Progress in supercapacitors: roles of two dimensional nanotubular materials

Powering the Future by Iron Sulfide Type Material (FexSy) Based Electrochemical Materials for Water Splitting and Energy Storage Applications: A Review

Water electrolysis is among the recent alternatives for generating clean fuels (hydrogen). It is an efficient way to produce pure hydrogen at a rapid pace with no unwanted by-products. Effective and cheap water-splitting electrocatalysts with enhanced activity, specificity, and stability are currently widely studied. In this regard, noble metal-free transition metal-based catalysts are of high interest. Iron sulfide (FeS) is one of the essential electrocatalysts for water splitting because of its unique structural and electrochemical features. This article discusses the significance of FeS and its nanocomposites as efficient electrocatalysts for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), and overall water splitting. FeS and its nanocomposites have been studied also for energy storage in the form of electrode materials in supercapacitors and lithium- (LIBs) and sodium-ion batteries (SIBs). The structural and electrochemical characteristics of FeS and its nanocomposites, as well as the synthesis processes, are discussed in this work. This discussion correlates these features with the requirements for electrocatalysts in overall water splitting and its associated reactions. As a result, this study provides a road map for researchers seeking economically viable, environmentally friendly, and efficient electrochemical materials in the fields of green energy production and storage.

Li Salt Assisted Highly Flexible Carbonaceous Ni3N@polyimide Electrode for an Efficient Asymmetric Supercapacitor

This work used a highly flexible, sustainable polyimide tape as a substrate to deposit ductile-natured carbonaceous Ni3N (C/Ni3N@polyimide) material for supercapacitor application. C/Ni3N was prepared using a co-sputtering technique, and this method also provided better adhesion of the electrode material over the substrate, which is helpful in improving bending performance. The ductile behavior of the sputter-grown electrode and the high flexibility of the polyimide tape provide ultimate flexibility to the C/Ni3N@polyimide-based supercapacitor. To achieve optimum electrochemical performance, a series of electrochemical tests were done in the presence of various electrolytes. Further, a flexible asymmetric supercapacitor (NC-FSC) (C/Ni3N//carbon@polyimide) was assembled by using C/Ni3N as a cathode and a carbon thin film as an anode, separated by a GF/C-glass microfiber soaked in optimized 1 M Li2SO4 aqueous electrolyte. The NC-FSC offers a capacitance of 324 mF cm-2 with a high areal energy density of 115.26 μWh cm-2 and a power density of 811 μW cm-2, with ideal bending performance.

Synthesis of Zinc Oxide Nanorods from Zinc Borate Precursor and Characterization of Supercapacitor Properties

The synthesis of zinc oxide (ZnO) was accomplished from zinc borate (Zn3B2O6) minerals to be used as electrodes in supercapacitor applications. The concentrations of obtained zinc (Zn) metal after treatment with hydrochloric acid (HCl) were determined by atomic absorption spectroscopy (AAS). Direct synthesis of ZnO on a nickel (Ni) foam surface was conducted by employing the hydrothermal technique using a solution with the highest Zn content. The results showed the successful synthesis of ZnO nanorods on the surface of Ni foam with an average wall size of approximately 358 nm. Cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) measurements revealed that the synthesized electrode exhibited battery-type charge storage characteristics, reaching a maximum specific capacitance of approximately 867 mF·cm-² at a current density of 2 mA·cm-². Additionally, the energy and power densities of the electrode at a current density of 2 mA·cm-² were calculated as 19.3 mWh·cm-² and 200 mW·cm-², respectively. These results exhibited promising performance of the single-component electrode, outperforming the existing counterparts reported in the literature.

Recent Advances in the Preparation and Application of Two-Dimensional Nanomaterials

Two-dimensional nanomaterials (2D NMs), consisting of atoms or a near-atomic thickness with infinite transverse dimensions, possess unique structures, excellent physical properties, and tunable surface chemistry. They exhibit significant potential for development in the fields of sensing, renewable energy, and catalysis. This paper presents a comprehensive overview of the latest research findings on the preparation and application of 2D NMs. First, the article introduces the common synthesis methods of 2D NMs from both "top-down" and "bottom-up" perspectives, including mechanical exfoliation, ultrasonic-assisted liquid-phase exfoliation, ion intercalation, chemical vapor deposition, and hydrothermal techniques. In terms of the applications of 2D NMs, this study focuses on their potential in gas sensing, lithium-ion batteries, photodetection, electromagnetic wave absorption, photocatalysis, and electrocatalysis. Additionally, based on existing research, the article looks forward to the future development trends and possible challenges of 2D NMs. The significance of this work lies in its systematic summary of the recent advancements in the preparation methods and applications of 2D NMs.

A La2O3/MXene composite electrode for supercapacitors with improved capacitance and cycling performance

Developing efficient electrode materials is a key towards high power electrochemical energy storage devices. Two-dimensional (2D) MXene shows excellent conductivity and electrochemical performance among other materials. However, the restacking of MXene layers may degrade their specific capacity and cycling performance. Considering this challenge, here we have designed a composite made of 2D MXene nanosheets and lanthanum oxide (La2O3) nanoparticles to overcome the limitations. The bifunctionality of La2O3 nanoparticles prevents the restacking of MXene layers and enhances the electrochemical properties of the electrode due to its good Faradic characteristics. The specific capacitance of the La2O3/MXene composite electrode is 366 F/g at 1 A/g, which is 4.5 and 3 times higher than those of the individual La2O3 and MXene. The composite electrode displays a capacitance retention of 96% after 1,000 cycles, which is due to synergistic effects between the two components and indicates the potential of La2O3/MXene composite for supercapacitors.

