Christine Young

CNTs grown on nanoporous carbon from zeolitic imidazolate frameworks for supercapacitors.

Carbon nanotubes (CNT) grown on nanoporous carbon (NPC), which yields coexisting amorphous and graphitic nanoarchitectures, have been prepared on a large scale from zeolitic imidazolate framework (ZIF) by introducing bimetallic ions (Co2+ and Zn2+). Interestingly, the hybrid Co/Zn-ZIF-derived NPC showed rich graphitic CNTs on the surface. This NPC was utilized for a coin-type supercapacitor cell with an aqueous electrolyte, which showed enhanced retention at high current density and good stability over 10 000 cycles.

Nanoarchitecture of MOF-derived nanoporous functional composites for hybrid supercapacitors

A new nanoarchitecture approach based on metal–organic frameworks (MOF) is reported that can achieve high electrochemical energy storage via utilizing both electric double-layer supercapacitive and pseudocapacitive properties within a single nanoporous composite particle. Herein, a predesigned Co2+-excess bimetallic hybrid Co/Zn zeolitic imidazole framework was used to fabricate a composite containing N-doped nanoporous carbon with a rich carbon nanotube (CNT) content on particle surfaces without H2, with the carbon coexisting with Co nanoparticles (NPs) and Co3O4, through controlled carbonization at 800 °C and subsequent oxidation at 250–300 °C. Optimized nanoporous carbon composites were obtained by tracking the formation of Co3O4 and destruction of N-doped nanoporous carbon (NPC) via detailed X-ray diffraction and X-ray photoelectron spectroscopy analysis. The resulting material showed a high surface area of ∼202 m2 g−1 and included coexisting micro- and mesoporous N-doped carbon, CNTs, Co NPs, and Co3O4 (15 nm in size) after a thermal oxidation process in air at 250 °C for 5 h. Surprisingly, the as-prepared MOF-derived nanoarchitecture exhibited superior electrochemical storage performance, with a capacitance of 545 F g−1 within a wide potential window, achieving up to 320% enhanced capacitance compared to that of pristine nanoporous carbon, which is higher than those of most MOF-derived carbons reported so far. Our strategic nanoarchitecture design for MOFs offers a new opportunity for future applications in high performance energy storage systems.

High energy density supercapacitors composed of nickel cobalt oxide nanosheets on nanoporous carbon nanoarchitectures

Porous carbon–metal oxide hybrid materials are advanced functional composites with great potential for use in high energy density supercapacitors. Here we describe a hybrid structure composed of two-dimensional (2D) NiCo2O4 nanosheets synthesized on polyhedral-shaped nanoporous carbon (NC) particles. The NC particles were derived from the carbonization of zeolitic imidazole frameworks (ZIF-8). Supercapacitor devices assembled using NiCo2O4-NC nanoparticles had excellent capacitive properties with energy densities up to 28 W h kg−1 and power densities up to 8.5 kW kg−1.

Synthesis of MOF-525 Derived Nanoporous Carbons with Different Particle Sizes for Supercapacitor Application

Nanoporous carbon (NC) materials have attracted great research interest for supercapacitor applications, because of their excellent electrochemical and mechanical stability, good electrical conductivity, and high surface area. Although there are many reports on metal-organic framework (MOF)-derived carbon materials, previous synthetic studies have been hindered by imperfect control of particle sizes and shapes. Here, we show precise control of the particle sizes of MOF-525 from 100 nm to 750 nm. After conversion of MOF-525 to NC, the effects of variation of the particle size on the electrochemical performance have been carefully investigated. The results demonstrate that our NC is a potential candidate for practical supercapacitor applications.

