A modified "gel-blowing" strategy toward the one-step mass production of a 3D N-doped carbon nanosheet@carbon nanotube hybrid network for supercapacitors

Hydronium-Crosslinked Inorganic Hydrogel Comprised of 1D Lepidocrocite Titanate Nanofilaments

When a few drops of acid (hydrochloric, acrylic, propionic, acetic, or formic) are added to a colloid comprised of 1D lepidocrocite titanate nanofilaments (1DLs)-2 × 2 TiO6 octahedra in cross-section-a hydrogel forms, in many cases, within seconds. The 1DL synthesis process requires the reaction between titanium diboride with tetramethylammonium (TMA+), hydroxide. Using quantitative nuclear magnetic resonance (qNMR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC), the mass percent of TMA+ after synthesis is determined to be ≈ 13.1 ± 0.1%. The TMA+ is completely removed from the gels after 2 water soak cycles, resulting in the first completely inorganic, TiO2-based hydrogels. Ion exchanging the TMA+ with hydronium results in gels with relatively strong hydrogen bonds. The hydrogels' compression strengths increased linearly with 1DL colloid concentration. At a 1DL concentration of 45 g L-1, the compressive strength, at 80% deformation when acrylic acid is used, is ≈325 kPa. The strengths are ≈ 50% greater after the TMA+ is removed. The removal of all residual organic components in the hydrogels, including TMA+, is confirmed by qNMR, Fourier-transformed infrared spectroscopy (FTIR), and TGA/DSC. The 1DL phase is retained after gelation, TMA+ removal, and 80% compression.

Advances in Inorganic Foam Materials Fabricated Via Blowing Strategy: A Comprehensive Review

Two-dimensional (2D) materials with excellent properties and widespread applications have been explosively investigated. However, their conventional synthetic methods exhibit concerns of limited scalability, complex purification process, and incompetence of prohibiting their restacking. The blowing strategy, characterized by gas-template, low-cost, and high-efficiency, presents a valuable avenue for the synthesis of 2D-based foam materials and thereby addresses these constraints. Whereas, its comprehensive introduction has been rarely outlined so far. This review commences with a synopsis of the blowing strategy, elucidating its development history, the statics and kinetics of the blowing process, and the choice of precursor and foaming agents. Thereafter, we dwell at length on across-the-board foams enabled by the blowing route, like BxCyNz foams, carbon foams, and diverse composite foams consisting of carbon and metal compounds. Following that, a wide-ranging evaluation of the functionality of the foam products in fields such as energy storage, electrocatalysis, adsorption, etc. is discussed, revealing their distinctive strength originated from the foam structure. Finally, after concluding the current progress, we provide some personal discussions on the existing challenges and future research priorities in this rapidly developing method.

Hierarchical structure N, O-co-doped porous carbon/carbon nanotube composite derived from coal for supercapacitors and CO2 capture

The energy and environmental crises have forced us to search for a new green energy source and develop energy storage and environmental restoration technologies. Fabrication of carbon functional materials derived from coal has attracted increasing attention in the energy storage and gas adsorption fields. In this study, an N, O-co-doped porous carbon/carbon nanotube composite was prepared by functionalizing coal-based porous carbon with carbon nanotubes (CNTs) and ionic liquid via annealing. The resulting material not only inherited the morphology of CNTs and porous carbon, but also developed a three dimensional (3D) hierarchical porous structure with numerous heteroatom groups. The N, O co-doped porous carbon/CNT composite (N, O-PC-CNTs) showed a surface area of 2164 m² g^-1, and a high level of N/O dopants (8.0 and 3.0 at%, respectively). Benefiting from such merits, N, O-PC-CNTs exhibited a rather high specific capacitance of 287 F g^-1 at a current density of 0.2 A g^-1 and a high rate capability (70% and 64% capacitance retention at 10 and 50 A g^-1, respectively) in a three electrode system. Furthermore, an N, O-PC-CNT symmetrical supercapacitor showed a high cycling stability with 95% capacitance retention after 20 000 cycles at 20 A g^-1 and an energy density of 4.5 W h kg^-1 at a power density of 12.5 kW kg^-1 in 6 mol L^-1 KOH electrolyte. As a CO₂ adsorbent, N, O-PC-CNTs exhibited a high CO₂ uptake of 5.7 and 3.7 mmol g^-1 at 1 bar at 273 and 298 K, respectively. Moreover, N, O-PC-CNTs showed cycling stability with 94% retention of the initial CO₂ adsorption capacity at 298 K over 10 cycles. This report introduces a strategy to design a coal based porous carbon composite for use in efficient supercapacitor electrodes and CO₂ adsorbents.

