Pseudocapacitive Behavior

While pseudocapacitors represent a promising option for electrical energy storage, the performance of the existing ones must be dramatically enhanced to meet today's ever-increasing demands for many emerging applications. Here we report a nanostructured, mixed-valent manganese oxide film that exhibits anomalously high specific capacitance (∼2530 F/g of manganese oxide, measured at 0.61 A/g in a two-electrode configuration with loading of active materials ∼0.16 mg/cm 2 ) while maintaining excellent power density and cycling life. The dramatic performance enhancement is attributed to its unique mixedvalence state with porous nanoarchitecture, which may facilitate rapid mass transport and enhance surface double-layer capacitance, while promoting facile redox reactions associated with charge storage by both Mn and O sites, as suggested by in situ X-ray absorption spectroscopy (XAS) and density functional theory calculations. The new charge storage mechanisms (in addition to redox reactions of cations) may offer critical insights to rational design of a new-generation energy storage devices.

Manganese oxide films are produced by electrodeposition on a graphite sheet from a solution of manganese oxide with tetradecyltrimethylammonium bromide (TTAB) added as a surfactant. Effects of TTAB concentration on electrochemical and morphological properties of the films are observed. Under the bath conditions used in this work, the specific capacitance of the electrodeposited manganese oxide films has a maximum value of 343 F/g for TTAB concentration of 0.01 M. Change in the specific capacitance of the films with TTAB concentration is found to be associated with corresponding changes in the surface morphology of the films at those concentrations. Addition of TTAB up to 0.01 M is observed to increase the surface area of electrodeposited manganese oxide films, as the surface of the films is well covered with flake-like or petal-shaped arrays of nanofibers forming a three-dimensional network. Higher concentrations of TTAB than 0.01 M reduce the surface area of the films due to agglomeration and collapse of the nanofibers. The addition of 0.01 M TTAB to an electrochemical bath also improves supercapacitor capability such as rate capability, cycling stability, and electrode series resistance.

Manganese-nickel mixed oxide thin films were deposited by anodic electrodeposition on stainless steel substrate from an acetate solution using a potentiodynamic technique, at scan rate of 100 mV s-1 and room temperature. The effect of electrolyte pH, varied in the range from 4 to 7, on composition, morphology and capacitance behavior of oxide thin films was investigated. The nickel content in the oxide increased with increasing deposition pH, allowing to investigate the effect of the oxide composition on the capacitive behavior of as-grown manganese-nickel mixed oxides. Oxide films deposited from the electrolyte at pH 6, having a composition close to Ni0.10Mn0.90Ox showed the highest specific capacitance and the lowest charge transfer resistance. After annealing, the oxide had a complex structure of composite nature, consisting of intermixed amorphous and nanocrystalline phases. A birnessite type oxide with turbostratic disorder was identified as the major phase, in the presence of nickel hydroxide as a finely dispersed second phase. Annealing caused a drastic reduction of the charge transfer resistance and a limited increase of the specific capacitance, probably as the result of diverging effects on oxide properties, i.e. enhanced conductivity and porosity sintering. Cycle life testing of this material revealed a 25% increase of the specific capacitance over 5,000 cycles to a final value of 225 F g-1 (1 M Na2SO4, 50 mV s-1 , 0.11 mg cm-2 mass loading).

In the present investigation, we have successfully assembled symmetric supercapacitor device based on cobalt hydroxide [Co(OH) 2 ] thin film electrodes using 1 M KOH as an electrolyte. Initially, potentiodynamic electrodeposition method is employed for the preparation of Co(OH) 2 thin films onto stainless steel substrate. These films are characterized for structural and morphological elucidations using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The XRD reveals formation of ␤-Co(OH) 2 material with hexagonal crystal structure. The SEM images show formation of nanoflakes like microstructure with average flake width 100 nm. Electrochemical characterizations of Co(OH) 2 based symmetric supercapacitor cell are carried out using cyclic voltammetry, charge-discharge and electrochemical impedance spectroscopy (EIS) techniques. In the performance evaluation the maximum values of specific capacitance, specific energy and specific power are encountered as 44 F g −1 , 3.96 Wh kg −1 and 42 kW kg −1. The value of equivalent series resistance (ESR) is estimated as 2.3 using EIS.

