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This paper studies the effect of oxygen-containing functional groups on the stability of activated carbon (AC) used in surpercapacitors with H 2 SO 4 and KOH electrolytes, where AC prepared from rice husk by KOH activation (denoted as RHC) was used as electrode materials. Results show that RHC displays excellent stability in H 2 SO 4 electrolyte but poor stability in KOH electrolyte during long-term cycling. The different stability of the oxygen-containing functional groups of RHC in these two electrolytes caused the different change of the potential of positive electrode during the charge/discharge processes of supercapacitors, which leads to the different cycling stability of RHC in KOH and H 2 SO 4 electrolytes. The hydrolysis products of the carboxyl and lactones groups in RHC cause electrostatic repulsion and steric hindrance, which hinders the transportation of OH − into the pores of RHC. As a result, the capacitance of positive electrode decreases. The decreased capacitance of positive electrode causes the increase of maximum potential of positive electrode upon charge, which results in the oxidation and further decreased capacitance of positive electrode. The oxidation of positive electrode and the decrease of the capacitance of positive electrode are two mutually reinforcing processes, which causes the eventual failure of RHC in KOH electrolyte. The quinone-like groups of RHC are stable in H 2 SO 4 electrolyte and do not cause obvious decrease of capacitance. Hence, RHC obtains long cycling life in H 2 SO 4 electrolyte. [ABSTRACT FROM AUTHOR]

A new method of the formation of composite Co-Ru oxides/hydroxides material without a binder for supercapacitors has been proposed. The layers of mixed Co-Ru oxides/hydroxides were formed by the chemical reaction of RuCl3, dissolved in isopropyl alcohol, with a surface of electrochemically deposited nano-structured Co. The surface and bulk composition of synthesized Co-Ru oxides/hydroxides layers were studied by the X-ray photoelectron spectroscopy method. It was determined that the composite Co-Ru layer consisted of mixed oxyruthenium and cobalt hydroxide species of various oxidation states. The layer is characterized by a relatively uniform Co/Ru ratio throughout the bulk. An examination of the surface of formed layers by scanning electron microscopy showed its developed porous morphology. The electrochemical behaviour, the influence of Co substrate on the properties of Co-Ru oxide/hydroxides electrode and stability of the formed layer in 40 g l-1 NaOH solutions were evaluated by the cyclic voltammetry method. The specific capacitance values of ~1230 F g-1 for the composite Co-Ru oxides/hydroxides electrode on the nano-structured Co substrate were determined. Multiple CV cycling of electrodes confirmed good stability of the synthesized Co-Ru oxides/hydroxides layer without a binder. [ABSTRACT FROM AUTHOR]

Three nanoscale Ni-Schiff-base coordination polymer particles have been firstly prepared in poor solvent (DMF) through a precipitation method. XRD, TGA and EA results show that as-synthesized compounds are either amorphous or crystalline. High temperature annealing of these Ni-based compounds can result in pseudo-capacitive NiO electrodes. Series of electrochemical measurements illustrated that the as-prepared NiO material, especially for NiO nanospheres could deliver a maximum specific capacitance of 153 F g −1 and good stability over 1000 cycles with the capacitance retention of 100%, indicating the morphology and resistance effect on the diffusion-controlled redox reaction between the OH − ions and the NiO samples. [ABSTRACT FROM AUTHOR]

In the contribution, we explore an efficient synthetic platform to purposefully fabricate hollow mesoporous NiCo 2 S 4 (HM-NCS) ellipsoids for advanced electrochemical supercapcitors (ECSs). Uniform hollow NiCo 2 O 4 (NCO) as the intermidate is initially prepared by calcination, and subsequently chemically transformed into spinel HM-NCS ellipsoids through in situ anion-exchange reaction. Elaborate physicochemical and electrochemical investigations comparatively demonstrate that the resultant HM-NCS ellipsoids possess superior pseudo-capacitance of ∼495 F g −1 against its hollow NCO counterpart (∼185 F g −1 ) at the same rate of 10 A g −1 , benefiting from its larger surface area, thinner porous shells, smaller internal and charge-transfer resistances, and higher-content Ni (II)/Co (II) species. Remarkably, an asymmetric supercapacitor assembled with HM-NCS ellipsoids obtains a high energy density of ∼28.9 Wh kg −1 at a power density of ∼187.5 Wh kg −1 , and appealing cycle behaviors with a capacitance decay of ∼0.0058% per cycle over 5000 cycles at a high rate of 3 A g −1 . It strongly highlights that the cost-effective HM-NCS ellipsoids would be a competitive pseudo-capacitive electrode candidate for advanced ECSs applications. [ABSTRACT FROM AUTHOR]

The capacitive behaviour of four commonly studied electrochemical capacitor systems has been analyzed using the step potential electrochemical spectroscopy (SPECS) method. Electrode-electrolyte combinations with different charge storage mechanisms were characterized, including activated carbon in aqueous (H 2 SO 4 ) and organic (TEABF 4 in acetonitrile) electrolytes, manganese dioxide (Na 2 SO 4 ) and anhydrous ruthenium oxide (H 2 SO 4 ). The SPECS method was used to separate the charge storage contributions from double layer capacitance (C DL ) and diffusion-limited pseudo-capacitance (C D ) at scan rates ranging from 0.08 to 125 mV/s. The relative contributions from each process are related to the physicochemical properties of the electrode. Additionally, the effects of these electrode properties on the overall performance of each system, in terms of specific power and energy, are identified. [ABSTRACT FROM AUTHOR]

A simple and scalable method to fabricate enriched-nitrogen activated carbons (3.11-1.19 wt.%) by direct heat treatments of waste particleboards for high-performance supercapacitors was presented in this paper. The effects of the activation temperature on the textural properties and capacitive performance of the nitrogen-containing activated waste particleboard carbons (N-AWPCs) were analyzed. The N-AWPC prepared at 800 °C (N-AWPC800) show high specific surface areas, suitable pore size distributions and nitrogen content, all of which are essential for achieving high electrochemical performances as supercapacitor electrodes. The symmetric supercapacitor based on N-AWPC800 offers a specific capacitance of 263 and 119 F g at a current density of 0.05 A g use 7 M KOH and 1 M tetraethylammonium tetrafluoroborate in propylene carbonate (TEMA-BF/PC) as the electrolyte, respectively. The supercapacitor delivers high energy densities of 9.1-7.9 Wh kg under the power outputs of 15.6-2855.3 W kg in 7 M KOH and of 25.8-18.9 Wh kg under the power outputs of 18.6-3894.4 W kg in 1 M TEMA-BF/PC. [ABSTRACT FROM AUTHOR]