Superior cyclability of high surface area vanadium nitride in salt electrolytes

High surface area vanadium nitrides (VNs) have been extensively studied as materials for aqueous supercapacitors due to the high initial capacitance in alkaline media at low scan rates. However, low capacitance retention and safety limit their implementation. The use of neutral aqueous salt solutions has the potential to mitigate both of these concerns, but is limited in analysis. Hence, we report on the synthesis and characterization of high surface area VN as a supercapacitor material in a wide variety of aqueous chlorides and sulfates using Mg²⁺, Ca²⁺, Na⁺, K⁺, and Li⁺ ions. We observe the following trend in the salt electrolytes: Mg²⁺ > Li⁺ > K⁺ > Na⁺ > Ca²⁺. Mg²⁺ systems provide the best performance at higher scan rates with areal capacitances of 294 μF cm^-2 in 1 M MgSO₄ over a 1.35 V operating window at 2000 mV s^-1. Furthermore, VN in 1 M MgSO₄ maintained a 36% capacitance retention from 2 to 2000 mV s^-1 compared to 7% in 1 M KOH. Capacitance in 1 M MgSO₄ and 1 M MgCl₂ increased to 121% and 110% of their original values after 500 cycles and maintained capacitances of 589 and 508 μF cm^-2 at 50 mV s^-1 after 1000 cycles, respectively. In contrast, in 1 M KOH the capacitance decreases to 37% of its original value, reaching only 29 F g^-1 at 50 mV s^-1 after 1000 cycles. The superior performance of the Mg system is attributed to a reversible surface 2 e^- transfer pseudocapacitive mechanism between Mg²⁺ and VN_xO_y. These findings can be used to further the field of aqueous supercapacitors to build safer and more stable energy storage systems that can charge quicker compared to KOH systems.

Fishnet-like double active layer-loaded carbon fiber for electrical double-layer capacitors

The rational design and controllable synthesis of high-performance energy storage materials are important measures to address the growing demand for energy storage devices. This work involves the growth of a fishnet-like Fe₂O₃ nanorod@oxygen-rich carbon layer structure directly onto carbon fiber cloth as a binder-free electrode for symmetric capacitors. The growth of Fe₂O₃ nanorods provided a large specific surface area, and the coating of an oxygen-rich carbon layer protected the Fe₂O₃ nanorods as an active substance. Furthermore, oxidation treatment created rich electrochemically active sites by loading oxygen-containing functional groups onto the composite surface. As a result, the optimal OC@Fe₂O₃-ACC sample exhibited a high areal specific capacitance of 1687 mF cm^-2 at a current density of 1 mA cm^-2. Meanwhile, an excellent capacity retention rate of 58.7% was achieved at 15 mA cm^-2. Finally, the long-term cycling stability was verified with an 80% retention rate of the initial capacitance after 12 000 cycles.

Nanoscale electrochemical charge transfer kinetics investigated by electrochemical scanning microwave microscopy

We show how microwave microscopy can be used to probe local charge transfer reactions with unprecedented sensitivity, visualizing surface reactions with only a few hundred molecules involved. While microwaves are too fast under classical conditions to interact and sense electrochemical processes, this is different at the nanoscale, where our heterodyne microwave sensing method allows for highly sensitive local cyclic voltammetry (LCV) and local electrochemical impedance spectroscopy (LEIS). LCV and LEIS allow for precise measurement of the localized charge transfer kinetics, as illustrated in this study for a ferrocene self-assembled monolayer immersed in an electrolyte. The theoretical analysis presented here enables a consistent mapping of the faradaic kinetics and the parasitic contributions (nonfaradaic) to be spectrally resolved and subtracted. In particular, this methodology reveals an undistorted assessment of accessible redox site density of states associated with faradaic capacitance, fractional surface coverage and electron transfer kinetics at the nanoscale. The developed methodology opens a new perspective on comprehending electrochemical reactivity at the nanoscale.

Square-Facet Nanobar MOF-Derived Co3O4@Co/N-doped CNT Core-Shell-based Nanocomposites as Cathode Materials for High-Performance Supercapacitor Studies

The binary as well as ternary nanocomposites of the square-facet nanobar Co-MOF-derived Co₃O₄@Co/N-CNTs (N-CNTs: nitrogen-doped carbon nanotubes) with Ag NPs and rGO have been synthesized via an easy wet chemical route, and their supercapacitor behavior was then studied. At a controlled pH of the precursor solution, square-facet nanobars of Co-MOF were first synthesized by the solvothermal method and then pyrolyzed under a controlled nitrogen atmosphere to get a core-shell system of Co₃O₄@Co/N-CNTs. In the second step, different compositions of Co₃O₄@Co/N-CNT core-shell structures were formed by an ex-situ method with Ag NPs and rGO moieties. Among several bare, binary, and ternary compositions tested in 6 M aqueous KOH electrolyte, a ternary nanocomposite having a 7.0:1.5:1.5 stoichiometric ratio of Co₃O₄@Co/N-CNT, Ag NPs, and rGO, respectively, reported the highest specific capacitance (3393.8 F g^-1 at 5 mV s^-1). The optimized nanocomposite showed the energy density, power density, and Coulombic efficiency of 74.1 W h.kg^-1, 443.7 W.kg^-1, and 101.3%, respectively, with excellent electrochemical stability. After testing an asymmetrical supercapacitor with a Co₃O₄@Co/N-CNT/Ag NPs/rGO/nickel foam cathode and an activated carbon/nickel foam anode, it showed 4.9 W h.kg^-1 of energy density and 5000.0 W.kg^-1 of power density.

