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[Display omitted] • Lignocellulosic waste is used for the development of carbon-based electrodes. • Activated carbons were synthesized from cocoa husks using KOH as activating agent. • Materials with high surface areas and good porosity was development. • Different functional groups on their surface to improve energy storage. • Both properties contribute to the energy storage by a double electric layer. Activated carbon materials are widely used as high-performance electrodes for supercapacitors because they allow improving the electrochemical performance of these devices. The development of high surface areas and high porosity contributes to the energy storage by double electric layer, whereas the content of different functional groups on their surface to the pseudocapacitive storage. In addition, they can be obtained from lignocellulosic wastes providing a novel and economic perspective for the development of carbon-based electrodes. In this work, activated carbons were synthesized from cocoa husks using KOH as activating agent. The materials were obtained at three impregnation ratios (1:1, 3:1, 5:1) and three carbonization temperatures (500, 650, and 800 °C), optimizing the best conditions to obtain materials with high surface areas and porosity together with surface functional groups to improve energy storage. The results show that the 800 °C synthesized material with 3:1 impregnation ratio presents a capacitance of 120 F/g at 1 A/g, with a retention capacity of 93 % after 12,000 cycles, being the best electrochemical behavior among the carbons prepared. This is attributed to the adequate micro-mesoporosity, content of surface oxygenated functional groups and high surface area (1444 m2/g). [ABSTRACT FROM AUTHOR]

• The micropores in chitosan-based carbon (PC-C) are available to KOH electrolyte. • PC-C is not suitable for H 2 SO 4 electrolyte due to its small pore size. • Trimesic acid is introduced as a carbon precursor to tune the porous structure. • The modified carbon (PC-CT) shows expanded pore size and mesopres. • Compared with PC-C, PC-CT exhibits high-rate performance in H 2 SO 4 electrolyte. Microporous carbon (PC-C) was prepared using chitosan and ZnCl 2 as carbon precursor and activating agent, respectively. Electrochemical measurements and material characterization show that the microporous nature of PC-C limits the ion transfer in H 2 SO 4 electrolyte, resulting in a lower specific capacitance and rate performance in H 2 SO 4 electrolyte compared with KOH electrolyte. Trimesic acid was introduced into the carbon precursor to regulate the porous structure by generating more meso - and macropores, which facilitate the transmission of electrolyte ions with bigger ionic size. In this case, the specific capacitance of the modified carbon can reach up to 180 from 84.6 F g−1 in H 2 SO 4 electrolyte. The assembled supercapacitor cell in H 2 SO 4 electrolyte can deliver an energy density of 4.9 Wh kg−1 at a high-power density of 2500 W kg−1, which is much higher than that (0.4 Wh kg−1) of PC-C. Our study provides a guidance for the preparation and regulation of porous carbon suitable for different aqueous electrolytes. [ABSTRACT FROM AUTHOR]

• N -doped graphene is prepared from mechanical exfoliation process and nitrogen plasma irradiation. • MnO 2 nanoflakes are successfully electrodeposited on hydrothermal prepared NiCo 2 O 4 nanowires. • Asymmetric supercapacitor based on NiCo 2 O 4 @MnO 2 nanowires and N -doped graphene exhibits competitive performance. The design and fabrication of scalable energy storage systems are crucial for portable applications, demanding advanced materials through large-scale and facile processing. In this report, an asymmetric solid-state pseudocapacitor (ASPC) is assembled using a core–shell NiCo 2 O 4 @MnO 2 composite and solution-processed nitrogen-doped graphene (N -GP) as the positive and negative electrodes, respectively. With interconnected porous structures, the electrodes based on N -GP and NiCo 2 O 4 @MnO 2 offer high specific capacitance and rate capability, broad operation voltage, and a binder-free design with no added conductive agent. With these benefits, the ASPC with a PVA-KOH electrolyte exhibits a specific capacitance of 103.3F g−1 at 1 A/g and exceptional energy density of 36.73 Wh kg−1 at a power density of 792 W kg−1. In addition, the specific capacitance retention reaches 90.9 % after 5000 cycles, indicating excellent cycling stability. In the broader context of solid-state supercapacitors based on solution-processed graphene, this ASPC exhibits highly competitive performance, establishing it as a promising candidate for advanced energy storage. [ABSTRACT FROM AUTHOR]

[Display omitted] • Green synthesis of α-V 2 O 5 nanosheets using Aloe Vera leaf extract. • Electrochemical phase transformation of α-V 2 O 5 to NaV 3 O 8 nanosheets. • Structural and morphological evolutions during electrochemical phase transformation. • Specific capacitance of 640.10 F g−1 at 0.5 A g−1 NaV 3 O 8 nanosheets electrode. Nowadays, cost-effective and environmentally friendly supercapacitors (SCs) with high energy and power densities are gaining significant research attention since they could broaden the application of capacitors. The present study demonstrates a low-cost green synthesis technique to prepare the α-V 2 O 5 phase using Aloe Vera leaf extract. X-ray diffraction technique confirmed the formation of the orthorhombic α-V 2 O 5 phase. The prepared α-V 2 O 5 was employed as an electrode material for SC application. During an electrochemical cyclic voltammetry test in Na 2 SO 4 electrolyte, Na+ ions intercalation and de-intercalation processes resulted in a phase transformation of α-V 2 O 5 to NaV 3 O 8. Structural transformation (i.e., orthorhombic to monoclinic crystal structure) and morphological changes were also observed during the electrochemical phase conversion process. This electrochemical phase transformation process improved the overall supercapacitive performance of the α-V 2 O 5 material. Such electrochemically converted NaV 3 O 8 displayed a maximum specific capacitance of 640.1 F g−1 at 0.5 A g−1 with a long cyclic stability. Furthermore, the AC // NaV 3 O 8 asymmetric SC coin cell device delivered a maximum energy density of 62.6 Wh kg−1 and a power density of 7.3 kW kg−1 along with an excellent cycling stability of ∼81 % over 5000 GCD cycles. [ABSTRACT FROM AUTHOR]

• Aucklandia lappa straw-derived 3-dimensional porous carbon (ASC-3) is synthesized for the first time. • The ASC-3 shows hierarchical porous morphology and extremely high surface area (2427 m2 g−1). • The ASC-3 based electrode can deliver a high specific capacitance of 431.35 F g−1 at 0.5 A g−1. • Assembled liquid and all-solid-state supercapacitors exhibit a wide operating voltage window and high energy density. Efficient and sustainable biochar as electrode material is the key to constructing portably green energy storage equipment. Using waste aucklandia lappa straw as carbon precursor, biomass porous carbon was prepared by high temperature carbonization and KOH activation. The 3-dimensional porous carbon material was obtained by optimizing the proportion of activator, which has a high specific surface area (2427 m2 g−1), abundant pore structure and substantially high specific capacitance (up to 431.35 F g−1 at 0.5 A g−1). The assembled symmetrical supercapacitor exhibits a wide voltage range of 0–2.0 V and a high energy density of 36.51 Wh kg−1 in 1 M Na 2 SO 4 electrolyte. The all-solid-state supercapacitor with PVA/KOH gel as electrolyte has high response frequency and phase angle, which can provide high specific capacitance of 340.98 F g−1 and energy density of 19.59 Wh kg−1 at 0.5 A g−1. The capacitance retention rate is 89.47% after 10,000 cycles. Aucklandia lappa straw-derived porous carbon electrode material is an ideal candidate for the preparation of high-performance supercapacitor. [ABSTRACT FROM AUTHOR]

• Rare earth doped β-Bi 2 Mo 2 O 9 and graphene modified (GrM) β-Bi 2 Mo 2 O 9 is synthesized using cost effective gel matrix method. • The synthesized materials were characterized using various techniques. • Influence of various Eu concentration in their electrochemical behavior was investigated. • Asymmetric supercapacitor device is fabricated using 10% Eu: GrM-Bi 2 Mo 2 O 9 and its practical applicability is studied. The electrode material plays a crucial role in the performance of energy storage devices. Currently, the research focuses on enhancing the super-capacitive nature of the existing electrode materials in many ways. Herein, the influence of rare earth ions in the electrochemical characteristics of β-Bi 2-x Eu x Mo 2 O 9 and graphene-modified GrM-β-Bi 2-x Eu x Mo 2 O 9 is investigated. The gel matrix method is adopted for synthesizing the Bi 2-x Eu x Mo 2 O 9 (x = 1, 5 and 10 %) and GrM - Bi 2-x Eu x Mo 2 O 9 (x = 5,10 %). The as-synthesized material's structural formation, phase purity and structural modifications are studied using XRD, Raman and SEM. The chemical composition with their oxidation state is verified using XPS analysis. The electrochemical behavior of the pristine materials is examined with various analyses such as CV, GCD and EIS techniques in both three-electrode and two-electrode systems. The specific capacitance of GrM-Bi 1.8 Eu 0.2 Mo 2 O 9 is 904 F/g at 1 A/g with excellent cyclic stability of about 82.14 % at 5 A/g after 5000 cycles. An ASC device developed using GrM-Bi 1.8 Eu 0.2 Mo 2 O 9 exhibits columbic efficiency of 96.5 % with an extended cyclic life of 76.9 % after 10,000 cycles. The fabricated device possesses energy density and power density of 60.21 W h Kg−1 and 750 W Kg−1, respectively, at 1 A/g, acting as a favorable candidate for supercapacitor application. [ABSTRACT FROM AUTHOR]

