Three-dimensional porous carbonaceous network with in-situ entrapped metallic cobalt for supercapacitor application

Nanoarchitectonics of Three-Dimensional Carbon Nanofiber-Supported Hollow Copper Sulfide Spheres for Asymmetric Supercapacitor Applications

Three-dimensional carbon nanofiber (3D-CNF)-supported hollow copper sulfide (HCuS) spheres were synthesized by the facile hydrothermal method. The morphology of the as-synthesized HCuS@3D-CNF composite clearly revealed that the 3D-CNFs act as a basement for HCuS spheres. The electrochemical performance of as-synthesized HCuS@3D-CNFs was evaluated by cyclic voltammetry (CV) tests, gravimetric charge-discharge (GCD) tests, and Nyquist plots. The obtained results revealed that the HCuS@3D-CNFs exhibited greater areal capacitance (4.6 F/cm²) compared to bare HCuS (0.64 F/cm²) at a current density of 2 mA/cm². Furthermore, HCuS@3D-CNFs retained excellent cyclic stability of 83.2% after 5000 cycles. The assembled asymmetric device (HCuS@3D-CNFs//BAC) exhibits an energy density of 0.15 mWh/cm² with a working potential window of 1.5 V in KOH electrolyte. The obtained results demonstrate that HZnS@3D-CNF nanoarchitectonics is a potential electrode material for supercapacitor applications.

N,S-co-doped FeCo Nanoparticles Supported on Porous Carbon Nanofibers as Efficient and Durable Oxygen Reduction Catalysts

Finding high-performance, low-cost, efficient catalysts for oxygen reduction reactions (ORR) is essential for sustainable energy conversion systems. Herein, highly efficient and durable iron (Fe) and cobalt (Co)-supported nitrogen (N) and sulfur (S) co-doped three-dimensional carbon nanofibers (FeCo-N, S@CNFs) were synthesized via electrospinning followed by carbonization. The as-prepared FeCo-N,S@CNFs served as efficient ORR catalysts in alkaline 0.1 m KOH solutions that were N₂ and O₂ -saturated. The experimental results revealed that FeCo-N,S@CNFs were highly active ORR catalysts with defect-rich active pyridinic N and pyrrolic N and metal bonds to N and S atom sites, which enhanced the ORR activity. FeCo-N,S@CNFs exhibited a high onset potential (E_onset =0.89 V) and half-wave potential (E_1/2 =0.85 V), similar to the electrocatalytic activity of commercial Pt/C. Additionally, the durability of the as-prepared FeCo-N,S@CNFs catalysts was maintained for 14 h with long-term stability and high tolerance to methanol stability, accounting for their excellent catalytic ability. Furthermore, Co-N@CNFs, Fe-N@CNFs, and varying Fe and Co ratios were compared with those of FeCo-N,S@CNFs. Synergistic interactions between metals and heteroatoms were believed to play a significant role in enhancing the ORR activity. Owing to their excellent catalytic reduction ability, the as-prepared FeCo-N,S@CNFs can be widely used in battery-based systems and replace commercial Pt/C in fuel cell applications.

Biomass-Derived Porous Carbon Materials for Li-Ion Battery

Biomass-based carbon nanofibers (CNF) were synthesized using lignin extracted from sawdust and polyacrylonitrile (PAN) (30:70) with the help of the electrospinning method and subsequent stabilization at 220 °C and carbonization at 800, 900, and 1000 °C. The synthesized CNFs were studied by scanning electron microscopy, energy-dispersive X-ray analysis, Raman spectroscopy, and the Brunauer-Emmett-Teller method. The temperature effect shows that CNF carbonized at 800 °C has excellent stability at different current densities and high capacitance. CNF 800 in the first test cycle at a current density of 100 mA/g shows an initial capacity of 798 mAh/g and an initial coulomb efficiency of 69.5%. The CNF 900 and 1000 show an initial capacity of 668 mAh/g and 594 mAh/g, and an initial Coulomb efficiency of 52% and 51%. With a long cycle (for 500 cycles), all three samples at a current density of 500 mA/g show stable cycling in different capacities (CNF 800 in the region of 300-400 mAh/g, CNF 900 and 1000 in the region of 100-200 mAh/g).

