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Abstract: Electrode materials with low cost, large theoretical capacity, and fast ion/electron transport rate are highly desirable for capacitive applications. Pseudocapacitive iron oxide materials (e. g., Fe2O3, Fe3O4) satisfy the first two aspects, but are electrically/ionically insulating, hindering their practical applications in energy storage. Here, hybrid mesoporous iron oxide (Fe2O3/Fe3O4) materials are integrated with a three‐dimensional electrochemically exfoliated graphite substrate (EG) using an electrodeposition coupled with a post‐chemical transition strategy. The hybrid Fe2O3/Fe3O4 materials on EG exhibit an ultrahigh specific capacitance of 1530 F g−1 at current density of 1 A g−1. This material with such high capacitance ranks on the top of the reported iron oxide materials for capacitive applications. In addition, the assembled device with EG@Fe2O3/Fe3O4 as anode can deliver a high gravimetric energy density of 21.6 Wh kg−1 at a power density of 225 W kg−1, based on the total mass of the two electrodes (including the mass of the current collectors). This system can power various electronic devices, suggesting its great potential for energy storage applications. [ABSTRACT FROM AUTHOR]

Interconnected H 0.12 WO 3 ⋅H 2 O nanosheets with high electrochemical performances are fabricated on partial exfoliated graphite substrate (Ex-GF) by potential-limited pulse galvanostatic method (PLPG). The dead volume problem of bulk pesudocapacitive materials is addressed by the novel interconnected nanosheets structure, enabling a large specific capacitance of 5.95 F cm −2 (495.8 F g −1 ) at 2 mA cm −2 . Merited from the fluent electrolyte penetration channels established by the plenty voids among nanosheets, as well as fast electron transportation in the electronic conductive tungsten bronze which is directly grown from graphite substrate, the obtained WO 3 /Ex-GF demonstrates excellent rate capability. The material can maintain 60.0% of its capacitance when the discharge current density increases from 2 to 100 mA cm −2 . Moreover, WO 3 /Ex-GF doesn't show capacitance decay after 5000 galvanostatic charge-discharge cycles, displaying its super stability. Furthermore, a high performance asymmetric supercapacitor assembled by using WO 3 /Ex-GF and electrochemical fabricated MnO 2 /Ex-GF as negative and positive electrodes, respectively displays a high energy density of 2.88 mWh cm −3  at the power density of 11.1 mW cm −3 , demonstrating its potential application for energy storage. [ABSTRACT FROM AUTHOR]

Abstract: Hybrid films of polyaniline (PANI) and manganese oxide (MnO x ) were obtained through potentiodynamic deposition from solutions of aniline and MnSO4 at pH 5.6. The hybrid films demonstrated characteristic redox behaviors of PANI in acidic aqueous solution. Characterization of the hybrid films by XRD indicated the amorphous nature of MnO x in the films in which manganese existed in oxidation states of +2, +3 and +4, based on XPS measurement. Hybrid film of PANI and MnO x , PM120 obtained from the solution of 0.1M aniline and 120mM Mn2+ displayed a well opened nanofibrous structure which showed an 44% increase in specific capacitance from that of PANI (408Fg−1) to 588Fg−1, measured at 1.0mAcm−2 in 1M NaNO3 (pH 1). The hybrid film kept more than 90% of its capacitance after 1000 charging-discharging cycles, with a coulombic efficiency of 98%. The specific capacitance of a symmetric capacitor using PM120 as the electrodes is 112Fg−1. [Copyright &y& Elsevier]

Abstract: Partial exfoliation of graphene from graphite foil (GF) is achieved by a convenient one-step electrochemical exfoliation method to afford partially exfoliated graphene electrode (Ex-GF) with graphene sheets standing on GF matrix stably. Electropolymerization of pyrrole is carried out on Ex-GF with 1,5-naphthalene disulfonate (NDS) and 2-naphthalene sulfonate (NMS) as the ‘permanent’ doping anions to prepare Ex-GF/PPy-NDS and Ex-GF/PPy-NMS, respectively, in which the polymer is anchoring on the surfaces of graphene sheets. The PPy displays an opened structure due to the facilitated homogeneous nucleation on Ex-GF and so exhibits enhanced specific capacitance compared to the polymers deposited on pristine GF (to afford GF/PPy-NDS and GF/PPy-NMS). Specifically, Ex-GF/PPy-NDS film maintains 79% of its specific capacitance when the discharge current density increases from 1 to 20 A g−1. Moreover, discharge potential window of the polymer is enlarged to 1.3 V (from −0.8 to 0.5 V vs. SCE) due to the dual doping mode. Ex-GF/PPy-NDS film displays a high energy density of 82.4 Wh kg−1 at the power density of 650 W kg−1 and 65.1 Wh kg−1 at the power density of 13 kW kg−1. The cyclic charge/discharge stability of the polymer is also improved due to synergistic effect with partially exfoliated graphene. [Copyright &y& Elsevier]