MoS2 is a highly promising material for application in lithium-ion battery anodes due to its high theoretical capacity and low cost. However, problems with a fast capacity decay over cycling, especially at the first cycles, and poor rate performance have deterred its practical implementation. Herein, electrodes comprised solely of few-layers 2D MoS2 nanosheets have been manufactured by scalable liquid-phase exfoliation and spray deposition methods. The long-standing controversy questioning the reversibility of conversion processes of MoS2-based electrodes was addressed. Raman studies revealed that, in 2D MoS2 electrodes, conversion processes are indeed reversible, where nanostructure played a key role. Cycling of the electrodes at high current rates revealed an intriguing phenomenon consisting of a continuously increasing capacity after ca. 100–200 cycles. This phenomenon was comprehensively addressed by a variety of electrochemical and microscopy methods that revealed underlying physical activation mechanisms that involved a range of profound electrode structural changes. Activation mechanisms delivered a capacitive electrode of a superior rate performance and cycling stability, as compared to the corresponding pristine electrodes, and to MoS2 electrodes previously reported. Herein, we have devised a methodology to overcome the problem of cycling stability of 2D MoS2 electrodes. Moreover, activation of electrodes constitutes a methodology that could be applied to enhance the energy storage performance of electrodes based on other 2D nanomaterials, or combinations thereof, strategically combining chemistries to engineer electrodes of superior energy storage properties.

In this work, the MnO 2-ZnO thin films with nominal molar ratios of 8%, 16% and 25% of Zn to Mn were deposited on glass and Indium Tin Oxide (ITO) substrates by dip-coating sol-gel method and annealed in air at 300°C. The films were characterized by Cyclic Voltammetry measurement (CV), X-ray Diffraction spectroscopy (XRD), Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive Xray spectroscopy (EDX) and UV-Visible spectrophotometry. The XRD patterns indicated the amorphous structure for all samples. The CV measurements were performed in the potential window between −2 V and 2 V at a potential scan rate of 20 mV/s and 50 mV/s. The results of CVs at a scan rate of 20 mV/s in the first cycle showed that the sample with 25% of Zn content with the maximum anodic and cathodic charge density has a better performance compared to other samples and the capacitance decreases with increasing cycle number of all samples at 50 mV/s. Optical constants and optical band gaps of thin films were investigated by transmission and reflection. The AFM images revealed that roughness increases with increasing Zn concentration. The FE-SEM images showed nearly similar morphology for all thin films.

The re-stacking of Ti3C2Tx-MXene layers has been prevented by using two different approaches: a facile hard templating method and a pore-forming approach. The expanded MXene obtained by using MgO nanoparticles as hard templates displayed an open morphology based on crumpled layers. The corresponding electrode material delivered 180 F g-1 of capacitance at 1 A g-1 and maintained 99 % of its initial capacitance at 5 A g-1 over five thousand charge-discharge cycles. On the other hand, the MXene foam prepared after heating a MXene-urea composite at 550°C, showed numerous macropores on the surface layer and a complex open 3D inner-architecture. Thanks to this foamy porous structure, the binder-free electrode based on the resulting MXene foam displayed a great capacitance of 203 F g-1 at 5 A g-1 current density, 99 % of which was retained after five thousand cycles. In comparison, the pristine MXene-based electrode delivered 82 F g-1 , only, in the same operating conditions. An asymmetric device built on a negative MXene foam electrode and a positive MnO2 electrode exhibited an attractive energy density of 16.5 Wh kg-1 (or 10 Wh L-1) and 160 W kg-1 (or 8.5 kW L-1) power density. Altogether, the enhanced performances of these nano-engineered 2D materials are a clear demonstration of the efficiency of the chosen synthetic approaches to work out the re-stacking issue of MXene layers.

Bismuth ultra-thin films grown on n-GaAs electrodes via electrodeposition are porous due to a blockade of the electrode surface caused by adsorbed hydrogen when using acidic electrolytes. In this study, we discuss the existence of two sources of hydrogen adsorption and we propose different routes to unblock the n-GaAs surface in order to improve Bi films compactness. Firstly, we demonstrate that increasing the electrolyte temperature provides compact yet polycrystalline Bi films. Cyclic voltammetry scans indicate that this low crystal quality might be a result of the incorporation of Bi hydroxides within the Bi film as a result of the temperature increase. Secondly, we have illuminated the semiconductor surface to take advantage of photogenerated holes. These photocarriers oxidize the adsorbed hydrogen unblocking the surface, but also create pits at the substrate surface that degrade the Bi/GaAs interface and prevent an epitaxial growth. Finally, we show that performing a cyclic voltammetry scan before electrodeposition enables the growth of compact Bi ultra-thin films of high crystallinity on semiconductor substrates with a doping level low enough to perform transport measurements.