A hierarchical CuO nano-structure is prepared by directly growing CuO nanoflowers on carbon fiber fabric (CuO/CFF) via a hydrothermal method. The CuO/CFF is used as the electrode material of a supercapacitor for electrochemical energy storage. The supercapacitor displays superior electrochemical performance in aqueous electrolyte with the specific capacitance of 839.9 F/g at the scan rate of 1 mV/s, energy density of 10.05 Wh/kg and power density of 1798.5 W/kg, which are the highest values for the CuO/CFF electrodes. Moreover, a flexible symmetric solid-state symmetric supercapacitor is also fabricated by using the CuO/CFF as electrodes. The solid-state supercapacitor exhibits a specific capacitance of 131.34 F/g at the scan rate of 1 mV/s with a power density of 145.12 W/kg, and 95.8% capacitance retention after 2000 charge-discharge cycles. [ABSTRACT FROM AUTHOR]

Petroleum coke is a valuable and potential source for clean energy storage if it could be modified legitimately and facilely. In the present study, porous carbon with high surface area and abundant oxygen-containing groups was prepared from petroleum coke by chemical activation and modification processes. The as-prepared carbon exhibits a high surface area (1129 m · g) and stable micrographic structure. It presents a high specific capacitance and excellent rate performance in KOH electrolyte. Even at an ultrahigh current density of 50 A · g, the specific capacitance of the prepared carbon can still reach up to an unprecedented value of 261 F · g with a superhigh retention rate of 81 %. In addition, the energy density of this material in aqueous electrolyte can be as high as 13.9 Wh · kg. The high energy density and excellent rate performance ensure its prosperous application in high-power energy storage system. [ABSTRACT FROM AUTHOR]

Recently, porous nanostructured transition metal oxides with excellent electrochemical performance have become a new class of energy storage materials for supercapacitors. The ever-growing global demand of electrically powered devices makes it imperative to develop renewable, efficient and reliable electrochemical energy storage devices. This review article focuses on the Ni based transition metal oxides and their composite electrode materials including carbons, metals and transition metal oxides for supercapacitor applications, providing an overview on the charge mechanisms, methodologies and nanostructures discovered in recent years, and latest research findings. The NiO and their composites possess higher reversible capacity, good structural stability, and have been studied for usage as novel electrode materials for supercapacitors. Their fine-tuned physical and chemical properties make them ideal candidates for supercapacitor applications as they possess higher accessible electroactive sites, which will provide both high power density and also high energy density. Moreover, synergistic effects can be derived from the constituent materials of the NiO based composite electrodes. The potential problems like device fabrication, measurement techniques, and future prospects of utilizing these materials as supercapacitor electrodes highlighting the fundamental understanding of the relationship between electrochemical and structural performances are also discussed. [ABSTRACT FROM AUTHOR]

The development of electrode materials for Sodium-Ion Batteries (SIBs) has received more and more attention. Among them, vanadium sulfide, as a member of the transition metal sulfide family, owns the characteristics of rich electrochemical activity, high theoretical capacity and adjustable spatial structure. However, the complicated synthetic process, poor rate capability and intricate redox mechanism of vanadium sulfides make them less competitive for commercial use. In this work, a facile approach based on the ball-milling technique followed by adjusted annealing temperature is introduced to fabricate large-scale vanadium sulfides. This general phase-controlled method can bring three different crystal types of V 5 S 8 , V 3 S 4 and V 3 S 5. With homogeneous covering of super P and Carbon Nano Tubes (CNTs), a conductive network that favors the Na ions/electrons transport in the vanadium sulfides-based electrodes can be fabricated. The V 5 S 8 exhibits the best performance in SIBs with specific capacity of 918 mAh g−1 at 0.1 A g−1 (100 cycles). Moreover, V 5 S 8 electrode also exhibits an ultra-rate capability of 333 mAh g−1 at 50 A g−1 after cycling lifespan (4000 loops). The extremely high pseudo-capacitance characteristics of V 5 S 8 is significant during the SIBs discharge/charge. Additionally, the V 5 S 8 anode also shows the high energy density of 165 Wh kg−1 in SIBs full cell. [Display omitted] • The vanadium sulfides are fabricated by phase-controlled approach. • The exquisite architecture owns the enhanced conductivity and connected conductive networks. • The V 5 S 8 exhibits superior performance for SIBs half/full batteries. • The short and connected ion/electron transportation of V 5 S 8 is responsible for boosted kinetics. [ABSTRACT FROM AUTHOR]

Mesoporous carbon (MPC) with uniform inner mesopore structure and high specific surface area prepared by an MgO-templated method has been employed for a substrate of MnO 2 /C composite. The MnO 2 /C composite was synthesized by anodic or cathodic electrodeposition of MnO 2 from MnSO 4 or KMnO 4 precursor, respectively, on the MPC substrate. The XRD patterns of the composite confirmed that MnO 2 was effectively deposited on the substrate under both anodic and cathodic electrodeposition processes. From the SEM images, sheet-like MnO 2 was deposited by anodic deposition (a-MnO 2 /C) while needle-like MnO 2 deposition was observed for the cathodic deposition (c-MnO 2 /C). The voltammetric experiments showed that the capacitive behavior of the composite depended on the preparation method. The difference in the specific capacitance between a-MnO 2 /C and c-MnO 2 /C is considered to be mainly due to the shape of MnO 2 deposited on the MPC substrate. The electrochemical capacitance of c-MnO 2 /C was much higher than that of the substrate carbon. The observed capacitance increase in c-MnO 2 /C was attributed to the pseudo-capacitance of MnO 2 that utilized effectively in controlled pore structure of MPC. The composite electrode, prepared by the cathodic deposition (c-MnO 2 /C), showed high specific capacitance and good durability for constant-current charge–discharge cycling. [ABSTRACT FROM AUTHOR]

Pine needle β-Co(OH) 2 grown on Ni foam (β-Co(OH) 2 /NF) substrate was fabricated via a simple hydrothermal process for improved electrochemical properties. The sample has been characterized by FTIR, XRD, TG, SEM, TEM, cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance study. It exhibits high specific capacitance of 1215 F/g and 790 F/g at current density of 5 and 50 A/g, respectively. The capacitance can retain about 91.4% after 1000 charge-discharge cycles at a current density of 50 A/g. The β-Co(OH) 2 /NF has high specific capacitance and long cycle stability, which makes it suitable for supercapacitor application. [ABSTRACT FROM AUTHOR]

