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A pair of polyaniline (PANIs) samples was prepared from HCl or H2SO4 electrolytes containing 0.01 M of aniline, and then subjecting them to electropolymerization. The morphology, structure, and properties of the samples were characterized using scanning electron microscope, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The results demonstrate that the capacitance and morphology of the product depend exclusively on the reactive medium used. The PANI was used as a material electrode in a supercapacitor, and the electrochemical performance of the elaborated electrodes was evaluated using cyclic voltammetry, galvanostatic charge/discharge measurement, and electrochemical impedance spectroscopy. The optimal results for the specific capacitance of the PANI films were achieved under a 5-mVs−1 scan rate, ranging from 410.35 F/g for the FTO/PANI-H2SO4 to 758.72 F/g for the FTO/PANI-HCl. [ABSTRACT FROM AUTHOR]

In order to build electrochemical energy storage electrodes, carbon composite materials containing nanosized metal oxides might be desirable. This article describes the designing of TiO2 aerogel/graphene oxide (TiO2-A/GO) composites for electrochemical supercapacitors. TiO2-A was synthesized by a simple sol-gel process followed by annealing at 250°C and thereafter, different concentrations of GO were mixed to prepare TiO2-A/GO composites via sonochemical method. The intermixing of GO and TiO2-A in composite was confirmed by observing the structural and crystalline characterizations. Two electrode electrochemical system was used to elucidate the capacitive characteristics of TiO2-A/GO composite electrode by cyclic voltammetry analysis. In comparison with TiO2-A electrode, high specific capacitances (Cs) were recorded for TiO2-A/GO composite electrode. TiO2-A/2GO composite electrode attained the highest Cs value of ~338.2 Fg−1 at 10 mVs−1 with excellent cycle stability after 2000 cycles. Thus, the prepared TiO2-A/GO composites-based electrode can be a promising material to achieve good capacitive properties. [ABSTRACT FROM AUTHOR]

This review considers the literature on electrochemical supercapacitors operating at extreme temperatures from –80 to +220°C, which is very important for practice. The influence of the following methods and factors on the efficiency of the electrochemical supercapacitors at the extreme temperatures is considered: the using of ionic liquids as electrolytes; the using of modified gel electrolyte, a combined electrolyte, aqueous electrolytes with low freezing point; the using of acetonitrile as an electrolyte solvent; the using of clay as a solid electrolyte; application of solid-state electrochemical supercapacitors; application of electrodes with optimized porous structure; the using of graphene and pseudocapacitive electrodes; the using of solar cells; using of combined techniques to create supercapacitors for extreme temperatures. Undoubtedly, this review will be of great interest both for fundamental electrochemistry and for practice. [ABSTRACT FROM AUTHOR]

The development of carbon materials with desirable textures and new aqueous electrolytes is the key strategy to improve the performance of supercapacitors. Herein, a deep eutectic solvent (DES) was used for in situ templating of a carbon material. A carbon material was characterized (XRD, N2-physisorption, FTIR, SEM and EDS) and used as an electrode material for the first time in multivalent-based supercapacitors. In situ templating of carbon was performed using a novel DES, which serves as a precursor for carbon and for in situ generation of MgO. The generation of MgO and its roles in templating of carbon were discussed. Templating of carbon with MgO lead to an increase in surface area and a microporous texture. The obtained carbon was tested in multivalent-ion (Al3+ and Mg2+) electrolytes and compared with H2SO4. The charge-storage mechanism was investigated and elaborated. The highest specific capacitance was obtained for the Al(NO3)3 electrolyte, while the operating voltage follows the order: Mg(NO3)2 > Al(NO3)3 > H2SO4. Electrical double-layer capacitance (versus pseudocapacitance) was dominant in all investigated electrolytes. The larger operating voltage in multivalent electrolytes is a consequence of the lower fraction of free water, which suppresses hydrogen evolution (when compared with H2SO4). The GCD was experimentally performed on the Al(NO3)3 electrolyte, which showed good cyclic stability, with an energy density of 22.3 Wh kg−1 at 65 W kg−1. [ABSTRACT FROM AUTHOR]

