Mesoporous carbon nanofiber engineered for improved supercapacitor performance

Nanofibers Comprising Interconnected Chain-Like Hollow N-Doped C Nanocages as 3D Free-Standing Cathodes for Li-S Batteries with Super-High Sulfur Content and Lean Electrolyte/Sulfur Ratio

The development of a suitable cathode host that withstands high sulfur content/loading and low electrolyte/sulfur (E/S) ratio is particularly important for practically sustainable Li-S batteries. Herein, a facile approach is utilized to prepare free-standing 3D cathode substrates comprising nitrogen-doped carbon (N-C) scaffold and metal-organic framework derived interconnected chain-like hollow N-C nanocages, forming a highly porous N-C nanofiber (HP-N-CNF) framework. The N-C skeleton provides highly conductive pathways for fast lithium ion/electron diffusion. The hollow interconnected N-C nanocages not only offer enough space to absorb a high volume of active material but also effectively channelize severe volume stress during the electrochemical performance. The Li-S cell utilizing HP-N-CNF as cathode host displays exceptional battery parameters with high effective sulfur content (83.2 wt%), ultrahigh sulfur loading (14.3 mg cm^-2 ), and low E/S ratio (6.8 μL mg^-1 ). The Li-S cell exhibits a maximum areal capacity of 12.2 mAh cm^-2 which stabilizes at ≈5.5 mAh cm^-2 after the 130th cycle at 0.05 C-rate and is well above the theoretical threshold. Therefore, the proposed unique nanostructure synthesis approach would open new frontiers for developing more realistic and sustainable host materials with feasible battery parameters for various energy storage applications.

MOF derived double-carbon layers boosted the lithium/sodium storage performance of SnO2nanoparticles

Tin oxide (SnO₂) was considered as a promising alternative to commonly used graphite anode in energy storage devices thanks to its superior specific capacity. However, its electrochemical property was severely limited due to the inherent poor conductivity and drastic volume variation during the charging/discharging process. To overcome this disadvantage, we grew Sn-MOF directly on graphene oxide (GO) layers to synthesize a double carbon conductive network-encapsulated SnO₂nanoparticles (SnO₂/C/rGO) via a facile solvothermal method. During the process, Sn-MOF skeleton transformed into porous carbon shells, in which nanosized SnO₂particles (~8nm) were embedded, while GO template was reduced to highly conductive rGO layer tightly wrapping the SnO₂/C particles. This double-carbon structure endowed SnO₂/C/rGO anode with enhanced specific capacity and rate property both in lithium ion batteries (LIB) and sodium ion batteries (SIB). The SnO₂/C/rGO anode showed a highly reversible specific capacity of 1038.3 mAh g^-1at 100 mA g^-1, and maintained a stable capacity of 720.2 mAh g^-1(70.1%) under 500 mA g^-1after 150 cycles in LIBs. Similarly, highly reversible capacity of 350.7 mAh g^-1(81.1%) under 100 mA g^-1after 150 cycles was also achieved in SIBs. This work provided a promising strategy in improving the electrochemical properties of SnO₂nanoparticles (NPs), as well as other potential anode materials suffering from huge volume change and poor conductivity.

MOF-derived porous carbon nanofibers wrapping Sn nanoparticles as flexible anodes for lithium/sodium ion batteries

Facile synthesis of flexible electrodes with high reversible capacity plays a key role in meeting the ever-increasing demand for flexible batteries. Herein, we incorporated Sn-based metal-organic framework (Sn-MOF) templates into crosslinked one-dimensional carbon nanofibers (CNFs) using an electrospinning strategy and obtained a hierarchical porous film (Sn@C@CNF) after a carbothermal reduction reaction. Merits of this modification strategy and its mechanism in improving the electrochemical performance of Sn nanoparticles (NPs) were revealed. Electrospun CNFs substrate ensured a highly conductive skeleton and excellent mechanical toughness, making Sn@C@CNF a self-supported binder-free electrode. Serving as a self-sacrificing template, Sn-MOF provided Sn NPs and derived into porous structures on CNFs after pyrolysis. The hierarchical porous structure of the carbon substrate was beneficial to enhancing the Li⁺/Na⁺ storage of the active materials, and the carbon wrappings derived from polyacrylonitrile (PAN) nanofibers and the MOF skeleton could jointly accommodate the violent volume variation during cycling, enabling Sn@C@CNF to have excellent cycle stability. The Sn@C@CNF anode exhibited a stable discharge specific capacity of 610.8 mAh g^-1 under 200 mA g^-1 for 180 cycles in lithium ion batteries (LIBs) and 360.5 mAh g^-1 under 100 mA g^-1 after 100 cycles in sodium ion batteries (SIBs). As a flexible electrode, Sn@C@CNF demonstrated a stable electromechanical response to repeated 'bending-releasing' cycles and excellent electrochemical performance when assembled in a soft-pack half-LIB. This strategy provided promising candidates of active materials and fabrication methods for advanced flexible batteries.