This paper involves preparation of four different crystal phases (δ, γ, α and λ) of MnO 2 by redox, solid reaction, hydrothermal routes and delithiation of LiMn 2 O 4 , respectively. The obtained MnO 2 samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and the Brunauer–Emmett–Teller (BET) method for micro-structural, morphological and porosity studies. Cyclic voltammetric and galvanostatic tests were carried out to evaluate their capacitive properties in an anti-freezing aqueous electrolyte at different operating temperatures ranging from 25 to −35 °C. The δ-MnO 2 prepared by a redox method exhibits the best electrochemical performances when conducted either in the single electrode tests (from 174.7 to 148.6 F g −1 ) or in the capacitor measurements (from 47.4 to 42 F g −1 ) as the operating temperature decreased from 25 °C down to the low temperature of −35 °C. Moreover, electrochemical impedance spectroscopy has been investigated and the activation energy values of different impedance components have been analyzed. It has been discovered that the operation temperature has more effect on the charge transfer resistance than diffusion resistance. To some degrees, these results have guiding significance for the low-temperature applications of manganese oxides-based electrochemical capacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Surfactant assisted synthesis of novel NiO nanostructures via simple sol–gel route. • Tunning morphology for boosting electrochemical properties. • High specific capacitance, energy density, power density, cycling stability. • The enhanced performance by nanoflower type morphology. • Superficial/scalable fabrication methodology for pseudo-capacitor advancements. Nickel oxide (NiO) nanostructures with diverse morphology were prepared by facile sol–gel route using cationic, anionic, and non-ionic surfactants as stabilizing agents. The effects of surfactants on the physical and morphological properties of NiO were investigated. In addition, the electrochemical properties of grown products were also studied. We have observed that cationic surfactant (CTAB) leads to petal-nanoparticle interconnected nanoflower-like morphology. The electrochemical study revealed that all electrodes have pseudocapacitive nature with Faradic charge-storage mechanism. The CTAB assisted electrode owns large specific capacitance/energy density/power density of 397F/g/27.57 Wh/kg/0.54 KW/kg at 1 A/g current density in 1.0 M KOH electrolyte with superior cycling stability. The formation of nanoflower-like morphology in CTAB assisted electrode provides a larger surface area for ions transportation, higher conductivity, fast charge transfer, higher current density, and high electrochemical active surface area, attributing to boosted supercapacitive behavior of synthesized electrodes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hierarchical Mo 2 C-MXene@MoO 2 @C was fabricated via a self-assembly strategy. • Mo 2 C-MXene@MoO 2 @C exhibited abundant Mo-N bonds and weakened Mo-O bond. • Strong adsorption and low migration energy barrier of Li+ favored fast kinetics. • Fast diffusion kinetics enhanced the diffusion-controlled charge storage behavior. • The optimized electrode delivered superior rate capability and cyclic performance. Molybdenum dioxide (MoO 2) with high theoretical capacity and low cost has triggered extensive interest as a renowned anode for lithium ion batteries (LIBs). However, the sluggish diffusion kinetics and severe capacity decay obstructed its practical application. Herein, hierarchical spherical Mo 2 C-MXene@MoO 2 @C was fabricated through a self-assembly and carbonization strategy. DFT calculations and experimental results revealed that the incorporation of metallic Mo 2 C-MXene and carbon into MoO 2 not only modulated the charge distribution and weakened Mo-O bond of MoO 2 , but also promoted the adsorption of Li+ on MoO 2 and lowered the migration energy barrier for Li+, thereby accelerating the electrochemical kinetics, inducing a strong diffusion-controlled charge storage behavior and improving the electrochemical reversibility. In addition, the introduction of MXene reinforced the structural integrity of MoO 2 during ion insertion and extraction, which ameliorated the electrochemical stability. Beneficiating from the above synergistic effect, the optimized Mo 2 C-MXene@MoO 2 @C delivered remarkable cycling capacity (854.5 mAh g−1 after 500 cycles at 0.5 A g−1) and superior rate capacity (644.4 mAh g−1 at 1 A g−1) for lithium storage. This work disclosed the charge storage mechanism of MoO 2 and provided new guidance for the rational design of novel electrode materials for secondary batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis of novel Nd 2 CeMO 3 (M = Er, Sm, V) nanostructures via sol–gel route. • Detail analysis by XRD, FTIR, FE-SEM, EDX, IV, CV, GCD, EIS, and ECSA. • High specific capacitance (1319F/g), energy density (225 Wh/kg), and power density (82.4 W/kg). • The boosted electrochemical performance of Nd 2 O 3 by Ce-Er co-doping. • The scalable methodology for next-generation supercapacitor electrode designs. Rare earth neodymium oxide-based Nd 2 CeMO 3 (M = Er, Sm, V) nanostructures were synthesized using a simple and versatile sol–gel method for supercapacitor applications and characterized with various analytical techniques. X-ray diffraction confirmed the effective doping of Ce and the co-doping of Er, Sm, and V in the Nd 2 O 3 matrix having a single hexagonal phase. FTIR further confirmed the formation of neodymium oxide matrix having metal–oxygen-metal bonding vibration. FE-SEM images revealed nanoplates type morphology, and EDX evident the existence of desired elements Nd, Ce, Er, Sm, V, and O in grown samples. IV results showed that the electrical conductivity of co-doped samples was high. The electrochemical measurements such as CV, GCD, EIS, and ECSA exhibited that all the fabricated nanostructures have pseudo-capacitive nature. However, the Er-Ce co-doped Nd 2 O 3 electrode has higher specific capacitance (1319F/g), energy density (225 Wh/kg), and power density (82.4 W/kg), using 1 M KOH electrolyte having 5 A/g current density. Further, the single Ce doped and Sm, V co-doped electrodes have shown higher performance than pure Nd 2 O 3 electrodes. In addition, the Nd 2 CeErO 3 electrode presented superb cycling stability; maintained 96 % initial specific capacitance at the 1000th cycle. The formation of the plate-like morphology in the Nd 2 CeErO 3 electrode provides a larger surface area for ions transportation, also higher conductivity, fast charge transfer (EIS results), and high electrochemical active surface area (ECSA results) are considered responsible for boosting supercapacitive behavior. This superficial and scalable fabrication methodology (co-doping) offers an effective route to boost the electrochemical performance of Nd 2 O 3 and introduce novel electrode designs for next-generation supercapacitor advancements. [ABSTRACT FROM AUTHOR]