Excellent performance supercapacitors with the compounding of Ni(OH)2 and ZIF-67 derived Co-C-N nanosheets as flexible electrode materials

Owing to the advantages of high theoretical capacity, low cost, and excellent chemical stability, Ni(OH)₂ is considered as a potential candidate for electrode materials of supercapacitors. However, its further applications are limited by its adverse surface chemical properties. In this paper, a composite material consisting of ZIF-67 derived Co-C-N nanosheets and Ni(OH)₂ was synthesized facilely on carbon cloth in situ, and based on the collective advantages of the various components, excellent electrochemical performance could be achieved when used as a flexible electrode material of supercapacitors. In detail, the as-obtained sample Ni(OH)₂/Co-C-N/CC exhibits an ultrahigh specific capacitance of 2100 F g^-1 at a current density of 1 A g^-1. Moreover, the further assembled asymmetric supercapacitor device exhibits a maximum energy density of 78.6 W h kg^-1 at a power density of 749.4 W kg^-1. Furthermore, the device also shows outstanding cycling stability with 90.2% capacitance retention after 5000 cycles of charge-discharge. Basically, the remarkable performance can be attributed to the well-developed structure, abundant active sites, complex beneficial components, and their intrinsic properties. Significantly, rational design can broaden the research directions of corresponding electrode materials.

The role of 2D material families in energy harvesting: An editorial overview

The ever increasing proportion of an energy consuming society and the boost in industrialization accelerated the depletion of fossil fuel based energy sources at an alarming rate. This emphasizes the necessity of sustainable energy generation and storage to meet the daily energy demands. But, these alternative renewable energy sources like solar and wind power are intermittent and highly depend on weather, place and individuals. This creates the inevitability of suitable energy storage devices like batteries and supercapacitors. The interfacing of energy storing devices is required to maintain the supply chain equilibrium, power efficiency, regulate power fluctuations and reduce pollution. Besides, the boom in electric mobility and consumer electronics also require uninterrupted power supply. Hence, in the upcoming years the energy storing devices play a vital role in addressing the energy crisis. Innovations in new materials and technologies will be the core area of research and development in the coming future. 2D materials like graphene,transition metal carbides and nitrides (MXenes), transition metal borides (MBenes) and so on are the new class of materials among them MXenes are getting more attention in energy storage owing to its exceptional properties.

Electrodeposition of CoxNiVyOz Ternary Nanopetals on Bare and rGO-Coated Nickel Foam for High-Performance Supercapacitor Application

We report a simple strategy to grow a novel cobalt nickel vanadium oxide (Co_xNiV_yO_z) nanocomposite on bare and reduced-graphene-oxide (rGO)-coated nickel foam (Ni foam) substrates. In this way, the synthesized graphene oxide is coated on Ni foam, and reduced electrochemically with a negative voltage to prepare a more conductive rGO-coated Ni foam substrate. The fabricated electrodes were characterized with a field-emission scanning electron microscope (FESEM), energy-dispersive X-ray spectra (EDX), X-ray photoelectron spectra (XPS), and Fourier-transform infrared (FTIR) spectra. The electrochemical performance of these Co_xNiV_yO_z-based electrode materials deposited on rGO-coated Ni foam substrate exhibited superior specific capacitance 701.08 F/g, which is more than twice that of a sample coated on bare Ni foam (300.31 F/g) under the same experimental conditions at current density 2 A/g. Our work highlights the effect of covering the Ni foam surface with a rGO film to expedite the specific capacity of the supercapacitors. Despite the slightly decreased stability of a Co_xNiV_yO_z-based electrode coated on a Ni foam@rGO substrate, the facile synthesis, large specific capacitance, and preservation of 92% of the initial capacitance, even after running 5500 cyclic voltammetric (CV) scans, indicate that the Co_xNiV_yO_z-based electrode is a promising candidate for high-performance energy-storage devices.

2D Personality of Multifunctional Carbon Nitrides towards Enhanced Catalytic Performance in Energy Storage and Remediation

Numerous scholars in the scientific and management areas have been overly focused on contemporary breakthroughs in two-dimensional objects for multiple prospective applications. Photochemical and electrocatalytic functions of integrated circuits associated with multi-component tools have been enhanced by designing the macro- and microstructures of the building blocks. Therefore, the current research attempts to explore a larger spectrum of layered graphitic carbon nitrides (g-C3N4) and their derivatives as an efficient catalyst. By executing systematic manufacturing, optimization, and evaluation of its relevance towards astonishing energy storage devices, adsorption chemistry, and remediation, many researchers have focused on the coupling of such 2D carbon nitrides combined with suitable elementals. Hybrid carbon nitrides have been promoted as reliable 2D combinations for the enhanced electrophotocatalytic functionalities, proved by experimental observations and research outputs. By appreciating the modified structural, surface, and physicochemical characteristics of the carbon nitrides, we aim to report a systematic overview of the g-C3N4 materials for the application of energy storages and environments. It has altered energy band gap, thermal stability, remarkable dimensional texturing, and electrochemistry, and therefore detailed studies are highlighted by discussing the chemical architectures and atomic alternation of g-C3N4 (2D) structures.

