Designing a carbon nanofiber-encapsulated iron carbide anode and nickel-cobalt sulfide-decorated carbon nanofiber cathode for high-performance supercapacitors

Hydrothermal Fabrication and Electrochemical Property of a 0D/2D Hybrid Nanostructure with Graphitic Carbon Nitride-Incorporated Nickel Molybdenum Sulfide

As a kind of energy storage device, supercapacitors have attracted substantial attention on account of their large capacity, cycling stability, and high energy density. Here, a 0D/2D structured composite with graphitic carbon nitride (g-C3N4) nanosheet (2D)-incorporated nickel molybdenum sulfide [Ni2MoS4(NMS)] nanoparticles(0D) (NMS/g-C3N4) was synthesized through a two-step hydrothermal method using NiSO4·6H2O and Na2MoO4·2H2O as raw materials and thiourea as the sulfurizing agent. The incorporation of g-C3N4 nanosheets enhanced the dispersibility of NMS nanoparticles for preventing volumetric expansion during the charge-discharge cycles. The dispersed NMS nanoparticles and g-C3N4 nanosheets formed a 0D/2D hybrid nanostructure and could offer more active sites. The electrochemical results manifested that the formulated composite obtained a specific capacitance of 1800.6 F·g-1 at a current density of 1 A·g-1, and the specific capacitance of the NMS/g-C3N4 composite could retain 50.1% after 1000 cycles at a current density of 10 A·g-1, representing 12.5% improvement in capacitance retention compared to the pristine NMS composite. It indicates that the NMS/g-C3N4 composite holds promising potential as a supercapacitor electrode material.

ZnO-MnO2 co-modified hierarchical porous carbon nanofiber film electrodes for high-energy density supercapacitors

This study focuses on preparing composite hierarchical porous carbon nanofiber film that includes ZnO and MnO2. Using electrospinning technology, hierarchical porous structure was introduced into the nanofibers, enhancing energy density through the synergistic effect of zinc oxide and manganese dioxide. The zinc-manganese dioxide co-modified hierarchical porous carbon nanofiber film (ZnMnO-HPC) exhibits outstanding electrochemical performance when used as supercapacitor electrode, with a specific capacity reaching 401.77 C/g at 0.5 A/g, and 201.29 C/g at high current density of 5 A/g. ZnMnO-HPC also exhibits remarkable energy density when assembled with activated carbon electrode into asymmetric capacitor, reaching 38.37 Wh/kg at a power density of 407 W/kg and 19.5 Wh/kg at a power density of 12,800 W/kg, indicating promising applications in the high-energy-density supercapacitor field.

Plasma-assisted synthesis of ultra-fine NiCo2O4/NiCo-layered double hydroxides nanoparticles-decorated electrospun carbon nanofibers with enhanced electrochemical performance

Nickel cobaltate/NiCo-layered double hydroxides (NiCo2O4/NiCo-LDH) as energy storage materials offer considerable potential for various applications. However, many of current methods for synthesizing NiCo2O4/NiCo-LDH suffer from long synthesis times, complex preparation process, and high temperatures and high pressures. In this study, we present a green, simple, and efficient approach known as assisted liquid-phase plasma electrolysis, which realizes the rapid fabrication of ultra-fine NiCo2O4/NiCo-LDH nanoparticle-decorated electrospun carbon nanofibers (NiCo2O4/NiCo-LDH/CNFs) composites. Ultra-fine NiCo2O4/NiCo-LDH nanoparticles (<70 nm) are uniformly deposited on the CNF surface. The CNFs are intertwined to form a highly conductive three-dimensional mesh structure, which synergizes the NiCo2O4/NiCo-LDH nanoparticles with a high specific capacitance in favor of ion/electron transport efficiency. In addition, the cooperative effect between the two phases of NiCo2O4 and NiCo-LDH further improves the electrochemical properties. The NiCo2O4/NiCo-LDH/CNFs composites exhibit a high specific capacitance of 1534.7 F/g at 1 A/g and a capacitance retention of 93.9 % after 5000 cycles. An assembled asymmetric supercapacitor using activated carbon and NiCo2O4/NiCo-LDH/CNFs composites achieves an energy density of 33.8 Wh/kg at a power density of 400 W/kg and a capacitance retention of 93.0 % after 5000 cycles. Notably, two series-connected NiCo2O4/NiCo-LDH/CNFs ASC supercapacitors can light up an LED bulb, which maintains a certain brightness even after 50 min. Hence, this work provides a new and efficient route for synthesizing carbon-based NiCo2O4/NiCo-LDH composites for use as advanced energy storage materials.