A practical approach for controlling the morphology and electrochemical properties of electroactive materials is proposed. In this study, manganese oxide films were galvanostatically deposited in the presence of a small amount of carbon nanotube (CNT). The resulting film cannot be considered as a CNT-based nanocomposite, as no CNT is detected by electron microscopy. However, the manganese oxide electrodeposited delivers an excellent pseudo-capacitive behavior to be used as a superior supercapacitor. The samples prepared by applying a current density of 3.0 mA cm −2 showed a specific capacitance of 280 F g −1 . As it seems that the capacitance of this electrode is related to the chemisorption of the alkali cation, an extremely high specific capacitance of 434 F g −1 was achieved in a saturated medium of Li electrolyte. This high specific capacitance can be attributed to a bulk process. The presence of carbon nanotubes results in the formation of nanostructured films which provide a better accessibility for capacitive behavior. Although the exact mechanism for this phenomenon is still vague, the presence of carbon nanotubes (probably as a solid charge carrier) close to the electrode surface is apparently responsible for a different pathway for the electrodeposition process. [ABSTRACT FROM AUTHOR]

High-performance supercapacitor electrodes with a novel hierarchical structure of MnO 2 /ZnO/carbon-fabric were rationally designed, and prepared by a simple three-step-solution method. The design comprises ZnO nanowires radially grown on each micron-size fiber of a carbon-fabric electrode, with a thin MnO 2 shell on each ZnO nano-core. This multi-scale hierarchical structure yields: (a) high specific area of pseudo-capacitive MnO 2 to maximize specific capacitance; (b) effective MnO 2 -electrolyte interface to facilitate fast charging/discharging; and (c) conductive MnO 2 –ZnO-electrode path to reduce energy loss. In addition, the overall capacitor performance is optimized by choosing proper thickness of MnO 2 shell and aspect ratio of ZnO nano-core. The design was realized and validated with the development of a simple three-step-solution method: (a) radial deposition of nano-ZnO on carbon fabric; (b) coating ZnO by a thin layer of carbon; and (c) reduction of MnO 4 − and replacement of this carbon overlayer by MnO 2. With this design and method, high specific capacitance of 886 F g −1 was found from electrodes with 5 nm MnO 2 on ZnO having an average diameter of 50 nm and aspect ratio of 30. These samples showed specific energy of 16 Wh kg −1 and specific power of 27 kW kg −1 at current density of 20 mA cm −2 , and good long-term cycling stability. [ABSTRACT FROM AUTHOR]

Three new different comonomers of carbazole-EDOT derivatives had been previously synthesized and characterized in detail. In this study, electroactive materials were electropolymerized onto multi-walled carbon nanotube (MWCNT) modified glassy carbon (GC) electrode in 0.1 M sodium dodecyl sulphate (SDS) solution. The electrochemical impedance spectroscopic results of Nyquist, and Bode-magnitude and Bode-phase plots show that polymers/MWCNT composites possess good capacitive characteristics. P(Com2)/MWCNT/GCE system's specific capacitance was up to Sc = 132.6 F g−1at the scan rate of 70 mV s−1from the area formula, Eq. (1). Furthermore, P(Com2)/MWCNT composite had very rapid charge/discharge ability with specific capacitance of Sc = 75.23 F g−1at DC potential of 0.3 V from Nyquist plot, and Sc = 90.53 F g−1at the scan rate of 60 mVs−1from charge formula, Eq. (2), which is important practical advantage. In addition, such composite had a good cycling performance and a wide potential window. Long-term stability of the capacitor was also tested by CV, and the results indicated that, after 500 cycles, the specific capacitance was still at ∼100.0%, ∼89%, and ∼97.0% of the initial capacitance for P(Com1)/MWCNT, P(Com2)/MWCNT, and P(Com3)/MWCNT, respectively. An equivalent circuit model of Rs(C1(R1(Q(R2W))))(CGCRGC) was obtained to fit the experimental and theoretical data. Solution resistance (Rs) and resistance from GCE decrease gradually. However, capacitance of film (C1), constant phase element (Q), and n values increase for P(Com1), P(Com2), and P(Com3)/MWCNT, respectively. Therefore, more homogeneous and less rough surface composite film was obtained by addition of MWCNT in the composite material. [ABSTRACT FROM AUTHOR]

Highlights: [•] Various morphologies of CuO nanostructures were synthesized by controlling chemical and physical parameters of reaction. [•] The applicability of the prepared samples evaluated as the active material in pseudocapacitor application. [•] Specific capacitance of CuO nanoparticles (158F.g−1) was higher than nanorods (110F.g−1) and nanospheres (92F.g−1). [Copyright &y& Elsevier]

• Na 2 Ti 6 O 13 nanorods are prepared by the hydrothermal and solid-phase sintering methods. • Na 2 Ti 6 O 13 nanorods has large interlayer spacing (about 0.798 nm). • Na 2 Ti 6 O 13 nanorods exhibit high cycle capacity and high rate capability. • The pseudo-capacitance contribution rate and Na+ diffusion coefficient are calculated. [Display omitted] In this study, Na 2 Ti 6 O 13 nanorods with large interlayer spacing (about 0.798 nm) were synthesized by the hydrothermal and solid-phase sintering methods, and applied to the anode of sodium ion batteries (SIBs). The influence of different calcination temperatures on the electrochemical properties of Na 2 Ti 6 O 13 nanorods were all studied. Benefitting from the nanorods structure and the large interlayer spacing, the Na 2 Ti 6 O 13 prepared at 800 °C possessed fast Na+ diffusion and achieved high discharge capacities of 168.2 and 115.2 mA h g−1 at different current densities of 20 and 500 mA g−1, respectively, and remained at 131.1 and 96.7 mA h g−1 after 100 cycles, which exhibited the best cycling stability, fast Na+ diffusion characteristics, and excellent rate performance. Supported by electrochemical impedance spectroscopy, we found that the value of R ct became larger and the D Na + became smaller with the progress of charge and discharge, which might be the cause of the decrease in the specific discharge capacity. The detailed analysis of cyclic voltammetry test confirmed that the proportion of pseudo-capacitance gradually decreased with the electrochemical reaction process keeping, from 83.8% at the beginning to 60.9% at the 100th cycle. This work establishes a valuable basis for the future study of Na 2 Ti 6 O 13 as outstanding anode material for SIBs. [ABSTRACT FROM AUTHOR]

Highlights: [•] The capacitive EIS measurement was performed at different bias potentials. [•] EIS monitored both the degradation of the platinum catalyst and the carbon support. [•] A linear relationship between the pseudo capacitance and ECSA was established. [•] The potential dependent proportionality constants do not vary between catalysts. [•] These constants are universally applicable across Pt catalysts. [Copyright &y& Elsevier]