Ni1-xSrxCo2O4-δ nanoparticles were prepared by a simple one pot chemical synthesis route. From XRD data, the samples were indexed to the spinel cubic (FCC) structure. From FTIR data, the presence of metal-oxygen bond in the samples was confirmed. The presence of major nano- and few micron-sized particles was confirmed by particle size and SEM analysis. The electrochemical performance of the materials was studied by cyclic voltammetry technique in 6 M KOH at different scan rates (10–100 mV). Ni0.90Sr0.10Co2O4-δ resulted in high capacitance value (72.24 Fg−1 at 10 mV s−1). Hence, nickel cobaltite electrode may be useful in supercapacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Optimized porous electrode structure. • Use of carbon nanotubes, graphenes as materials. • High power supercapacitors. One of the main advantage of electrochemical supercapacitors (ECSCs) over batteries are sufficiently higher values of specific power. These values for batteries are from several tens to ∼200–300 W kg−1. Earlier it was found that the specific power of ECSCs is up to 2 kW kg−1 under sufficiently high values of the specific energy. However, recently the supercapacitors, specific power of which reaches up to 500–700 kW kg−1, were reported. These ECSCs can be called as supercapacitors of ultra-high power. This review is devoted namely to these ECSCs. Here the main factors that provide the achievement of these very high values of specific power are described. These factors include: the optimized porous structure of the electrodes, the use of carbon nanotubes, graphenes, and their combination as electrode materials. [ABSTRACT FROM AUTHOR]

The electrochemical (EC) supercapacitor, known for its rapid charging, reliability, and versatile applications, demands optimized electrode characteristics and an understanding of their electrochemical behaviour. Although boron-doped diamond (BDD) holds promise as a supercapacitor electrode, a crucial gap exists in comprehending its material behaviour under specific growth conditions. Here, nitrogen-incorporated BDD (N-BDD) films with different microstructures are investigated. The morphology of N-BDD films is varied by tuning the substrate temperature (T s) from 400 °C to 850 °C during the growth process. The diamond films grown at lower T s = 400 °C consist of faceted grains, and the grain sizes shrink as T s is increased (550 °C and 700 °C). Interestingly, the films grown at 850 °C (N-BDD 850°C) show nanowire-like morphology with enhanced electrical conductivity. The spectroscopy and microscopy results reveal the concurrence of sp 3 -diamond and sp 2 -graphitic phases in the nanowire morphology. The EC supercapacitor studies disclose that formation of nanowire-like morphology for N-BDD 850°C increases the active surface area and electron transport properties; hence, higher current response and enhanced specific capacitance (0.09 F cm−2 at a current density of 1.53 mA cm−2) are observed. Lifecycle stability of 82% is observed after 5000 cycles indicating the efficient performance of N-BDD 850°C films. [Display omitted] • Temperature dependent morphological and microstructural variations in diamond. • Nanowire-like morphology forms at a high substrate temperature. • Presence of sp2-graphitic content in sp 3-diamond implying suitable electrode. • Capacitive current enhancement with the increase in substrate temperature. • 82% capacity retention after 5000 cycles of charging and discharging. [ABSTRACT FROM AUTHOR]

• Applications of organic electrolytes in EDLCs, pseudocapacitors and hybrid-capacitors. • Energy density of ESs can be enhanced by using organic electrolytes with wide potential range. • Effects of pore size, electrode-electrolyte interaction, impurities, temperature and many other factors on performance of ESs are discussed. • Methods for the development of newer organic electrolytes have been presented. The article presents an overview of applications of organic electrolytes in electrochemical supercapacitors. Organic electrolytes with large potential range dominate the commercial market. There are some associated drawbacks with organic electrolytes such as relatively high cost, smaller specific capacitance, high resistance, greater flammability, volatility, and toxicity. To encounter these disadvantages, methods for the development of newer organic salts and solvents are also discussed. [ABSTRACT FROM AUTHOR]

Summary: Ordered mesoporous carbons (OMCs) possess great advantages, such as large surface area, uniform pore distribution, high porosity, and physical and chemical stability. However, the monotonic and long porous channels in OMCs hinder their further application, especially in energy storage. Here, we synthesized mesoporous carbon hollow spheres (MCHSs) with a "Dual‐templating method" using dandelion‐like silica spheres (DSSs) as the template. Through the dual‐templating method, the MCHSs directly replicated the mesoporous edge of DSSs as a thick mesoporous shell but substituted the clogged central core with hollow‐core. The combined structure with mesoporous carbon spheres and hollow‐core has various advantages over conventional OMCs. The radial and hierarchical pores in the sphere provide a large surface area (1319 m2 g−1), short diffusion path, and open‐pore that facilitates ion transfer to any direction. Simultaneously, the hollow sphere carved in the center of the MCHSs allows space for the improvement of ion mobility and electrolyte retention. Also, the dense structure of the MCHSs allows more compact packing and high tap density when MCHSs were applied as an electrode. The MCHSs exhibit high specific capacitance and present a well‐developed EDLC shape at all scan rates (10 to 1000 mV s−1), the results show a superior electrochemical performance compared with other recent mesoporous carbon allotropes. [ABSTRACT FROM AUTHOR]

