Polyacrylonitrile-b-Polystyrene Block Copolymer-Derived Hierarchical Porous Carbon Materials for Supercapacitor

The use of block copolymers as a sacrificial template has been demonstrated to be a powerful method for obtaining porous carbons as electrode materials in energy storage devices. In this work, a block copolymer of polystyrene and polyacrylonitrile (PS-b-PAN) has been used as a precursor to produce fibers by electrospinning and powdered carbons, showing high carbon yield (~50%) due to a low sacrificial block content (f_PS ≈ 0.16). Both materials have been compared structurally (in addition to comparing their electrochemical behavior). The porous carbon fibers showed superior pore formation capability and exhibited a hierarchical porous structure, with small and large mesopores and a relatively high surface area (~492 m²/g) with a considerable quantity of O/N surface content, which translates into outstanding electrochemical performance with excellent cycle stability (close to 100% capacitance retention after 10,000 cycles) and high capacitance value (254 F/g measured at 1 A/g).

Synthesis of Hollow N,P-Doped Carbon/Co2P2O7 Nanotubular Crystals as an Effective Electrocatalyst for the Oxygen Reduction Reaction

Herein, N,P-rich carbon/carbon/Co₂P₂O₇ hollow nanotubes with a multilayered wall structure were successfully fabricated for the ORR electrocatalyst. The hollow tube structure catalysts were obtained by carbonizing Co₂P₂O₇/C coated with the phytate-doped PANI. The Co₂P₂O₇/C was obtained by phosphorylating a basic cobalt carbonate with phytic acid (PA). Onset and positive half-wave potentials were measured at 0.90 and 0.84 V, respectively, with a diffusion-limited current density of 4.58 mA/cm². Effect of the thickness of polyaniline (PANI) in the electrocatalyst precursor was also investigated. The specific surface area as well as the content of graphitic N altered as the time of PANI polymerization increased, resulting in remarkably different catalytic activities. This study of hollow nanotube catalysts exhibits efficient noble-metal-free oxygen reduction reaction electrocatalysts for other chemical systems, which will provide abundant electrochemical active centers and sufficient energy.

Block Copolymer Self-Assembly Guided Synthesis of Mesoporous Carbons with In-Plane Holey Pores for Efficient Oxygen Reduction Reaction

In this paper, we report a simple approach, using interfacial self-assembly of block copolymers (BCPs) on self-sacrificial templates, for preparing mesoporous carbons with in-plane holey pores, including nitrogen atom-doped carbon nanosheets and nanoflowers (denoted as NHCSs and NHCFs). The approach employed sheet- or flower-like layered double hydroxide as the templates, P123 copolymer as the pore-directing agent, and m-phenylenediamine as the carbon source. The holey mesopores may shorten the mass transfer distance to the internal active sites of stacked nanosheets, while the three-dimensional (3D) packing mode of nanosheets can reduce pore blockage caused by their tight stacking. Profiting from these structural advantages, acting as electrocatalysts for oxygen reduction reaction (ORR), both NHCSs and NHCFs show excellent catalytic performance better than that of carbon nanosheets without holey pores. Particularly, NHCFs exhibit a high half-wave-potential (0.82V) and a limiting current density (5.4 mA cm^-2 ), close to those of commercial Pt/C catalysts. This study provides valuable clues on building mesoporous materials with in-plane holey pores as well as on the effect of pore structure and stacking mode of 2D materials on their electrocatalytic ORR performance. This article is protected by copyright. All rights reserved.

High-efficiency adsorption of Cr(VI) and RhB by hierarchical porous carbon prepared from coal gangue

Coal gangue (CG) is one of the largest industrial solid wastes in the world produced during the process of coal mining. The accumulation of CG is easy to cause ion leakage, which is harmful to the environment and human body. The recovery and utilization of CG are imminent. In the process, a hierarchical porous carbon (HPC) adsorbent with excellent adsorption property for Cr(VI) and rhodamine B (RhB), was prepared from CG by a two-step method and characterized by SEM, TEM, XRD, XPS, TPD and BET. The results revealed that the specific surface area of HPC is up to 2012.7 m² g^-1, and its adsorption capacities for Cr(VI) and RhB are reached 320.51 and 3086.42 mg g^-1. The adsorption mechanism of RhB was the synergetic effect of physics and chemistry. While XPS results suggested that hierarchical porous carbons (HPCs) only have a chemisorption effect on Cr(VI). This study provided an idea for the preparation of HPCs from CG to remove inorganic and organic pollutants such as heavy metal Cr(VI) and RhB in water.

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.