Preparation of Nanostructural Carbon Nanofibers and Their Electrochemical Performance for Supercapacitors

Molybdenum single-atoms decorated multi-channel carbon nanofibers for advanced lithium-selenium batteries

The cathode in lithium-selenium (Li-Se) batteries has garnered extensive attention owing to its superior specific capacity and enhanced conductivity compared to sulfur. Nonetheless, the adoption and advancement of Li-Se batteries face significant challenges due to selenium's low reactivity, substantial volume fluctuations, and the shuttle effect associated with polyselenides. Single-atom catalysts (SACs) are under the spotlight for their outstanding catalytic efficiency and optimal atomic utilization. To address the challenges of selenium's low chemical activity and volume expansion in Li-Se batteries, through electrospun, we have developed a lotus root-inspired carbon nanofiber (CNF) material, featured internal multi-channels and anchored with molybdenum (Mo) single atoms (Mo@CNFs). Mo single atoms significantly enhance the conversion kinetics of selenium (Se), facilitating rapid formation of Li2Se. The internally structured multi-channel CNF serves as an effective host matrix for Se, mitigating its volume expansion during the electrochemical process. The resulting cathode, Se/Mo@CNF composite, exhibits a high discharge specific capacity, superior rate performance, and impressive cycle stability in Li-Se batteries. After 500 cycles at a current density of 1 C, it maintains a capacity retention rate of 82% and nearly 100% coulombic efficiency (CE). This research offers a new avenue for the application of single-atom materials in enhancing advanced Li-Se battery performance.

Highly conductive and porous lignin-derived carbon fibers

Bio-based carbon fibers derived from lignin have gained significant attention due to their diverse and renewable sources, ease of extraction, and low cost. However, the current limitations of low specific surface area and insufficient electrical conductivity hinder the widespread application of lignin-derived carbon fibers (LCFs). In this work, highly conductive and porous LCFs are developed through melt-blowing, pretreatment, and carbonization processes. The effects of the carbonization temperature and heating rate on the structures and properties of the LCFs are systematically investigated. The resultant LCFs exhibit high electrical conductivity (71 400 S m-1) and a large specific surface area (923 m2 g-1). The assembled lithium-ion battery based on the LCF anodes demonstrates a long cycle life of >800 cycles and a high specific capacity of 466 mA h g-1. The findings of this study hold practical significance for promoting the utilization of lignin in the fields of energy storage, adsorption, and beyond.

Application of Electrospun Nanofibers for Fabrication of Versatile and Highly Efficient Electrochemical Devices: A Review

Electrochemical devices convert chemical reactions into electrical energy or, vice versa, electricity into a chemical reaction. While batteries, fuel cells, supercapacitors, solar cells, and sensors belong to the galvanic cells based on the first reaction, electrolytic cells are based on the reversed process and used to decompose chemical compounds by electrolysis. Especially fuel cells, using an electrochemical reaction of hydrogen with an oxidizing agent to produce electricity, and electrolytic cells, e.g., used to split water into hydrogen and oxygen, are of high interest in the ongoing search for production and storage of renewable energies. This review sheds light on recent developments in the area of electrospun electrochemical devices, new materials, techniques, and applications. Starting with a brief introduction into electrospinning, recent research dealing with electrolytic cells, batteries, fuel cells, supercapacitors, electrochemical solar cells, and electrochemical sensors is presented. The paper concentrates on the advantages of electrospun nanofiber mats for these applications which are mostly based on their high specific surface area and the possibility to tailor morphology and material properties during the spinning and post-treatment processes. It is shown that several research areas dealing with electrospun parts of electrochemical devices have already reached a broad state-of-the-art, while other research areas have large space for future investigations.

A Review of Electrospun Carbon Nanofiber-Based Negative Electrode Materials for Supercapacitors

The development of smart negative electrode materials with high capacitance for the uses in supercapacitors remains challenging. Although several types of electrode materials with high capacitance in energy storage have been reported, carbon-based materials are the most reliable electrodes due to their high conductivity, high power density, and excellent stability. The most common complaint about general carbon materials is that these electrode materials can hardly ever be used as free-standing electrodes. Free-standing carbon-based electrodes are in high demand and are a passionate topic of energy storage research. Electrospun nanofibers are a potential candidate to fill this gap. However, the as-spun carbon nanofibers (ECNFs) have low capacitance and low energy density on their own. To overcome the limitations of pure CNFs, increasing surface area, heteroatom doping and metal doping have been chosen. In this review, we introduce the negative electrode materials that have been developed so far. Moreover, this review focuses on the advances of electrospun nanofiber-based negative electrode materials and their limitations. We put forth a future perspective on how these limitations can be overcome to meet the demands of next-generation smart devices.