We present a detailed study on graphene-coated aluminum thin films for Li-ion battery anode applications. The best electrode ageing behavior is obtained for Al films encapsulated with four porous graphene layers. Graphene encapsulation prevents "crushed" Al nanoparticles from detaching from the anode, thus allowing prolonged charge-discharge cycling. Graphene also provides surface conduction paths for electrons as well as diffusion paths for Li atoms. For the first time, we report the electrochemical room temperature formation of phases such as LiAl and even LiAl, with a higher Li content than β-LiAl. More interestingly, we observe a progressive change of the composite thin film electrode, switching from a pure galvanic to a pseudocapacitive behavior as the size of the Al grains decreases from ∼100 to 5-10 nm due to repeated Li alloying-dealloying. The capacity values of ∼900 and 780 mAh/g are obtained after, respectively, 500 and 1000 charge-discharge cycles at 0.1C. Our ...

Energy storage devices with high energy density have been used in many electronic devices in recently years. A supercapacitor is one such device, but lower energy density has limited its applications. In this study, manganese oxide deposited on a titanium substrate at various deposition temperatures using the galvanostatic electrodeposition method as the electrodes of a supercapacitor was investigated. The specific capacitance of a supercapacitor is depended on the deposition temperature and is affected by the surface morphology and roughness of the electrode surface. At a deposition temperature of 15? C, manganese oxide showed a needle-like appearance, a roughness of 60.0 nm, and a maximum specific capacitance of 225.3 Fg 1. The chargingdischarging behavior of a supercapacitor was analyzed in 0.1 M Na 2 SO 4 aqueous electrolyte at various measuring temperatures and operating potential voltage ranges. The supercapacitor achieved a high energy density of 37.70 Whkg 1 in a 0.1 M Na 2 SO 4 electrolyte at 25? C in an operation range of 0 to 1.3 V.

We report a surfactant-free, facile, and scalable synthesis of porous nickel oxalate (NiOX) and its derived cabbage-like nickel oxide (NiO) nanostructures. These cabbage-like NiO nanostructures are derived from NiOX by simple open atmosphere annealing for a prolong time at different temperatures. Structural data revealed the NiOX as NiC 2 O 4 •2H 2 O with defective layered carbon and NiO phase formation before and after annealing, respectively. Morphological changes have been observed using a scanning electron microscope, which revealed the effect of annealing in inducing the surface area, by surface modified phase formation. Further, surface area analysis corroborated the above finding confirming an increase in surface area after annealing. As a proof-of-concept application, these as-synthesized and annealed powders are used as electrode materials for super capacitor and electrochemically tested in a three-electrode configuration using KOH as electrolyte. It is estimated that the electrodes fabricated using as-synthesized NiOX, annealed at exhibit specific capacity (Cs) of 428 Cg −1 (@ 2 Ag −1) in a potential range of − 0.3 to + 0.4 V following the electrical double layer charge storage mechanism. After annealing, the Cs value of this material increased by twofold having the highest estimated value of 888 Cg −1 (0 to + 0.46 V) for 450°C in comparison to 835 and 547 Cg −1 for 350 and 550°C annealed samples at 3 Ag −1 , respectively, following pseudo-capacitive mechanism. Further, a symmetric device was fabricated using 450°C annealed sample which exhibit a maximum energy density of 26.1 Wh kg −1 and power density of 302.5 W kg −1 at a current density of 1 Ag −1. Moreover, a systematic study on the facile synthesis of NiOX powder and its further modification to tune the structure, morphology, electrochemical charge storage capacity, and working potential window for super capacitor application has been demonstrated.

The influence of several parameters in the preparation procedure of thermal-electrolytic Ag/AgCl electrodes on the resulting electrode performance has been studied. In particular, we report the effect on electrode performance of subtle variations in the preparation of silver oxide paste used for electrode manufacture, in thermal annealing conditions employed and in the procedure for electrochemically converting a fraction of the electrode from silver to silver chloride. Scanning electron microscopy and electrochemical impedance spectroscopy have been used to study the characteristics of the electrodes produced. This work reveals a correlation between the electrochemical behaviour and surface physical characteristics-in particular electrode porosity. The outputs of this study have positive implications for improving the accuracy and comparability of primary pH measurement.

Three dimensional (3D) electrode design offers great advantages over its 2D counterparts, including higher mass loading of active material and enhanced ion diffusion and electron charge transfer. Commercial 3D porous structures (i.e. Ni foams) do not fit the purpose of the ideal 3D electrode for supercapacitors, in which surface area per cm 2 is more important than large pore volume. These characteristics, however, can be tuned by the hydrogen bubble template (DHBT) electrodeposition, a route that has been used to tailor 3D nanostructured (multi-) metallic porous surfaces. In addition to higher surface area and tailored porosity these 3D nanostructures can be subsequently functionalized with different species, such as metal oxides or other compounds. Therefore, this work reports the facile two-step electrochemical fabrication of 3D composite electrode composed of a bimetallic foam functionalized with manganese oxide. The effect of applied current densities on the distribution and structure of manganese oxide (MnOx) over the bare foam is discussed. The results demonstrate that this route paves the way to design high surface area architectures for charge storage electrodes with enhanced electrochemical performance (388 F g-1 per mg of electrodeposited MnOx at 0.5 A