Porous electrochemical supercapacitive materials, as an important type of new-generation energy storage devices, require detailed analysis and knowledge of their capacitive performances under different charging/discharging regimes. An investigation of the responses to dynamic perturbations of typical representatives, noble metal oxides, carbonaceous materials and RuO2-impregnated carbon blacks, by electrochemical impedance spectroscopy (EIS) is presented. This presentation follows a brief description of supercapacitive behavior and origin of pseudo-capacitive response of noble metal oxides. For all the investigated materials, the electrical charging/discharging equivalent of the EIS response was found to obey the transmission line model envisaged as a so-called "resistor/capacitor (RC) ladder". The ladder features are correlated to material physicochemical properties, its composition and the composition of the electrolyte. Fitting of the EIS data of different supercapacitive materials to appropriate RC ladders enables in-depth profiling of the capacitance and pore resistance of their porous thin-layers and finally the complete revelation of capacitive energy storage issues. [ABSTRACT FROM AUTHOR]

Manganese oxide electrodes possessing pseudo-capacitance behaviors were successfully made with a simple sol–gel method. The experimental results showed that the specific capacitance was 101.2F/g for pure manganese oxide films after annealing at 300°C. However, the specific capacitance increased to 232.3F/g with iron acetate (1.0mol% Fe) addition and after annealing at 350°C. The surface morphology observations revealed that the annealing temperature of 350°C produced a higher surface area film with smaller pores. X-ray diffraction results showed that the manganese-iron oxide was composed of Mn3O4 and Mn2O3 phases, without iron oxide diffraction peaks. The manganese-iron oxide electrode with Mn3O4 and Mn2O3 phases exhibited good electrochemical performance and capacitance efficiency. [ABSTRACT FROM AUTHOR]

Abstract: The electrochemical behavior of anodically deposited Mn oxide in N-butyl-N-methylpyrrolidinium–dicyanamide (BMP–DCA) ionic liquid (IL) at various temperatures (30–80 °C) is investigated. Cyclic voltammetry (CV) is used to evaluate the electrochemical performance of the Mn oxide. Surface morphology of the deposited oxide after charging/discharging is examined by scanning electron microscopy (SEM). The experimental data show that the Mn oxide electrode exhibits good pseudo-capacitance performance even at 80 °C. In the ionic liquid studied, the specific capacitance increases with increasing BMP–DCA IL temperature. A specific capacitance of 93 F g−1 in a potential window of 3 V is obtained at 80 °C, which is about 50% higher than that obtained at 30 °C. The experimental results also show that the capacitance-retained ratio of the oxide electrode increases with increasing temperature at a high potential sweep rate. Furthermore, the capacitance decline about 40% after 500 repeated charging/discharging cycles in BMP–DCA IL at 80 °C is observed, which is better than that measured in an aqueous electrolyte. [Copyright &y& Elsevier]

Abstract: Carbon aerogel (CA) was prepared by a sol-gel polymerization of resorcinol and formaldehyde, and a series of activated carbon aerogels (ACA-X, X = H3PO4, K2CO3, KOH, and ZnCl2) were then prepared by a chemical activation using different activation agent (X represented an activation agent). Specific capacitances of activated carbon aerogels were measured by cyclic voltammetry and galvanostatic charge/discharge methods in 6 M KOH electrolyte. Among the samples prepared, ACA-K2CO3 showed the highest specific capacitance (152 F/g). In order to combine excellent electrochemical performance of activated carbon aerogel with pseudo-capacitive property of manganese oxide, 7 wt% manganese oxide was doped on activated carbon aerogels (Mn/ACA-X) by an incipient wetness impregnation method. Capacitance measurements revealed that Mn/ACA-K2CO3 showed the highest specific capacitance (189 F/g). The enhanced capacitance of Mn/ACA-K2CO3 was attributed to the fine pore structure and outstanding electric properties of activated carbon aerogel as well as the faradaic redox reactions of manganese oxide. [Copyright &y& Elsevier]

Abstract: In order to better analyze and to explain the electrochemical and physical behavior during both charge and discharge of a manganese dioxide based ECs, an original electrochemical model is developed in this paper. The 1D model is an adaptation of the transmission line model (TLM), taking into account the cation diffusion in the solid oxide. A linear relation between redox potential and oxidation state is used and leads to a physical relation between its slope and the pseudo capacitance of the material, confirmed by an experimental investigation of cyclic voltammograms. The model can be applied for any metal oxide pseudo-capacitive material. [Copyright &y& Elsevier]

Abstract: The positive and negative capacitance behaviors of heat-treated activated carbons are separately studied in a three-electrode configuration using 6M KOH and 1M H2SO4 as electrolytes. Heat treatment of activated carbons at 400–800°C causes slight changes in surface area accompanied by a significant removal of oxygen-containing functional groups. Consequently, the specific surface capacitance with a 25% reduction in the negative and an 8% reduction in the positive are monitored in KOH electrolyte. The unequal capacitance reductions as well as the asymmetric CV curves reveal that the negative pseudo-capacitances are much larger than the positive ones in KOH electrolyte. These results could be ascribed to the redox reactions preferring in the negative region. The insertion process of cation also plays a significant effect on the asymmetric capacitance behavior. Compared with the identical electrochemical response in H2SO4 electrolyte, huge difference in the capacitance values of both electrodes in KOH electrolyte will give a less contribution to the cell capacitance. To optimize the cell performance, a suitably increasing the weigh of active materials in the positive, especially for activated carbon with high level of oxygen-containing functional groups, is recommended. [Copyright &y& Elsevier]

Thin polypyrrole (PPy) films (thickness = 5-10 nm) were electrochemically deposited in situ on a carbon paste (97% of graphite plus 3% of Teflon) by means of cyclic voltammetry (CV), from an acetonitrile solution of pyrrole (0.2 M) and NaClO (0.1 M). The obtained PPy/graphite composite electrode was investigated by CV and chronopotentiometry in 0.3 M NaClO aqueous electrolytic solution. The capacitance of a composite electrode, calculated by CV, was about 10 F g. The capacitance value of the composite electrode was approximately nine times larger than that of pure graphite. The massic charge and discharge capacity ( Q) values, calculated by chronopotentiometry, were considerably higher for the composite electrode-by more than 60 times-than for the pure graphite electrode. Electrochemical impedance spectroscopy (EIS) measurements, performed under stationary conditions, led to an interfacial capacitance value intermediate between that of pure graphite and that of the composite electrode. [ABSTRACT FROM AUTHOR]

Abstract: One-dimensional growth of polyaniline (PANI) was conducted on carbon cloth through a pulse potentiostatic method. Hydrolysis of PANI was depressed, and the generated PANI film (PPM) displayed improved electroactivities. The specific capacitance of PPM was increased by 39% when compared to that of PANI film made by the conventional potentiostatic method (PM). The influences of the upper limit potential of the pulse potentiometry and the acidity of the polymerization solution on surface morphologies, electroactivities and conformation of the PANI films were studied by SEM, cyclic voltammetry, chronopotentiometry and UV–Vis spectrometry. [Copyright &y& Elsevier]