• N -doped carbon materials were synthesized by a simple peroxidation and carbonization process using ionic liquid-lignin solution. • The ionic liquid functioned as both a solvent, template agent, and heteroatom source. • The as-prepared porous carbon microspheres exhibited an enhanced capacitive performance. Ionic liquids (ILs) have been extensively sought after for green solvents, catalysts, adsorbents, and carbon precursors. Herein, 1-ethyl-3-methylimidazolium acetate ([Emim][Ac])–lignin nitrogen-doped carbon microspheres (ECLMs) were easily synthesized through pre-oxidation and carbonization processes using a solution containing [Emim][Ac] and alkali lignin. The pre-oxidation process is analogous to the ionothermal carbonization method, wherein [Emim][Ac] serves as a reaction medium for preparing the ELCMs precursor. During the carbonization process, [Emim][Ac] served as a templating agent and heteroatom source to facilitate nitrogen doping and formation of micropores and mesopores. The as-synthesized ELCMs exhibits a considerably high specific surface area of 1267.2 m2/g and an optimal nitrogen-doping level of 2.21 %. This reveals its potential as a promising candidate for electrode materials in supercapacitor. The ELCMs demonstrate a remarkable specific capacitance of 262.5 F/g at 0.5 A/g and excellent rate capability in a three-electrode system. Additionally, the symmetric supercapacitor fabricated with electrode materials of ELCMs and a cellulose separator exhibits excellent cycling stability, with an impressive capacitance retention rate of 91.0 % after undergoing 5000 cycles at 5 A/g. Moreover, it achieves an ideal energy density of 4.17 Wh/kg at power density of 126 W/kg. This study investigates an effective strategy for designing and synthesizing different heteroatom-doped carbon materials from IL-biomass resources to enhance their applicability in energy storage devices. [ABSTRACT FROM AUTHOR]

• Synthesized and optimized NCPGE [(1:4){PVDF-HFP + EC-PC-TEABF 4 } + SiO 2 (15 wt%)] showed highest conductivity of 8.2 × 10−3 Scm−1. • Ionic transference number ∼ 0.96 and relatively larger electrical potential window ∼ 3.5 V proved synthesized NCPGE as potential candidate for application in supercapacitors. • Electrochemical performance evaluation of fabricated supercapacitor by impedance spectroscopy, cyclic voltammetry and galvanostatic charge discharge techniques. • High conductivity, large potential window, stable performance at higher scan rates confirm that the dispersion of SiO 2 nanoparticles in PGE has significantly improved the quality of synthesized electrolyte. Nano-composite polymer gel electrolyte (NCPGE) films are prepared by incorporating liquid electrolyte (EC-PC-TEABF 4) into polyvinyldinefloroide co-hexafluoropropylene (PVDF-HFP) polymer with dispersed SiO2 nano-particles using solution cast technique. The NCPGE is optimized for the highest ionic conductivity by varying wt% of SiO2 nanoparticles in PGE [(1:4){PVDF-HFP + EC-PC-TEABF 4 }]. Highest conductivity of 8.2 × 10−3 Scm−1 is found for optimized composition [(1:4){PVDF-HFP + EC-PC-TEABF 4 } + SiO 2 (15 wt%)] of NCPGE. Structural and morphological studies have been done using XRD, FTIR, and SEM. Frequency dependent dielectric behaviour is understood using dielectric constant and modulus analysis in a wide range of frequencies. The ionic transference number is 0.96 and an electrochemical potential window of ∼ 3.5 V has been obtained. Fabrication of electric double layer capacitor (EDLC) is done by sandwiching NCPGE between activated carbon (AC) electrodes. The electrochemical performance of fabricated supercapacitor is evaluated by impedance spectroscopy, cyclic voltammetry, and galvanostatic charge–discharge techniques. Results show significant improvement in the quality of synthesized electrolyte. [ABSTRACT FROM AUTHOR]

[Display omitted] • The capacitance of electrodeposited MnCO 3 is enhanced by the choice of intercalating cation. • The capacitance properties depend on the ionic radii and charge of the intercalating cation. • Reversible insertion of La3+ exchange more electrons per adsorption site than Mg2+ and Na+. • In addition, the solution and charge transfer resistance values are low for La(ClO 4) 3 electrolyte. • E-MnCO 3 delivers better rate performance and cycle-life in La(ClO 4) 3 electrolyte. Modifying electrolytes is an effective way of improving the capacitance properties. However, this strategy is not explored much compared to tuning the physicochemical properties of the electrode material. Herein, the capacitance properties of electrodeposited MnCO 3 (E-MnCO 3) are improved by the choice of aqueous electrolyte. MnCO 3 is electrodeposited on stainless steel foil and characterized by XRD, Raman spectroscopy and SEM. The capacitance properties of E-MnCO 3 are studied in aqueous solutions of NaClO 4 , Mg(ClO 4) 2 and La(ClO 4) 3. Owing to higher ionic conductivity, lower solution and charger transfer resistance, and an increase in the number of electrochemical active sites per cation adsorption/intercalation, E-MnCO 3 delivers higher specific capacitance and better rate capability in La(ClO 4) 3 than in other electrolytes. The capacitance properties of E-MnCO 3 in various electrolyte follow the order: La(ClO 4) 3 > Mg(ClO 4) 2 > NaClO 4. [ABSTRACT FROM AUTHOR]

[Display omitted] • The physical and electrochemical of LiCl as a simple and cheap "water-in-salt" electrolyte is reported. • A stable potential window of "water-in-salt" between 2.4 and 3.0 V (depend on electrode materials). • Electrochemical behaviour in each of the model electrode including glassy carbon, graphite, and activated carbon. • LiCl as an electrolyte in pouch cell supercapacitor without any corrosion. • A comparison of electrolyte properties between LiCl and LiTFSI. The search for alternative electrolytes is extremely topical in recent years with the "water-in-salt" electrolyte especially, lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) coming to the fore in the context of high-voltage electrolytes. However, "water-in-LiTFSI" exhibits ultra-high cost and low ionic transport when compared with the aqueous lithium- halide, -nitrate as well as -sulphate salts. This work rediscovered the properties of a "water-in-salt" made from a superconcentrated 20 m (equivalent to 14.28 M) lithium chloride electrolyte. The electrolyte was tested using various carbon-based materials as a model system, and the finding was then expanded to a pouch cell supercapacitor. It is found that the use of superconcentrated LiCl could enhance the potential window of the supercapacitor in both half-cell electrodes (approximately of 3.0 V), and pouch-cell devices (1.4 V evaluated at 100 mV s−1). This work shows the fundamental insight into the physical and electrochemical properties of LiCl for possible alternative use as a cheap "water-in-salt" electrolyte in energy storage apart from LiTFSI. [ABSTRACT FROM AUTHOR]

[Display omitted] • This article conveys the significance of black phosphorus (BP) in the application of electrochemical supercapacitors. • The properties and synthesis methods of BP are reviewed and explained. • Current shortcomings and the scope for improvement of BP have been concisely discussed. Black phosphorus (BP) has emerged to be a promising material in various fields like material science, condensed matter physics, chemistry, etc. Bearing the properties like narrow and direct band gaps, remarkable flexibility, high conductivity, electron mobility, and theoretical capacity, along with an anisotropic structure opens doors for BP in the field of energy storage devices. Also, the spacing between the layers of BP is 0.55 nm which has proved to be higher than graphene which supports better ion transportation in the case of supercapacitors (SCs). In this article, we briefly discuss many BP-based electrodes which were synthesized using the top-down and bottom-up approaches, the properties possessed by the material, and their application in SCs. The review also examines the strategies which can amplify the electrochemical performances proving to help fabricate the supercapacitor electrodes and devices. The potential of BP in constructing low-cost, flexible, and high-performing materials for SCs is also discussed. The review finally states the current shortcomings in the available literature and the direction of research which can provide a stage for never-ending improvements in this subject. [ABSTRACT FROM AUTHOR]

Abstract Pseudocapacitive materials are promising to increase specific capacity of carbon-based electrodes, but suffer from poor rate capability. In the work, novel Li:CuO/reduced graphene oxide flexible electrodes demonstrate enhanced electrical conductivity and specific capacitance obtained via the incorporation of Li into CuO particles. The degree of capacitance enhancement increases with scan rate, reaching a maximum value of 40% at a high scan rate of 500 mV/s. Galvanostatic charge/discharge measurements show high volumetric capacitance, energy density, and power density. Cyclic life tests show excellent stability over 10,000 cycles, with a capacitance retention of 93.2% at a scan rate of 100 mV/s. Graphical abstract High-performance Li:CuO/RGO flexible electrodes for supercapacitors are demonstrated for the first time. Li doping enhances electrical conductivity, energy density, and rate capability of CuO/RGO electrodes, opening up the opportunity to fabricate low-cost and excellent supercapacitor electrodes. Unlabelled Image Highlights • Li-doped CuO were synthesized to improve the performance of RGO-based supercapacitors. • Conductivity, energy density, and rate capability of CuO/RGO electrodes were enhanced by Li doping. • The Li:CuO/RGO electrode demonstrates high volumetric capacitance and energy density. • Cyclic life tests show excellent stability over 10,000 cycles, with a capacitance retention of 93.2%. [ABSTRACT FROM AUTHOR]