The present paper reveals the formation of cobalt ferrite (CoFe 2 O 4) thin film on stainless steel substrate by simple chemical route from an alkaline bath containing Co 2+ and Fe 2+ ions. The films are characterised for structural, surface morphological and FT-IR properties. The XRD and FT-IR studies revealed formation of single phase of CoFe 2 O 4. The formation of nano-flakes-like morphology is observed from scanning electron microscope. The electrochemical behaviour of CoFe 2 O 4 film has been studied using cyclic voltammetry in 1 M NaOH electrolyte. The maximum specific capacitance of 366 F g −1 is obtained at the scan rate of 5 mV s −1. Using AC impedance technique equivalent series resistance (ESR) value is found to be 1.1 .

Considering the limit of resources and the frequent use of energy, energy storage is nowadays the subject that everyone cares about. In the present work, we investigate trijunction metal oxides as supercapacitor electrode for energy storage application. A MnO 2 /NiO/ZnO trijunction electrode is synthesized for the first time using a successive three electrochemical deposition steps onto stainless steel (SS) substrate. This approach can effectively yield a good distribution and adhesion of all metal oxides onto the substrate with enhanced hydrophilic

While pseudocapacitors represent a promising option for electrical energy storage, the performance of the existing ones must be dramatically enhanced to meet today's ever-increasing demands for many emerging applications. Here we report a nanostructured, mixed-valent manganese oxide film that exhibits anomalously high specific capacitance (∼2530 F/g of manganese oxide, measured at 0.61 A/g in a two-electrode configuration with loading of active materials ∼0.16 mg/cm 2) while maintaining excellent power density and cycling life. The dramatic performance enhancement is attributed to its unique mixedvalence state with porous nanoarchitecture, which may facilitate rapid mass transport and enhance surface double-layer capacitance, while promoting facile redox reactions associated with charge storage by both Mn and O sites, as suggested by in situ X-ray absorption spectroscopy (XAS) and density functional theory calculations. The new charge storage mechanisms (in addition to redox reactions of cations) may offer critical insights to rational design of a new-generation energy storage devices.

Porous network-like MnO2 thick films are successfully synthesized on a flexible stainless steel (SS) mesh using a simple and low-cost electrodeposition method followed by an electrochemical activation process. Morphology, chemical composition and crystal structure of the prepared electrodes before and after the activation process are determined and compared by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses. The results show that the implementation of the electrochemical activation process does not change the chemical composition and crystal structure of the films, but it influences the surface morphology of the MnO2 thick layer to a flaky nanostructure. Based on the electrochemical data analysis, the maximum specific capacitance of 1400 mF (381 F g-1) and 3700 mF (352 F g-1) are measured for small (2.6 cm 2) and large (10 cm 2) surface area electrodes, respectively. In addition, a flexible symmetric MnO2//MnO2 solid state supercapacitor shows a capacitance of 0.3 F with about 98% retention at different bending angles from 0° to 360°.

Fabrication of the Mn 3 O 4 thin film electrodes is an important area of research for the development of supercapacitors. Investigations were made to improve the electrochemical properties of the electron beam evaporated Mn 3 O 4 films. The films grown on stainless steel substrates at a substrate temperature of 473 K with subsequent annealing at 573 K for 4 h were in a single phase, which corresponds to the tetragonal structure of Mn 3 O 4 with I41/amd (141) space group. The Raman studies were also confirmed the single phase of Mn 3 O 4 films. The AFM data revealed that the surface of the films covered with dispersed vertical grains of size 36 nm with the rms surface roughness of 18 nm. The SEM image displayed the flower like growth of Mn 3 O 4 on the substrate. The films deposited at 573 K exhibited a specific capacitance of 568 F g −1 at a current density of 1 A g −1 in 1 M Na 2 SO 4 aqueous electrolyte with excellent capacitance retention of 93% even after 5000 cycles. The films annealed above 600 K were found to have mixed phases and corresponding capacitance decreased with annealing temperatures. The films annealed at 773 K exhibited only Mn 2 O 3 phase with a lower specific capacitance of 240 F g −1 .

