ZnS/SnS2 Heterostructures Encapsulated in N-Doped Carbon Nanofibers for High-Performance Alkali Metal-Ion Batteries

Heterogeneous composite ZnS/SnS2 is designed to meet various requirements for alkali metal-ion batteries. The composite is prepared using an electrostatic spinning method and encapsulated in N-doped carbon fibers after high-temperature vulcanization. The special structure of the composite provides a dependable interconnection and fast conductive network for alkali metal ions. The conductive carbon network shortens the diffusion path and greatly improves the migration efficiency of the alkali metal ions in the electrode. As expected, when the current density is 0.1 A g-1, the ZnS/SnS2@NCNFs maintain a high discharge capacity of more than 1437.5, 1321.2, and 861.6 mA h g-1 for lithium-ion, sodium-ion, and potassium-ion batteries, respectively. What is more, a full cell using a prelithiated composite anode and a LiFePO4 cathode is tested and shows excellent electrochemical performance. This work provides new perspectives for the development of novel anodes that can efficiently store alkali metal ions, as well as for the fine-structure design of materials.

N-Doped Porous Carbon-Nanofiber-Supported Fe3C/Fe2O3 Nanoparticles as Anode for High-Performance Supercapacitors

Exploring anode materials with an excellent electrochemical performance is of great significance for supercapacitor applications. In this work, a N-doped-carbon-nanofiber (NCNF)-supported Fe3C/Fe2O3 nanoparticle (NCFCO) composite was synthesized via the facile carbonizing and subsequent annealing of electrospinning nanofibers containing an Fe source. In the hybrid structure, the porous carbon nanofibers used as a substrate could provide fast electron and ion transport for the Faradic reactions of Fe3C/Fe2O3 during charge-discharge cycling. The as-obtained NCFCO yields a high specific capacitance of 590.1 F g-1 at 2 A g-1, superior to that of NCNF-supported Fe3C nanoparticles (NCFC, 261.7 F g-1), and NCNFs/Fe2O3 (NCFO, 398.3 F g-1). The asymmetric supercapacitor, which was assembled using the NCFCO anode and activated carbon cathode, delivered a large energy density of 14.2 Wh kg-1 at 800 W kg-1. Additionally, it demonstrated an impressive capacitance retention of 96.7%, even after 10,000 cycles. The superior electrochemical performance can be ascribed to the synergistic contributions of NCNF and Fe3C/Fe2O3.

Anchoring Ni/NiO heterojunction on freestanding carbon nanofibers for efficient electrochemical water oxidation

Rational design of low-cost and efficient electrocatalyst for the anodic oxygen evolution reaction (OER) to replace noble-metal-based catalysts is greatly desired for the large-scale application of water electrocatalysis. And compared with the conventional powdery catalysts, the freestanding electrode architecture is more attractive owing to the enhanced kinetics and stability. In this work, we report an electrospinning-carbonization-post oxidation strategy to develop the freestanding N-doped carbon nanofibers anchored with Ni/NiO nanoparticles (denoted as Ni/NiO-NCNFs) as efficient OER electrocatalyst. In the synthesized Ni/NiO-NCNFs, the conductive ultrathin carbon layer could promote electron transfer and thus improve the electrocatalytic activity. Meanwhile, the ratio between Ni and NiO could be regulated by tuning the oxidation duration, so as to optimize the adsorption energy of intermediates and improve the OER activity. The Ni/NiO-NCNFs prepared with the oxidation time of 3 h exhibit a promising OER activity and long-term operation durability in 0.1 M KOH solution, requiring an overpotential as small as 153 mV to achieve a current density of 10 mA cm^-2. Its overpotential is far lower than that of the reported OER catalysts. This work offers an efficient pathway to develop low-cost and highly active freestanding transitional metal-based OER electrocatalyst for potential renewable electrochemical energy conversion.

Bismuth Nanoparticles Encapsulated in Nitrogen-Rich Porous Carbon Nanofibers as a High-Performance Anode for Aqueous Alkaline Rechargeable Batteries

The aqueous alkaline rechargeable batteries (AARBs) have an attractive potential for electrochemical energy storage devices. In view of the advantages of high theoretical capacity and desirable negative operating window, bismuth (Bi) has been deemed as a hopeful anode material for AARBs. Unfortunately, intensive reported works of Bi anode are still confronted with limited capacity and poor cycling stability. Herein, the designed electrodes of different size Bi nanoparticles embedded in porous carbon nanofibers with a contrasting nitrogen doping content are obtained by electrospinning and thermal treatment processes. The effect of the N dopant in carbon shell is demonstrated on the Bi core, which is in favor of enhancing the capacity of Bi anodes. More importantly, the core structure with highly dispersed ultrasmall Bi nanoparticles (<20 nm) in carbon matrix plays a crucial role in long-term durability. Accordingly, the optimized polydisperse ultrasmall Bi nanoparticles confined in N-rich porous carbon nanofibers electrode (Bi@NPCF) presents an admirable capacity of 196.1 mAh g^-1 at 3 A g^-1 and outstanding durable lifespan (retain 116.95% after 10 000 cycles). In addition, the fabricated Bi@NPCF//NiCo₂ O₄ battery exhibits an exceptional energy and power density with durable stability (95.9% after 5000 cycles).