Abstract Herein, we report cuprous oxide nanocubes decorated reduced graphene oxide (CNC-rGO) immersed in chitosan matrix as a versatile and enhanced electrochemically active electrode material for both supercapacitor and hydrogen peroxide (H 2 O 2) sensor applications. The CNC-rGO was synthesized by one-pot scalable chemical precipitation method. The morphology and crystal structure of as-synthesized hybrid material was characterized by field emission scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The CNC-rGO hybrid material immersed in the chitosan matrix was used as an enhanced electrochemically active electrode material for supercapacitor and hydrogen peroxide (H 2 O 2) sensor. The fabricated CNC-rGO hybrid in chitosan matrix as an electrode showed remarkable charge storage capacity of 772.3 F g−1 (12.87 mA h g−1) at a current density of 0.2 A g−1 with high cyclic stability over 2000 charge-discharge cycles. Similarly, H 2 O 2 sensing performance of the same electrode exhibits very high sensitivity of 0.33 A M−1 cm−2 within a linear range of detection of 20–160 μM. Thus, the synthesized CNC-rGO hybrid material composed of numerous cuprous nanocubes on rGO nanosheets with large active sites showed enhanced electrochemical activity beneficial towards the supercapacitor and H 2 O 2 sensor applications. Graphical abstract Unlabelled Image Highlights • Cuprous oxide nanocubes decorated reduced graphene oxide was synthesized by simple one-step chemical precipitation method. • The as-synthesized hybrid material was embedded in chitosan matrix for its high stability electrode material. • This electrode delivered excellent specific capacitance of 772.3 F g-1 (12.87 mA h g-1) at a current density of 0.2 A g-1. • It also has high cyclic stability over 2000 charge-discharge cycles with 14% of capacity fading. • Similarly, the hybrid electrode exhibits very high sensitivity of 0.33 A M-1 cm-2 towards H 2 O 2 sensing. [ABSTRACT FROM AUTHOR]

Abstract Several authors reported that the naked tungsten oxide (WO 3) is basically poor in capacitance. In this report, we have made an attempt to enhance the capacitive performance of WO 3 through compositing. The different ratios of ZnS (2 wt%, 4 wt%, 6 wt%) was loaded with WO 3 and hybridized WO 3 -ZnS nanocomposites were prepared by the microwave-assisted wet chemical method. The XRD analysis revealed the mixed state of the orthorhombic and monoclinic structure of WO 3. In addition to that, some peaks corresponding to the cubic structure of ZnS was also observed. The average particle size was calculated as ±19 nm. Microscopic studies like SEM and HRTEM analysis revealed that as-prepared nanocomposites consisted of irregular particles of relatively uniform size. The existences of functional groups are analyzed using FTIR and confirmed the chemical bonding nature and the phase shift between W O and Zn. The TGA/DTA analysis shows that as the prepared structure is stable up to 400 °C temperature afterwards gradual weight loss was started. Finally, the electrochemical properties have been investigated in H 2 SO 4 and KOH electrolyte by cyclic voltammetry and galvanic charge-discharge analysis. The maximum specific capacitances of as-synthesized samples were calculated as 44 F/g, 105 F/g, 120 F/g and 215 F/g correspondingly for the WO 3 (a) particle and hybridized WO 3 -ZnS (b, c, d) nanocomposites in 20% KOH electrolyte. Similarly, in H 2 SO 4 electrolyte, bare WO 3 showed maximum capacitance of 246 F/g and WO 3 -ZnS (d) exhibited a maximum capacitance of 17 F/g, whereas remaining samples exhibited less than 10 F/g. The long cyclic analysis showed that coulombic efficiency of WO 3 -ZnS composite in KOH electrolyte is more than 100% up to 4000 cycles and capacitance retention is 71%. Highlights • Hybrid WO 3 -ZnS nanocomposites were prepared. • Supercapacitor performance was analyzed in two electrolytes such as KOH and H 2 SO 4. • The capacitance was enhanced in KOH electrolyte from 44 F/g (WO 3) to 172 F/g (WO 3 -ZnS). • The capacitance was reduced from 246 F/g (WO 3) to 17 F/g (WO 3 -ZnS) in H 2 SO 4 electrolyte. • WO 3 -ZnS composites showed capacitance retention of ̴71% up to 4000 cycles. [ABSTRACT FROM AUTHOR]

Abstract The development of an effective route to high-performance nanoporous carbon electrode materials derived from cost-effective biomass is critical but remains a great challenging for supercapacitors. Nitrogen-doped hierarchical porous carbons (HPCs) were synthesized via two steps by using (CH 3 COOK) chemical activation method. To this end, beancurd was applied as the carbon source, and CH 3 COOK was used as the activator due to its non-toxic and mildness features, avoiding the use of corrosive activator (KOH, ZnCl 2 , etc.). The optimized carbon possesses a high BET specific surface area and nitrogen content are 1735 m2 g−1 and 1.33 at.%, respectively. The electrochemical test was carried out in H 2 SO 4 and KOH aqueous electrolytes, the sample possesses ultrahigh specific capacitance of 315 and 245 F g−1 at 0.1 A g−1, respectively. Furthermore, the hierarchical carbon-derived supercapacitor displayed excellent cycling stability at a current density of 1 A g−1 (about 93.5% retention after 10,000 cycles), compared favorably with the literature. This new strategy would open an exciting route to explore the micro- meso -macro hierarchical porous carbon, specially made from beancurd, as promising electrode material for electric double layer capacitors. Graphical abstract Unlabelled Image Highlights • Nitrogen-doped hierarchical porous carbons (HPCs) were synthesized via two steps method. • The preparation method is cost-effective, green and scalable. • CH 3 COOK was used as the activator avoiding the use of corrosive activator (KOH, ZnCl 2 , etc.). • The excellent electrochemical performance is attributed to the hierarchical porous structure and heteroatom doping • The prepared HPCs specially made from beancurd has promising applications in electric double layer capacitors [ABSTRACT FROM AUTHOR]

Abstract In this work, Bi 3.64 Mo 0.36 O 6.55 /Bi 3.84 W 0.16 O 6.24 (BMW1) and Bi 2 MoO 6 /Bi 2 WO 6 (BMW2) nanocomposite were successfully prepared by a facile hydrothermal method with different PH. The Synthesis of good crystallization BMW1 and BMW2 with nanoparticles and nanosheet-like morphology is revealed from XRD, SEM, TEM and XPS, respectively. The BMW1 and BMW2 nanocomposite affords an excellent structural stability and fast electron and ion transportation compared with pure Bi 2 Mo 6 and Bi 3.64 Mo 0.36 O 6.55 , which can beneficial for improving the electrochemical performance. The pseudocapacitive behaviour of nanocomposite is analyzed by cyclic voltammetry (CV), chronopotentiometry (CP) and AC impendence in the 1 M KOH electrolyte. The as-prepared materials specific capacitance reaches to 1056 F g−1 and 699 F g−1 at 1 A g−1, respectively. Moreover, the as-prepared nanocomposite exhibits high cycle stability, and 80% of its initial capacitance is retained after continuous 3000 cycles. Especially, the higher electrochemical performance of BMW1 compared with BMW2, which is possibly ascribed to the higher Bi content. These results demonstrated nanocomposite and high Bi content materials might be a promising electrode material for pseudocapacitor. Highlights • Different compositions of bismuth nanocomposites hydrothermally obtained by adjusting the pH. • Electrochemical performance show that nanocomposites of are superior to single nanomaterials. • The nanocomposites with high-Bi content have higher specific capacitance and better stability. [ABSTRACT FROM AUTHOR]