In this research work, we report a facile one pot synthesis of Sn doped SrO (Sr1-xSnxO1-δ; where x = 0.1, 0.2, 0.3 and 0.4) based two dimensional nanoparticles. The physico-chemical properties of the prepared materials were characterized by XRD, EDAX, SEM and TEM. XRD confirmed that the prepared samples are cubic. The presence of appropriate atomic percentage of elements was predicted by EDAX. SEM and TEM data confirmed the presence of nanostructured grains in the samples. The electrochemical techniques such as, cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy (EIS) were employed to characterize the reproducible performance of the Sn doped SrO nanostructured electrode materials in 1 M of H2SO4 medium. Among the different samples studied, Sr0.6Sn0.4O1-δshowed a maximum specific capacitance of 56.49 Fg-1 at a scan rate of 5 mV. Hence, Sn doped SrO can be good electrode material for electrochemical supercapacitor applications. [ABSTRACT FROM AUTHOR]

Hybrid halide perovskites have become highly popular mixed electronic−ionic material over the past decade due to a wide range of applications in flexible optoelectronics especially for energy conversion and light‐emitting devices. While ion migration in these materials is the main cause of device instability under heat and light, this property can make them ideal for energy storage applications such as Li‐ion batteries, photorechargeable batteries, and supercapacitors. Herein, progress so far in the field of perovskite material‐based electrochemical supercapacitors is summarized, unraveling charge storage mechanisms in these types of devices, as well as important perspectives for future development of the field. In these types of materials, the total charge/energy storage can be modulated by the induced field due to ion migration inside the bulk perovskite film. The electronic−ionic coupling in metal halide perovskite materials is crucial for the charge storage mechanism in perovskite‐based energy storage devices. A general strategy is proposed to prepare the porous perovskite electrode from the powder of perovskite single crystals for high‐performance perovskite supercapacitors. The modified power law equation for perovskite‐based energy storage devices is proposed. In the end, the possibility of photorechargeable perovskite‐based energy storage devices is also discussed. [ABSTRACT FROM AUTHOR]

We report hierarchical‐ordered ZIF−L(Zn)@Ti3C2Tx MXene core–sheath fibers, in which a ZIF−L(Zn) nanowall array sheath is grown vertically on an anisotropic Ti3C2Tx core by Ti−O−Zn/Ti−F−Zn chemical bonds. Through highly efficient microfluidic assembly and microchannel reactions, ZIF−L(Zn)@Ti3C2Tx exhibits well‐developed micro‐/mesoporosity, ordered ionic pathways, fast interfacial electron conduction and large‐scale fabrication, significantly boosting charges dynamic transport and intercalation. The resultant ZIF−L(Zn)@Ti3C2Tx fiber presents large capacitance (1700 F cm−3) and outstanding rate performance in a 1 M H2SO4 electrolyte. Additionally, ZIF−L(Zn)@Ti3C2Tx fiber‐based solid‐state asymmetric supercapacitors deliver high energy density (19.0 mWh cm−3), excellent capacitance (854 F cm−3), large deformable/wearable capabilities and long‐time cyclic stability (20 000 cycles), which realize natural sunlight‐induced self‐powered applications to drive water level/earthquake alarm devices. [ABSTRACT FROM AUTHOR]

Morphological modification in materials aids multi-channel electron access sites for easier electrolyte ion access for many electrochemical devices including energy storage devices. Controlled synthesis of such multichannel morphologies of metal oxides offers significant challenges. Herein, we report a template-assisted electrodeposition technique for the synthesis of Cu nanowires, which are transformed into either CuO nanotubes by controlled annealing or CuO hierarchical nanospikes using a simple hydroxyl ion impregnation technique and subsequent annealing. These materials are tested as electrodes in charge storage systems in 6 M KOH electrolyte in a three-electrode system; both electrodes have shown battery-type charge storage behaviour. Despite the chemical similarity between the two materials, the CuO nanospikes electrodes showed improved charge transport between electrode-electrolyte interface compared to the CuO nanotubes. With the cost-effectiveness, easy availability, and multi-channel morphology of CuO nanospikes along with the promising performance of the electrode in a three-electrode system, the present research offers future potential in developing low cost and high performing energy storage devices. [ABSTRACT FROM AUTHOR]

The nickel oxide (NiO) thin films are prepared with different level of cobalt (Co) doping (2–10 wt%) on conducting (FTO) by using spray pyrolysis technique. The effect of Co doping on the microstructure and electrochemical performance of NiO thin film electrodes are thoroughly investigated. The X-ray diffraction results exhibited the polycrystalline cubic NiO structure with (111) as preferential orientation. The XPS analysis revealed existence of Co in NiO thin films. The field emission scanning electron microscopy (FE-SEM) of 4% Co:NiO thin films presented porous surface morphology. The maximum specific capacitance 835F. g−1 is attained at scan rate of 5 mV s−1 from cyclic voltammetry in 2 M KOH electrolyte for 4% Co doped NiO thin film. Further, exhibited the maximum specific capacitance of 246.80F.g−1 at current density of 0.2 mA/cm2 with 96% capacity retention after 1000 cycle.