Preparation and Electrical Properties of Silicone Composite Films Based on Silver Nanoparticle Decorated Multi-Walled Carbon Nanotubes

The electrical properties of silicone composite films filled with silver (Ag) nanoparticle-decorated multi-walled carbon nanotubes (MWNT) prepared by solution processing are investigated. Pristine MWNT is oxidized and converted to the acyl chloride-functionalized MWNT using thionyl chloride, which is subsequently reacted with amine-terminated poly(dimethylsiloxane) (APDMS). Thereafter, APDMS-modified MWNT are decorated with Ag nanoparticles and then reacted with a poly(dimethylsiloxane) solution to form Ag-decorated MWNT silicone (Ag-decorated MWNT-APDMS/Silicone) composite. The morphological differences of the silicone composites containing Ag-decorated MWNT and APDMS-modified MWNT are observed by transmission electron microscopy (TEM) and the surface conductivities are measured by the four-probe method. Ag-decorated MWNT-APDMS/Silicone composite films show higher surface electrical conductivity than MWNT/silicone composite films. This shows that the electrical properties of Ag-decorated MWNT-APDMS/silicone composite films can be improved by the surface modification of MWNT with APDMS and Ag nanoparticles, thereby expanding their applications.

Mesoporous Carbon Fibers with Tunable Mesoporosity for Electrode Materials in Energy Devices

To improve the properties of mesoporous carbon (MC), used as a catalyst support within electrodes, MC fibers (MCFs) were successfully synthesized by combining organic–organic self-assembly and electrospinning deposition and optimizing heat treatment conditions. The pore structure was controlled by varying the experimental conditions. Among MCFs, MCF-A, which was made in the most acidic condition, resulted in the largest pore diameter (4–5 nm), and the porous structure and carbonization degree were further optimized by adjusting heat treatment conditions. Then, since the fiber structure is expected to have an advantage when MCFs are applied to devices, MCF-A layers were prepared by spray printing. For the resistance to compression, MCF-A layers showed higher resistance (5.5% change in thickness) than the bulk MC layer (12.8% change in thickness). The through-plane resistance was lower when the fiber structure remained more within the thin layer, for example, +8 mΩ for 450 rpm milled MCF-A and +12 mΩ for 800 rpm milled MCF-A against the gas diffusion layer (GDL) 25BC carbon paper without a carbon layer coating. The additional advantages of MCF-A compared with bulk MC demonstrate that MCF-A has the potential to be used as a catalyst support within electrodes in energy devices.

Encapsulation of Co3 O4 Nanocone Arrays via Ultrathin NiO for Superior Performance Asymmetric Supercapacitors

Designing of multicomponent transition metal oxide system through the employment of advanced atomic layer deposition (ALD) technique over nanostructures obtained from wet chemical process is a novel approach to construct rational supercapacitor electrodes. Following the strategy, core-shell type NiO/Co₃ O₄ nanocone array structures are architectured over Ni-foam (NF) substrate. The high-aspect-ratio Co₃ O₄ nanocones are hydrothermally grown over NF following the precision controlled deposition of shell NiO considering Co₃ O₄ nanocone as host. NiO thickness of 5 nm exhibits the highest specific capacity of 1242 C g^-1 (2760 F g^-1 ) at current density 2 A g^-1 , which is greater than pristine Co₃ O₄ @NF (1045.8 C g^-1 or 2324 F g^-1 ). The rate capability with 5 nm NiO/Co₃ O₄ @NF nanocone structures is about 77% whereas Co₃ O₄ @NF retains 46 % of capability at 10 A g^-1 . The ultrathin ALD 5 nm NiO accelerates both rate capability and 95.5% cyclic stability after 12 000 charge-discharge cycles. An asymmetric device fabricated between 5 nm NiO/Co₃ O₄ @NF (positive) || activated carbon (negative) achieves an energy density of 81.45 Wh kg^-1 (4268 W kg^-1 ) with good cycling device stability. Additionally, LEDs can be energized by two ASC device in series. This work opens the path in both advanced electrode material and surface modification of earth-abundant systems for efficient and real-time supercapacitor applications.

State of the Art and New Directions on Electrospun Lignin/Cellulose Nanofibers for Supercapacitor Application: A Systematic Literature Review

Supercapacitors are energy storage devices with high power density, rapid charge/discharge rate, and excellent cycle stability. Carbon-based supercapacitors are increasingly attracting attention because of their large surface area and high porosity. Carbon-based materials research has been recently centered on biomass-based materials due to the rising need to maintain a sustainable environment. Cellulose and lignin constitute the major components of lignocellulose biomass. Since they are renewable, sustainable, and readily accessible, lignin and cellulose-based supercapacitors are economically viable and environmentally friendly. This review aims to systematically analyze published research findings on electrospun lignin, cellulose, and lignin/cellulose nanofibers for use as supercapacitor electrode materials. A rigorous scientific approach was employed to screen the eligibility of relevant articles to be included in this study. The research questions and the inclusion criteria were clearly defined. The included articles were used to draw up the research framework and develop coherent taxonomy of literature. Taxonomy of research literature generated from the included articles was classified into review papers, electrospun lignin, cellulose, and lignin/cellulose nanofibers for use as supercapacitor electrode materials. Furthermore, challenges, recommendations, and research directions for future studies were equally discussed extensively. Before this study, no review on electrospun lignin/cellulose nanofiber-based supercapacitors has been reported. Thus, this systematic review will provide a reference for other researchers interested in developing biomass-based supercapacitors as an alternative to conventional supercapacitors based on petroleum products.