Ready-to-use binder-free Co(OH)2 plates@porous rGO layers/Ni foam electrode for high-performance supercapacitors

In this work, an outstanding nano-structured composite electrode is fabricated through the co-deposition of Co(OH)₂ nanoplates and porous reduced GO (p-rGO) nanosheets onto Ni foam (NF). Through field emission scanning electron microscopy and transmission electron microscopy observations, it was confirmed that porous reduced graphene oxide sheets are completely wrapped by uniform hexagonal Co(OH)₂ plates. Due to the unique architecture of both components of the prepared composite, a high surface area of 234.7 m² g⁻¹ and mean pore size of 3.65 nm were observed for the Co(OH)₂@p-rGO composite. The constructed Co(OH)₂@p-rGO/NF composite electrode shows higher energy storage capability compared to that of Co(OH)₂/NF and p-rGO/NF electrodes. The Co(OH)₂/NF electrode shows specific capacitances of 902 and 311 F g^–1 at 5 and 30 A g^–1, while the Co(OH)₂@p-rGO/NF electrode delivers 1688 and 1355 F g^–1 under the same current loads, respectively. Furthermore, when the current load was increased from 1 to 30 A g^–1, 74.5% capacitance retention was observed for the Co(OH)₂@p-rGO/NF electrode, indicating its outstanding high-power capability, while the Co(OH)₂/NF electrode retained only 38.5% of its initial capacitance. The fabricated Co(OH)₂@p-rGO/NF//rGO/NF ASC device shows an areal capacitance of 3.29 F cm⁻², cycling retention of 91.2% after 4500 cycles at 5 A g⁻¹ and energy density of 68.7 W h kg⁻¹ at a power density of 895 W kg⁻¹. The results of electrochemical tests prove that Co(OH)₂@p-rGO/NF exhibits good performance as a positive electrode for use in an asymmetric supercapacitor device. The prepared porous composite electrode is thus a promising candidate for use in supercapacitor applications.

Fabrication mechanism of a ready-to-use Co(OH)2@p-rGO/NF electrode: (a) base generation step, (b) electrophoretic deposition of rGO onto NF and (c) chemical formation of Co(OH)2 on rGO.

A mesoporous ternary transition metal oxide nanoparticle composite for high-performance asymmetric supercapacitor devices with high specific energy

We report on the optimized fabrication and electrochemical properties of ternary metal oxide (Ti-Mo-Ni-O) nanoparticles as electrochemical supercapacitor electrode materials. The structural, morphological, and elemental composition of the fabricated Ti-Mo-Ni-O via rapid breakdown anodization are elucidated by field emission scanning electron microscopy, Raman, and photoelectron spectroscopy analyses. The Ti-Mo-Ni-O nanoparticles reveal pseudocapacitive behavior with a specific capacitance of 255.4 F g^-1. Moreover, the supercapacitor device Ti-Mo-Ni-O NPs//mesoporous doped-carbon (TMN NPs//MPDC) device exhibited a superior specific energy of 68.47 W h kg^-1 with a corresponding power density of 2058 W kg^-1. The supercapacitor device shows 100% coulombic efficiency with 96.8% capacitance retention over 11 000 prolonged charge/discharge cycles at 10 A g^-1.

Boosting capacitive performance of manganese oxide nanorods by decorating with three-dimensional crushed graphene

This work reports the rational design of MnO_x nanorods on 3D crushed reduced graphene oxide (MnO_x/C-rGO) by chemical reduction of Ni-incorporated graphene oxide (GO) followed by chemical etching to remove Ni. The resulting MnO_x/C-rGO composite synergistically integrates the electronic properties and geometry structure of MnO_x and 3D C-rGO. As a result, MnO_x/C-rGO shows a significantly higher specific capacitance (C_sp) of 863 F g^-1 than MnO_x/2D graphene sheets (MnO_x/S-rGO) (373 F g^-1) and MnO_x (200 F g^-1) at a current density of 0.2 A g^-1. Furthermore, when assembled into symmetric supercapacitors, the MnO_x/C-rGO-based device delivers a higher C_sp (288 F g^-1) than MnO_x/S-rGO-based device (75 F g^-1) at a current density of 0.3 A g^-1. The superior capacitive performance of the MnO_x/C-rGO-based symmetric device is attributed to the enlarged accessible surface, reduced lamellar stacking of graphene, and improved ionic transport provided by the 3D architecture of MnO_x/C-rGO. In addition, the MnO_x/C-rGO-based device exhibits an energy density of 23 Wh kg^-1 at a power density of 113 Wkg^-1, and long-term cycling stability, demonstrating its promising potential for practical application.

