The development of pseudocapacitive materials for energy‐oriented applications has stimulated considerable interest in recent years due to their high energy‐storing capacity with high power outputs. Nevertheless, the utilization of nanosized active materials in batteries leads to fast redox kinetics due to the improved surface area and short diffusion pathways, which shifts their electrochemical signatures from battery‐like to the pseudocapacitive‐like behavior. As a result, it becomes challenging to distinguish “pseudocapacitive” and “battery” materials. Such misconceptions have further impacted on the final device configurations. This Review is an earnest effort to clarify the confusion between the battery and pseudocapacitive materials by providing their true meanings and correct performance metrics. A method to distinguish battery‐type and pseudocapacitive materials using the electrochemical signatures and quantitative kinetics analysis is outlined. Taking solid‐state supercapacitors (SSCs, only polymer gel electrolytes) as an example, the distinction between asymmetric and hybrid supercapacitors is discussed. The state‐of‐the‐art progress in the engineering of active materials is summarized, which will guide for the development of real‐pseudocapacitive energy storage systems.

Superhydrophobic/superoleophilic composites HFGO@ZIF-8 have been prepared from highly fluorinated graphene oxide (HFGO) and the nanocrystalline zeolite imidazole framework ZIF-8. The structure-directing and coordination-modulating properties of HFGO allow for the selective nucleation of ZIF-8 nanoparticles at the graphene surface oxygen functionalities. This results in localized nucleation and size-controlled ZIF-8 nanocrystals intercalated in between HFGO layers. The composite microstructure features fluoride groups bonded at the graphene. Self-assembly of a unique micro-mesoporous architecture is achieved, where the micropores originate from ZIF-8 nanocrystals, while the functionalized mesopores arise from randomly organized HFGO layers separated by ZIF-8 nanopillars. The hybrid material displays an exceptional high water contact angle of 162° and low oil contact angle of 0° and thus reveals very high sorption selectivity, fast kinetics, and good absorbencies for nonpolar/polar organic solvents and oils from water. Accordingly, Sponge@HFGO@ZIF-8 composites are successfully utilized for oil-water separation.

Here we have used Raman spectroscopy to investigate molecular level changes in the zeolitic imidazolate framework ZIF-8 (a prototypical zeolite-like porous metal organic framework) as a function of temperature. Temperature dependent Raman spectra suggest that at low temperature the softening of the C-H stretching frequencies is due to the decrease in steric hindrance between the methyl groups of methyl imidazole. The larger separation between the methyl groups opens the window for increased nitrogen and methane uptake at temperatures below 153 K. The appearance of Raman bands at 2323 cm(-1) and 2904 cm(-1) at or below 153 K in ZIF-8 are characteristic signatures of the adsorbed nitrogen and methane gases respectively. Nanoscale ZIF-8 uptakes more molecules than bulk ZIF-8, and as a result we could provide evidence for encaged CO2 at 203 K yielding its Raman mode at 1379 cm(-1).

Hybrid nanocomposites of graphene oxide (GO) with ZIF-8 exhibit tunable nanoscale morphology and porosity, both determined by the GO content, coordination modulation being responsible for such properties. These materials also give rise to high CO2 storage capability and can be used as precursors to prepare GO@ZnS nanocomposites.

The design of advanced high-energy-density supercapacitors requires the design of unique materials that combine hierarchical nanoporous structures with high surface area to facilitate ion transport and excellent electrolyte permeability. Here, shape-controlled 2D nanoporous carbon sheets (NPSs) with graphitic wall structure through the pyrolysis of metal-organic frameworks (MOFs) are developed. As a proof-of-concept application, the obtained NPSs are used as the electrode material for a supercapacitor. The carbon-sheet-based symmetric cell shows an ultrahigh Brunauer-Emmett-Teller (BET)-area-normalized capacitance of 21.4 µF cm (233 F g ), exceeding other carbon-based supercapacitors. The addition of potassium iodide as redox-active species in a sulfuric acid (supporting electrolyte) leads to the ground-breaking enhancement in the energy density up to 90 Wh kg , which is higher than commercial aqueous rechargeable batteries, maintaining its superior power density. Thus, the new material provides a double profits strategy such as battery-level energy and capacitor-level power density.