Structural design toward functional materials by electrospinning: A review

Electrospinning as one of the most versatile technologies have attracted a lot of scientists’ interests in past decades due to its great diversity of fabricating nanofibers featuring high aspect ratio, large specific surface area, flexibility, structural abundance, and surface functionality. Remarkable progress has been made in terms of the versatile structures of electrospun fibers and great functionalities to enable a broad spectrum of applications. In this article, the electrospun fibers with different structures and their applications are reviewed. First, several kinds of electrospun fibers with different structures are presented. Then the applications of various structural electrospun fibers in different fields, including catalysis, drug release, batteries, and supercapacitors, are reviewed. Finally, the application prospect and main challenges of electrospun fibers are discussed. We hope that this review will provide readers with a comprehensive understanding of the structural design and applications of electrospun fibers in different fields.

Key issues facing electrospun carbon nanofibers in energy applications: on-going approaches and challenges

Electrospun carbon nanofibers (CNFs), with one-dimensional (1D) morphology, tunable size, mechanical flexibility, and functionalities by themselves and those that can be added onto them, have witnessed the intensive development and extensive applications in energy storage and conversion, such as supercapacitors, batteries, and fuel cells. However, conventional solid CNFs often suffer from a rather poor electrical conductivity and low specific surface area, compared with the graphene and carbon nanotube counterparts. A well-engineered porous structure in CNFs increases their surface areas and reactivity, but there is a delicate balance between the level and type of pores and mechanical robustness. In addition, CNFs by themselves often show unsatisfactory electrochemical performance in energy storage and conversion, where, to endow them with high and durable activity, one effective approach is to dope CNFs with certain heteroatoms. Up to now, various activation strategies have been proposed and some of them have demonstrated great success in addressing these key issues. In this review, we focus on the recent advances in the issue-oriented schemes for activating the electrospun CNFs in terms of enhancing the conductivity, modulating pore configuration, doping with heteroatoms, and reinforcing mechanical strength, in close reference to their applications in supercapacitors. The basic scientific principles involved in these activation processes and their effectiveness in boosting the electrochemical performance of CNFs are examined. Finally, some of the on-going challenges and future perspectives in engineering CNFs for better performance are highlighted.

Dendritic Nanostructured Waste Copper Wires for High-Energy Alkaline Battery

Rechargeable alkaline batteries (RABs) have received remarkable attention in the past decade for their high energy, low cost, safe operation, facile manufacture, and eco-friendly nature. To date, expensive electrode materials and current collectors were predominantly applied for RABs, which have limited their real-world efficacy. In the present work, we propose a scalable process to utilize electronic waste (e-waste) Cu wires as a cost-effective current collector for high-energy wire-type RABs. Initially, the vertically aligned CuO nanowires were prepared over the waste Cu wires via in situ alkaline corrosion. Then, both atomic-layer-deposited NiO and NiCo-hydroxide were applied to the CuO nanowires to form a uniform dendritic-structured NiCo-hydroxide/NiO/CuO/Cu electrode. When the prepared dendritic-structured electrode was applied to the RAB, it showed excellent electrochemical features, namely high-energy-density (82.42 Wh kg-1), excellent specific capacity (219 mAh g-1), and long-term cycling stability (94% capacity retention over 5000 cycles). The presented approach and material meet the requirements of a cost-effective, abundant, and highly efficient electrode for advanced eco-friendly RABs. More importantly, the present method provides an efficient path to recycle e-waste for value-added energy storage applications.

Improved pseudocapacitive charge storage in highly ordered mesoporous TiO2/carbon nanocomposites as high-performance Li-ion hybrid supercapacitor anodes

A Li-ion hybrid supercapacitor (Li-HSCs), an integrated system of a Li-ion battery and a supercapacitor, is an important energy-storage device because of its outstanding energy and power as well as long-term cycle life. In this work, we propose an attractive material (a mesoporous anatase titanium dioxide/carbon hybrid material, m-TiO₂-C) as a rapid and stable Li⁺ storage anode material for Li-HSCs. m-TiO₂-C exhibits high specific capacity (∼198 mA h g⁻¹ at 0.05 A g⁻¹) and promising rate performance (∼90 mA h g⁻¹ at 5 A g⁻¹) with stable cyclability, resulting from the well-designed porous structure with nanocrystalline anatase TiO₂ and conductive carbon. Thereby, it is demonstrated that a Li-HSC system using a m-TiO₂-C anode provides high energy and power (∼63 W h kg⁻¹, and ∼4044 W kg⁻¹).

A mesoporous TiO₂/carbon nanocomposite prepared by block copolymer self-assembly improves pseudocapacitive behavior and achieves high energy/power density Li-ion hybrid supercapacitors.