Extensive research suggests a bright future for the graphene market. However, for a long time there has been a huge gap between laboratory-scale research and commercial application due to the challenging task of reproducible bulk production of high-quality graphene at low cost. Electrochemical exfoliation of graphite has emerged as a promising wet chemical method with advantages such as upscalability, solution processability and eco-friendliness. Recent progress in the electrochemical exfoliation of graphite and prospects for the application of exfoliated graphene, mainly in the fields of composites, electronics, energy storage and conversion are discussed.

Microporous membranes act as selective barriers and play an important role in industrial gas separation and water purification. The permeability of such membranes is inversely proportional to their thickness. Synthetic two-dimensional materials (2DMs), with a thickness of one to a few atoms or monomer units are ideal candidates for developing separation membranes. Here, groundbreaking advances in the design, synthesis, processing, and application of 2DMs for gas and ion separations, as well as water desalination are presented. This report describes the syntheses, structures, and mechanical properties of 2DMs. The established methods for processing 2DMs into selective permeation membranes are also discussed and the separation mechanism and their performances addressed. Current challenges and emerging research directions, which need to be addressed for developing next-generation separation membranes, are summarized.

Two-dimensional (2D) transition-metal dichalcogenides (TMDs) have drawn much attention due to their unique physical and chemical properties. Using TMDs as templates for the generation of 2D sandwich-like materials with remarkable properties still remains a great challenge due to their poor solvent processability. Herein, MoS₂-coupled sandwich-like conjugated microporous polymers (M-CMPs) with high specific surface area were successfully developed by using functionalized MoS₂ nanosheets as template. As-prepared M-CMPs were further used as precursors for preparation of MoS₂-embedded nitrogen-doped porous carbon nanosheets, which were revealed as novel electrocatalysts for oxygen reduction reaction with mainly four-electron transfer mechanism and ultralow half-wave potential in comparison with commercial Pt/C catalyst. Our strategy to core–shelled sandwich-like hybrids paves a way for a new class of 2D hybrids for energy conversion and storage.

Two-dimensional (2D) transition-metal dichalcogenides (TMDs) have drawn much attention due to their unique physical and chemical properties. Using TMDs as templates for the generation of 2D sandwich-like materials with remarkable properties still remains a great challenge due to their poor solvent processability. Herein, MoS₂-coupled sandwich-like conjugated microporous polymers (M-CMPs) with high specific surface area were successfully developed by using functionalized MoS₂ nanosheets as template. As-prepared M-CMPs were further used as precursors for preparation of MoS₂-embedded nitrogen-doped porous carbon nanosheets, which were revealed as novel electrocatalysts for oxygen reduction reaction with mainly four-electron transfer mechanism and ultralow half-wave potential in comparison with commercial Pt/C catalyst. Our strategy to core–shelled sandwich-like hybrids paves a way for a new class of 2D hybrids for energy conversion and storage.

To achieve sustainable production of H₂ fuel through water splitting, low-cost electrocatalysts for the hydrogen-evolution reaction (HER) and the oxygen-evolution reaction (OER) are required to replace Pt and IrO₂ catalysts. Herein, for the first time, we present the interface engineering of novel MoS₂/Ni₃S₂ heterostructures, in which abundant interfaces are formed. For OER, such MoS₂/Ni₃S₂ heterostructures show an extremely low overpotential of ca. 218 mV at 10 mA cm⁻², which is superior to that of the state-of-the-art OER electrocatalysts. Using MoS₂/Ni₃S₂ heterostructures as bifunctional electrocatalysts, an alkali electrolyzer delivers a current density of 10 mA cm⁻² at a very low cell voltage of ca. 1.56 V. In combination with DFT calculations, this study demonstrates that the constructed interfaces synergistically favor the chemisorption of hydrogen and oxygen-containing intermediates, thus accelerating the overall electrochemical water splitting.