Three-dimensional NiCoS nanotubes@NiCo-LDH nanosheets core-shell heterostructure for high-rate capability alkaline zinc-based batteries

Aqueous alkaline zinc-based batteries (AAZBs) are promising for large-scale applications due to their high working voltage, safety, and low cost. However, the further development of AAZBs has been significantly hindered by the low electronic conductivity and poor cycling stability of traditional nickel/cobalt-based cathode materials. In this work, a binder-free electrode was successfully designed by electrodepositing NiCo-LDH nanosheets on NiCoS nanotube arrays that were grown on nickel foam (NiCoS@NiCo-LDH). The unique three-dimensional core-shell heterostructures not only enhance electrical conductivity but also offer abundant active sites and rapid ion/electron transport channels, thereby improving its electrochemical performance. The as-fabricated NiCoS@NiCo-LDH electrode delivers a capacity of 312 mA h g-1 (0.624 mA h cm-2) at 2 mA cm-2 and exhibits high rate capability with 90% capacity retention at 10 mA cm-2. Additionally, the assembled NiCoS@NiCo-LDH//Zn battery exhibits a high energy density of 435.3 W h kg-1 at a power density of 4.1 kW kg-1 and maintains 95.9% of its capacity after 3000 cycles at a current density of 20 mA cm-2.

Controllable synthesis of Fe3C-reinforced petal-like lignin microspheres with boosted electrochemical performance and its application in high performance supercapacitors

One more effective measure to solve the energy crisis caused by the shortage of fossil energy is to convert natural renewable resources into high-value chemical products for electrochemical energy storage. Lignin has broad application prospects in this field. In this paper, three kinds of lignin with different molecular weights were obtained by the ethanol/water grading of Kraft lignin (KL). Then, different surface morphology lignin microspheres were prepared by spray drying. Finally, petal-like microspheres were successfully prepared by mixing and grinding the above four kinds of surface morphology lignin microspheres with potassium ferrate and cyanogen chloride and carbonizing at 800 °C and were later used as electrode materials for supercapacitors. Compared with the other microspheres, LMS-F3@Fe3C has the highest specific surface area (1041.42 m2 g-1), the smallest pore size (2.36 nm) and the largest degree of graphitization (ID/IG = 1.06). At a current density of 1 A g-1, the maximum specific capacitance is 786.7 F g-1. At a power density of 1000 W kg-1, the high energy density of 83.3 Wh kg-1 is displayed. This work provides a novel approach to the modulation of surface morphology and structure of lignin microspheres.

Inhabiting Inactive Transition by Coupling Function of Oxygen Vacancies and Fe─C Bonds achieving Long Cycle Life of an Iron-Based Anode

Fe-based battery-type anode materials with many faradaic reaction sites have higher capacities than carbon-based double-layer-type materials and can be used to develop aqueous supercapacitors with high energy density. However, as an insurmountable bottleneck, the severe capacity fading and poor cyclability derived from the inactive transition hinder their commercial application in asymmetric supercapacitors (ASCs). In this work, driven by the "oxygen pumping" mechanism, oxygen-vacancy-rich Fe@Fe3 O4 (v) @Fe3 C@C nanoparticles that consist of a unique "fruit with stone"-like structure are developed, and they exhibit enhanced specific capacity and fast charge/discharge capability. Experimental and theoretical results demonstrate that the capacity attenuation in conventional iron-based anodes is greatly alleviated in the the Fe@Fe3 O4 (v) @Fe3 C@C anode because the irreversible phase transition to the inactive γ-Fe2 O3 phase can be inhibited by a robust barrier formed by the coupling of oxygen vacancies and Fe─C bonds, which promotes cycle stability (93.5% capacity retention after 24 000 cycles). An ASC fabricated using this Fe-based anode is also observed to have extraordinary durability, achieving capacity retention of 96.4% after 38 000 cycles, and a high energy density of 127.6 W h kg-1 at a power density of 981 W kg-1 .