Abstract: Pseudo-capacitance of composite materials where ruthenium oxide particles are loaded on activated carbon has been evaluated in the electrolyte of 1-ethyl-3-methyl imidazolium tetrafluoroborate dissolved in acetonitrile. The composite materials prepared by conventional a sol–gel method have dispersed structure of ruthenium oxide particle of tens nanometer diameter on the surface of activated carbon. The extent of the pseudo-capacitance of the composite electrodes in the imidazolium salt electrolyte, estimated by the comparison of the capacitance per surface area of electrode in different non-aqueous electrolyte, is ca. 3–5μFcm−2 in addition to the double-layer capacitance of ca. 6μFcm−2, depending on the loading status of ruthenium oxide. The symmetric cell consisting of the composite electrode containing 18wt% of ruthenium oxide and the imidazolium salt electrolyte provides cell capacitance based on the pseudo-capacitance by a constant-current test. [Copyright &y& Elsevier]

Abstract: The B/C/N composites were synthesized by a very simple method, that is, carbonization at HTT=800–1200°C of the precursor prepared by drying a solution mixture of polyacrylamide and boric acid, followed by boiling in water to remove borate by-products. The amount of insoluble B species in the composite increased linearly from 4.8 to 18.6mass% with raising HTT. The XRD and FT-IR revealed that turbostratic h-BN started to form at around 1000°C as a by-product. By XPS, major B and N components in the composite were N#x2013;B–O type B, pyridinic N, pyrrolic N, and quaternary N. A fraction for Nluding h-BN in the total B or N components increased with raising HTT and it exceeded 50at% between 900 and 1000°C. It was suggested that in the composites formed at HTT>1000°C the amounts of h-BN increased, leading to reduction in other B and N components. The S BET was almost unchanged up to 1000°C, 410–420m2 g−1. Large and broad redox peaks arisen from plural reactions appeared in the cyclic voltammogram (CV) measured in 1moldm−3 H2SO4 for the composites formed at HTT≤1000°C. These peaks disappeared in 1moldm−3 solutions of Na2SO4 and Li2SO4. By comparing CV with that for C/N composite formed from PAA by the MgO template method, the pseudo-capacitance owing to reactions of N2013;B–O components with protons was found to be added to commonly observed pseudo-capacitance for nitrogen-doped carbons. The capacitances for the composites formed at 850–950°C exceeded 300Fg−1 at 2mVs−1 in the acid electrolyte and the retention at 50mVs−1 was 78–80%. The shape of CV in the neutral electrolytes was trapezoid and the current density increased with lowering potential, suggesting adsorption and desorption of Na+ and Li+ ions. This was considered to be due to doped nitrogen, indicating the development of pseudo-capacitance. The capacitance per S BET was 0.33–0.74Fm−2 and 0.17–0.32 Fm−2, larger for lower HTT, in the acid and neutral electrolytes, respectively. [Copyright &y& Elsevier]

Abstract: Protic ionic liquids (PILs) were used as novel electrolyte for carbon-based supercapacitors. The cyclic voltammograms in three-electrode cells show reversible redox humps, revealing pseudo-faradaïc charge transfer. Oxidative treatment of activated carbon enriches the surface functionality and leads to a higher capacitance owing to a stronger pseudo-faradaïc contribution. The capacitors using PILs demonstrate a higher voltage window than with aqueous H2SO4, while keeping the same values of capacitance, and being able to operate at lower temperature. A combination of activated carbons and PILs holds promise for improving the energy characteristics of supercapacitors. [Copyright &y& Elsevier]

Abstract: Carbons containing nitrogen (C–N composites) were derived from three commercial organic compounds, poly(vinylpyrrolidone) (PVP), polyacrylamide (PAA), and trimethylolmelamine (TMM) using the MgO template method. The C–N composites formed in nitrogen at 700–1000°C had nitrogen content, W N, of 3–23mass% and the specific surface area by N2 adsorption, S BET, of 60–2000m2 g−1 without activation. Generally high nitrogen content of the starting compound led to larger W N, but W N was not proportional to the N/C mole ratio in the compounds. The value of S BET strongly depended on the compound: S BET (PVP)> S BET (PAA)≫ S BET (TMM). There was a tendency for W N to decrease with increasing S BET. The capacitance measured in 1moldm−3 H2SO4 by cyclic voltammetry, C M in Fg−1, suggested that both W N and S BET are influential in gaining large C M. For the composites with W N >5mass%, the capacitance normalized by S BET, C A = C M/S BET, was 0.17–0.65Fm−2, which was larger than the electric double layer capacitance (0.05–0.15Fm−2), indicating that the pseudo-capacitance contributes significantly to C M. The value of C A increased with increasing W N, but a correlation between C A and particular nitrogen species on the surface measured by XPS was obscure. It was suggested that the large C A is not simply explained by redox reactions of the surface functional groups. The composite derived from PAA at 900°C showed 234Fg−1 at 2mVs−1 and 181Fg−1 at 100mVs−1 with acceptable yield of the composite. [Copyright &y& Elsevier]

Abstract: Hydrothermal decomposition of permanganate, conducted in a range of pH-controlled solutions (from strongly acidic to strongly basic), is used to prepare manganese dioxides that are well-suited for use as supercapacitor electrode materials. While permanganate is thermodynamically unstable, the kinetics of its decomposition in an aqueous environment are very slow, until the temperature is raised to ∼200°C. Although the resultant materials are relatively crystalline and have low total pore volume, their prominent meso-porosity leads to good electrochemical performance. Best behaviour is obtained for material from permanganate decomposition in 0.01M H2SO4 solution, for which composite electrodes (150μm thick) yield ∼150Fg−1 at 5mVs−1 in a 9M KOH electrolyte. [Copyright &y& Elsevier]

Abstract: Cobalt hydroxide nano-flakes are successfully synthesized by a facile chemical precipitation method. Electrochemical characterization is performed using cyclic voltammetry, chronopotentiometry and impedance spectroscopy, respectively. These cobalt hydroxide nano-flakes maintain high utilization at high rates of discharge. A maximum specific capacitance of 735Fg−1 can be achieved in 2M aqueous KOH with the potential range from −0.2 to 0.4V (vs. SCE) in a half-cell setup configuration for the nano-flakes Co(OH)2 electrode, suggesting its potential application in electrochemical capacitors. Furthermore, the effect of annealing temperatures on the electrochemical capacitance characteristics is also been systematically explored. [Copyright &y& Elsevier]