Engineering NiCo2S4 nanoparticles anchored on carbon nanotubes as superior energy-storage materials for supercapacitors

A one-step hydrothermal method was used to successfully synthesize NiCo2S4 nanocomposites anchored on carbon nanotubes as excellent energy storage materials for supercapacitors.

Food seasoning-derived gel polymer electrolyte and pulse-plasma exfoliated graphene nanosheet electrodes for symmetrical solid-state supercapacitors

The symmetrical solid-state supercapacitors using graphene nanosheet electrodes and table salt-derived green gel polymer electrolyte which provide a stable energy storage device, and good electrochemical capability are introduced.

Synthesis of different manganese tungstate nanostructures for enhanced charge-storage applications: theoretical support for experimental findings

Due to the dual features of EDLC and pseudocapacitance the low-temperature developed MnWO4 nanostructures with different aspect ratio showed good electrochemical properties. DFT study provided the quantum capacitance value.

Cellulose-Derived Nanostructures as Sustainable Biomass for Supercapacitors: A Review

Sustainable biomass has attracted a great attention in developing green renewable energy storage devices (e.g., supercapacitors) with low-cost, flexible and lightweight characteristics. Therefore, cellulose has been considered as a suitable candidate to meet the requirements of sustainable energy storage devices due to their most abundant nature, renewability, hydrophilicity, and biodegradability. Particularly, cellulose-derived nanostructures (CNS) are more promising due to their low-density, high surface area, high aspect ratio, and excellent mechanical properties. Recently, various research activities based on CNS and/or various conductive materials have been performed for supercapacitors. In addition, CNS-derived carbon nanofibers prepared by carbonization have also drawn considerable scientific interest because of their high conductivity and rational electrochemical properties. Therefore, CNS or carbonized-CNS based functional materials provide ample opportunities in structure and design engineering approaches for sustainable energy storage devices. In this review, we first provide the introduction and then discuss the fundamentals and technologies of supercapacitors and utilized materials (including cellulose). Next, the efficacy of CNS or carbonized-CNS based materials is discussed. Further, various types of CNS are described and compared. Then, the efficacy of these CNS or carbonized-CNS based materials in developing sustainable energy storage devices is highlighted. Finally, the conclusion and future perspectives are briefly conferred.

Facile decoration of two-dimensional Ti3C2Txnanoplates with CuS nanoparticles via a facilein situsynthesis strategy at room temperature for superhigh specific capacitance of supercapacitors

Although supercapacitors have attracted more and more attention owing to their fast charging speed and high power density, their wide applications have still been limited by their low energy density. In this study, a new CuS-nanoparticle-decorated Ti₃C₂T_xelectrode material is fabricated via a facilein situsynthesis strategy at room temperature. CuS nanoparticles, generated from thein situreaction of Cu (NO₃)₂·3H₂O with Na₂S·9H₂O, are anchored between the Ti₃C₂T_xinterlayers through electrostatic interaction. This type of structural construction is found capable of not only reducing the surface oxidation of Ti₃C₂T_x, but also preventing the accumulation of CuS nanoparticles by the template effect of Ti₃C₂T_xnanoplates. As a result, the CuS/Ti₃C₂T_xnanohybrid delivers a maximum specific capacitance of 911 F g^-1at 1 A g^-1and a good cycling stability. A symmetric supercapacitor fabricated using the CuS/Ti₃C₂T_xnanohybrid as the electrode material exhibits an energy density of 43.56 W h kg^-1with a power density of 475 W kg^-1. Consequently, this work provides a new perspective of microstructural design for the preparation of electrode materials with superhigh specific capacitance through an easy and low-costin situ-reaction method at room temperature.

Designing a Graphene Coating-Based Supercapacitor with Lithium Ion Electrolyte: An Experimental and Computational Study via Multiscale Modeling

Graphene electrodes are investigated for electrochemical double layer capacitors (EDLCs) with lithium ion electrolyte, the focus being the effect of the pore size distribution (PSD) of electrode with respect to the solvated and desolvated electrolyte ions. Two graphene electrode coatings are examined: a low specific surface area (SSA) xGNP-750 coating and a high SSA coating based on a-MWGO (activated microwave expanded graphene oxide). The study comprises an experimental and a computer modeling part. The experimental part includes fabrication, material characterization and electrochemical testing of an EDLC with xGNP-750 coating electrodes and electrolyte 1M LiPF6 in EC:DMC. The computational part includes simulations of the galvanostatic charge-discharge of each EDLC type, based on a continuum ion transport model taking into account the PSD of electrodes, as well as molecular modeling to determine the parameters of the solvated and desolvated electrolyte ions and their adsorption energies with each type of electrode pore surface material. Predictions, in agreement with the experimental data, yield a specific electrode capacitance of 110 F g-1 for xGNP-750 coating electrodes in electrolyte 1M LiPF6 in EC:DMC, which is three times higher than that of the high SSA a-MWGO coating electrodes in the same lithium ion electrolyte.