Manganese oxide (MnO x ), as a benchmark pseudocapacitive material, has aroused great interest in electrochemical energy storage community. However, ion transport is seriously hindered in the densely packed bulk materials of highly loaded MnO x electrodes. Here, the structural engineering for the electrodeposited MnO x materials is realized by tuning the concentration of the complexing agents used in the electrodeposition process. The fabricated highly porous nanostructure in the thick oxide layer can minimize the ion diffusion distances to the interior electrode surface, and the optimized content of the hydrous species can facilitate the solid-phase diffusion of the electrolyte ions in the oxide lattice. The deposited MnO x electrode with a high mass loading of 7.02 mg cm −2 exhibits excellent rate capability due to the dual-tuning effect. An excellent specific capacitance of 161.2 F g −1 (1.13 F cm −2 ) at a high current density of 20 mA cm −2 can be obtained, which is comparable to the capacitance delivered by the low mass loading electrode at the same current density (214.8 F g −1 for 0.54 mg cm −2 sample), indicating its high material utilization. The performance of the fabricated electrode ranks on the top of the reported MnO x materials with high mass for capacitive applications. [ABSTRACT FROM AUTHOR]

In this work, a core-shell structured pseudocapacitive anode is fabricated through electrochemical deposition of highly loaded (3.89 mg cm −2 ) polypyrrole (PPy) on individual carbon tubes in electrochemically pretreated carbon nanotube film (ECNT) to afford ECNT/PPy electrode. The core-shell structure significantly promotes the charge transfer for energy storage reaction and buffers the volume change of PPy during charge/discharge cycles, leading to much improved pseudocapacitive behaviors for ECNT/PPy. It can retain 75.2% of its capacitance (965.3 mF cm −2 at 1 mA cm −2 ) when the discharge current increased 40 times to 40 mA cm −2 . After 10,000 galvanostatic charge/discharge cycles, ECNT/PPy can maintain 89.1% of its initial capacitance. The asymmetric supercapacitor (ASC) assembled by using ECNT/PPy and CNT/MnO 2 as anode and cathode, respectively demonstrate a high volumetric energy density of 3.63 mWh cm −3 at the power density of 13.86 mW cm −3 . After 10,000 galvanostatic charge/discharge cycles, the ASC can retain 89.0% of its capacitance, showing its good cyclic stability. [ABSTRACT FROM AUTHOR]

Research on anode materials with high capacitive performance is lagging behind that of cathode materials, which has severely hindered the development of high-efficient energy storage devices. Compared with other anode materials, Fe 3 O 4 exhibits highly desirable advantages due to its low cost, high theoretical capacity and preferable electronic conductivity of ∼10 2 S cm −1 . Herein, hierarchical honeycomb Fe 3 O 4 is integrated on functionalized exfoliated graphite through electrochemical deposition and the following chemical conversion. The hierarchical honeycomb Fe 3 O 4 is constructed by the oxide nanorods, which are assembled by a number of nanoparticles. This unique porous structure not only ensures fast ion diffusion in the electrode, but also provides large amount of active sites for electrochemical reactions. The exfoliated graphene atop the graphite base can act as 3D conductive scaffold to facilitate the electron transport of the electrode. Therefore, FEG/Fe 3 O 4 exhibits large specific capacitances of 327 F g −1 @1 A g −1 and 275 F g −1 @10 A g −1 . Good cycling stability is also achieved due to the flexibility of the graphene substrate. The assembled asymmetric device using FEG/Fe 3 O 4 as anode can deliver a high energy density of 54 Wh kg −1 . [ABSTRACT FROM AUTHOR]

Direct electrochemical growth of polyaniline nanowire arrays (PANI NWAs) on surfaces of graphene sheets in partially exfoliated graphite foil (Ex-GF) was achieved through electropolymerization of aniline to fabricate hierarchical nanostructured pseudocapacitive electrodes. The PANI NWAs were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Due to the combined merits of PANI NWA and graphene sheets, the hierarchical nanostructured electrodes demonstrated high pseudocapacitive performances. More importantly, fast capacitance fading of pseudocapacitive materials upon mass loading increase can be suppressed by the novel structure, making it a good candidate for supercapacitor electrode with high areal capacitance. The PANI NWA with a high mass loading of 5.89 mg cm −2 showed an exceptionally high areal capacitance of 3.57 F cm −2 and a quite high specific capacitance 607 F g −1 . 72.4% of the capacitance can be retained when the discharge current increase 10 times, demonstrating its high rate capability. [ABSTRACT FROM AUTHOR]