The development of carbon materials with desirable textures and new aqueous electrolytes is the key strategy to improve the performance of supercapacitors. Herein, a deep eutectic solvent (DES) was used for in situ templating of a carbon material. A carbon material was characterized (XRD, N2-physisorption, FTIR, SEM and EDS) and used as an electrode material for the first time in multivalent-based supercapacitors. In situ templating of carbon was performed using a novel DES, which serves as a precursor for carbon and for in situ generation of MgO. The generation of MgO and its roles in templating of carbon were discussed. Templating of carbon with MgO lead to an increase in surface area and a microporous texture. The obtained carbon was tested in multivalent-ion (Al3+ and Mg2+) electrolytes and compared with H2SO4. The charge-storage mechanism was investigated and elaborated. The highest specific capacitance was obtained for the Al(NO3)3 electrolyte, while the operating voltage follows the order: Mg(NO3)2 > Al(NO3)3 > H2SO4. Electrical double-layer capacitance (versus pseudocapacitance) was dominant in all investigated electrolytes. The larger operating voltage in multivalent electrolytes is a consequence of the lower fraction of free water, which suppresses hydrogen evolution (when compared with H2SO4). The GCD was experimentally performed on the Al(NO3)3 electrolyte, which showed good cyclic stability, with an energy density of 22.3 Wh kg−1 at 65 W kg−1.

The electrochemical charge storage mostly relies on the electrical properties of complex interfaces and electrode materials as well as the dynamic ions diffusion in the electrolytes. Nickel‐cobalt layered double hydroxides (LDHs) with tunable chemical composition are promising for electrochemical supercapacitors, where the theoretical performance could be up to 3000 F g−1. However, the experimental performances of NiCo‐LDHs are still limited by low charge transfer rate and slow dynamic ions diffusion. Here, a 3D lattice matching Ni0.85Co0.15(OH)2@α‐Co(OH)2 heterostructure is epitaxially grown. The experimental results and theoretical calculation confirm that such a 3D heterostructure could improve charge transfer abilities and accelerated ions diffusion. The specific capacitance of 2480 F g−1 and retained 71% of the initial capacitance at high current density of 30 A g−1 have been achieved by optimal Co(OH)2 amount of 20 mg (NCC‐20). Asymmetric button devices and soft‐pack devices have been demonstrated with exceptional energy densities of 69.2 and 65.7 Wh kg−1 at power densities of 0.79 and 0.78 kW kg−1, and maintained 88% and 80% initial capacitance under 10 000 cycles, respectively. The general design principles clearly demonstrate the importance of electrochemical interface and dynamic process, paving the way to push forward the application capability of electrochemical devices. [ABSTRACT FROM AUTHOR]

One limitation of wearable electronics, and at the same time a challenge, is the lack of energy storage devices with multiple functionalities produced using clean and environmental‐friendly strategies. Here, a multifunctional conductive hydrogel containing poly(3,4‐ethylenedioxythiophene) (PEDOT) and alginate is fabricated, to be used as electrodes in supercapacitors, by applying water‐mediated self‐assembly and polymerization processes at room temperature. The interpenetration of both polymers allows the combination of flexibility and self‐healing properties within the same hydrogel together with the intrinsic biocompatibility and sustainability of such materials. Initially, PEDOT:polystyrene sulfonate and alginate aqueous solutions are mixed in two different proportions (1:1 and 1:3) and ionically crosslinked with CaCl2. Subsequently, re‐interpenetration of poly(hydroxymethyl‐3,4‐ethylenedioxythiophene) by anodic polymerization in CaCl2 aqueous solution is achieved. Re‐interpenetrated 1:3 PEDOT/alginate hydrogels show excellent capacitance values (35 mF cm−2) and good capacitance retention. In addition, the electrochemical properties are not significantly changed after many cutting/self‐healing cycles as observed by cyclic voltammetry. Therefore, this sustainably produced hydrogel shows promising properties for use in wearable energy storage devices. [ABSTRACT FROM AUTHOR]

Peptide-based supramolecular hydrogels, as a new type of biological nanoarchitectonic structure, hold great promise for a wide range of biomedical and nanotechnological applications, such as tissue engineering, drug delivery, and electronic and photonic energy storage. In this work, a cyclic dipeptide (CDP) cyclo-(Trp-Tyr) (C-WY), which has exceptional structural rigidity and high stability, is selected as a hydrogelator for the formation of supramolecular hydrogels. The unique hydrogen bonding in C-WY endows a high propensity for self-assembly and the resulting hydrogels are revealed to be crystalline. The crystalline hydrogels possess excellent mechanical capacity and superior tolerance to various harsh conditions, including in the presence of charged biopolymers, extreme acid/base environments, and changing thermal conditions. Such high tolerance enables the crystalline hydrogels to be applied in the complex and harsh environments of electrochemistry. In addition, this study demonstrates that the self-assembly of cyclic dipeptides results in highly robust hydrogels which can be applied for electrochemical applications such as electrochemical supercapacitors.