To achieve sustainable production of H₂ fuel through water splitting, low-cost electrocatalysts for the hydrogen-evolution reaction (HER) and the oxygen-evolution reaction (OER) are required to replace Pt and IrO₂ catalysts. Herein, for the first time, we present the interface engineering of novel MoS₂/Ni₃S₂ heterostructures, in which abundant interfaces are formed. For OER, such MoS₂/Ni₃S₂ heterostructures show an extremely low overpotential of ca. 218 mV at 10 mA cm⁻², which is superior to that of the state-of-the-art OER electrocatalysts. Using MoS₂/Ni₃S₂ heterostructures as bifunctional electrocatalysts, an alkali electrolyzer delivers a current density of 10 mA cm⁻² at a very low cell voltage of ca. 1.56 V. In combination with DFT calculations, this study demonstrates that the constructed interfaces synergistically favor the chemisorption of hydrogen and oxygen-containing intermediates, thus accelerating the overall electrochemical water splitting.

A novel tetrabenzo[a,f,j,o]perylene, namely “bistetracene” in which two tetracenes are connected side by side with two bonds, was synthesized and characterized. An optical energy gap of about 1.56 eV is derived from the UV/Vis absorption spectrum, showing the low optical gap feature of such zigzag-edged polycyclic aromatic hydrocarbons (PAHs). Theoretical calculations and physical property investigations manifest that such a PAH possesses a prominent biradical character in the ground state, which is the first example among bistetracene derivatives. However, the bistetracene can easily undergo oxidation to tetrabenzo[a,f,j,o]perylene-9,19-dione (diketone) under ambient conditions. Thereby, such zigzag-edged PAH provides insight into understanding the edge state of other expanded homologues, such as peri-tetracenes or peri-pentacenes.

Limited strategies have been established to prepare monodisperse mesoporous carbon nanospheres (MCNs) with tailored pore sizes. In this work, a method is reported to synthesize MCNs by combining polymerization of aniline with co-assembly of colloidal silica nanoparticles. The controlled self-assembly behavior of colloidal silica enables the formation of uniform composite nanospheres and convenient modulation over mesopores. After carbonization and removal of sacrificial templates, the resultant MCNs possess tunable mesopores (7–42 nm) and spherical diameters (90–300 nm), as well as high surface area (785–1117 m² g⁻¹), large pore volume (1.46–2.01 cm³ g⁻¹) and abundant nitrogen moieties (5.54–8.73 at %). When serving as metal-free electrocatalysts for the oxygen reduction reaction (ORR), MCNs with an optimum pore size of 22 nm, compared to those with 7 and 42 nm, exhibit the best ORR performance in alkaline medium.

The chemical nature of the edge periphery essentially determines the physical properties of graphene. As a molecular-level model system, large polycyclic aromatic hydrocarbons, that is, so-called nanographenes, can be chemically modified through either edge functionalization or doping with heteroatoms. Although the synthetic methods for edge substitution are well-developed, incorporation with heteroatoms by the bay annulation of large PAHs remains an enormous challenge. In this study, we present a feasible peripheral sulfur annulation of hexa-peri-hexabenzocoronene (HBC) by thiolation of perchlorinated HBC. The tri-sulfur-annulated HBC and di-sulfur-annulated HBC decorated with phenylthio groups were obtained and characterized by X-ray diffraction, revealing their distinct sulfur-annulated peripheral structure. Associated with theoretical calculations, we propose that the regioselective sulfur annulation results from the minimization of strain in the aromatic backbone. We further demonstrate the structure-correlated property modulation by sulfur annulation, manifested by a decrease in band gap and tunable redox activity.

The rational construction of covalent or noncovalent organic two-dimensional nanosheets is a fascinating target because of their promising applications in electronics, membrane technology, catalysis, sensing, and energy technologies. Herein, a large-area (square millimeters) and free-standing 2D supramolecular polymer (2DSP) single-layer sheet (0.7–0.9 nm in thickness), comprising triphenylene-fused nickel bis(dithiolene) complexes has been readily prepared by using the Langmuir–Blodgett method. Such 2DSPs exhibit excellent electrocatalytic activities for hydrogen generation from water with a Tafel slope of 80.5 mV decade⁻¹ and an overpotential of 333 mV at 10 mA cm⁻², which are superior to that of recently reported carbon nanotube supported molecular catalysts and heteroatom-doped graphene catalysts. This work is promising for the development of novel free-standing organic 2D materials for energy technologies.

