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

Templated Synthesis of Exfoliated Porous Carbon with Dominant Graphitic Nitrogen

We present here a new approach for the synthesis of nitrogen-doped porous graphitic carbon (g-NC) with a stoichiometry of C6.3H3.6N1.0O1.2, using layered silicate as a hard sacrificial template. Autogenous exfoliation is achieved due to the heterostacking of 2D silicate and nitrogen-doped carbon layers. Micro- and meso-porosity is induced by melamine and cetyltrimethylammonium (C16TMA). Our density functional calculations and X-ray photoelectron spectroscopy (XPS) observations confirm that the most dominant nitrogen configuration in g-CN is graphitic, while pyridinic and pyrrolic nitrogens are thermodynamically less favored. Our large-scale lattice dynamics calculations show that surface termination with H and OH groups at pores accounts for the observed H and O in the composition of the synthesized g-NC. We further evaluate the electrocatalytic and the supercapacitance activities of g-NC. Interestingly, this material exhibits a specific capacitance of ca. 202 F g-1 at 1 A g-1, retaining 90% of its initial capacitance after 10,000 cycles.

ZIF-8 thin films by a vapor-phase process: limits to growth

Metal-organic frameworks are a class of porous materials that show promising properties in the field of microelectronics. To reach industrial use of these materials, gas phase techniques are often preferred and were recently introduced. However, the thicknesses achieved are not sufficient, limiting further development. In this work, an improved gas phase process allowing ZIF-8 layer formation of several hundreds of nm using cyclic ligand/water exposures is described. Then, by a combination of in-depth surface analyses and molecular dynamics simulations, the presence and role of hydroxyl defects in the ZIF-8 layer to reach this thickness are established. At the same time, this study unveils an inherent limit of the method: thickness growth is consubstantial with defect repairing upon the crystallites ripening; such defect repairing eventually leads to the decrease of the pore window below the diffusion radius of the incoming linker, thus apparently capping the maximum MOF thickness observable for this type of material topology through this growth method.

Organoamine Templated Multifunctional Hybrid Metal Phosphonate Frameworks: Promising Candidates for Tailoring Electrochemical Behaviors and Size-Selective Efficient Heterogeneous Lewis Acid Catalysis

The successful discovery of novel multifunctional metal phosphonate framework materials that incorporate newer organoamines and their utilization as a potential electroactive material for energy storage applications (supercapacitors) and as efficient heterogeneous catalysts are the most enduring challenges at present. From this perspective, herein, four new inorganic-organic hybrid zinc organodiphosphonate materials, namely, [C₅H₁₄N₂]₂[Zn₆(hedp)₄] (I), [C₅H₁₄N₂]_0.5[Zn₃(Hhedp) (hedp)]·2H₂O (II), [C₆H₁₆N₂][Zn₃(hedp)₂] (III), and [C₁₀H₂₄N₄][Zn₆(Hhedp)₂(hedp)₂] (IV) (H₄hedp = 1-hydroxyethane 1,1-diphosphonic acid), have been synthesized through the introduction of different organoamines and then structurally analyzed using various techniques. The compounds (I-IV) possess a three-dimensional network through alternate connectivity of zinc ions and diphosphonate ligands, as confirmed using single-crystal X-ray diffraction. The investigations of electrochemical charge storage behaviors of the present compounds indicate that compound III exhibits a high specific capacitance of 190 F g^-1 (76 C g^-1) at 1 A g^-1, while compound II shows an excellent cycling stability of 90.11% even after 5000 cycles at 5 A g^-1 in the 6 M KOH solution. Further, the present materials have also been utilized as active heterogeneous Lewis acid catalysts in the ketalization reaction. The screening of various substrate scopes during the catalytic process confirms the size-selective heterogeneous catalytic nature of the framework compounds. To our utmost knowledge, such a size-selective heterogeneous Lewis acid catalytic behavior has been observed for the first time in the amine templated inorganic-organic hybrid framework family. Moreover, the excellent size-selective catalytic efficiencies with the d¹⁰ metal system and recyclability performances make the compounds (I-IV) more efficient and promising Lewis acid heterogeneous catalysts.

ZIF-Derived Metal/N-Doped Porous Carbon Nanocomposites: Efficient Catalysts for Organic Transformations

Recently, zeolitic imidazolate framework (ZIF)-derived metal/N-doped porous carbon nanocomposites (M@NCs) have emerged as a class of appealing heterogeneous catalysts applied in organic synthesis, and the striking features mainly involve low-cost...

High Energy Density Heteroatom (O, N and S) Enriched Activated Carbon for Rational Design of Symmetric Supercapacitors

Carbon-based symmetric supercapacitors (SCs) are known for their high power density and long cyclability, making them an ideal candidate for power sources in new-generation electronic devices. To boost their electrochemical performances, deriving activated carbon doped with heteroatoms such as N, O, and S are highly desirable for increasing the specific capacitance. In this regard, activated carbon (AC) self-doped with heteroatoms is directly derived from bio-waste (lima-bean shell) using different KOH activation processes. The heteroatom-enriched AC synthesized using a pretreated carbon-to-KOH ratio of 1:2 (ONS@AC-2) shows excellent surface morphology with a large surface area of 1508 m²  g^-1 . As an SC electrode material, the presence of heteroatoms (N and S) reduces the interfacial charge-transfer resistance and increases the ion-accessible surface area, which inherently provides additional pseudocapacitance. The ONS@AC-2 electrode attains a maximum specific capacitance (C_sp ) of 342 F g^-1 at a specific current of 1 Ag^-1 in 1 m NaClO₄ electrolyte at the wide potential window of 1.8 V. Moreover, as symmetric SCs the ONS@AC-2 electrode delivers a maximum specific capacitance (C_sc ) of 191 F g^-1 with a maximum specific energy of 21.48 Wh kg^-1 and high specific power of 14 000 W kg^-1 and excellent retention of its initial capacitance (98 %) even after 10000 charge/discharge cycles. In addition, a flexible supercapacitor fabricated utilizing ONS@AC-2 electrodes and a LiCl/polyvinyl alcohol (PVA)-based polymer electrolyte shows a maximum C_sc of 119 F g^-1 with considerable specific energy and power.