Electrochemical supercapacitors (SC) with high power and long cycle life have been extensively studied and applied in certain areas. However, a majority of the efforts have been devoted to developing SCs with improved performance through novel electrode/electrolytes design. The full mechanistic understanding of SCs based on different electrode materials has not yet been realized. In addition, exploration of new functions for SCs to widen their applications must be accelerated. In this essay, the use of advanced characterization methods (in situ X‐ray diffraction, in situ X‐ray scattering, in situ atomic force microscopy, in situ nuclear magnetic resonance, in situ Raman/infrared spectroscopy, electrochemical quartz crystal microbalance, scanning electrochemical microscopy, etc.) to unveil the electrochemical process of SCs from different aspects will be discussed. The working principles, information to be extracted, and case studies of respective methods will be presented. The multipronged mechanism studies of electrode properties inspire and enable exploration of extra functions within the same electrochemical SCs. Realization of mechanically deformable, low‐temperature, color tunable, self‐healable, and self‐chargeable SCs; integrated SC‐sensors; and SC‐actuators with adoption of new electrode/electrolyte/current collectors/configurations are showcased. The remaining issues hindering the wide exploitation of SCs and the future development trend of SCs are also discussed. [ABSTRACT FROM AUTHOR]

Unraveling the influence of incorporating transition metal elements on layered transition metal chalcogenides for energy storage application remains a challenge. Herein, niobium (Nb)‐doped layered titanium disulfide (TiS2) is applied to generate novel compounds Ti1−xNbxS2 (x=0.05, 0.1 and 0.20). Interestingly, TiS3 nanobelts are formed in the resulting materials, which is proven by systematic morphological and structural characterization. It has been found that Nb‐doped TiS2 compounds demonstrate superior electrochemical capacitive activity, reaching up to a 63.2 % increase in gravimetric capacitance in 1 M Na2SO4 electrolyte compared with that of the Nb‐free TiS2. This remarkably enhanced capacity behavior is attributed to Nb doping resulting a structural transition of Layered TiS2 to TiS3 nanobelts. [ABSTRACT FROM AUTHOR]

We report the effect of hydrothermal synthesis conditions on the morphological, optical and electrochemical properties of as-prepared iron oxide (γ-Fe2O3) and hydroxide (α-FeOOH) nanostructures. The physico-chemical identification of these Fe-based nanostructures using X-ray diffraction, scanning/transmission electron microscopy, porosity and Raman spectroscopy analyses revealed a temperature-depended phase transformation. A maghemite and goethite iron-based nanostructured formation was observed in nanorod and trigonal nanofiber shape-like morphology with mean diameters ranging from 32 to 50 nm. The textural analysis of the nanofibers confirmed mesoporosity with a specific surface area of ~ 129 m2 g−1 (in γ-Fe2O3) and 23 m2 g−1 (in α-FeOOH). The electrochemical performance of the iron oxide and hydroxide nanofiber electrodes with and without the addition of activated carbon (AC) was also investigated. The sample electrodes composed of γ-Fe2O3, γ-Fe2O3/AC, α-FeOOH and α-FeOOH/AC showed remarkable specific capacities of 164 mAh g−1, 330 mAh g−1, 51 mAh g−1 and 69 mAh g−1 at 1 A g−1 gravimetric current. The influence of the phase transformation linked to the synthesis temperature, and the inclusion of an electric double-layer AC material into the nanofibers clearly demonstrates an enhancement in their energy-storage capability. Furthermore, the Fe-based nanofibers exhibited excellent cycling stability with good capacity retention of 73% and 99.8%, respectively, after 2000 cycles at a high 30 A g−1 gravimetric current as well as low resistance obtained by impedance spectroscopy analysis. The implication of the results depicts the potential of adopting these γ-Fe2O3 nanorods as suitable material electrodes in electrochemical energy-storage devices. [ABSTRACT FROM AUTHOR]

We prepare defective carbon nanosheets (DCNS) that is obtained by chemical activation of Syzygium cumini leaves and employ them as electrode materials for electrochemical supercapacitors. DCNS exhibits large specific surface area (ca. 1184.4 m2/g), electrical conductivity of ca. 1.23 × 10‐2 S/cm, moderate level of structural defects of ca. 0.72, and sufficient oxygen‐containing functional groups as well. It leads to induce huge electroactive sites, which correspond to high specific capacitance of ca. 222.26 F/g with a better durability. The low‐cost, eco‐friendly, and electroactive carbon materials could play an important role for its applications in energy‐storage devices such as batteries. [ABSTRACT FROM AUTHOR]