Effect of the Heating Rate to Prevent the Generation of Iron Oxides during the Hydrothermal Synthesis of LiFePO4

Lithium-ion batteries (LIBs) have gained much interest in recent years because of the increasing energy demand and the relentless progression of climate change. About 30% of the manufacturing cost for LIBs is spent on cathode materials, and its level of development is lower than the negative electrode, separator diaphragm and electrolyte, therefore becoming the "controlling step". Numerous cathodic materials have been employed, LiFePO4 being the most relevant one mainly because of its excellent performance, as well as its rated capacity (170 mA·h·g-1) and practical operating voltage (3.5 V vs. Li+/Li). Nevertheless, producing micro and nanoparticles with high purity levels, avoiding the formation of iron oxides, and reducing the operating cost are still some of the aspects still to be improved. In this work, we have applied two heating rates (slow and fast) to the same hydrothermal synthesis process with the main objective of obtaining, without any reducing agents, the purest possible LiFePO4 in the shortest time and with the lowest proportion of magnetite impurities. The reagents initially used were: FeSO4, H3PO4, and LiOH, and a crucial phenomenon has been observed in the temperature range between 130 and 150 °C, being verified with various techniques such as XRD and SEM.

Altered electrochemical properties of iron oxide nanoparticles by carbon enhance molecular biocompatibility through discrepant atomic interaction

Recent advancement in nanotechnology seeks exploration of new techniques for improvement in the molecular, chemical, and biological properties of nanoparticles. In this study, carbon modification of octahedral-shaped magnetic nanoparticles (MNPs) was done using two-step chemical processes with sucrose as a carbon source for improvement in their electrochemical application and higher molecular biocompatibility. X-ray diffraction analysis and electron microscopy confirmed the alteration in single-phase octahedral morphology and carbon attachment in Fe3O4 structure. The magnetization saturation and BET surface area for Fe3O4, Fe3O4/C, and α-Fe2O3/C were measured as 90, 86, and 27 emu/g and 16, 56, and 89 m2/g with an average pore size less than 7 nm. Cyclic voltammogram and galvanostatic charge/discharge studies showed the highest specific capacitance of carbon-modified Fe3O4 and α-Fe2O3 as 213 F/g and 192 F/g. The in vivo biological effect of altered physicochemical properties of Fe3O4 and α-Fe2O3 was assessed at the cellular and molecular level with embryonic zebrafish. Mechanistic in vivo toxicity analysis showed a reduction in oxidative stress in carbon-modified α-Fe2O3 exposed zebrafish embryos compared to Fe3O4 due to despaired influential atomic interaction with sod1 protein along with significant less morphological abnormalities and apoptosis. The study provided insight into improving the characteristic of MNPs for electrochemical application and higher biological biocompatibility.

Recent Progress on Two-Dimensional Carbon Materials for Emerging Post-Lithium (Na+, K+, Zn2+) Hybrid Supercapacitors

The hybrid ion capacitor (HIC) is a hybrid electrochemical energy storage device that combines the intercalation mechanism of a lithium-ion battery anode with the double-layer mechanism of the cathode. Thus, an HIC combines the high energy density of batteries and the high power density of supercapacitors, thus bridging the gap between batteries and supercapacitors. Two-dimensional (2D) carbon materials (graphite, graphene, carbon nanosheets) are promising candidates for hybrid capacitors owing to their unique physical and chemical properties, including their enormous specific surface areas, abundance of active sites (surface and functional groups), and large interlayer spacing. So far, there has been no review focusing on the 2D carbon-based materials for the emerging post-lithium hybrid capacitors. This concept review considers the role of 2D carbon in hybrid capacitors and the recent progress in the application of 2D carbon materials for post-Li (Na+, K+, Zn2+) hybrid capacitors. Moreover, their challenges and trends in their future development are discussed.

Transition metal dichalcogenide (TMDs) electrodes for supercapacitors: a comprehensive review

As globally, the main focus of the researchers is to develop novel electrode materials that exhibit high energy and power density for efficient performance energy storage devices. This review covers the up-to-date progress achieved in transition metal dichalcogenides (TMDs) (e.g. MoS₂, WS₂, MoSe_2,and WSe₂) as electrode material for supercapacitors (SCs). The TMDs have remarkable properties like large surface area, high electrical conductivity with variable oxidation states. These properties enable the TMDs as the most promising candidates to store electrical energy via hybrid charge storage mechanisms. Consequently, this review article provides a detailed study of TMDs structure, properties, and evolution. The characteristics technique and electrochemical performances of all the efficient TMDs are highlighted meticulously. In brief, the present review article shines a light on the structural and electrochemical properties of TMD electrodes. Furthermore, the latest fabricated TMDs based symmetric/asymmetric SCs have also been reported.

Amalgamation of MnWO4 nanorods with amorphous carbon nanotubes for highly stabilized energy efficient supercapacitor electrodes

Enhanced electrochemical performance of supercapacitors can be achieved through optimal hybridization of electroactive nanomaterials, as it effectively increases the overall surface area and ensures greater electrolyte-electrode interaction. This work reports the realization of a manganese tungstate and amorphous carbon nanotube (MnWO4-aCNT) hybrid and its utilization as the electrodes for a solid-state asymmetric supercapacitor. Large-scale synthesis of aCNTs was carried out via an economical solid-state reaction at low temperature and the walls of these nanotubes were decorated with MnWO4 nanorods via a surfactant-free in situ hydrothermal process. The as-fabricated electrode based on this hybrid over nickel foam delivered a high specific capacitance of 542.18 F g-1 at a scan rate of 2 mV s-1, which is much superior to the values of the structural units separately. This MnWO4-aCNT based electrode showed a high-rate capacity with ∼100% capacitance retention and a coulombic efficiency of ∼100% even after operation for 15 000 cycles. A solid-state asymmetric supercapacitor based on this hybrid attained an energy density of 5.6 W h kg-1 and a power density as high as 893.6 W kg-1. Significantly enhanced electrochemical behaviour registered from the hybrid sample is accounted for by its enhanced surface area and thereby greater number of redox reaction sites along with the positive synergetic effect of the building blocks. This study unlocks further exploration possibilities with other types of aCNT-based hybrid materials for the development of highly stable, non-toxic and cost-effective sustainable energy storage systems.