Progress in supercapacitors: roles of two dimensional nanotubular materials

Overcoming the global energy crisis due to vast economic expansion with the advent of human reliance on energy-consuming labor-saving devices necessitates the demand for next-generation technologies in the form of cleaner energy storage devices. The technology accelerates with the pace of developing energy storage devices to meet the requirements wherever an unanticipated burst of power is indeed needed in a very short time. Supercapacitors are predicted to be future power vehicles because they promise faster charging times and do not rely on rare elements such as lithium. At the same time, they are key nanoscale device elements for high-frequency noise filtering with the capability of storing and releasing energy by electrostatic interactions between the ions in the electrolyte and the charge accumulated at the active electrode during the charge/discharge process. There have been several developments to increase the functionality of electrodes or finding a new electrolyte for higher energy density, but this field is still open to witness the developments in reliable materials-based energy technologies. Nanoscale materials have emerged as promising candidates for the electrode choice, especially in 2D sheet and folded tubular network forms. Due to their unique hierarchical architecture, excellent electrical and mechanical properties, and high specific surface area, nanotubular networks have been widely investigated as efficient electrode materials in supercapacitors, while maintaining their inherent characteristics of high power and long cycling life. In this review, we briefly present the evolution, classification, functionality, and application of supercapacitors from the viewpoint of nanostructured materials to apprehend the mechanism and construction of advanced supercapacitors for next-generation storage devices.

N-Doped yolk-shell carbon nanotube composite for enhanced electrochemical performance in a supercapacitor

Carbon nanotubes (CNTs) have been intensively studied as electrode materials in supercapacitors due to their unique tubular structure, high mechanical strength, and excellent conductivity. However, the low surface area, poor pore distribution and inert surface severely limit their electrochemical performance. Herein, a process of co-assembly of CNTs with 1-cetyl-3-methylimidazolium bromide ([C₁₆Mim]Br), tetraethoxysilane and resorcinol/formaldehyde resin (RF) is used to prepare a series of composites of CNTs with mesoporous carbon (MC/CNT). The amount of CNTs used strongly affects the structures of the MC/CNT composite, in which the composite structure is adjusted from yolk-shell CNTs combined with folded MC spheres to uniform yolk-shell CNTs, and then to CNTs with uniformly located irregular carbon fragments. The use of [C₁₆Mim]Br effectively assists the assembly of the RF/silica hybrid on the CNTs due to the electrostatic interaction among them, and this also leads to N-doping in the MC/CNT composite. The existence of MC provides uniform mesopores and increases the surface area of the composite materials, offers rich active sites, and at the same time, the CNTs supply sp²-hybridized carbon which benefits the conductivity. As the electrode material in the supercapacitor, MC/CNT with a uniform yolk-shell structure shows high electrochemical performance, demonstrating its excellent promise for energy storage applications.

Mass production of nitrogen and oxygen codoped carbon nanotubes by a delicately-designed Pechini method for supercapacitors and electrocatalysis

Heteroatom-doped carbon nanotubes (CNTs) have great potential in various fields owing to their extraordinary electronic, structural, and mechanical properties. However, large-scale production of heteroatom-doped CNTs in a simple, economical, and highly efficient manner still remains challenging. Here, we report a modified Pechini method (MPM) for high-yield synthesis of N- and O-codoped CNTs (N,O-CNTs), by rapid pyrolysis of a NiCo-polymer precursor forming via a simple sol-gel process. The carbon source (i.e., citric acid) is inexpensive, and the NiCo-polymer material is the single precursor for the preparation of N,O-CNTs via a thermolysis process without the introduction of additional catalysts or carrier gas. Appropriate NiCo-organic coordination and controlled pyrolysis (i.e. heating rate, pyrolysis temperature, and holding time) are demonstrated to play vital roles in this MPM, which are critical for quick generation of small NiCo nanocatalysts with high catalytic activity and simultaneous formation of sufficient space inside the material. The growth mechanism is well studied. Benefitting from the hierarchically porous structure and the synergistic effect of N,O-codoping in the CNTs, the as-synthesized N,O-CNTs manifest excellent electrochemical performance in both supercapacitors and electrocatalysis. Density functional theory simulations show that N and O dopants could increase the densities of states of CNTs near the Fermi level and charge densities of adjacent C atoms, thus leading to improved electrochemical activity. We anticipate that this work will open up a new avenue for a high-yield and economical synthesis of heteroatom-doped CNTs for energy-related applications and beyond.