Strategic design of triphenylamine- and triphenyltriazine-based two-dimensional covalent organic frameworks for CO2 uptake and energy storage

Hexagonally ordered covalent organic frameworks (COFs) are interesting new crystalline porous materials that have massive potential for application in gas storage. Herein, we report the synthesis of two series of two-dimensional hexagonally ordered COFs—TPA-COFs and TPT-COFs—through one-pot polycondensations of tris(4-aminophenyl)amine (TPA-3NH2) and 2,4,6-tris(4-aminophenyl)triazine (TPT-3NH2), respectively, with triarylaldehydes featuring different degrees of planarity, symmetry, and nitrogen content. All the synthesized COFs exhibited high crystallinity, large BET surface areas (up to 1747 m2 g−1), excellent thermal stability, and pore size distributions from 1.80 to 2.55 nm. The symmetry and planarity of the monomers strongly affected the degrees of crystallinity and the BET surface areas of the resultant COFs. In addition, these COFs displayed excellent CO2 uptake efficiencies of up to 65.65 and 92.38 mg g−1 at 298 and 273 K, respectively. The incorporation of the more planar and higher-nitrogen-content triaryltriazine unit into the backbones of the TPA-COFs and TPT-COFs enhanced the interactions with CO2, leading to higher CO2 uptakes. Moreover, the synthesized COFs exhibited electrochemical properties because of their conjugated structures containing redox-active triphenylamine groups. This study exposes the importance of considering the symmetry and planarity of the monomers when designing highly crystalline COFs; indeed, the structures of COFs can be tailored to vary their functionalities for specific applications.

Advanced Functional Carbons and Their Hybrid Nanoarchitectures towards Supercapacitor Applications

Porous carbons have attracted much attention as electrode materials for supercapacitors due to their enormous surface area, high electrical conductivity, excellent corrosion resistance, high temperature stability, and relatively low cost. The design of porous architectures is considered key for determining electrochemical performance. Pore size distribution, pore size, and pore connectivity strongly affect electrochemical performance. Various carbon materials with pore size ranging from micro- to macropores were extensively studied. Herein, various types of porous carbon-based and hybrid materials from different approaches and their electrochemical applications are summarized. Appropriate tuning of the pore size of carbon materials is essential for ensuring good transport of ions with different sizes throughout the electrolyte, so that the electrode materials can be fully utilized. Many carbon materials were produced from a series of carbonization and activation processes that possess controllable pore structures, including activated carbons, graphite, carbon nanotubes, carbon aerogels, and templated porous carbons. Templated carbon materials were prepared by various approaches, such as direct carbonization from carbon precursors and soft- and hard-template methods. To enhance the electrochemical performance of the electrode materials, heteroatoms, such as nitrogen, sulfur, and boron, were doped into porous carbons. In addition, to optimize the overall capacitance without destroying the stability and morphology of electrode materials, pseudocapacitive materials, such as transition-metal oxides, were introduced into the carbon frameworks. In this review, recent advances in the fabrication of nanoarchitectured porous carbons and metal oxides through various approaches for supercapacitor applications are summarized.

Ni–Co Binary Hydroxide Nanotubes with Three-Dimensionally Structured Nanoflakes: Synthesis and Application as Cathode Materials for Hybrid Supercapacitors

Nickel-cobalt binary hydroxide nanotubes were fabricated by a facile synthetic approach by using Cu2 O nanowires as sacrificial templates. The surface morphology of the binary hydroxide nanotubes can be easily controlled by adjusting the molar ratio of Ni to Co. With increasing Co content, the surfaces of the nanotubes tend to form hierarchical nanoflakes. The obtained nanotubes with high specific surface area exhibit typical battery-like electrochemical behavior. Among them, Ni-Co hydroxide nanotubes with Ni:Co=48:52 showed outstanding electrochemical characteristics, with a specific capacity of 209.9 mAh g-1 at 1 Ag-1 and remarkable cycling stability with 84.4 % capacity retention after 10 000 cycles at 20 A g-1 . With the advantages of their unique nanostructure and the synergistic effect of the two elements, the Ni-Co binary hydroxide nanotubes are expected to be effective potential cathode materials for hybrid supercapacitors.