Abstract Transition metal oxides/hydroxides materials attract much attention in the field of energy storage materials because of their high theoretical specific capacity and low cost. However, it is normally difficult to improve the capacitance of the electrode by simply increasing the mass loading or thickness of the electrode. To raise the utilizing efficiency of the active material, hierarchical integrated electrodes assembled by NiCo hydroxide nanowires arrays and reduced graphene oxide interlayers are well designed and synthesized. The surface morphology and inner structure of the hierarchical electrode are characterized by SEM. The electrochemical performances of the electrodes are evaluated by three-electrode and two-electrode system in 2 M KOH respectively. Assisted with two reduced graphene oxide interlayers, NiCo hydroxide nanowires arrays exhibit a specific capacity of 2.41 C cm−2 at 1 mA cm−2. Even at a high current density of 50 mA cm−2, nearly 47% of the capacity could still remain. The results show that, the multi-level nanowires arrays structure provides multi-dimensional transmission path for ions and electrons, and achieved higher specific capacities and rate properties. Graphical abstract Image 1 Highlights • A multi-step hydrothermal method is proposed to prepare hierarchical electrode. • Combination of multi-layer NiCo-H NWAs and rGO interlayers are required. • The hierarchical structure provides multi-dimensional transmission path for ions and electrons. [ABSTRACT FROM AUTHOR]

Abstract Edge-carboxylated graphene nanoplatelets (ECG), prepared by a mechano-chemical reaction (or ball milling method) in the presence of dry ice, are eligible for an efficient electrode materials for electrochemical supercapacitors. ECG contained a higher content of edge-carboxylic groups with less structural defects, compared with the nitrogen-doped carboxylic graphene (NGOOH) prepared from the conventional solution-exfoliation of graphite. The structural defects level of ECG is ca. 16.2%, while it was ca. 48.9% for NGOOH. The edge-carboxylation increases the electroactive surface area, hydrophilicity and wettability of graphene without serious deterioration of the intrinsic properties e.g., chemical, mechanical and electronic properties. In result, it is more effective in enabling ion adsorption and rapid electrolyte diffusion within the pores of graphene which results in a significant increase of specific capacitance (C sp) to 365.72 F/g at a current density of 1 A/g, with a good charge–discharge property and rate capability for ECG. On the other hand, the C sp significantly decreases to ca. 175.05 F/g for NGOOH , as its high level of structural defects seriously affected its electronic properties. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract: In this work, we were committed to building a nickel oxide (NiO) octahedron with skeleton crystal structure as a capacitor electrode for supercapacitance through a template-free and efficient one-step process. Initially, nickel nitrate hexahydrate (Ni(NO3)2·6H2O) and anhydrous ethanol mixtures were used as a material. The final samples were prepared by calcining the precursor at different temperatures. The mechanism of crystal recrystallization at different temperatures during calcination was discussed. Generally speaking, in the process of rapid growth with only diffusion mechanism, crystal imperfections such as crystal plane depression and skeleton crystal will be formed. At the lower temperature calcination, small depressions are produced due to the effect of crystal face Ostwald ripening. At higher temperatures, the crystal edge growth rate is faster than the surface growth rate during Ostwald ripening and recrystallization, resulting in the formation of NiO octahedron with a large surface depression skeleton crystal structure. The electrochemical test results of the samples showed that the surface depression NiO octahedron has fine supercapacitive behaviors and specific capacitance values (640 F g−1) at the discharging current of 0.5 A g−1 in the 3 mol L−1 KOH electrolyte and maintain excellent cycling stability, remaining constant after 2000 cycles. Electrochemical impedance measurements confirmed the capacitance performance of NiO electrodes.Skeleton crystal is a special form of crystal crystallization. Rock salt structure is an important part of the formation of skeleton crystal. The growth rate of the edge of the NiO crystal is higher than that of the crystal surface, and the (111) plane decreases or even disappears, eventually forming a skeleton crystal NiO octahedral structure. A special morphology of NiO skeleton crystal octahedron was synthesized by a one-step template-free method.The formation mechanism of surface depression NiO octahedron was explained based on the definition of skeleton crystal.The effect of surface depression on electrochemical performance is explained. [ABSTRACT FROM AUTHOR]

In the present article we report synthesis and electrochemical supercapacitor applications of sprayed bismuth oxide (Bi 2 O 3 ) interconnected upright standing nano-plate-based electrode material via a simple spray pyrolysis aqueous route onto a flexible 3D Ni-foam at 623 ± 2 K. The Bi 2 O 3 Ni-foam was initially characterized for its structure, morphology and phase-purity analyses and then envisaged as electrode materials in supercapacitor applications. Polycrystalline, cubic crystal structure of Bi 2 O 3 nanoplate films were hydrophobic in character. The cyclic voltammetry curves of Bi 2 O 3 electrode, scanned at scan rates from 5 to 1000 mV/s in 1 M Na 2 SO 4 electrolyte in the potential window of −0.8 – 1.9 V vs. Ag/AgCl confirm a mixed-type capacitive behavior. Using charge-discharge study, the calculated maximum values of specific energy, specific power and columbic efficiency were 702.97 Wh/kg, 334.7 kW/kg and 99.9%, respectively. Electrochemical impedance measurement scanned in the frequency range of 1 mHz–1 MHz confirms ∼6 Ω solution resistance and ∼13 Ω charge transfer resistance. An excellent electrochemical stability of 92% at 100 mV/s scan rate even after 5000 redox cycles demonstrates an industrial potential of Bi 2 O 3 electrode materials. [ABSTRACT FROM AUTHOR]