Abstract To design a highly efficient electrocatalyst for cathodes to suppress the high overpotential for the oxygen reduction reaction (ORR) continually remains a prime goal of fuel cell study. Herein, the production of metal–free hollow nitrogen–doped carbon microspheres (HN–CMs) as an efficient electrode material for the supercapacitors and ORR in an alkaline media is reported. Initially, the PS@PANI core–shell microspheres were produced by coating polyaniline (PANI) layers on polyvinylpyrrolidone (PVP) functionalized polystyrene (PS) microspheres via in–situ chemical polymerization of aniline monomers in presence of ammonium persulphate (APS) as an oxidant. Finally, the core was removed by carbonizing the core–shell microspheres under the N 2 atmosphere at 500 °C for 2 h to obtain the HN–CMs as an electrocatalyst. The structure and morphologies of the microspheres were examined by SEM, TEM, XRD, FT–IR, BET, and Raman spectroscopy. The electrochemical analysis was performed by CV, GCD, and EIS. The obtained electrocatalyst exhibited improved electrochemical performances for supercapacitors application and demonstrated better electrocatalytic activity for ORR. For this electrocatalyst, the maximum specific capacitance of 266.7 F g−1 was obtained in 1 M KOH at scan rate of 5 mV s−1. Additionally, it has superior catalytic activity and stability via 4-electron process during ORR in the alkaline solution. The contribution of highly intact spherical/hollow structure, good surface area, and large contents of graphitic/pyridinic nitrogen of HN–CMs can improve the mass transportation by facilitating the diffusion pathways which results in the enhancement of its electrochemical and electrocatalytic properties. As a metal–free and cost–effective electrode material, this is supposed to be promising for supercapacitors and fuel cells. Graphical abstract Unlabelled Image Highlights • The core–shell microspheres of PS@PANI are prepared by a template method. • The PS@PANI is carbonized to obtain the hollow nitrogen–doped carbon microspheres (HN–CMs). • HN–CMs have the larger surface area, high pore volume, and nitrogen–incorporated defects of graphitic carbon structure. • It shows excellent electrochemical properties towards supercapacitors and excellent electrocatalytic activity towards ORR. [ABSTRACT FROM AUTHOR]

Abstract Over the past few decades, doped ZnO structures have attracted significant attention because of their distinctive properties and a wide range of applications in catalysis and energy-storage devices. However, effective simple synthesis of doped ZnO structures for photoelectrocatalytic and supercapacitor applications still remains challenging. In this study, Ni-doped ZnO structures were synthesized at different Ni concentrations. Analysis of the obtained samples confirmed the formation of Ni-doped ZnO; 1.5 mol% Ni-doped ZnO showed enhanced water splitting activity and supercapacitor properties. The highest photocurrent density of 4.6 mA/cm2 was obtained in a 0.1 M KOH solution at an applied bias photon-to-current efficiency of 4.2%, which is almost twice that obtained with pristine ZnO (2.8%), indicating an enhanced electron-hole separation. Doped ZnO exhibits a photocurrent 1.78 times higher than pristine ZnO under light illumination. Ni-doping induces effective charge separation and transfer, efficiently diminishing the recombination rate and reducing intrinsic defects. Further, the highest specific capacity of ~96 F g−1 was observed for 1.5% Ni-doped ZnO at an applied scan rate of 10 mV s−1. The optimized sample, 1.5% Ni-doped ZnO, exhibited a high specific capacitance retention and coulombic efficiency of ~98% and ~99.2%, respectively. These results are expected to be very helpful in developing cheap and simple fabrication methods and efficient electrode materials for photoelectrochemical water splitting and supercapacitor applications. Graphical abstract Unlabelled Image Highlights • Photoelectrochemical and supercapacitor properties of Ni-doped ZnO has been systematically investigated. • The 1.5 mol% Ni-doped ZnO showed the highest photocurrent density of 4.6 mA/cm2. • The highest specific capacitance of 1.5 mol% Ni-doped ZnO was obtained of ~ 96 F g−1 at 10mVs-1. • The optimal 1.5 % Ni-doped ZnO shows the highest specific capacitance retention and Coulombic efficiency of ~98 % and ~99.2 %, respectively. [ABSTRACT FROM AUTHOR]

Abstract Three newly synthesized N ‑benzoyl derivatives of isoleucine (3‑methyl 2‑[(4‑methylbenzoyl) amino] pentanoic acid (C-Me(, 2‑(benzoyl amino) 3‑methyl pentanoic acid (C-H) and 2‑[(4‑chlorobenzoyl) amino] 3‑methyl pentanoic acid (C-Cl) were synthesized via Schotten-Baumann method. Afterward, dealing with improving electrochemical properties of the poly ortho aminophenol (POAP), we fabricated POAP/C-Me, POAP/C-H and POAP/C-Cl films through electro-polymerization of POAP by employing of N ‑benzoyl derivatives of isoleucine to consider as the active electrode for SCs. Based on the electronic wave function (DFT-method), the local intramolecular the electron density and its Laplacian, corresponding to atomic electronic kinetic energy, and molecular virial forces (in the molecular planes) of the molecular system is studied in this work calculated. Analysis of these results show that the atomic-scale electronic properties are generally depend on the bonding and electronic molecular structures and electron donating group on the N ‑benzoyl derivatives has main important effect rather than electron withdrawing group. Based on electrochemical analyzing of POAP/C-Me, the specific capacitance, retention capacity and cycle stability as desirable factors in electrochemical SCs, exhibited more improved performances than electron withdrawing group in POAP/C-Cl film. According to electrochemical and quantum chemical evaluation, C-Me has improvement effect on electrochemical performance of POAP/C-Me electroactive film. This study reveals that POAP/C-Me with high fractal dimension, high specific capacitance and long cycle-life is suitable for application in energy storage materials. Graphical abstract Unlabelled Image Highlights • Developing a simple and green route for synthesis of composite of conductive polymer • A comparative study was carried out on three compounds of amino acid derivative using DFT and electrochemical techniques. • Presenting a novel and efficient composite materials for electrochemical redox capacitors [ABSTRACT FROM AUTHOR]

In this work, nanostructured composites of Cr 2 O 3 -graphene oxide (Cr 2 O 3 /GO) with conducting polymers; polyaniline (PANI) and polypyrrole (PPy) with the shape of cauliflower were synthesized via s simple and low cost one-step chronoamperometry method. The structures and morphologies of the resulting ternary nanocomposites were characterized by using Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The electrochemical capacitive properties of the prepared nanocomposites were evaluated by using cycle voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The as-synthesized Cr 2 O 3 /GO/PANI and Cr 2 O 3 /GO/PPy composites exhibit a highest specific capacitance of 525 and 495 F g −1 at 5 A g −1 in the three-electrode tests, respectively. Interestingly, Cr 2 O 3 /GO/PANI and Cr 2 O 3 /GO/PPy composites retain 84 and 80% of their initial capacitance values after 4000 charge-discharge cycles, suggesting good electrochemical stability of the nanocomposite electrodes. The assembled symmetric devices based on Cr 2 O 3 /GO/PANI and Cr 2 O 3 /GO/PPy composites show a high specific capacitance of 263 and 100 F g −1 at the current density of 5 A g −1 , respectively. [ABSTRACT FROM AUTHOR]

Carbon Sphere(CS) varied with high porous pristine nickel oxide (NiO) (CS@NiO) core shell has been successfully synthesized in different mole ratios of CS:NiO, i.e., 0:1(ncs0), 0.5:1(ncs1), 1:1(ncs2), 1.5:1(ncs3) and 2:1(ncs4) via low temperature water-bath method without further calcination. XRD results confirm that NiO and CS@NiO are in cubic structure. FT-IR studies confirm the complexation of NiO and CS. In TEM, CS appears as distinctly distributed spheres; ncs0 appears as uniformly distributed flakes; ncs3 appears as sphere enshrouded with NiO interlinked to one another. N 2 adsorbtion/desorbtion isotherms (BET) have been observed for ncs0 and ncs3; and noted that the ncs3 exhibits uniform pore distribution of 3.7 nm. The electrochemical performance of pure NiO and CS@NiO nanocomposites is studied using Cyclic Voltammetry, Galvanostatic Charge/Discharge and Electrochemical Impedance spectroscopy. The nanocomposite in the ratio 1.5:1 (ncs3) is found to exhibit good specific capacitance of 825 F g −1 at current density of 1 A g −1 which is 50% higher than the pure porous NiO(ncs0). Cyclic stability of the same is tested for continuous 3500 cycles. The enhancement of better specific capacitance and cyclic stability of ncs3 may be attributed to its uniform distribution of mesopores and more electrode/electrolyte interaction. [ABSTRACT FROM AUTHOR]

NiV 2 O 6 /C composites are prepared via a solid-state conversion process by low temperature (150 °C) annealing nickel‑vanadium-based coordination polymer, [Ni(phen)H 2 O][V 2 O 6 ]. The obtained NiV 2 O 6 /C nanoribbons are interconnected to form a sponge-like morphology, when the composites are first used as supercapacitor electrode, it exhibits a specific capacitance of 745.6 F g −1 at 0.5 A g −1 with a good rate capability of 520.0 F g −1 (69.7% retention) at 10 A g −1 (20-folds). The NiV 2 O 6 /C composite exhibits good cycling performance, the capacitance retentions at 6000th and 12000th charging/discharging cycles at 2 A g −1 are 81.5% and 77.8% relative to the original capacitances, respectively. The morphological and compositional changes of the NiV 2 O 6 /C composite electrode before and after 12,000 GCD cycles (two-electrode system) are carefully elaborated through a series of characterization (SEM, EDS, and XPS). Furthermore, the NiV 2 O 6 /C nanoribbons possess reversible electrochromism, which is probably related to the intervalence charge transfer (IVCT, V IV  → V V ). [ABSTRACT FROM AUTHOR]