Abstract: V2O5/ordered mesoporous carbon (CMK-3) composites were prepared by an ultrasonic method. The microstructures of such composites were characterized by X-ray diffraction (XRD), nitrogen adsorption and desorption, X-ray photoelectron spectra (XPS) and transmission electron microscopy (TEM). The results showed that the ultrasonic synthesis method was flexible and efficient to highly disperse V2O5 nanoparticles in CMK-3. The electrochemical property of the V2O5/CMK-3 composites has also been investigated. The specific capacitance of the new composites was significantly improved (124F/g) compared to that of CMK-3 (77F/g). The high capacitance was mainly derived from the high specific surface area of CMK-3 and the pseudo-capacitance of V2O5. Therefore, the V2O5/CMK-3 composites can be a potential electrode material applied in the capacitors. [Copyright &y& Elsevier]

N-rich carbon enclosed Mn 2 O 3 nanorod as the capacitive electrode exert the synergistic effect of the pseudo-capacitance and intrinsic defects as the electrosorption sites. [Display omitted] • Mn 2 O 3 doped N-rich carbon nanorods were designed as capacitive dye removal electrode; • During synthesis process, Mn 5 O 8 was first transformed to Mn 3 O 4 and then converted to Mn 2 O 3 ; • Mn 2 O 3 provide huge pseudo-capacitance and supply additional defects to improve the electrosorption performance; • Capacitive adsorption of ionic dye. This paper aims to explanation on the effects of pseudo-capacitance on the capacitive performance of defective carbon-based materials. A series composite samples of Mn 2 O 3 doped porous carbon were prepared with combining N induced intrinsic defects, we testified it as the electrode for flow capacitive Rhodamine B (RhB) removal performance. It is proved that the presence of Mn 2 O 3 can indeed supply additional defects and pseudo-capacitance. Furthermore, the optimized Mn 2 O 3 @NCT-2 presented high quality capacity of 200F/g at 1 A/g in 1.0 M NaCl. Our results also displayed an extremely high RhB-adsorption capacity of 766.5 mg/g at an applied voltage of 1.2 V. These acquired new knowledge could advance expand a significant defect-engineering tactics to further improve the desalination nature of electrode materials. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is an emerging brackish water desalination technology, Manganese dioxide (MnO 2) is a promising material for CDI because of its good pseudo-capacitance performances. However, the agglomeration phenomenon of MnO 2 nanosheets is serious in the application process. It is critical to improve the performance of MnO 2 by increasing its dispersibility. In this work, the x-MnO 2 /HCS was prepared by in-situ growth of MnO 2 on the surface of hollow carbon spheres (HCS), which were prepared with P123 and sodium oleate (SO) as templates and glucose as carbon precursor. The load of MnO 2 in x-MnO 2 /HCS was controlled by adjusting the addition amount of KMnO 4 (x is the mass ratio of KMnO 4 : HCS, x = 2, 4 and 8). Then put HCS and x-MnO 2 /HCS as anode and cathode respectively assembled into HCS||x-MnO 2 /HCS (H||x-M/H) asymmetric cells for CDI tests. The influence of different KMnO 4 addition amount on the performances of x-MnO 2 /HCS electrodes were studied. Results show that HCS with good sphericity and uniform size, excellent electrical conductivity and hydrophilicity, which effectively reduces the agglomeration of MnO 2 and makes more active sites to participate in ions intercalation, enhance the capacitive performance of the composites. Electrochemical tests show that the 4-MnO 2 /HCS exhibits the highest specific capacitance (264.75 F/g). And the CDI tests show that H||4-M/H cell has the largest adsorption capacity (30.86 mg/g), the highest charge efficiency (76%), the lowest energy consumption (0.018 kwh/mol) and excellent cycling stability (92.4%). [Display omitted] • Lamellar MnO 2 is dispersed on the surface of HCS to form a conductive structure. • x-MnO 2 /HCS improved dispersibility active sites and conductivity. • 4-MnO 2 /HCS electrode shows outstanding desalination capacity and rate. [ABSTRACT FROM AUTHOR]

Abstract: A manganese oxide material was synthesised by an easy precipitation method based on reduction of potassium permanganate(VII) with a manganese(II) salt. The material was treated at different temperatures to study the effect of thermal treatment on capacitive property. The best capacitive performance was obtained with the material treated at 200°C. This material was used to prepare electrodes with different amounts of polymer binder, carbon black and graphite fibres to individuate the optimal composition that gave the best electrochemical performances. It was found that graphite fibres improve the electrochemical performance of electrodes. The highest specific capacitance (267Fg−1 MnO x ) was obtained with an electrode containing 70% of MnO x , 15% of carbon black, 10% of graphite fibres and 5% of PVDF. This electrode, with CB/GF ratio of 1.5, showed a higher utilization of manganese oxide. The results reported in the present paper further confirmed that manganese oxide is a very interesting material for supercapacitor application. [Copyright &y& Elsevier]

Abstract: Enhancement of electrochemical capacitance and morphological variations of various acetylene blacks caused by electrochemical polarization are presented. Acetylene blacks of different mean particle diameters were modified by air-oxidation and heat treatment to diversify the morphologies of the acetylene blacks before electrochemical polarization. The various acetylene blacks were electrochemically oxidized at 1.6V (vs. Ag/AgCl) for 10s and the polarization step was repeated until the capacitance values did not change any longer. These polarization steps enhanced the capacitances of the acetylene blacks and the specific enhancement factors range from 2 to 5.5. Such an enhancement is strongly related to morphological modification as revealed by transmission electron microscopic observations. The electrochemical polarization resulted in formation of tiny graphene sheets on the wide graphitic carbon surfaces, which were most responsible for the observed capacitive enhancement. Although the pseudo-capacitance increased after polarization by forming oxygenated species on the surfaces, its contribution to the total capacitance was less than 10%. The mechanism of the formation of the tiny graphene sheets during the electrochemical oxidation is described schematically. [Copyright &y& Elsevier]

Abstract: Manganese dioxide has been synthesized by a new simple self-reacting microemulsion method. The synthesized MnO2 has been found to be amorphous structure containing a moderate amount of water by X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analysis. Particles in a spherical shape with about 4nm in diameter have been observed by transmission electron microscopy. Cyclic voltammetic tests have been performed between −0.5 and 0.5V versus Hg/Hg2SO4 in 1molL−1 Na2SO4 solution at sweep rates up to 50mVs−1. A specific capacitance value as high as 246.2Fg−1 was obtained, which was much higher than 146.5Fg−1 of MnO2 prepared by chemical co-precipitation. After 600 cycles, only 6% decrease of specific capacitance was measured which indicated that such a material possesses good cycling property. [Copyright &y& Elsevier]

