NiCo-compounds inside and outside N-doped carbon nanotubes to construct a double-enhanced hierarchical structure for high energy density supercapacitors.

Attaining a high energy density that aligns with practical application requirements is a crucial indicator in the advancement of supercapacitors. In this paper, a hybrid hierarchical electrode structure of N-doped carbon nanotube (NCNT) spheres encapsulated with NiCo-Se nanoparticles (NPs) and coated with nickel-cobalt layered double hydroxide (NiCo-LDH) multilayer nanosheets was successfully synthesized on a nickel foam (NF) substrate. The self-supporting strategy enables nickel-cobalt Prussian blue analogues (Ni-Co PBAs) to be directly attached to the NF surface, which results in fluffy NCNTs with a high length-diameter ratio and considerable yield and greatly enhances the conductivity of the electrode material. The synergistic interaction between the dual transition metal compounds inside and outside the NCNTs enables the hybrid electrode material to achieve an impressive specific capacity of 1899 F g-1 (211.0 mA h g-1) at 1 A g-1. The asymmetric supercapacitor (ASC) exhibits an excellent energy density of 57.6 W h kg-1 at a power density of 798 W kg-1. This study not only provides an attractive strategy for obtaining CNTs with excellent properties from Ni-Co PBA and synthesizing hybrid electrodes with efficient synergistic effects, but also achieves a high energy density that aligns with the practical application demands of supercapacitors.

Two-Steps Method to Prepare Multilayer Sandwich Structure Carbon Fiber Composite with Thermal and Electrical Anisotropy and Electromagnetic Interference Shielding.

Carbon fiber (CF) composites performance enhancement is a research hotspot at present. In this work, first, a sandwich structure composite, CF@(carbon nanotube/Fe3O4)/epoxy (CF@(CNT/Fe3O4)/EP), is prepared by the free arc dispersion-CFs surface spraying-rolling process method, herein, CFs in the middle layer and (CNT/Fe3O4)/EP as top and substrate layer. Then, CF@(CNT/Fe3O4)/EP (on both sides) and CFs (in the middle) are overlapped by structure design, forming a multilayer CF@(CNT/Fe3O4)/EP-CFs composite with a CFs core sheath. A small amount of CNT/Fe3O4 is consumed, (CNT/Fe3O4)/EP and CFs core sheath realize thermal and electrical anisotropy and directional enhancement, and multilayer sandwich structure makes the electromagnetic interference (EMI) shielding performance better strengthened by multiple absorption-reflection/penetration-reabsorption. From CF-0 to CF-8, CNT/Fe3O4 content only increases by 0.045 wt%, axial thermal conductivity (λ‖) increases from 0.59 W/(m·K) to 1.1 W/(m·K), growth rate is 86%, radial thermal conductivity (λ⟂) only increases by 0.05 W/(m·K), the maximum λ‖/λ⟂ is 2.9, axial electrical conductivity (σ‖) increases from 6.2 S/cm to 7.7 S/cm, growth rate is 24%, radial electrical conductivity (σ⟂) only increases by 0.7 × 10-4 S/cm, the total EMI shielding effectiveness (EMI SET) increases by 196%, from 10.3 dB to 30.5 dB. This provides a new idea for enhancing CFs composite properties.

Efficient Synthesis of Fe/N-Doped Carbon Nanotube as Highly Active Catalysts for Oxygen Reduction Reaction in Alkaline Media.

It is of significant implication to fabricate high-performance, durable and low-cost catalysts toward to oxygen reduction reaction (ORR) to drive commercial application of fuel cells. In our work, we synthesize the Fe/N-CNT catalyst via one-pot grinding combined with calcination using a mixture of carbamide, CNTs and iron salts as precursors, the as-synthesized catalysts show the structure that Fe nanoparticles are encapsulated in the tube of intertwined CNTs with abundant active sites. The catalyst is synthesized at 800 °C (Fe/N-CNT-800-20) obtain high graphitization degree and high N doped content, especially the high content and proportion of Fe-N and pyridinic-N, exhibiting outstanding ORR activity. Moreover, too high calcination temperature (850 °C) and high Fe content (25%) lead to the agglomeration of Fe during the calcination, which blocked some catalytic sites, leading to poor ORR activity. This facile synergy route will provide new thoughts for the fabrication and optimization of catalysts.