[Display omitted] • MOF derived NiCo 2 O 4 nanosheets arrays were successfully designed. • The MOF derived NiCo 2 O 4 porous structure with ultrahigh-conductivity provides a highway for electron transfer. • The optimal NiCo 2 O 4 -MOF electrode with the annealing temperature 300 °C achieves the maximum specific capacity of 188 mAhg−1 at 5 Ag−1 and the excellent rate capability of 85.25% after 3000 cycles. • The supercapacitor of NiCo 2 O 4 -MOF//AC achieves an excellent electrochemical property. The electrochemical performance of the faradaic battery-type metal oxide electrodes is dependent on the calcination temperature. Herein, we report metal–organic framework (MOF) derived bimetallic oxide (NiCo 2 O 4 -MOF) electrode materials for high-performance supercapacitor (SC) applications. Remarkably, the optimal NCM electrode with the annealing temperature 300 °C (NCM-300) achieves the maximum specific capacity of 188 mAh/g at 5 Ag−1 and the excellent rate capability of 85.25% after 3000 cycles, far exceeding those of their single counterpart. Interestingly, designed asymmetric device (ASC) using NiCo 2 O 4 -MOF (positive electrode) and activated carbon (AC) (negative electrode) showed excellent energy density 84.26 Wh kg−1 at a power density of 1185 W kg−1 with 83.23% capacitance retention after 10,000 cycles. This report illustrates a novel route for synthesis and fabrication of metal oxides derived MOF having a large porosity which is beneficial to the electrochemical energy storage applications. [ABSTRACT FROM AUTHOR]

• A review of CV curve measures for supercapacitors has been made. • A model of supercapacitors' CV measuring was developed by De Levie approach. • Analytical and numerical solutions of the problem agree well. • The electrical potential distribution in supercapacitor electrodes was found. In this article, we analyzed a method of cyclic voltammetry (CV) with respect to diagnostics of supercapacitors. The main goal deals with the study of the voltage sweep rate limits allowing to reach equilibrium conditions during recording of CV curves. A mathematical model of cycling based on the De Levie model has been developed. Using this model, the CV curves of a supercapacitor with two symmetric porous electrodes and a separator have been calculated numerically for different sweep rates. These curves are in a good agreement with experimental CV curves. For the first time, an exact analytical solution is obtained for linear voltage sweep for a symmetric supercapacitor during the charge process. The concept of equilibrium CV curves is proposed and the criterium for the equilibrium conditions depending on voltage sweep rate and other parameters of the system is established. When the potential sweep rate exceeds the equilibrium conditions, the CV curves deviate from a rectangular shape and take the form of a " modified ellipses with sharp edges ". A review of publications related with experimental measurements of CV curves has been provided using the developed concept of equilibrium conditions. Application of the mathematical model to experimental CV curves makes it possible to reveal the presence of Faraday reactions. [ABSTRACT FROM AUTHOR]

Iron‑vanadium oxysulfide (Fe-VO-S) nanostructures with different Fe:VO atomic ratios are synthesized by a facile and low cost electrochemical deposition method. The synthesis of the various samples is confirmed by the physicochemical characterizations such as Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). For different Fe-VO-S nanostructures, the correlation between the physicochemical and the electrochemical properties is investigated. It is found that the Fe:VO atomic ratio has an important effect on the structure and size of the resulted particles. Also, the morphology of Fe-VO-S nanostructures has a remarkable influence on the electrochemical performance of the prepared samples. In addition, ternary Fe-VO-S nanostructures show better electrochemical performances compared to binary VO-S, in terms of high specific capacitance value and good cycling stability, because of the combined contributions from both of Fe and VO elements in the ternary nanostructures. Especially, the as-prepared Fe-VO-S nanostructure with Fe:VO molar ratio of 2:1 shows the highest specific capacitance value of 217 F g −1 at a current density of 3 A g −1 and also exhibits good cycling stability with 92% capacitance retention at a current density of 5 A g −1 after 4000 cycles. In addition, the Fe-VO-S nanostructure with the mentioned molar ratio of Fe:VO can be successfully applied to assemble a symmetric supercapacitor device and achieves good capacitive performances with a high specific capacitance (117 F g −1 at 3 A g −1 ), excellent energy density (9.3 Wh kg −1 at 2200 W kg −1 ) and power density (7200 W kg −1 at 1.2 Wh kg −1 ). [ABSTRACT FROM AUTHOR]

Three-dimensional freestanding hierarchical porous carbon materials with high specific surface areas (up to 1688 m 2  g −1 ) were prepared by the one-step carbonization of sucrose and zinc chloride (ZnCl 2 ), defined as SCs for simplicity. Herein, ZnO particles served as the etchant and template to produce micropores and mesopores. The formation mechanism, morphology and structure were investigated by a series of techniques. The SCs exhibited highly enhanced electrochemical performances as supercapacitors, and the one synthesized at 800 °C (SC-800) showed high specific capacitances of 130 F g −1 and 124 F g −1 at the current densities of 1 and 20 A g −1 in 1 M TEABF 4 /AN, respectively. This device delivered the high energy density of 55 Wh kg −1 to afford the power density of 2.5 kW kg −1 (voltage range of 3 V) and good cycling stability (85% capacitance retention after 10,000 cycles). [ABSTRACT FROM AUTHOR]

We report on the synthesis of manganese zinc ferrite (MnZnFe 2 O 4 ) nanoneedles via a simple one-pot coprecipitation method and their characterization using energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HR-TEM) and N 2 adsorption/desorption techniques. The electrochemical performance of MnZnFe 2 O 4 nanoneedles-based supercapacitors was investigated, showing superior specific capacitance of 783 F g −1 , which is significantly higher than that reported for any ferrite material. Also, the spinel MnZnFe 2 O 4 exhibits very high columbic efficiency and an excellent long-term stability. The fabricated asymmetric supercapacitor based on MnZnF 2 O 4 nanoneedles/activated carbon electrodes can deliver 15.8 Wh kg −1 energy density at a power density of 899.7 W kg −1 . The contribution of the double layer capacitance was found to be only 3.14% of the total specific capacitance and mainly based on psuedocapacitance faradaic mechanism. Therefore, the fabricated MnZnFe 2 O 4 electrode is a promising candidate for supercapacitor applications. [ABSTRACT FROM AUTHOR]

Controlling surface morphology of transition metal oxides play a key role in various applications. Here, we report new and facile route of dibenzothiazolyl dibenzo-18-crown-6 ether (DDCE) assisted synthesis of CuO nanosheets by hydrothermal method. DDCE is used as task specific structure directing agent for the shape controlled synthesis of CuO nanosheets. The effect of DDCE on morphology, surface area and electrochemical properties of CuO nanosheets is studied. The synthesized CuO nanosheets exhibited excellent capacitive properties such as high specific capacitance 130.6 F g −1 at 10 mV s −1 . These CuO nanosheets play important role in ion transportation and provide more active sites for electrochemical reactions. This work represents a new approach for preparation of CuO nanostructures by hydrothermal method. The prepared CuO nanostructures can be potential electrode material for high performance supercapacitors for the next generation energy storage devices. [ABSTRACT FROM AUTHOR]

Exploration of carbon nanoarchitectures with lower cost and excellent rate capability is of great importance, however, still remains a significant challenge. In the present work, a facile procedure for the fabrication of porous carbon nanocages (PCNCs) with a superior rate capability for supercapacitors has been developed. This approach is based on directly carbonization of sodium polyacrylate and subsequently chemical etching through a simple immersing-filtration-activation process. The extraordinary structures and morphologies of PCNCs has lots of structural advantages for supercapacitor applications. The supercapacitor assembled with the optimized sample can deliver a large specific capacitance (161 F/g at 1 A/g), superior rate capability (capacitance retention as high as 77.6% at 30 A/g), tiny IR drop (0.407 V at 30 A/g). Furthermore, in view of the wide working voltage (2.7 V) and excellent rate capability, the energy densities can retain at 30.2 Wh/kg at a large power density of 20.3625 kW/kg. Remarkably, the as-assembled supercapacitor can light 11 red light-emitting diodes (LED, 1.5 V) in parallel highlighting its enormous potential for practical applications. [ABSTRACT FROM AUTHOR]

A hybrid approach is beneficial to simultaneously exploit the characteristics of capacitive and transition materials to increase the energy density and power density of supercapacitors. In order to achieve optimal electrochemical performance, by means of a facile hydrothermal co-synthesis, we synthesize a three-dimensional porous aerogel consisting of MoS 2 nanosheets and reduced graphene oxide (rGO) with a controllable composition and morphological structure. The MoS 2 /rGO porous aerogel hybrids working as electrode material for supercapacitors, can efficiently enhance surface charge transport, provide more chemical reaction sites, shorten the migration path for electrons and ions, and facilitate the electrolyte diffusion. Using electrochemical feature in two-electrode configurations and symmetric cell devices, we obtain a specific capacitance of 472 F/g with excellent rate capability and cycling stability (98.9% retention after 30,000 cycles) at the current density of 1.0 A/g. Additionally, our designed supercapacitors are flexible under mechanical deformations, which are useful for the next generation wearable electronic devices. [ABSTRACT FROM AUTHOR]