Nanoflake bismuth ferrite thin film was synthesized by means of electrodeposition technique at room temperature. The morphology and phase evaluation of the synthesized electrode were analyzed using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and surface wettability techniques. Specifically, the bismuth ferrite nanoflake electrode exhibited high specific capacitance of 72.2 F g-1 at a current density of 1 A g-1 , and high rate capability with 37 % retention of capacitance even up to 20A g-1 , and excellent cycling stability with 82.8 % retention of the initial capacitance after 1500 charge/discharge cycles, supporting that the bismuth ferrite thin-film electrode could be a potential candidate for supercapacitor application.

Two-dimensional (2D) materials are suitable hosts for the intercalation of extrinsic guest ions such as Li, Na and K as the interlayer coupling is weak. This allows ion intercalation engineering of 2D materials, which may be a key to advancing technological applications in energy storage, neuromorphic electronics, and bioelectronics. However, ions that are extrinsic to the host materials possess challenges in fabrication of devices as there are extra steps of ion intercalation. This results in degradation of the long-term stability of the intercalated atomically thin structures. Here, we introduce large-area single-crystal ultra-thin layered MnO2 via chemical vapor deposition, spontaneously intercalated by potassium ions during the synthesis. We studied the ultra-thin 2D K-MnO2 in detail and showed that charge transport in these crystals is dominated by motion of hydrated potassium ions in the interlayer space. Moreover, K-MnO2 crystals exhibit reversible layered-to-spinel phase tra...

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In this communication we present supercapacitance property of MnO 2 thin-films which are fabricated on stainless steel (SS) substrate by electro-deposition method carried out in different pH of the electrolyte. A significant improvement of the device performance of acid mediated grown (AMG) MnO 2 over normal MnO 2 (grown in neutral medium) has been achieved. We have also investigated role of interfacial structure on the internal resistance of the device material. AMG MnO 2 film exhibits superior device performance with specific capacitance of 652 F/g which is 2 times better than that obtained in normal MnO 2 and also energy density of 90.69 Wh/kg.

In present investigation MnO 2 thin films have been prepared by potentiodynamic (PD), potentiostatic (PS) and galvanostatic (GS) modes of electrodeposition. The effects of different modes on structural, surface morphological and supercapacitive properties of MnO 2 thin films have been investigated. Formation of amorphous phase of MnO 2 by all three modes is confirmed from X-ray diffraction (XRD) patterns. Significant change in the surface morphologies of MnO 2 thin films due to different modes has been observed. The supercapacitive properties of MnO 2 thin films have been studied in 1 M Na 2 SO 4 electrolyte. The maximum supercapacitance obtained for potentiodynamic, potentiostatic and galvanostatic modes is 237, 196 and 184 F g −1 , respectively. Additionally charge-discharge and impedance of MnO 2 thin films have been investigated.

Amorphous MnO 2 and Ag-doped MnO 2 thin films were galvanostatically deposited on a polished stainless steel substrate from 20 mM KMnO 4 aqueous solutions without and with AgNO 3 additions at cathodic current density of 1 mA/cm 2 for the application in electrodes of electrochemical supercapacitors. The supercapacitive properties of the deposited thin films have been studied in 0.5 M Na 2 SO 4 electrolyte by cyclic voltammetry, impedance spectroscopy, and charge-discharge measurement techniques. The Ag-free MnO 2 film showed better capacitive behavior and lower charge transfer resistance compared to the Ag-doped MnO 2 films. The specific capacitance and charge transfer resistance values for Ag-free MnO 2 films were 160 F/g at a scan rate 10 mV/s and 3.87 Ω, respectively. Cyclic stability using charge-discharge measurement technique indicates the excellent stability of Ag-free MnO 2 films and its possible use as a low cost electrode for supercapacitor applications.

In this paper, an example of phase analysis during annealing is presented using in-situ TEM. The example is demonstrated on amorphous Cu-Mn/C thin films focusing on phase identification in a multicomponent system. The transient states following the crystallization of the amorphous Cu-Mn alloy and the reaction with the C substrate were analyzed by evaluating the diffraction patterns recorded at different temperatures. The camera constant was calibrated using the internal standard method. The change in composition of the Cu(Mn) solid solution was calculated by separating the effect of thermal expansion and solute concentration. Identification of the forming phases was aided by analyzing and comparing the probability of formation of all phases in the Cu-Mn-C-O system. After the crystallization of amorphous Cu-Mn alloy into Cu(Mn) and α-Mn-based solid solutions, the formation of the following carbide phases was observed: Mn23C6, Mn5C2 and Mn7C3.