Sustainable supercapacitors of nitrogen-doping porous carbon based on cellulose nanocrystals and urea

The development of porous carbon materials from sustainable natural sources is an attractive topic in the field of energy storage materials. This study proposed the production of nitrogen-doped porous carbon (NPC) materials from the renewable cellulose nanocrystal (CNC) as carbon source and water-soluble urea as nitrogen source without any external activation. The liquid compounding treatment and subsequent carbonization provided the NPC materials a uniform and stable N-doping (7.4% nitrogen content), high specific surface area (366.5 m²/g) and various superior electrochemical properties. The fabricated NPC sample (CU-3, with the weight ratio of 1:10 for CNC and urea) exhibited a high specific capacitance of 570.6 F/g at a current density load of 1 A/g and good cycling stability (91.2% capacitance retention after 1000 cycles at a current density of 10 A/g) in the 6 M KOH electrolyte. Applying this NPC material as the electrode component in the assembled symmetric supercapacitor demonstrated the promising electrochemical stability with the specific capacitances of 88.2 F/g at the current density of 1 A/g and capacitance retention of 99.8% after 5000 cycles. The developed N-doped porous carbon material from CNCs and urea is expected to be a sustainable electrode component for the supercapacitor materials.

Asymmetric supercapacitor of functionalised electrospun carbon fibers/poly(3,4-ethylenedioxythiophene)/manganese oxide//activated carbon with superior electrochemical performance

Asymmetric supercapacitors (ASC) have shown a great potential candidate for high-performance supercapacitor due to their wide operating potential which can remarkably enhance the capacitive behaviour. In present work, a novel positive electrode derived from functionalised carbon nanofibers/poly(3,4-ethylenedioxythiophene)/manganese oxide (f-CNFs/PEDOT/MnO₂) was prepared using a multi-step route and activated carbon (AC) was fabricated as a negative electrode for ASC. A uniform distribution of PEDOT and MnO₂ on f-CNFs as well as porous granular of AC are well-observed in FESEM. The assembled f-CNFs/PEDOT/MnO₂//AC with an operating potential of 1.6 V can achieve a maximum specific capacitance of 537 F/g at a scan rate of 5 mV/s and good cycling stability (81.06% after cycling 8000 times). Furthermore, the as-prepared ASC exhibited reasonably high specific energy of 49.4 Wh/kg and low charge transfer resistance (R_ct) of 2.27 Ω, thus, confirming f-CNFs/PEDOT/MnO₂//AC as a promising electrode material for the future energy storage system.

Low-Cost Carbon Fibre Derived from Sustainable Coal Tar Pitch and Polyacrylonitrile: Fabrication and Characterisation

Preparation of high-value pitch-based carbon fibres (CFs) from mesophase pitch precursor is of great importance towards low-cost CFs. Herein, we developed a method to reduce the cost of CFs precursor through incorporating high loading of coal tar pitch (CTP) into polyacrylonitrile (PAN) polymer solution. The CTP with a loading of 25% and 50% was blended with PAN and their spinnability was examined by electrospinning process. The effect of CTP on thermal stabilization and carbonisation of PAN fibres was investigated by thermal analyses methods. Moreover, electrospun PAN/CTP fibres were carbonised at two different temperatures i.e., 850 °C and 1200 °C and their crystallographic structures of resulting such low-cost PAN/CTP CFs were studied through X-ray diffraction (XRD) and Raman analyses. Compared to pure PAN CFs, the electrical resistivity of PAN/25% CTP CFs significantly decreased by 92%, reaching 1.6 kΩ/sq. The overall results showed that PAN precursor containing 25% CTP resulted in balanced properties in terms of spinnability, thermal and structural properties. It is believed that CTP has a great potential to be used as an additive for PAN precursor and will pave the way for cost-reduced and high-performance CFs.

Mechanics of Emulsion Electrospun Porous Carbon Fibers as Building Blocks of Multifunctional Materials

Many multifunctional composite structures incorporate porosity at various length scales to increase the available surface area of a functional component. One material system of particular interest is activated or porous carbon fibers and nanofibers that can serve as structural reinforcement as well as providing active surface for added functionality. A key question in the design and manufacture of these fibers is to what degree the induced pore affects the mechanical properties by inducing discontinuities in the material. To address this problem, mechanics of porous carbon nanofibers (CNFs) was studied for the first time as a function of their porous structure. Hollow CNF with porous shell was prepared by coaxial electrospinning a polyacrylonitrile/poly(methyl methacrylate) (PMMA) blend shell with a PMMA core. PMMA was removed by thermal decomposition during pyrolysis to form pores. Solid-shell CNF was prepared as a control with no PMMA in the shell. Results show that the modulus and strength of the porous-shell CNF with a porosity of 19.2 ± 1.3% were 65.0 ± 6.2 and 1.28 ± 0.14 GPa respectively, 13.9 ± 2.1% and 35.5 ± 4.9% lower than those of the solid-shell CNF. Finite-element analysis models were developed to decouple the effect of stress concentration and reduced load-bearing area in porous CNFs on their mechanical properties. The model predictions were in general agreement with the experimental results and were used to identify the most critical parameters that can affect load bearing in porous nanofibers. Considering the comparison of the experimental and modeling results, the intrinsic material strength (of the solid parts) does not seem to be affected by inducing pores; thus, fiber and pore geometries might be developed where the load paths are designed for even less of a strength loss.