Embedding Co2P nanoparticles in Cu doping carbon fibers for Zn-air batteries and supercapacitors

Developing highly efficient and non-precious materials for Zn-air batteries (ZABs) and supercapacitors (SCs) are still crucial and challenging. Herein, electronic reconfiguration and introducing conductive carbon-based materials are simultaneously conducted to enhance the ZABs and SCs performance of Co₂P. We develop a simple and efficient electrospinning technology followed by carbonization process to synthesize embedding Co₂P nanoparticles in Cu doping carbon nanofibers (Cu-Co₂P/CNFs). As a result, the 7% Cu-Co₂P/CNFs presents high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity (half-wave potential of 0.792 V for ORR, an overpotential of 360 mV for OER). The ZABs exhibit a power density of 230 mW cm^-2and excellent discharge-charge stability of 80 h. In addition, the 7% Cu-Co₂P/CNFs show the specific capacitance of 558 F g^-1at 1 A g^-1. Moreover, the 7% Cu-Co₂P/CNFs//CNFs asymmetric supercapacitor was assembled applying 7% Cu-Co₂P/CNFs electrode and pure CNFs, which exhibits a high energy density (25.9 Wh kg^-1), exceptional power density (217.5 kW kg^-1) and excellent cycle stability (96.6% retention after 10 000 cycles). This work may provide an effective way to prepared Co₂P based materials for ZABs and SCs applications.

An electrochemically reduced ultra-high mass loading three-dimensional carbon nanofiber network: a high energy density symmetric supercapacitor with a reproducible and stable cell voltage of 2.0 V

Commercial supercapacitors need a high mass loading of more than 10 mg cm^-2 and a high working potential window to resolve the low energy density concern. Herein, we have demonstrated a thick, ultrahigh mass loading (35 mg cm^-2) and wide cell voltage electrochemically reduced layer-by-layer three-dimensional carbon nanofiber network (LBL 3D-CNF) electrode via electrospinning, sodium borohydride treatment, carbonization, and electro-reduction techniques. During the electro-reduction technique, Na⁺ is adsorbed onto the various defect sites of LBL 3D-CNFs, which properly inhibits the formation of the intermediate HER (hydrogen evolution reaction) product, leading to a wide cell voltage, whereas the LBL 3D-CNF network evokes an opportunity for storing a greater number of charges, resulting in excellent electrochemical performances. A symmetric supercapacitor with a reproducible and stable cell voltage of 2.0 V is constructed and demonstrated. The as-constructed device can deliver an areal energy output of 1922 μW h cm^-2 at a power density of 3979 W kg^-1 equal to a gravimetric energy density of 27 W h kg^-1, and an outstanding cyclic durability of 97.4% after 20 000 GCD cycles. These record-breaking performances would make our device one of the most promising candidates from an industrial point of view.

Laser In-Situ synthesis of metallic cobalt decorated porous graphene for flexible In-Plane microsupercapacitors

Transition metal nanoparticles-graphene nanocomposites incorporate the advantages of graphene and metal nanoparticles, which arouse extensive attention. Here, we design a novel, facile and versatile method for in-situ synthesis of laser-induced porous graphene (LIG) decorated with cobalt particles (Co). The LIG/Co nanocomposites are fabricated through one-step laser direct scribing on a customized film composed of polyimide (PI) powder, polyvinyl alcohol (PVA), and cobalt chloride (CoCl₂·6H₂O) precursors. Benefiting from the unique properties of Co nanoparticles embedded LIG, the obtained optimal in-plane micro-supercapacitors (IMSC) based on LIG/Co-1.5 possesses an excellent areal capacitance of 110.11 mF cm^-2 and a superior energy density of 9.79 μWh cm^-2, which are about 79 times that of pure LIG-based IMSCs. Simultaneously, the LIG/Co-1.5 MSCs also present good cycling stability, remarkable modular integration capability, and outstanding mechanical flexibility, showing potential for practical applications. Additionally, the density functional theory (DFT) calculations indicate that the decorating of cobalt particles elevates electron transfer. Moreover, the interaction between electrolyte and electrodes is also improved with the introduction of cobalt particles. Therefore, this strategy offers a new avenue for facile and large-scale manufacturing of various metallic atoms in-situ decorating in porous graphene.