K-birnessite type MnO 2 (δ-MnO 2 ) nanosheets were synthesized via hydrothermal technique and investigated the influence of proton beam irradiations on their structural and electrochemical properties. The effect of various proton beam irradiation conditions (proton energy and dose) on MnO 2 nanosheets were studied using X-ray diffraction, SEM, TEM, UV absorption, X-ray photoelectron spectroscopy and Raman spectral analysis. The proton irradiation displayed considerable structural transformation from δ-MnO 2 to α-MnO 2 /δ-MnO 2 and the morphology from nanosheets to distorted nanotubes. The electrochemical properties of the samples were analyzed using cyclic voltammetry, galvanostatic charge/discharge test and impedance spectroscopic techniques. The sample showed a comparable improvement in the specific capacitance value up to a certain extent of proton irradiation. The MnO 2 nanosheets irradiated with proton energy of 7.8 MeV and dose 10 14  p cm −2 exhibited a maximum specific capacitance value of 159 Fg −1 . But, the sample irradiated with high proton energy (9.8 MeV) and dose (10 16  p cm −2 ) showed 114 Fg −1 specific capacitance which is much less than that of unirradiated sample (142 Fg −1 ). [ABSTRACT FROM AUTHOR]

In this work, TiO 2 /graphene nanocomposite was synthesized by facile, surfactant free, in-situ microwave irradiation method, a quick but also are eco-friendly approach. The structure, morphology, composition and thermal stability of the composites were characterized by using XRD, SEM, FT-IR, Raman spectroscopy, and TGA analyses. XRD result shows the tetragonal anatase phase of pure TiO 2 , TiO 2 in the composite and their crystallite size were estimated to be 2.8 and 2 nm respectively. The SEM and HR-TEM analyses demonstrate the spherical TiO 2 nanoparticles intercalated on the graphene sheets. TGA results reveal higher thermal stability of the TiO 2 /graphene nanocomposite over graphene oxide and TiO 2 nanoparticles. XPS studies confirm the binding states of the composite structure. The nanocomposites used as the supercapacitor electrode in three electrode system exhibited higher specific capacitance value of 585 Fg − 1 at a current density of 1 Ag − 1 in 1 M H 2 SO 4 as compared to graphene oxide (174 Fg − 1 ) and TiO 2 electrode (66 Fg − 1 ). The enhanced capacitive performance is due to the intercalation of TiO 2 nanoparticles on the graphene sheet. The in-situ microwave irradiation method brings a viable, low-cost and facile synthesis of different metal oxide/graphene based composites with promising properties for energy-storage applications in supercapacitors. [ABSTRACT FROM AUTHOR]

A composite composed of reduced graphene oxide hydrogel/carbon dots (rGH/CDs) is prepared hydrothermally. The composite has a three-dimensional (3D) interconnected network structure and exhibits good electrical conductivity and mechanical robustness, making it ideal electrode materials in supercapacitors. The carbon dots (CDs) in the reduced graphene oxide hydrogel promotes electron transport and reduces the internal resistance and charge transfer resistance in addition to providing a large surface area. The flexible solid-state supercapacitor comprising the 130 μm thick rGH/CDs electrode delivers excellent performance including high gravimetric specific capacitance of 264 F g − 1 (up to 301 F g − 1 for a 40 μm thick electrode), areal specific capacitance of 394 mF cm − 2 (up to 432 F cm − 2 for a 200 μm thick electrode), excellent cycling stability (9.1% deterioration after 5000 cycles), larger energy density (35.3 Wh kg − 1 ), as well as high power density (516 W kg − 1 ). This study demonstrates the tremendous potential of rGH/CDs in high-performance flexible energy storage devices. [ABSTRACT FROM AUTHOR]

Nickel Foam as a substrate for morphology controllable synthesis of hierarchical nanocomposites with three-dimensional architecture is gaining substantial rank as effective energy materials for high-performance energy conservation and energy conversion devices. Herein, we report our findings in fabrication of 3D hierarchical, Ni 2 + /Mn 2 + /Al 3 + - layered triple hydroxide @ nitrogen-doped graphene wrapped hybrid on a nickel foam (marked as NMA-L@NG-NF) electrode, via a two-step hydrothermal method: primarily in situ hydrothermal growth of NiMnAl-LTH nanosheets over the surface of nickel foam, followed by secondary hydrothermal wrapping of NG graphene over the surface of NiMnAl-L@NF. The phase purity, structure, morphology and functionalities of the synthesized NMA-L@NG-NF hybrid electrodes were characterized comprehensively by XRD, FT-IR, Raman, XPS, EDS and SEM techniques. The results show that the obtained structure (NMA-L@NG-NF) possessed hierarchical flower-like configuration, which were self-assembled from LTH nanosheets and grafted successfully onto the framework of NF substrate during the hydrothermal process. Moreover, when tested as a binder-free electrode in a half cell three-electrode configuration, the NMA-L@NG-NF hybrid display significantly high specific capacity (452 mAh/g at 5 A/g), the excellent rate capability (75.8% at 20 A/g), the excellent cycling stability (91.4% of its initial capacity was retains at a current density of 10 A/g after 5000 cycles, with ∼ 100% Coulombic efficiency) and very low R CT value (0.34 Ω before and 0.62 Ω after 5000 charge discharge cycle from impedance measurements). It could be anticipated that the synthesized NMA-L@NG-NF hybrid is thus a highly promising electrode by virtue of their outstanding applications in high-performance energy storage and energy conversion devices. [ABSTRACT FROM AUTHOR]

We report a facile in situ synthesis approach to incorporate rare earth metal oxide (Eu 2 O 3 ) into the polypyrrole matrix and evaluate its electrochemical performance as supercapacitor electrode material. Polypyrrole, having good conductivity, higher chemical and thermal stability proves to be a very interesting electrode material. Eu 2 O 3 further augments the capacitance of the material owing to its variable oxidation states. Also, owed to the higher stability, it provides additional support to the polymer backbone imparting extra thermal and cyclic stability to the hybrid composite so formed. The PPy/Eu 2 O 3 -32 composite exhibits a volumetric capacitance of 535 F cm − 3 at the current density of 1 A g − 1 . This material also exhibits an improved energy density of 13.5 Wh L − 1 and a maximum power density of 4597.25 W L − 1 . Further, a good rate capability (18% loss of specific capacitance from 1 to 10 A g − 1 ) and high coulombic efficiency (99.8% at 10 A g − 1 ) proves integration of Eu 2 O 3 with PPy to be an effective way to eliminate the drawbacks of PPy in pristine form. [ABSTRACT FROM AUTHOR]

[Display omitted] • In-situ grown electrode materials exhibit large surface area and high porosity. • The material exhibits a high capacitance retention rate of 82.9 % at 10 A/g. • Assembled ACS devices can provide high energy density and high-power density. A neuronal nickel–cobalt–manganese sulfide material with a large surface area and high porosity can be homogeneously grown along a nickel foam via a simple one-step hydrothermal procedure. An optimal molar ratio of Ni, Co, Mn, and thiourea of 3:1:1:5 was obtained by adjusting the molar ratio of thiourea. This binder-free composite material supported by a nickel foam can be directly used as a battery-type electrode for supercapacitors. Under the optimal hydrothermal conditions, the battery-type electrode exhibited excellent electrochemical properties with a favorable specific capacitance (2805.3F/g, 1 A/g) and good rate properties (87.7 %, 10 A/g) because of the synergistic effect of the multiple transition metals. Furthermore, the battery-type electrode exhibited a remarkable capacitance retention rate (82.9 %, 10 A/g) after 10,000 cycles of electric charging and discharging owing to the addition of Mn, which suggests excellent cycle stability. Furthermore, an asymmetric supercapacitor (ASC) device prepared using the battery-type electrode material and activated carbon electrode exhibited a considerable energy density (86.9 W h kg−1) at a high power density (799.1 W kg−1). After charging for 26 s to 3.2 V, two ASC devices in series could light two red-light-emitting diodes for at least 300 s. Thus, a simple and effective synthesis scheme can be designed to prepare high-performing supercapacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • N/S co-doped carbon nanosheets derived from sugarcane processing by-products are synthesized. • Sulfonated potassium fulvic acid is used as both carbon source and heteroatom dopant. • The symmetric supercapacitor delivers a maximum energy and power density of 0.92 mW cm−2 and 184.5 μWh cm−2, respectively. Developing sustainable carbon materials from biomass for supercapacitors is a promising solution to alleviate energy and environmental pressures. In this paper, novel N/S co-doped carbon nanosheets derived from sugarcane processing by-products are proposed. Flexible and binder-free electrodes based on carbon felt and sulfonated potassium fulvic acid were prepared by a simple impregnation-carbonization method. The maximum areal specific capacitance, power density and energy density of the symmetric supercapacitor are 409.9 mF cm−2 (1 mA cm−2), 0.92 mW cm−2 and 184.5 μWh cm−2, respectively. The operating voltage of the device increases to 1.8 V by using LiCl electrolyte. After 10,000 cycles, the capacitance remains 90 % of its initial value. Besides, the device possesses good flexibility, which can be bent at different angles and has a capacitance retention of 92.3 % after 5000 bending cycles. The supercapacitor is of great significance for the recovery of crop processing by-products to prepare flexible electronic devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ternary NiCo 2 Al 0.02 -LDH/ N - Cc @PANI electrode have been synthesized. • A novel porous hollow capsule structure of nitrogen-doped carbon is designed and used as a conductive matrix material. • NiCo 2 Al 0.02 -LDH/ N - Cc @PANI electrode exhibits a fascinating capacitance of up to 1630F/g. • The assembled device could easily power a LED bulb. This paper designs and produces ternary NiCo 2 Al x -LDH grown directly on a novel porous hollow structure of nitrogen-doped carbon capsule (N - Cc) conducting matrix with a PANI coating layer. The carefully designed NiCo 2 Al x -LDH/ N - Cc @PANI electrodes exhibit electrochemical properties that are highly prized for their energy storage utility: specifically, a gravimetric capacitance of 1630F/g, an energy density of 55.75 Wh kg−1 at the power density of 750 W kg−1, and cyclic stability that achieves capacitance retention of 93.1 % after 5000 uninterrupted charge–discharge cycles. It should be noted that the electrode's excellent storage performance benefitted from the use of Al, which was crucial in stabilizing the LDH structure. It should also be pointed out that the 3D interconnected porous structure composed of N - Cc provides a greater accessible surface area and shortens the ion/electron transport distance, whilst PANI ensuring the LDHs remain firmly in contact with the conductive substrate. [ABSTRACT FROM AUTHOR]