Boron-Decorated Pillared Graphene as the Basic Element for Supercapacitors: An Ab Initio Study

In this work, using the first-principle density functional theory (DFT) method, we study the properties of a new material based on pillared graphene and the icosahedral clusters of boron B12 as a supercapacitor electrode material. The new composite material demonstrates a high specific quantum capacitance, specific charge density, and a negative value of heat of formation, which indicates its efficiency. It is shown that the density of electronic states increases during the addition of clusters, which predictably leads to an increase in the electrode conductivity. We predict that the use of a composite based on pillared graphene and boron will increase the efficiency of existing supercapacitors.

Enhanced Supercapacitor Performance and Electromagnetic Interference Shielding Effectiveness of CuS Quantum Dots Grown on Reduced Graphene Oxide Sheets

This study is focused on the preparation of the CuS/RGO nanocomposite via the hydrothermal method using GO and Cu-DTO complex as precursors. X-ray diffraction, Fourier-transform infrared spectroscopy, and Raman and X-ray photoelectron spectroscopy study revealed the formation of the CuS/RGO nanocomposite with improved crystallinity, defective nanostructure, and the presence of the residual functional group in the RGO sheet. The morphological study displayed the transformation of CuS from nanowire to quantum dots with the incorporation of RGO. The galvanostatic charge/discharge curve showed that the CuS/RGO nanocomposite (12 wt % Cu-DTO complex) has tremendous and outperforming specific capacitance of 3058 F g-1 at 1 A g-1 current density with moderate cycling stability (∼60.3% after 1000 cycles at 10 A g-1). The as-prepared nanocomposite revealed excellent improvement in specific capacitance, cycling stability, Warburg impedance, and interfacial charge transfer resistance compared to neat CuS. The fabricated nanocomposites were also investigated for their bulk DC electrical conductivity and EMI shielding ability. It was observed that the CuS/RGO nanocomposite (9 wt % Cu-DTO) exhibited a total electromagnetic shielding efficiency of 64 dB at 2.3 GHz following absorption as a dominant shielding mechanism. Such a performance is ascribed to the presence of interconnected networks and synergistic effects.

Superior light absorbing CdS/vanadium sulphide nanowalls@TiO2 nanorod ternary heterojunction photoanodes for solar water splitting

Vanadium sulphide is an emerging infrared active photocatalyst that has not been utilized to its maximum potential.

Heterostructured Titanium Oxynitride-Manganese Cobalt Oxide Nanorods as High-Performance Electrode Materials for Supercapacitor Devices

Metal oxynitrides have been considered recently as emerging electrode materials for supercapacitors. Herein, we converted titanate nanotubes into a series of titanium oxynitride (TiON) nanorods at nitridation temperatures of 800, 900, and 1000 °C in ammonia gas and tested them as supercapacitor electrodes. TiON-800, TiON-900, and TiON-1000 showed capacities of 60, 140, and 71 F g^-1, respectively, at a current density of 1 A g^-1. However, because of TiON's low capacity, a heterostructure (TiON-900/MnCo₂O₄) was designed based on the optimized TiON with MnCo₂O₄ (MCO). The heterostructure TiON-900-MCO and MCO electrode materials showed specific capacities of 515 and 381 F g^-1, respectively, at a current density of 1 A g^-1. The cycling stability retention of TiON-900 and MCO were 75 and 68%, respectively; moreover, the heterostructure of TiON-900-MCO reached 78% at a current density of 5 A g^-1 over 5000 cycles. The increased capacity and sustained cycling stability retention are attributable to the synergistic effect of TiON-900 and MCO. A coin cell (CC)-type symmetric supercapacitor prototype of TiON-900-MCO was fabricated and tested in the voltage range of 0.0-2.0 V in 1 M LiClO₄ in propylene carbonate/dimethyl carbonate electrolyte, and a 79% cycling retention capacity of TiON-900-MCO-CC was achieved over 10 000 cycles at a current density of 250 mA g^-1. We demonstrated a prototypical single cell of TiON-900-MCO-CC as a sustained energy output by powering a red-light emitting diode that indicated TiON-900-MCo electrode materials' potential application in commercial supercapacitor devices.