In this study, porous manganese oxide (MnO x) thin films were synthesized via electrostatic spray deposition (ESD) and evaluated as pseudocapacitive electrode materials in neutral aqueous media. Very interestingly, the gravimetric specific capacitance of the ESD-based electrodes underwent a marked enhancement upon electrochemical cycling, from 72 F•g −1 to 225 F•g −1 , with a concomitant improvement in kinetics and conductivity. The change in capacitance and resistivity is attributed to a partial electrochemical phase transformation from the spinel-type hausmannite Mn 3 O 4 to the conducting layered birnessite MnO 2. Furthermore, the films were able to retain 88.4% of the maximal capacitance after 1000 cycles. Upon verifying the viability of the manganese oxide films for pseudocapacitive applications, the thin films were integrated onto carbon micro-pillars created via carbon microelectromechanical systems (C-MEMS) for examining their application as potential microelectrode candidates. In a symmetric two-electrode cell setup, the MnO x /C-MEMS microelectrodes were able to deliver specific capacitances as high as 0.055 F•cm −2 and stack capacitances as high as 7.4 F•cm −3 , with maximal stack energy and power densities of 0.51 mWh•cm −3 and 28.3 mW•cm −3 , respectively. The excellent areal capacitance of the MnO x-MEs is attributed to the pseudocapacitive MnO x as well as the three-dimensional architectural framework provided by the carbon micro-pillars.

Nickel (Ni) foam-based symmetric/asymmetric electrochemical supercapacitors benefit from a randomly 3D structured porous geometry that functions as an active material support and as a current collector. The surface composition stability and consistency of the current collector is critical for maintaining and consistency supercapacitor response, especially for various mass loading and mass coverage. Here we detail some annealing environment conditions that change the surface morphology, chemistry and electrochemical properties of Ni foam by NiO formation. Air-annealing at 400 and 800 °C and annealing also in N2 and Ar at 800°C result in the in-situ and ex-situ formation of NiO on the Ni foam (NiO@Ni). Oxidation of Ni to NiO by several mechanisms in air and inert atmospheres to form an NiO coating is subsequently examined in supercapacitors, where the electrochemical conversion through Ni(OH)2 and NiOOH phases influence the charge storage process. In parallel, the grain boundary density reduction by annealing improves the electronic conductivity of the foam current collector. The majority of stored charge occurs at the oxidized Ni-electrolyte interface. The changes to the Ni metal surface that can be caused by chemical environments, heating and high temperatures that typically occur when other active materials are grown on Ni directly, should be considered in the overall response of the electrode, and this may be general for metallic current collectors and foams that can oxidize at elevated temperatures and become electrochemically active.

Nanoflake bismuth ferrite thin film was synthesized by means of electrodeposition technique at room temperature. The morphology and phase evaluation of the synthesized electrode were analyzed using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and surface wettability techniques. Specifically, the bismuth ferrite nanoflake electrode exhibited high specific capacitance of 72.2 F g-1 at a current density of 1 A g-1 , and high rate capability with 37 % retention of capacitance even up to 20A g-1 , and excellent cycling stability with 82.8 % retention of the initial capacitance after 1500 charge/discharge cycles, supporting that the bismuth ferrite thin-film electrode could be a potential candidate for supercapacitor application.

As a first report, use of room temperature non-aqueous chemical bath deposited Sb 2 S 3 thin film as active material for supercapacitor application; opens new era in energy storage field. Obtained films were characterized by using structural, surface morphological and compositional analysis. The electrochemical performance has been evaluated by using cyclic voltammetry, galvanostatic chargeedischarge and electrochemical impedance techniques. The maximum specific capacitance of 248 F/g at 0.5 A/g has been achieved within 0.2 to À0.5 V potential windows in 1M Na 2 SO 4 electrolyte. In addition, the Ragone plot confirms the better specific power and specific energy for Sb 2 S 3 electrode.

Nickel (Ni) foam-based symmetric/asymmetric electrochemical supercapacitors benefit from a randomly 3D structured porous geometry that functions as an active material support and as a current collector. The surface composition stability and consistency of the current collector is critical for maintaining and consistency supercapacitor response, especially for various mass loading and mass coverage. Here we detail some annealing environment conditions that change the surface morphology, chemistry and electrochemical properties of Ni foam by NiO formation. Air-annealing at 400 and 800 °C and annealing also in N2 and Ar at 800°C result in the in-situ and ex-situ formation of NiO on the Ni foam (NiO@Ni). Oxidation of Ni to NiO by several mechanisms in air and inert atmospheres to form an NiO coating is subsequently examined in supercapacitors, where the electrochemical conversion through Ni(OH)2 and NiOOH phases influence the charge storage process. In parallel, the grain boundary density reduction by annealing improves the electronic conductivity of the foam current collector. The majority of stored charge occurs at the oxidized Ni-electrolyte interface. The changes to the Ni metal surface that can be caused by chemical environments, heating and high temperatures that typically occur when other active materials are grown on Ni directly, should be considered in the overall response of the electrode, and this may be general for metallic current collectors and foams that can oxidize at elevated temperatures and become electrochemically active.