In this work, Co 3 S 4 /NF@NiCo-LDH nanocomposites were successfully synthesized on nickel foam (NF) by three-step hydrothermal method. The Co 3 S 4 nanowires act as a scaffold and the LDHs continuously fills the gaps between the Co 3 S 4 nanowires. Finally, the Co 3 S 4 nanowires are compeletly covered by NiCo-LDH nanoflowers with a diameter of about 8 μm. The specific capacitances of Co 3 S 4 /NF and Co 3 S 4 /NF@NiCo-LDH nanocomposites are 1306.2F g−1 and 3480.0F g−1 at a current density of 1 A/g, respectively. The electrochemical energy storage performance of Co 3 S 4 nanowire can be effectively enhanced by compounding NiCo-LDH. An all-solid-state asymmetric supercapacitor device assembled with Co 3 S 4 /NF and Co 3 S 4 /NF@NiCo-LDH as cathode and active carbon as anode exhibited good performance that the specific capacitances of the device can be calculated to be 218.9F g−1 at current density of 1.0 A/g, the maximum energy were 59.5 Wh kg−1 at the power density of 700 W kg−1. The energy storage properties of the devices connected with different manners were also studied. It is obvious that two devices connected in series demonstrated the typical voltage extendtion and the ones in parallel improved the specific capacitance. Furthermore, a red LED light can be lit by two devices connected in series. Therefore, the study shows the promising practical applications of Co 3 S 4 /NF@NiCo-LDH supercapacitor and laid the foundation for the design of a new generation of high performance supercapacitors. [Display omitted] • Co 3 S 4 /NF@NiCo-LDH nanocomposites were synthesized. • Co 3 S 4 /NF@NiCo-LDH//activated carbon all-solid-state asymmetric supercapacitor an energy density of 275.2 Wh kg−1, with a power density of 5760 W kg−1. • The series Co 3 S 4 /NF@NiCo-LDH//activated carbon supercapacitor devices exhibited the typical enhancement of the operating voltage window and the parallel devices significantly improved the capacitance. • The Co 3 S 4 /NF@NiCo-LDH electrode material displayed the good electrochemical performances in solid-state supercapacitors and promising practical application prospects in integrated circuits for energy storage. In the study, Co 3 S 4 /NF@NiCo-LDH nanocomposites were successfully synthesized on nickel foam (NF) by a simple and cost-effective hydrothermal method. The supercapacitors with Co 3 S 4 /NF@NiCo-LDH as electrode materials exhibited an ultra-high specific capacitance of 3480.0F g−1 at a current density of 1 A/g. Co 3 S 4 /NF@NiCo-LDH//activated carbon (AC) all-solid-state asymmetric supercapacitor (ASS) was assembled with PVA/KOH as the electrolyte. The ASS device exhibits excellent cycling stability of 77.97 % capacitance retention after 5000 cycles at 10 A/g. The maxmum energy density of Co 3 S 4 /NF@NiCo-LDH//AC ASS was 275.2 Wh kg−1, with the power density of 5760 W kg−1. Especially, the ASS devices connected in different manners presented the typical performances of integrated circuits: voltage enhancement for series devices and current enhancement for parallel devices. Therefore, the study presented great practical potentials for new energy storage devices in integrated circuits. [ABSTRACT FROM AUTHOR]

• Co 3 O 4 /Nitrogen-doped carbon (Co 3 O 4 /NC) composite was successfully prepared by a two-step calcination method with ZIF-67 as precursor. • The specific capacitance of Co 3 O 4 /NC at a current density of 1 A g−1 is 1144F g−1. • The Co 3 O 4 /NC//AC two-electrode capacitor generates the highest energy density of 40 Wh kg−1 at a power density of 1037 W kg−1. Metal-organic frameworks with high specific surface area and controlled morphology have great potential for lithium-ion battery applications. Here, the ZIF-67 precursor was prepared by the room temperature stirring method. Then Co 3 O 4 /NC composite electrodes with hollow polyhedral structure were successfully prepared by a two-step calcination method, and their electrochemical properties were discussed. The specific capacitance of Co 3 O 4 /NC at a current density of 1 A g−1 is 1144F g−1 (much higher than the specific capacitance of pure Co 3 O 4), and the retention rate is 45.4 % under a 20 A g−1 of current density. In addition, the asymmetric supercapacitor (ASC) device consisting of Co 3 O 4 /NC composite electrodes and activated carbon produced the highest energy density of 40 Wh kg−1 at a power density of 1037 W kg−1. At a current density of 5 A g−1, the capacitor retains 87.6 % of its initial capacitance after 10,000 charge/discharge cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] • Capsaicin modified N-doped graphene (Cap-NG) is prepared by hydrothermal method. • Cap prevents the stacking of NG by non-covalently functionalization. • Cap improves the specific capacitance of NG to 312F g−1 at 1 A g−1. • Cap-NG shows an excellent cycle stability of 102.9 % after 10,000 cycles. Organic molecules with multi-electron redox active centers exhibit great potential in electrochemical storage. Immobilizing them on the graphene surface through π-π interaction can effectively improve the pseudocapacitance. Nature capsaicin (Cap) molecule, with redox active sites, is good benefit for enhance the capacitance performance of the nitrogen doped graphene (NG) by non-covalent modification. In this work, the Cap-functionalized NG (Cap-NG) is successfully prepared by one-step hydrothermal method combined with vacuum freeze-drying technology. The electrochemical measurements show that the optimal Cap-NG exhibits a high capacitance of 312 F g−1 at 1 Ag−1 and an excellent durable cycling life of 102.9 % after 10,000 charging/discharging cycle times at a current density of 20 Ag−1. Furthermore, the Cap-NG-based symmetrical supercapacitor (SSC) demonstrates an energy density of 8 Wh kg−1 at 596 W kg−1. Moreover, density functional theory (DFT) calculations are used to elaborate the origin of pseudocapacitance by researching the adsorption configuration, binding energy and charge storage mechanism of Cap on NG sheet as well as to calculate the density of states (Dos). This study further enriches the application of natural capsaicin molecule on energy storage, and provides another way to build a green and environment-friendly SCs. [ABSTRACT FROM AUTHOR]