MOF-Derived Fe7 S8 Nanoparticles/N-Doped Carbon Nanofibers as an Ultra-Stable Anode for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have aroused wide concern due to their potential applications in large-scale energy-storage systems. In this work, a hybrid of Fe₇ S₈ nanoparticles/N-doped carbon nanofibers (Fe₇ S₈ /N-CNFs) is designed and synthesized via electrospinning. As an anode for SIBs, Fe₇ S₈ /N-CNFs exhibit a high reversible capacity of 649.9 mAh g^-1 at 0.2 A g^-1 after 100 cycles, and superior cycling stability for 2000 cycles at 1 A g^-1 with only 0.00302% capacity decay per cycle. Such excellent performance originates from: i) Fe₇ S₈ nanoparticles (average diameter of 17 nm), which shorten the Na⁺ diffusion distance; ii) the unique 3D N-CNFs, which enhance the conductivity, alleviate the self-agglomeration and large volume change of Fe₇ S₈ nanoparticles, and offer numerous active sites for Na⁺ adsorption and paths for electrolyte diffusion. The fascinating structure and superior electrochemical properties of Fe₇ S₈ /N-CNFs shed light on developing high-performance SIBs anode materials.

In Situ Preparation of Cobalt Nanoparticles Decorated in N-Doped Carbon Nanofibers as Excellent Electromagnetic Wave Absorbers

Electrospinning and annealing methods are applied to prepare cobalt nanoparticles decorated in N-doped carbon nanofibers (Co/N-C NFs) with solid and macroporous structures. In detail, the nanocomposites are synthesized by carbonization of as-electrospun polyacrylonitrile/cobalt acetylacetonate nanofibers in an argon atmosphere. The solid Co/N-C NFs have lengths up to dozens of microns with an average diameter of ca. 500 nm and possess abundant cobalt nanoparticles on both the surface and within the fibers, and the cobalt nanoparticle size is about 20 nm. The macroporous Co/N-C NFs possess a hierarchical pore structure, and there are macropores (500 nm) and mesopores (2-50 nm) existing in this material. The saturation magnetization ( M_s) and coercivity ( H_c) of the solid Co/N-C NFs are 28.4 emu g^-1 and 661 Oe, respectively, and those of the macroporous Co/N-C NFs are 23.3 emu g^-1 and 580 Oe, respectively. The solid Co/N-C NFs exhibit excellent electromagnetic wave absorbability, and a minimum reflection loss (RL) value of -25.7 dB is achieved with a matching thickness of 2 mm for solid Co/N-C NFs when the filler loading is 5 wt %, and the effective bandwidth (RL ≤ -10 dB) is 4.3 GHz. Moreover, the effective microwave absorption can be achieved in the whole range of 1-18 GHz by adjusting the thickness of the sample layer and content of the dopant sample.

Controllable N-Doped CuCo2 O4 @C Film as a Self-Supported Anode for Ultrastable Sodium-Ion Batteries

Rational synthesis of flexible electrodes is crucial to rapid growth of functional materials for energy-storage systems. Herein, a controllable fabrication is reported for the self-supported structure of CuCo₂ O₄ nanodots (≈3 nm) delicately inserted into N-doped carbon nanofibers (named as 3-CCO@C); this composite is first used as binder-free anode for sodium-ion batteries (SIBs). Benefiting from the synergetic effect of ultrasmall CuCo₂ O₄ nanoparticles and a tailored N-doped carbon matrix, the 3-CCO@C composite exhibits high cycling stability (capacity of 314 mA h g^-1 at 1000 mA g^-1 after 1000 cycles) and high rate capability (296 mA h g^-1 , even at 5000 mA g^-1 ). Significantly, the Na storage mechanism is systematically explored, demonstrating that the irreversible reaction of CuCo₂ O₄ , which decomposes to Cu and Co, happens in the first discharge process, and then a reversible reaction between metallic Cu/Co and CuO/Co₃ O₄ occurrs during the following cycles. This result is conducive to a mechanistic study of highly promising bimetallic-oxide anodes for rechargeable SIBs.