In this communication we present supercapacitance property of MnO 2 thin-films which are fabricated on stainless steel (SS) substrate by electro-deposition method carried out in different pH of the electrolyte. A significant improvement of the device performance of acid mediated grown (AMG) MnO 2 over normal MnO 2 (grown in neutral medium) has been achieved. We have also investigated role of interfacial structure on the internal resistance of the device material. AMG MnO 2 film exhibits superior device performance with specific capacitance of 652 F/g which is 2 times better than that obtained in normal MnO 2 and also energy density of 90.69 Wh/kg.

Mn oxide and/or Co oxide are deposited on flexible carbon cloth by a cathodic potentiodynamic procedure from their respective sulfates. In KOH electrolyte, the charge stored from reversible redox reactions of the two oxides (battery response) overlaps with the charge stored from the double layer of the carbon cloth (supercapacitor response). These charges or capacities are compared. For the electrodes having one oxide only, either Mn or Co oxide, the highest capacity is obtained for 8 wt% oxide load. To overcome this limitation, both Mn and Co oxide are simultaneously or sequentially electrodeposited on carbon cloth over a broad compositional range. The electrode capacity can reach 71 mA • h • g −1 or 0.9 mA • h • cm −2 , which are higher than the values found for the bare carbon cloth. The electrode capacity depends on the relative content of the carbon cloth and the two deposited oxides according to the rule of mixtures. The decrease of the specific surface area of the carbon cloth is discussed in relation to the deposited oxide. The high capacity retention vs current is due to the contribution of the carbon cloth substrate. The electrode cycle life is discussed on the basis of the supercapacitor response and battery one.

A B S T R A C T Manganese-nickel mixed oxide thin films were deposited by anodic electrodeposition on stainless steel substrate from an acetate solution using a potentiodynamic technique, at scan rate of 100 mV s À1 and room temperature. The effect of electrolyte pH, varied in the range from 4 to 7, on composition, morphology and capacitance behavior of oxide thin films was investigated. The nickel content in the oxide increased with increasing deposition pH, allowing to investigate the effect of the oxide composition on the capacitive behavior of as-grown manganese-nickel mixed oxides. Oxide films deposited from the electrolyte at pH 6, having a composition close to Ni 0.10 Mn 0.90 O x showed the highest specific capacitance and the lowest charge transfer resistance. After annealing, the oxide had a complex structure of composite nature, consisting of intermixed amorphous and nanocrystalline phases. A birnessite type oxide with turbostratic disorder was identified as the major phase, in the presence of nickel hydroxide as a finely dispersed second phase. Annealing caused a drastic reduction of the charge transfer resistance and a limited increase of the specific capacitance, probably as the result of diverging effects on oxide properties, i.e. enhanced conductivity and porosity sintering. Cycle life testing of this material revealed a 25% increase of the specific capacitance over 5,000 cycles to a final value of 225 F g À1 (1 M Na 2 SO 4 , 50 mV s À1 , 0.11 mg cm À2 mass loading).

A B S T R A C T The present study addresses the synthesis of manganese-nickel oxide thin films via potentiodynamic anodic electrodeposition as supercapacitor electrodes. We study in particular the effect of the deposition scan rate and of the Ni(II) to Mn(II) molar ratio in the deposition bath on the capacitive behaviour of mixed oxide electrodes. The increase of the nickel content in oxide thin films of composition Ni x Mn 1-x O y (with x in the range from 0 to 0.17) results in the increase of specific capacitance up to a maximum for about 10 at% Ni. The deposition scan rate affects the capacitive behaviour of mixed oxide electrodes through its effects on layer morphology and surface structure. In particular, thin film electrodes at about 10 at% Ni show a maximum in the specific capacitance for deposition scan rate of 600 mV s À1 , which is shown to be related to the attendant modifications in surface morphology and topography. After annealing at 200 C, 6 h, partial crystallization of the amorphous structure of the as-grown mixed oxide takes place with formation of dispersed nanocrystalline domains. The annealed electrode at 10 at% Ni, with mass loading of 0.30 mg cm À2 , show the highest specific capacitance (250 F g À1 , at 0.1 A g À1), and specific energy and power as high as 34.5 Wh kg À1 (at 50 W kg À1), and 4.3 kW kg À1 (at 15.7 Wh kg À1). Mixed oxide of the same composition and mass loading reveal a 122% capacitance retention after 10,000 cycles in 1 M Na 2 SO 4 at 20 A g À1 .