• The zeolitic imidazole framework was used as the template. • The hollow polyhedral MnCoNi-LDH was synthesized via the hydrothermal method. • The distinctive nanostructure of MnCoNi-LDH facilitates the diffusion of electrons and ions. • The device shows an ultrahigh specific capacitance and capacity retention. The ternary MnCoNi layered double hydroxides (MnCoNi-LDH) used in supercapacitors frequently encounters issues in low electronic conductivity and big volume expansion throughout charge–discharge, which compromise cycling stability. Herein, MnCoNi-LDH is effectively produced via the straightforward one-pot hydrothermal method with ZIF-67 as the template, which delivers an ultrahigh specific capacitance performance of 2254 F g−1 at a current density of 1 A/g. More importantly, the capacitance lost is only 8.47 % after 5000 cycles at 10 A/g. The fabricated MnCoNi-LDH consists of the hollow polyhedral nanostructure with interior nanoporous channels and nanosheet on the surface, which supply high specific areas and a huge quantity of redox active sites. It is found the exceptional performance of ternary MnCoNi-LDH is related to its distinctive nanostructure, the synergy effect among metal ions and the enhanced ion transmission speed and the conductivity. Additionally, when the ternary MnCoNi-LDH is employed in a flexible solid-state hybrid supercapacitor, the device has an excellent specific capacitance of 303.08 mF cm−2 at a current density of 1 mA cm−2, a high energy density of 47.42 Wh kg−1 at a power density of 404.1 W kg−1 and retains 96.3 % of capacitance after 5000 cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe 2 O 3 -Cr 2 O 3 Nanocomposite was synthesized by facile hydrothermal method. • Fe 2 O 3 -Cr 2 O 3 NC has spherical shaped morphology. • Fe 2 O 3 -Cr 2 O 3 NC delivers high specific capacitance of 906.9F/g. • Fe 2 O 3 -Cr 2 O 3 NC exhibits capacitive retention of about 79.2% for 5000 charge–discharge cycles. • Fe 2 O 3 -Cr 2 O 3 //AC ASC delivers the energy density of 77.17 Wh/kg corresponding to the power density of 650 W/kg. upercapacitor electrode materials with multiple redox-active sites and superior electrical conductivity are highly desirable for future energy storage devices in a cost-effective manner. Here, the nanocomposite (NC) based on the sesquioxides of iron oxide-chromium oxide (Fe 2 O 3 -Cr 2 O 3) is synthesized by a one-step hydrothermal approach. Fe 2 O 3 -Cr 2 O 3 NC electrode delivers a high specific capacity of 544.2 Cg−1 at the scan rate of 10 mV/s. Trasatti method reveals the charge storage mechanism of Fe 2 O 3 -Cr 2 O 3 NC providing the total, outer, and inner capacity of 1118, 71.3, and 1047 Cg−1 respectively. In addition, the low solution resistance (R S) and charge transfer resistance (R ct) of 0.75 and 0.06 Ω respectively are being evaluated by Electrochemical Impedance Spectroscopy (EIS) analysis. Furthermore, the faradic charge–discharge curves with prolonged discharge time are achieved for the Fe 2 O 3 -Cr 2 O 3 NC electrode material with the maximum specific capacity of 814 Cg−1 at the current density of 1 Ag−1 and the capacitive retention of 79.2 % is maintained after 5000 consecutive charge–discharge cycles. Hence, the asymmetric supercapacitor (ASC) device is being constructed using Fe 2 O 3 -Cr 2 O 3 cathode and activated carbon (AC) anode, delivering a high energy density of 77.17 Wh kg−1 corresponding to the power density of 650 W kg−1. [ABSTRACT FROM AUTHOR]

[Display omitted] • F content and porous structure are tuned by heating and chemical reduction of FG. • Semi-ionic C-F species enhance the supercapacitive properties in KI electrolyte. • The introduction of KI promotes the specific capacitance up to 583 from 17 F/g. To investigate the effect of structural properties of fluorinated graphene (FG) on the supercapacitive properties in KI additive electrolyte, the porous structure and surface F element content of FG were adjusted via chemical reduction by hydrazine and heating treatment. Systematically electrochemical measurements show that there is a dramatical increase of specific capacitance (583 F/g) in KI-additive electrolyte due to the pseudocapacitance brought by KI compared with that (17 F/g) in pure H 2 SO 4 electrolyte. Investigation on the relationship between F content and areal capacitance show that small amount of F content, especially for semi-ionic C-F species with better electronic conductivity compared with covalent C-F species, can effectively promote the areal capacitance. With moderate F content and relatively high specific surface area, the assembled symmetric supercapacitor can deliver an energy density of 8.89 Wh kg−1 and exhibits a long cyclic stability. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate a facile and universal approach to fabricate the ACNF/PANI/NiO ternary composite as electrode materials for supercapacitors through the combination of electrostatic spinning, carbonization and in-situ polymerization methods. By utilizing electrospun NiO-incorperated PAN-based activated carbon nanofibers (ACNF) as carbon-based template, compact three-dimensional (3D) conductive nanofiber network structures are constructed with PANI nanoparticles densely coated on the activated carbon nanofibers, contribute to enhancing electrical conductivity and rapid electron transport during the charge-discharge processes. The deposited PANI in the ACNF/PANI/NiO composite all possesses well-organized uniformity on the NiO incorperated ACNF, producing myriads of open, hierarchical inflorescence-like nanoflakes, which not only increase the specific surface area of the composite but also promote the surface redox reaction of electrode and electrolyte solution. As a consequence, the ACNF/PANI/NiO-0.3 composite exhibits a high specific capacitance of 1157 F·g − 1 at 1 A·g − 1 , and it still maintains 720 F·g − 1 at a high loading current density of 10 A·g − 1 . Besides, the ACNF/PANI/NiO-0.3 composite retains 93.89% of the original capacity after 5000 continuous charge-discharge cycles at 10 A·g − 1 , exhibiting outstanding cycle stability. In addition, an asymmetric supercapacitor fabricated with ACNF/PANI/NiO-0.3 composite demonstrated excellent energy density of 20.14 Wh·kg − 1 at a power density of 102.67 W·kg − 1 . [ABSTRACT FROM AUTHOR]

Electrochemically deposited manganese dioxide films have shown excellent supercapacitor properties when deposited over stainless steel substrates. Deposited films are characterized using X-ray diffraction and microscopic techniques. Effect of annealing on the supercapacitor properties of the films has been evaluated. Manganese dioxide films of different thicknesses are produced by varying the deposition time in electrochemical deposition process. Specific capacitance was higher in thinner films. Specific capacitance of 615 Fg − 1 is obtained from the cyclic voltammetry (CV) measurements at 20 mVs − 1 scan rates. Electrochemical properties of the films are investigated with many other electrochemical test procedures. Electrochemical property of the films is mapped using scanning electrochemical microscope (SECM). [ABSTRACT FROM AUTHOR]

We report here that poly- o -phenylenediamine as a solid carbon source can be facilely carbonized to produce three-dimensional nitrogen-doped graphene (3DNGN) with the aid of Ni(NO 3 ) 2 powder. In situ formed Ni nanoparticles by decomposition of Ni(NO 3 ) 2 serve as both template and catalyst for the formation of 3DNGN. The 3DNGN with interconnected porous structure and high content of nitrogen doping can ensure large electrolyte-accessible surface area, rapid ion transportation, and fast electron transport, resulting in high electrochemical performance. The 3DNGN shows a high specific capacitance of 312 F g − 1 at 1 A g − 1 with good capacitance retention capability and good cycling stability, and outputs a high average energy power density of 10.8 W h kg − 1 and a high maximum power density of 595 kW kg − 1 in aqueous KOH electrolyte. Due to the great pseudocapacitance in aqueous H 2 SO 4 electrolyte, the specific capacitance of the 3DNGN can reach a high value of 345 F g − 1 at 1 A g − 1 . [ABSTRACT FROM AUTHOR]

Straightforward and scalable fabrications of energy storage electrode materials with high electrochemical performance are of great interest for applications in batteries and supercapacitors. Herein, we report a one-step process for producing high-performance NiO/reduced graphene oxide (RGO) nanocomposites using a ball mill based method, which is simple, environmentally friendly, and cost-effective. Graphite oxide (GO) and nickel power were pulverized in a ball mill, to produce NiO/RGO nanocomposites. GO played an important role in promoting a redox reaction between GO and metallic nickel, which produced a strong bond between the as-formed Ni oxide and RGO. The electrochemical performances of NiO/RGO were investigated by cyclic voltammetry (CV), galvanostatic charge/discharge measurement, and impedance spectroscopy. The NiO/RGO electrodes exhibited high specific capacitance (590 F g − 1 at 1 A g − 1 ), a high rate capability (88% retention at a high rate of 15 A g − 1 ), and an excellent cycling stability (100% retention after 1000 charge/discharge cycles). [ABSTRACT FROM AUTHOR]

Using p -phenylenediamine (PPD) or p -nitroaniline (PNA) as effective redox additive can largely improve the capacitive performances of supercapacitors when incorporated into KOH solution. And how to vividly differentiate the roles of amine and nitro groups adherent to phenyl ring really is an interesting scientific issue. Herein, with the help of a series of capacitive techniques, it is discerned that the PPD can release two protons and two electrons, while the PNA realizes the gain/loss of one proton and one electron, in particular accompanied with the partial reduction of nitro group. Clearly, introducing PPD or PNA substances into KOH solution can largely improve the specific capacitance as well as the resultant energy densities, but slightly deteriorates the energy efficiency. Besides, the incorporation of PNA leads to higher cycling stability than that of the PPD, which is primarily incurred by the fact that the nitro group adherent to phenyl ring delivers better stability. Furthermore, the potential window of 0–1 V or − 0.5–0.5 V strongly affects the capacitive performances. The present research results are expected to provide us the guidance for the usage of PPD or PNA when incorporated into KOH solution for elevating the supercapacitors' performances. [ABSTRACT FROM AUTHOR]

The ordered arrays of nanostructure with vertically aligned tube like structure hold great promise as an electrode material for high-performance energy storage devices. Such binder-free structure of Titanium dioxide (TiO 2 ) has been synthesized by anodization of titanium (Ti) foil. The use of TiO 2 nanotube as an electrode material attain a specific capacitance of 207 F g − 1 at 5 mV s − 1 scan rate in 1 M potassium hydroxide (KOH) electrolyte. Extra ordinary cycling performance with 103% capacitance retention of their initial capacitance for 1500 cycles has been achieved, suggests its promising candidate as highly stable electrode material for supercapacitor application. [ABSTRACT FROM AUTHOR]