Construction of ZIF@electrospun cellulose nanofiber derived N doped metallic cobalt embedded carbon nanofiber composite as binder-free supercapacitance electrode

In this study, binder-free hybrid supercapacitance electrode based on N, Co co-doped porous carbon polyhedral encapsulated carbon nanofibers composites (N-Co/CNF) was prepared through pyrolyzing cobalt based zeolitic imidazolate frameworks (ZIF-67(Co)) incorporated electrospun cellulose nanofibers. With rational combination of the conductivity provided by cellulose derived CNF, promising porosity provided by CNF and ZIF-67(Co) derived porous carbon and uniformly dispersed metallic cobalt nanoparticles, the N-Co/CNF displayed excellent electrochemical properties. Specifically, the N-Co/CNF pyrolyzed at 800 °C possessed superior electrochemical performance in 1 M H₂SO₄ electrolyte, including a specific capacitance of ~433 F/g and 84% of the capacitance retention after 3000 consecutive charge-discharge cycles. This significantly exceeded the performance of cellulose derived CNF based pure carbonaceous electrode. Therefore, the present study provides a new view on the construction of high performance hybrid supercapacitance electrode which introduces renewable biomass resources like cellulose as both carbonaceous material precursors and conductive binders.

Integrating the Essence of a Metal-Organic Framework with Electrospinning: A New Approach for Making a Metal Nanoparticle Confined N-Doped Carbon Nanotubes/Porous Carbon Nanofibrous Membrane for Energy Storage and Conversion

The fabrication of an economic and efficient multifunctional advanced nanomaterial with a rational composition and configuration by a facile methodology is a crucial challenge. Herein, we are the first to report the growth of Co nanoparticle-integrated nitrogen-doped carbon nanotubes (N-CNTs) on porous carbon nanofibers by simply heating in the situ-developed metal-organic framework (MOF)-based electrospun nanofibrous membrane with no need for an external supply of any additional precursors and reducing gases. The long and entangled N-CNTs originating from highly porous and graphitic carbon nanofibers offer good flexibility, large surface area, high porosity, high conductivity, the homogeneous incorporation of heteroatoms and metallic constituents, and an abundant exposure of active nanocatalytic sites. The as-developed nanoassembly demonstrates attractive characteristics for electrocatalytic hydrogen and oxygen evolution reactions and electrochemical energy storage. This strategy of integrating the essence of an MOF with electrospinning offers a new, direct, and cost-effective approach for making N-doped CNT-based multifunctional membranes.

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.

Structural Batteries: A Review

Structural power composites stand out as a possible solution to the demands of the modern transportation system of more efficient and eco-friendly vehicles. Recent studies demonstrated the possibility to realize these components endowing high-performance composites with electrochemical properties. The aim of this paper is to present a systematic review of the recent developments on this more and more sensitive topic. Two main technologies will be covered here: (1) the integration of commercially available lithium-ion batteries in composite structures, and (2) the fabrication of carbon fiber-based multifunctional materials. The latter will be deeply analyzed, describing how the fibers and the polymeric matrices can be synergistically combined with ionic salts and cathodic materials to manufacture monolithic structural batteries. The main challenges faced by these emerging research fields are also addressed. Among them, the maximum allowable curing cycle for the embedded configuration and the realization that highly conductive structural electrolytes for the monolithic solution are noteworthy. This work also shows an overview of the multiphysics material models developed for these studies and provides a clue for a possible alternative configuration based on solid-state electrolytes.