Three nickel oxide (NiO) electrodes of different morphologies have been successfully engineered through a controlled potentiodynamic electrodeposition process in the presence of different nickel precursors. The effect of nickel precursors on the structural, morphological and pseudocapacitive properties of NiO thin film electrodes have been systematically investigated. The structural information obtained from the X-ray diffraction patterns confirm the formation of cubic structured NiO. The field-emission scanning electron microscopic images endorses for the evolution of uniformly distributed up-grown nanoflakes, irregular nanoflake-like and well-covered porous architecture comprised of interconnected uniform nanoflakes of NiO nanostructures with surface contact angle values 126 , 148 and 104. The effect of the developed NiO nanostructures on pseudocapacitance behavior has been thoroughly investigated using cyclic voltammetry, chronopotentiometric charge–discharge and electrochemical impedance spectroscopy measurement techniques. The optimal specific capacitance of 893 F g À1 has been achieved for NiO electrode with interconnected nanoflake-type morphology at the scan rate of 5 mV s À1. Furthermore, these NiO electrodes have demonstrated long-term cycling stability in KOH electrolyte. The electrochemical impedance spectroscopy measurements carried out on developed NiO nanostructured electrodes corroborate that, NiO electrode composed of uniformly distributed interconnected nanoflakes is the best and most suitable electrode for good capacity electrochemical supercapacitors.

Considerable efforts have been devoted to the synthesis and characterization of novel nanoporous materials because of their versatile applications, such as gas storage, catalysis, and energy storage applications. Controllable synthesis of coordination polymers (CPs) with two-and three-dimensional architectures has given impetus to the development of nanomaterials with many exciting properties and applications. Here, we focus on CP-derived nanoporous materials and study their electrochemical performance as electrode materials in supercapacitors. Nanoporous carbon is prepared by simple carbonization of zinc-containing zeolitic imidazolate framework (ZIF-8). On the other hand, nanoporous nickel oxide (NiO) is prepared by thermal treatment of cyano-bridged CPs. By using the above two electrodes, we fabricate a novel asymmetric supercapacitor. These CP-derived nanoporous materials exhibit excellent electrochemical performance with high specific energy and specific power, and excellent cycling stability.

NiO/C nanocomposite was prepared directly by means a one-step electrochemical technique based on electrochemical dispergation of nickel by the alternating current. The prepared material was well characterized using different analytical techniques such as X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and N 2 adsorption/desorption. The X-ray diffraction and Raman scattering investigations of the freshly prepared sample confirmed the formation of ˇ-NiO. The morphology of synthesized NiO/C can be described as dispersed on carbon support nano-leaves consisting of tightly packed array of nanoparticles (around 10 nm in diam) with length of 500-2000 nm and ∼20 nm thick. NiO/C composite possesses high specific surface area of 137 m 2 g −1 and a micro-meso-macroporous structure with a distribution of the pore size from 1 to 200 nm. The electrochemical properties of the nanostructured NiO/C were investigated using cyclic voltammetry (CV) and galvanostatic charge-discharge tests. The synthesized NiO/C composite exhibited pseudo-capacitive behavior with the mass capacitance value as high as 1012 F g −1 and 750 F g −1 measured from CV and discharge curves, respectively. Compared with the theoretical specific capacitance of NiO 2573 F g −1 , the degree of electrochemical utilization is 97% for NiO in the synthesized NiO/C composite. The superior electrochemical performance is attributed to the hierarchically porous structure of the synthesized NiO/C, its with a high specific surface area as well as a wide pore size distribution. Considering the excellent performance and facile preparation, this NiO/C composite should have great potential for application in energy storage and conversion devices.

a b s t r a c t a-La 2 S 3 thin films have been synthesized for the first time by successive ionic layer adsorption and reaction (SILAR) method and used for supercapacitor application. These films are characterized for crystal structure, surface morphology and wettability studies using X-ray diffraction (XRD), Fourier Transform-Raman (FT-Raman) spectroscopy, scanning electron microscopy (SEM) and contact angle measurements.

Interconnected porous MnO nanoflakes on nickel foam were prepared by a reduction of hydrothermal synthesized MnO 2 precursor in hydrogen. The architectures were applied to lithium ion batteries as electrodes. Compared with the as-synthesized MnO 2 anode, porous MnO nanoflakes showed superior cycling stability and rate performance. A high reversible capacity of 568.7 mA h g À1 was obtained at a current density of 246 mA g À1 for the second discharge. It retained a capacity of 708.4 mA h g À1 at the 200th charge-discharge cycle after cycling with various current densities up to 2460 mA g À1 and delivered a capacity of 376.4 mA h g À1 at a current density as high as 2460 mA g À1 , indicating that the architecture of the porous MnO nanoflakes grown on Ni foam is a promising electrode for lithium ion batteries.