The chemical nature of the edge periphery essentially determines the physical properties of graphene. As a molecular-level model system, large polycyclic aromatic hydrocarbons, that is, so-called nanographenes, can be chemically modified through either edge functionalization or doping with heteroatoms. Although the synthetic methods for edge substitution are well-developed, incorporation with heteroatoms by the bay annulation of large PAHs remains an enormous challenge. In this study, we present a feasible peripheral sulfur annulation of hexa-peri-hexabenzocoronene (HBC) by thiolation of perchlorinated HBC. The tri-sulfur-annulated HBC and di-sulfur-annulated HBC decorated with phenylthio groups were obtained and characterized by X-ray diffraction, revealing their distinct sulfur-annulated peripheral structure. Associated with theoretical calculations, we propose that the regioselective sulfur annulation results from the minimization of strain in the aromatic backbone. We further demonstrate the structure-correlated property modulation by sulfur annulation, manifested by a decrease in band gap and tunable redox activity.

A novel tetrabenzo[a,f,j,o]perylene, namely “bistetracene” in which two tetracenes are connected side by side with two bonds, was synthesized and characterized. An optical energy gap of about 1.56 eV is derived from the UV/Vis absorption spectrum, showing the low optical gap feature of such zigzag-edged polycyclic aromatic hydrocarbons (PAHs). Theoretical calculations and physical property investigations manifest that such a PAH possesses a prominent biradical character in the ground state, which is the first example among bistetracene derivatives. However, the bistetracene can easily undergo oxidation to tetrabenzo[a,f,j,o]perylene-9,19-dione (diketone) under ambient conditions. Thereby, such zigzag-edged PAH provides insight into understanding the edge state of other expanded homologues, such as peri-tetracenes or peri-pentacenes.

Limited strategies have been established to prepare monodisperse mesoporous carbon nanospheres (MCNs) with tailored pore sizes. In this work, a method is reported to synthesize MCNs by combining polymerization of aniline with co-assembly of colloidal silica nanoparticles. The controlled self-assembly behavior of colloidal silica enables the formation of uniform composite nanospheres and convenient modulation over mesopores. After carbonization and removal of sacrificial templates, the resultant MCNs possess tunable mesopores (7–42 nm) and spherical diameters (90–300 nm), as well as high surface area (785–1117 m² g⁻¹), large pore volume (1.46–2.01 cm³ g⁻¹) and abundant nitrogen moieties (5.54–8.73 at %). When serving as metal-free electrocatalysts for the oxygen reduction reaction (ORR), MCNs with an optimum pore size of 22 nm, compared to those with 7 and 42 nm, exhibit the best ORR performance in alkaline medium.

Graphene nanoribbons (GNRs) with an unprecedented “necklace-like” structure were synthesized through a bottom-up chemical approach, based on the oxidative cyclodehydrogenation of tailor-made polyphenylene precursors. A polycyclic aromatic hydrocarbon consisting of 84 sp² carbons (C84) was also synthesized and characterized as a model compound. Characterizations by a combination of MALDI-TOF MS and FTIR, Raman, and UV/Vis absorption spectroscopy validated the formation of the necklace-like GNRs. The absorption spectrum and DFT calculations revealed a bandgap of approximately 1.4 eV for this novel GNR system, which has not been attained with other GNR structures, enabling further fine-tuning of GNR bandgaps by structural modulation.

The rational construction of covalent or noncovalent organic two-dimensional nanosheets is a fascinating target because of their promising applications in electronics, membrane technology, catalysis, sensing, and energy technologies. Herein, a large-area (square millimeters) and free-standing 2D supramolecular polymer (2DSP) single-layer sheet (0.7–0.9 nm in thickness), comprising triphenylene-fused nickel bis(dithiolene) complexes has been readily prepared by using the Langmuir–Blodgett method. Such 2DSPs exhibit excellent electrocatalytic activities for hydrogen generation from water with a Tafel slope of 80.5 mV decade⁻¹ and an overpotential of 333 mV at 10 mA cm⁻², which are superior to that of recently reported carbon nanotube supported molecular catalysts and heteroatom-doped graphene catalysts. This work is promising for the development of novel free-standing organic 2D materials for energy technologies.