MOF-derived manganese oxide/carbon nanocomposites with raised capacitance for stable asymmetric supercapacitor

Owing to immense application potentials in electrochemical energy storages, metal organic framework (MOF)-derived metal oxide/carbon nanocomposites have attracted extensive interest of research. Although thermolysis has been widely employed to convert MOFs into various active materials, a large set of in situ changes in chemical composition, phase(s) and morphology requires delicate control over heating parameters. Through an innovative two-stage process, Mn-MIL-100 is first transformed into MnO@C by annealing at 700 °C under N₂ flow, which is then transformed into Mn₃O₄@C at 200 °C in air, while retaining a high surface area. The appropriate retention of carbon content for Mn₃O₄@C can also be easily obtained with the control of heating time. In contrast, thermolysis of MnO@C at higher temperatures gives rise to manganese oxides with negligible carbon content and a greatly reduced surface area. The optimized Mn₃O₄@C-2 h, derived from MnO@C at 200 °C for 2 hours, showed the highest capacitance, far exceeding that of MnO@C and other derivatives. When combined with graphene oxide (GO) nanosheets to form a flexible Mn₃O₄@C/rGO paper electrode, it demonstrated a capacitance of 328.4 F cm⁻³. The Mn₃O₄@C/rGO-based asymmetric supercapacitor thus assembled also shows favorable performance. The present work demonstrates the excellent controllability afforded by the innovative two-stage thermolysis in optimizing the electrochemical performance of MOF-derived active materials as electrode materials in supercapacitors.

Owing to immense application potentials in electrochemical energy storages, metal organic framework (MOF)-derived metal oxide/carbon nanocomposites have attracted extensive interest of research.

A Review of Redox Electrolytes for Supercapacitors

Supercapacitors (SCs) have attracted widespread attention due to their short charging/discharging time, long cycle life, and good temperature characteristics. Electrolytes have been considered as a key factor affecting the performance of SCs. They largely determine the energy density based on their decomposition voltage and the power density from their ionic conductivity. In recent years, redox electrolytes obtained a growing interest due to an additional redox activity from electrolytes, which offers an increased charge storage capacity in SCs. This article summarizes the latest progress in the research of redox electrolytes, and focuses on their properties, mechanisms, and applications based on different solvent types available. It also proposes potential solutions for how to effectively increase the energy density of the SCs while maintaining their high power and long life.

Laser Induced Anchoring of Nickel Oxide Nanoparticles on Polymeric Graphitic Carbon Nitride Sheets Using Pulsed Laser Ablation for Efficient Water Splitting under Visible Light

A visible-light-active nickel oxide-graphitic carbon nitride (NiO@g-CN) hetero-structured nanocomposite was synthesized for the first time by pulsed laser ablation in liquid and used as a photoanode material in photoelectrochemical water-splitting reaction with a solar simulator. It was found that the photoelectrochemical performance of PLAL synthesized NiO@g-CN nanocomposite as photoanode, compared to g-CN as photoanode showed fourfold enhancements in photocurrent density under visible light. FT-IR, XRD, FE-SEM, and EDX consistently showed the proper anchoring of nano-sized NiO on g-CN. UV-DRS and the band gap estimation showed the narrowing down of the band gap energy and consequent enhancement in the visible-light absorption, whereas photoluminescence spectroscopy confirmed the reduction of the recombination of photo-excited electron hole pairs as a result of the anchoring of NiO on g-CN. The photoelectrochemical performance of g-CN and the NiO@g-CN nanocomposite photoanodes was compared by linear sweep voltammetry (LSV), Chronoamperometry (I-t), and Electrochemical Impedance Spectroscopy (EIS). All of these results of the characterization studies account for the observed fourfold enhancement of photocurrent density of NiO@g-CN nanocomposite as photoanode in the photoelectrochemical reaction.

Magnetite ultrafine particles/porous reduced graphene oxide in situ grown onto Ni foam as a binder-free electrode for supercapacitors

Here, we report a simple and green electrochemical route to fabricate a porous network of a Fe₃O₄ nanoparticle-porous reduced graphene oxide (p-rGO) nanocomposite supported on a nickel-foam substrate, which is directly used as a binder-free charge storage electrode. Through this method, pristine Fe₃O₄ NPs/Ni, p-rGO/Ni and Fe₃O₄ NPs@p-rGO/Ni electrodes are fabricated and compared. In the fabricated Fe₃O₄ NPs@p-rGO/Ni electrode, the porous rGO sheets served as a conductive network to facilitate the collection and transportation of electrons during the charge/discharge cycles, improving the conductivity of magnetite NPs and providing a larger specific surface area. As a result, the Fe₃O₄ NPs@p-rGO/Ni exhibited a specific capacitance of 1323 F g⁻¹ at 0.5 A g⁻¹ and 79% capacitance retention when the current density is increased 20 times, where the Fe₃O₄ NPs/Ni electrode showed low specific capacitance of 357 F g⁻¹ and 43% capacity retention. Furthermore, the composite electrode kept 95.1% and 86.7% of its initial capacitances at the current densities of 1 and 4 A g⁻¹, respectively, which were higher than those of a Fe₃O₄/NF electrode at similar loads (i.e. 80.4% and 65.9% capacitance retentions at 1 and 4 A g⁻¹, respectively). These beneficial effects proved the synergistic contribution between p-rGO and Fe₃O₄. Hence, such ultrafine magnetite particles grown onto a porous reduced GO network directly imprinted onto a Ni substrate could be a promising candidate for high performance energy storage aims.

Here, we report a simple and green electrochemical route to deposition of Fe₃O₄ nanoparticle-porous reduced graphene oxide (p-rGO) nanocomposite onto nickel foam substrate, which is directly used as a binder-free charge storage electrode.