carbon atoms are more active than the basal-plane ones for the ORR. This provides a direct way to identify the active sites of carbon materials for the ORR. Ball-milled graphite and carbon nanotubes with more exposed edges were also prepared and showed significantly enhanced ORR activity. DFT calculations elucidated the mechanism by which the charged edge carbon atoms result in the higher ORR activity.

Terpyridine-functionalized graphene oxides were prepared for self-assembly into 3D architectures with various metal ions (e.g., Fe, Ru). The resulting electrode materials showed significantly improved electroactivities for efficient energy conversion and storage. They showed promise for application in the oxygen reduction reaction (ORR), photocurrent generation, and supercapacitance.

Carbon-based metal-free electrocatalysts for the oxygen reduction reaction (ORR) in alkaline medium have been extensively investigated with the aim of replacing the commercially available, but precious platinum-based catalysts. For the proper design of carbon-based metal-free electrocatalysts for the ORR, it would be interesting to identify the active sites of the electrocatalyst. The ORR was now studied with an air-saturated electrolyte solution droplet (diameter ca. 15 μm), which was deposited at a specified position either on the edge or on the basal plane of highly oriented pyrolytic graphite. Electrochemical measurements suggest that the edge carbon atoms are more active than the basal-plane ones for the ORR. This provides a direct way to identify the active sites of carbon materials for the ORR. Ball-milled graphite and carbon nanotubes with more exposed edges were also prepared and showed significantly enhanced ORR activity. DFT calculations elucidated the mechanism by which the charged edge carbon atoms result in the higher ORR activity.

A class of 2D covalent organic polymers (COPs) incorporating a metal (such as Fe, Co, Mn) with precisely controlled locations of nitrogen heteroatoms and holes were synthesized from various N-containing metal–organic complexes (for example, metal–porphyrin complexes) by a nickel-catalyzed Yamamoto reaction. Subsequent carbonization of the metal-incorporated COPs led to the formation of COP-derived graphene analogues, which acted as efficient electrocatalysts for oxygen reduction in both alkaline and acid media with a good stability and free from any methanol-crossover/CO-poisoning effects.

The efficient fluorescence resonance energy transfer (FRET) between amphiphilic dendrimers with oligo(p-phenylenevinylene) core branches and oligo(ethylene oxide) termini have been observed in micelles. All dendrimers show the critical micelle concentration and lower critical solution temperature as well as fluorescent emission. Tailoring electronic structures of the conjugated amphiphiles for FRET have been conveniently achieved by varying the branch number and/or the conjugated core structure. The Stern-Volmer constants (K_SV) for FRET were found to be 4.51 × 10⁻⁵ and 8.78 × 10⁻⁵ M for Den 30–40 and Den 50–40, respectively. The effects external stimuli such as solvent and temperature on FRET have been also investigated. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Two model polymers, containing fluorene as an electron-donating moiety and benzothiadiazole (BT) as an electron-accepting moiety, have been synthesized by Suzuki coupling reaction. Both polymers are composed of the same chemical composition, but the BT acceptor can be either at a side-chain (i.e., S-polymer) or along the polymer main chain (i.e., M-polymer). Their optical, electrochemical, and photovoltaic properties, together with the field-effect transistor (FET) characteristics, have been investigated experimentally and theoretically. The FET carrier mobilities were estimated to be 5.20 × 10⁻⁵ and 3.12 × 10⁻⁴ cm² V⁻¹ s⁻¹ for the S-polymer and M-polymer, respectively. Furthermore, polymeric solar cells (PSCs) with the ITO/PEDOT:PSS/S-polymer or M-polymer:PC₇₁BM(1:4)/Al structure were constructed and demonstrated to show a power conversion efficiency of 0.82 and 1.24% for the S-polymer and M-polymer, respectively. The observed superior device performances for the M-polymer in both FET and PSCs are attributable to its relatively low band-gap and close molecular packing for efficient solar light harvesting and charge transport. This study provides important insights into the design of ideal structure–property relationships for conjugate polymers in FETs and PSCs. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012