Abstract: The electrochemical double-layer capacitive properties of mesoporous carbon (MC) materials with a moderate amount of nitrogen functionality are reported. Ordered mesoporous carbon is prepared using mesoporous silica (MS) as a template and sucrose as a carbon source. Two types of N-doped MCs are prepared by ammoxidation performed at different stages of the MC preparation process—ammoxidation before (NC) and after (CN) carbonization. Irrespective of the ammoxidation sequence, N-doped MCs maintain mesoporous properties such as a high surface area with narrow pore-size distribution. However, the amounts and chemical states of incorporated nitrogen are highly dependent on the sequence of ammoxidation. In a cyclic voltammetry test, N-doped MCs, compared with MC, exhibit higher capacitance in addition to fast charge/discharge characteristics, which results from their mesoporosity and the pseudo-capacitive effect of incorporated nitrogen. In particular, the NC-type MCs show the best capacitive properties among the materials studied due to the large amount of pyridinic species that modifies the electron donor/acceptor properties of the surface and thereby results in an enhanced, fast and reversible faradaic redox reaction. [Copyright &y& Elsevier]

Abstract: Ruthenium oxide/ordered mesoporous carbon composites materials were prepared by impregnating an ordered mesoporous carbon CMK-3 with RuCl3 · xH2O solution followed by annealing in nitrogen atmosphere from 80 to 400°C. The content of ruthenium oxide in the composites ranged from 10.0 to 30.7wt.%. X-ray diffraction (XRD), thermogravimetric analysis (TGA), nitrogen adsorption measurement and transmission electron microscopy (TEM) were used to characterize the composites. The results showed that the ruthenium oxide deposited on CMK-3 mesoporous carbon was hydrous and amorphous when annealed up to 400°C. The specific capacitance of the composites was determined by cyclic voltammetry. Such composites had high specific capacitance, which was derived from the high specific surface area of CMK-3 mesoporous carbon and the pseudo-capacitance of amorphous RuO2. In addition, the specific capacitance depended on the annealing temperature and the RuO2 content. As the temperature increased, the specific capacitance decreased. In contrast, the specific capacitance increased with higher RuO2 content and reached 633F/g with a heavy content. However, as the RuO2 content increased, its contribution to the pseudo-capacitance became poorer. The rate capability of the composite electrodes also decreased as a function of RuO2 content, due to an increase in the equivalent series resistance (ESR) and the overall capacitance. [Copyright &y& Elsevier]

Abstract: Carbonaceous materials containing nitrogen (C/N materials) were prepared by a pyrolysis of 2,3,6,7-tetracyano-1,4,5,8-tetraazanaphthalene (CAN). A C/N material prepared by the pyrolysis of CAN at 1070K (CAN-1070K) had a C/N atomic ratio of 3.0 and a non-crystalline carbonaceous structure with a BET surface area of 880m2 g−1. The material CAN-1070K showed large capacitances of 160–180Fg−1 and 110–120Fcm−3 in case of current density of 10mAcm−2 (2Ag−1) by using three-electrode cell in 1M H2SO4 aqueous solution, in comparison with that of activated carbon (160Fg−1 and 55Fcm−3) having BET surface area of 2300m2 g−1. ESCA study indicated that pyridinic and quarternary nitrogen atoms existed in the C/N materials, which could result in producing a pseudo-capacitance in addition to the electric double layer capacitance. Also introduction of nitrogen into the carbonaceous material could enhance the wettability of material, which might also improve the capacitance. [Copyright &y& Elsevier]

Abstract: Fibrous morphology and nano-crystalline nature of the anodically deposited manganese oxide were confirmed by a transmission electron microscope (TEM). The oxide electrode exhibited an ideal capacitive behavior as indicated by cyclic voltammetry (CV). In order to explore the energy storage mechanism, variation of electronic and structural aspects of the manganese oxide induced by changing the applied potential was studied in situ in aqueous 2M KCl by Mn K-edge X-ray absorption spectroscopy (XAS). Position shift of the adsorption edge, toward higher energy during oxidation and backward lower energy during reduction, was clearly recognized. The experimental results directly proved for the first time that the pseudo-capacitance of the manganese oxide was attributed to its continuous and reversible faradic redox reaction during the charge–discharge process. [Copyright &y& Elsevier]

Abstract: Nano-thin polypyrrole (PPy) layers with thickness from ∼5nm to several 10snm were deposited on vapor grown carbon fibers (VGCF) by an in situ chemical polymerization. Using different concentrations of the pyrrole could control the thicknesses of deposited PPy layers. Surface morphology and thickness of the deposited PPy layers were confirmed by means of scanning electron microscopy and scanning transmission emission microscopy. Pseudo-capacitive behavior of the deposited PPy layers on VGCF investigated by means of cyclic voltammetry. Then, the PPy/VGCF composites were mixed with activated carbons (AC) at various mixing ratios. For the PPy/VGCF/AC composite electrodes, characteristics of specific capacitance and power capability were examined by half-cell tests. As results of this study, it was investigated that nano-thin PPy layer below ∼10nm deposited on VGCF had high pseudo-capacitance and fast reversibility. Its specific capacitance per averaged weight of active material (PPy) was obtained as ∼588Fg−1 at 30mVs−1 and maintained as ∼550Fg−1 at 200mVs−1 of scan rate. Also, from the mixing 60wt.% of the PPy/VGCF with 25wt.% of AC, the PPy/VGCF/AC composite electrode exhibited higher power capability maintaining the specific capacitance per active materials of PPy and AC as ∼300Fg−1 at 200mVs−1 in 6M KOH. [Copyright &y& Elsevier]

Abstract: A new electrode consisting of iron(III) hexacyanoferrate(II) known as Prussian blue and Dibenzo-18-crown-6 macrocycle ion-pair complex formed in presence of chloroform was studied for its electrochemical behavior in 0.1M KCl solutions. The ion-pair complex exhibited cyclic voltammetric response combining the Faradic redox characteristics of Prussian blue and the non-Faradic capacitance behavior of crown ether. Pseudo-capacitance values from the cyclic voltammetric measurements of the ion-pair complex showed a nine-fold increase as against the crown ether and a 1.5 times increase compared to Prussian blue. The ion-pair complex was chemically and electrochemically stable up to the cycled 1000 runs. Double potential step chronocoulometric measurements done at the lowest time scale of 10s showed specific capacitance value of 28.95×103 Fg−1 for the reduction step and 52.92×103 Fg−1 for the oxidation step. Such pseudo-capacitive values are the requisite of electrochemical capacitors that can provide huge power pulse within a very short time. [Copyright &y& Elsevier]