In this work, the covalent attachment of an amine functionalized metal‐organic framework (UiO‐66‐NH2 = Zr6O4(OH)4(bdc‐NH2)6; bdc‐NH2 = 2‐amino‐1,4‐benzenedicarboxylate) (UiO‐Universitetet i Oslo) to the basal‐plane of carboxylate functionalized graphene (graphene acid = GA) via amide bonds is reported. The resultant GA@UiO‐66‐NH2 hybrid displayed a large specific surface area, hierarchical pores and an interconnected conductive network. The electrochemical characterizations demonstrated that the hybrid GA@UiO‐66‐NH2 acts as an effective charge storing material with a capacitance of up to 651 F g−1, significantly higher than traditional graphene‐based materials. The results suggest that the amide linkage plays a key role in the formation of a π‐conjugated structure, which facilitates charge transfer and consequently offers good capacitance and cycling stability. Furthermore, to realize the practical feasibility, an asymmetric supercapacitor using a GA@UiO‐66‐NH2 positive electrode with Ti3C2TX MXene as the opposing electrode has been constructed. The cell is able to deliver a power density of up to 16 kW kg−1 and an energy density of up to 73 Wh kg−1, which are comparable to several commercial devices such as Pb‐acid and Ni/MH batteries. Under an intermediate level of loading, the device retained 88% of its initial capacitance after 10 000 cycles.

A novel molecular design concept to control the emission of a metal-organic framework, {Mg(DHT)(DMF)(2)}(n), (DHT: 2,5-dihydroxyterephthalate), based on excited state proton transfer (ESIPT) of the organic linker, DHT, is demonstrated. The framework unveils permanent porosity and exhibits ligand-based multicolor emission that can be tuned and well controlled by the solvent molecules in solution as well as in the solid state.

formed from organic ligands and metal cations. [1][2][3][4][5][6][7][8][9][10] They are typically synthesized under mild conditions via coordinationdirected self-assembly processes and are also known as metal-organic coordination networks and porous coordination polymers. [11][12][13][14] Due to their high surface areas, large porosity, tunable pore sizes, and functionalities, MOFs have prospective applications in fields such as gas storage/separation, sensing or recognition, proton conduction, and magnetism. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] However, the advantageous unique structural features of even some of the best-performing MOFs are readily degraded because of their high moisture sensitivity, which may limit their practical applications. [29][30][31][32] Consequently, there is an ongoing search for highly hydrophobic, porous, sorbent materials to be employed in various large-scale applications in industry such as oil spill cleanup, hydrocarbon storage/separation, or water purification. [33][34][35][36][37] Many academics, industrial scientists, and engineers have therefore conducted research on the fabrication of superhydrophobic surfaces, which involves hydrophobic surface modification and creating surface roughness on the micrometer-or nanoscale. Hydrophobic surfaces are defined as substrates with an apparent contact angle greater than 90° with respect to water. On superhydrophobic materials, water droplets have contact angles above 150° and show very low adhesion because the drops partially rest on an air cushion. The surface energy and roughness govern the wettability of hydrophobic surfaces. In general, lower surface energies and higher roughness are associated with larger contact angles, lower contact angle hysteresis, and robust superhydrophobicity. Because of their ultralow surface energies (10-20 mN m −1 ), alkyl-based or fluorinated compounds are commonly used as hydrophobic modifiers to prepare surfaces with high intrinsic contact angles (>90°). [33][34][35][36][37][38][39][40][41][42] Recently, few methods have been developed for synthesizing hydrophobic MOFs including both pristine and composite systems. This review offers a comprehensive overview of the state of the art in hydrophobic MOF synthesis and the field's challenges and opportunities. Various synthetic strategies for preparing hydrophobic MOFs and their composites are introduced. We discuss the basics of wetting and critical challenges in the characterization of these hydrophobic materials. The potential applications of hydrophobic MOFs and related Metal-organic frameworks (MOFs) have diverse potential applications in catalysis, gas storage, separation, and drug delivery because of their nanoscale periodicity, permanent porosity, channel functionalization, and structural diversity. Despite these promising properties, the inherent structural features of even some of the best-performing MOFs make them moisture-sensitive and unstable in aqueous media, limiting their practical usefulness. This problem could be ...