Structural and electrochemical behaviors of electrophortically-deposited Fe3O4 and Fe3O4@C nanoparticles on carbon fiber (CF) were investigated. The nanoparticles were synthesized via a green-assisted hydrothermal route. The as-prepared samples were characterized by x-ray diffraction, transmission and scanning electron microscopies, Fourier transform infrared and UV-visible spectroscopies as well as by a vibration sample magnetometer. Surprisingly, the saturation magnetization (Ms) of the Fe3O4@C (~ 26.99 emu/g) was about 20% higher than that of Fe3O4 nanoparticles. A rather rectangular CV curve for both the elecrophortically-deposited Fe3O4 and Fe3O4@C on CF indicated the double-layer supercapacitor behavior of the samples. The synergistic effects of double shells improved the electrochemical behavior of Fe3O4@CF. The Fe3O4@C@CF composite exhibited a higher specific capacitance of ~ 412 F g−1 at scan rate of 0.05 V/s compared to the Fe3O4@CF with a value of ~ 193 F g−1. The superb electrochemical properties of Fe3O4@C@CF confirm their potential for applications as supercapacitors in the energy storage field. [ABSTRACT FROM AUTHOR]

In this study, a facile and low cost free-template hydrothermal precipitation method was used to synthesize mesoporous Ni-Co based bimetallic carbonates (CO 3 ) 2- and/or hydroxides (OH) − micro/nanostructures with different morphologies (1D, 2D and 3D) based on variant stoichiometric compositions. The effect of the growth temperature, synthesis time as well as the Ni/Co-precursors ratio on the physico-chemical properties and faradic electrochemical behavior of these products was investigated. The as-obtained bi-phase nanohybrids were characterized extensively structurally and morphologically. The textural analysis results confirmed the presence of mesoporous products with a BET-SSA ∼50 m 2  g −1 (0.52 cm 3  g −1 pore volume) for the 3D urchin-like structure and a BET-SSA ∼ 47.14 m 2  g −1 (0.31 cm 3  g −1 pore volume) was obtained for the 2D nanoflakes structure. The electrochemical measurements performed in a 6.0 MKOH aqueous electrolyte depicted excellent electrochemical performance ascribed to the optimized composition of Ni-Co LDH (or α-Ni(OH) 2 ) with Co 2 (OH) 3 Cl and their unique hierarchical mesoporous nanoflake and urchin-like architectures. In addition, an exceptionally notable specific capacitances (capacities) of 1700 F g −1 (161 mAh.g −1 ) and 1379 F g −1 (192 mAh.g −1 ) were obtained for both structures at 5 mV s −1 scan rate (0.5 A g −1 gravimetric current density) respectively. These are much better than mono - hydroxides synthesized in same conditions with 351 F g −1 (90 mAh.g −1 ) for Ni and 216 F g −1 (21.5 mAh.g −1 ) for Co. A good cyclic stability of ∼98% after 2000 charge-discharge cycles at 30 A g −1 was recorded depicting their potential as suitable materials for energy storage devices. [ABSTRACT FROM AUTHOR]

Abstract: Highly conductive metal selenides are gaining prominence as promising electrode materials in electrochemical energy‐storage fields. However, phase‐pure bimetallic selenides are scarcely retrieved, and their underlying charge‐storage mechanisms are still far from clear. Here, first a solvothermal strategy is devised to purposefully fabricate monodisperse hollow NiCoSe2 (H‐NiCoSe2) sub‐microspheres. Inherent formation of metallic H‐NiCoSe2 is tentatively put forward with comparative structure‐evolution investigations. Interestingly, the fresh H‐NiCoSe2 does not demonstrate striking supercapacitive behaviors when evaluated for electrochemical supercapacitors (ESs). But it exhibits competitive pseudocapacitance of ≈750 F g−1 at a rate of 3 A g−1 with a high loading of 7 mg cm−2 after ≈100 cyclic voltammetry (CV) cycles. With systematic physicochemical/electrochemical analyses, intrinsic energy‐storage mechanism of the H‐NiCoSe2 is convincingly revealed that the electrooxidation‐generated biactive CoOOH/NiOOH phases in aqueous KOH over CV scanning, rather than the H‐NiCoSe2 itself, account for the remarkable pesudocapacitance observed after cycling. An assembled H‐NiCoSe2‐based asymmetric device has delivered an energy density of ≈25.5 Wh kg−1 with a power rate of ≈3.75 kW kg−1, and long‐span cycle life. More significantly, the electrode design and new perspectives here hold profound promise in enriching material synthesis methodologies and in‐depth understanding of the complex charge‐storage process of newly emerging pseudocapacitive materials for next‐generation ESs. [ABSTRACT FROM AUTHOR]