Phytic acid controlled in situ synthesis of amorphous cobalt phosphate/carbon composite as anode materials with a high mass loading for symmetrical supercapacitor: amorphization of the electrode to boost the energy density

Transition metal phosphate (TMPi)-based composites as anode electrode materials in supercapacitor applications are less reported. Herein, we report a phytic acid (PA)-assisted in situ-formed amorphous cobalt phosphate/carbon (CoPi/C) composite grown on a flexible woven carbon cloth (CC) via a simple one-step carbonization approach. The tunable synthesis of amorphous and crystalline composites is shown by simply controlling the concentration of the cobalt salts. The strategy for high mass loading to 12 mg cm^-2 is also shown in this report. Importantly, the resulting amorphous electrode materials exhibit electric double-layer capacitance (EDLC) behavior that works over a wide potential range from -1.4 to +0.5 V in an aqueous solution of potassium hydroxide (2 M KOH) and from -1.5 to +1.5 V in sodium sulfate (1 M Na₂SO₄). The amorphous electrode as an anode is capable of delivering an areal capacitance up to 2.15 F cm^-2 at a current density of 4 mA cm^-2 (gravimetric capacitance up to 606.1 F g^-1 at 1 Ag^-1) and has a retention of 94.2% at 10 000 cycles. The flexible solid-state symmetric device fabricated shows an energy density of approximately 620.0 μW h cm^-2 at a power density of 4.7 mW cm^-2 (31.1 W h kg^-1 at 476.0 W kg^-1). This study offers a novel route for the generation of metal phosphate-based anode materials with high capacitance for symmetrical supercapacitor device with high energy density.

Oxygen-Plasma Surface Treatment of an Electrode Sheet Using Carbon from Japanese Distilled Liquor Waste for Double-layer Capacitors

Oxygen-plasma treatment was performed on an activated carbon sheet obtained from shochu (Japanese distilled liquor) waste using a high-frequency plasma generator. The capacitances of the activated carbon sheet electrode subjected to surface treatment were measured using cyclic voltammetry. The best results were obtained with a processing time of 60 min, an output power of 40 W, an interelectrode distance of 13 cm and an oxygen pressure of 40 Pa. The maximum capacitance was 247 F g−1. Investigation of the surface functional groups of the activated carbon sheet revealed that the oxygen-containing functional groups modified on the surface of the activated carbon sheet electrode contributed to the improvement in the capacitance. High-performance electric double-layer capacitors can be realized using the developed electrodes.

Structural correlation of a nanoparticle-embedded mesoporous CoTiO3 perovskite for an efficient electrochemical supercapacitor

We synthesized mesoporous cobalt titanate (CTO) microrods via the sol-gel method as an outstanding working electrode for the supercapacitor. The mesoporous CTO microrods were amassed in hexagonal shapes of an average width of ∼670 nm, and were composed of nanoparticles of average diameter ∼41 nm. The well crystalline CTO microrods of the hexagonal phase to the R3̄ space group possessed an average pore size distribution of 3.92 nm throughout the microrod. The mesoporous CTO microrods with increased textural boundaries played a vital role in the diffusion of ions, and they provided a specific capacitance of 608.4 F g-1 and a specific power of 4835.7 W kg-1 and a specific energy of 9.77 W h kg-1 in an aqueous 2 M KOH electrolyte, which was remarkably better than those of Ti, La, Cr, Fe, Ni, and Sr-based perovskites or their mixed heterostructures supplemented by metal oxides as an impurity. Furthermore, the diffusion-controlled access to the OH- ions (0.27 μs) deep inside the microrod conveyed high stability, a long life cycle for up to 1950 continuous charging-discharging cycles, and excellent capacitance retention of 82.3%. Overall, the mesoporous CTO shows its potential as an electrode for a long-cycle supercapacitor, and provides opportunities for additional enhancement after developing the core-shell hetero-architecture with other metal oxide materials such as MnO2, and TiO2.