In this paper, the well-defined nano-sheets of α-Co(OH) were prepared through the cathodic electrosynthesis from an additive-free aqueous cobalt nitrate bath. The pulse current cathodic electro-deposition (PC-CED) was used as the means for the controlling the OH− electrogeneration on the cathode surface. The characteristics and electrochemical behavior of the prepared cobalt hydroxide were also assessed through SEM, TEM, XRD, BET, and IR. The results proved the product to be composed of crystalline pure α phase of cobalt hydroxide with sheet-like morphology at nanoscale. Evaluations of the electrochemical behaviour of the α-Co(OH) nano-sheets revealed that they are capable to delivering the specific capacitance of 1122 F g at a discharge load of 3 A g and SC retention of 84% after 4000 continues discharging cycles, suggesting the nano-sheets as promising candidates for use in electrochemical supercapacitors. Further, the method used for the preparation of the compounds enjoys the capability of being scaled up. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel 2D pure and sulphur-doped V 2 O 5 flakes were successfully synthesized. • Orthorhombic crystal structure was confirmed from XRD analysis. • Doped 2D electrodes exhibited excellent specific capacitance of 749F/g. • Doped 2D electrodes showed about ∼ 2 folds enhancement in specific capacitance. • Doped electrodes have potential for PEC and energy storage devices. Development of high-performance energy storage devices with exceptional and consistent performance is of immense significance due to ecological concerns to meet the growing demands for high-performance energy conversion and storage. V 2 O 5 materials have attracted particular attention for energy storage owing to their excellent Faradaic performance, several oxidation valences, inexpensive, ease of synthesis, and non-toxic, all of which make them favorable materials for both energy conversion and storage applications. In this investigation, an efforts has been made to synthesize the novel 2D S-doped V 2 O 5 flakes via a facile hydrothermal procedure. The materials developed were utilized in photoelectrochemical (PEC) water oxidation as well as electrochemical energy storage supercapacitors. XRD analysis confirmed that V 2 O 5 crystal structure is orthorhombic, and doping of the sulfur ions into V 2 O 5 lattice, which has considerably narrowed the band gap from 2.17 eV to 2.02 eV. Nyquist plots revealed that the doped electrode showed reduced inner resistance (R S) and charge transmission resistance (R CT) compared to that of naked electrode. Density functional theory (DFT) calculations illustrate that sulfur-ion doping in the two-dimensional V 2 O 5 monolayer remarkably enhances the electrical properties of the materials. Furthermore, the doping of S into the host matrix causes a positive influence on its structure, electrical conductivity and ion diffusion. Doped V 2 O 5 2D flakes exhibited a specific capacitance of 749F/g at 1 A/g with excellent stability after 3000 cycles at 2.5 A/g compared to the undoped sample. Furthermore, 2D S-doped V 2 O 5 flakes showed ∼ 4.7 folds improvement in photocurrent density and reduced charge resistance than the undoped sample, indicating that doped V 2 O 5 has excellent photoelectrochemical (PEC) water oxidation properties. The fabricated 2D nanostructured materials can be the potential materials for constructing inexpensive and high-performance energy conversion (e.g., hydrogen production, green energy generation), and energy storage devices. [ABSTRACT FROM AUTHOR]

Low-cost resorcinol formaldehyde xerogels were prepared by using resorcinol and formaldehyde as precursors, NaCO as catalyst, and hexadecyltrimethy ammonium bromide as template through sol-gel process and ambient pressure drying without organic solvent replacement. The hexadecyltrimethy ammonium bromide template, which can be ablated completely when resorcinol formaldehyde xerogels were pyrolysised at 1000 °C, plays a role in generating pores. And the CO activation process was used to further dredge micropores in the carbon xergels. The high specific surface area and high density of carbon xerogels can be obtained, which are important factors for carbon xerogels to reserve high specific capacitance. The effect of the microstructure of carbon xerogels on their electrochemical performance is a more important factor that should be considered in practical applications. With the highest specific surface area of 2796 m g, the specific capacitance of carbon xerogels is 181 F g at the scan rate of 10 mV/s by cyclic voltammetry, however, the carbon xerogel with the specific surface area of 1139 m g has the largest specific capacitance of 211 F g at the same scan rate. Graphical Abstract: [ABSTRACT FROM AUTHOR]