Polyaniline-tungsten oxide composite films (PANI-WO x ) were prepared through concurrent electropolymerization of aniline and electrochemical deposition of tungsten oxide on partial exfoliated graphite (Ex-GF) for pseudocapacitive materials. The influence of aniline to WO x precursor ratio on pseudocapacitive properties of the afforded PANI-WO x /Ex-GF composite was investigated. PW-2:1/Ex-GF made from the solution containing aniline and WO x precursor in 2:1 ratio displayed a high specific capacitance (408 F g −1 /408 mF cm −2 at 1 A g −1 /1 mA cm −2 ) in a wide charge storage potential window of −0.6–0.7 V vs. SCE, leading to a high energy density of 95.8 Wh kg −1 at 650 W kg −1 . Due to the synergistic effect between WO x and PANI, the composite showed much improved cyclic stability (91.6% capacitance retention after 5000 galvanostatic charge–discharge cycles) compared to similarly prepared PANI/Ex-GF (69.1% capacitance after 5000 charge–discharge cycles). The assembled symmetric model supercapacitor, by using PW-2:1/Ex-GF as both of the electrodes, also displayed good stability and high energy density, demonstrating that the PANI-WO x composite is promising electrode material for high-performance supercapacitor. [ABSTRACT FROM AUTHOR]

Rate capability of polypyrrole (PPy) was improved through additional doping by oxygen containing functional groups introduced in the substrate of functionalized carbon cloth (FCC). The PPy deposited on surfaces of carbon fibers in FCC displayed good rate capability, 70% of its capacitance (341.2 mF cm −2 at 1 mA cm −2 ) can be retained when the charge/discharge current density increased 20 times to 20 mA cm −2 , while the PPy deposited on untreated carbon cloth (CC) could only retain 52% of its capacitance (308.7 mF cm −2 at 1 mA cm −2 ). PPy/FCC also displayed excellent cycling stability, 96% of its initial capacitance can be retained after 10,000 charge/discharge cycles. The asymmetric supercapacitor (ASC) assembled by using PPy/FCC as anode and crumpled MnO 2 nanosheets electrochemically deposited on carbon cloth (MnO 2 /CC) as cathode also displayed good rate capability. When the charge/discharge current density increased 10 times from 1 to 10 mA cm −2 , the ASC can retain 79% of its volumetric capacitance (from 1.78 to 1.41 F cm −3 ). The ASC demonstrated a high volumetric energy density of 0.80 mWh cm −3 at 12.85 mW cm −3 . After 10,000 galvanostatic charge/discharge cycles, the ASC can retain 90.7% of its capacitance, demonstrating its good cycling stability. [ABSTRACT FROM AUTHOR]

Abstract: Carbon cloth was functionalized through cyclic voltammetric scans in 2M H2SO4 to afford functionalized carbon cloth (FC). The FC was characterized by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). Self-doped polyaniline (SPAN) was deposited on FC through electro-co-polymerization of aniline and metanilic acid to get SPAN/FC which showed a specific capacitance of 408Fg−1 in 0.5M Na2SO4, based on a constant charge–discharge experiment at a current density of 1Ag−1. A symmetric model capacitor, SPAN/FC-SPAN/FC was assembled by using SPAN/FC as both of the electrodes and 0.5M Na2SO4 as the electrolyte. The charge storage property and charge–discharge cycling stability of SPAN/FC-SPAN/FC were investigated by galvanostatic experiment. [Copyright &y& Elsevier]

Abstract: We report for the first time the enhanced capacitance of multi-walled carbon nanotubes (MWCNTs) after exfoliation. Transmission electron microscopy studies confirmed that the MWCNTs were partially exfoliated with improved effective surface area. Carbon cloth electrode deposited with partially exfoliated carbon nanotubes (Ex-CNTs) yielded specific capacitances in a range of 130–165Fg−1 at charging/discharging current densities from 5 to 0.5Ag−1, with coulombic efficiencies of ∼98%. The specific capacitance of Ex-CNTs was an order of magnitude higher than untreated MWCNTs, and comparable to graphene at all charging/discharging current densities we studied. The enhanced capacitance can be attributed to improved effective surface area and increased defect density of the exfoliated tubular structure. The results declared that Ex-CNTs are promising electrode materials for high-capacitance supercapacitors. [Copyright &y& Elsevier]

Abstract: Composites of polyaniline (PANI) and a unique ordered mesoporous carbon MPC which possesses small pores inside the carbon walls have been prepared. The monomer (aniline) of PANI is firstly soaked in the small pores inside the carbon walls and then confined in the primary mesochannels as well with increasing the concentration of aniline in the soaking solution. After the following in situ polymerization, composites of PANI and MPC with bicontinuous interpenetrating framework are formed. The composites show significant redox activities at potentials negative to 0V vs. Hg/HgO in a strong alkaline solution, which is unusual for PANI and PANI based composites as PANI usually loses its electrochemical activity at pH>4. The specific capacitance of the composites is as high as 400Fg−1 at a high current density of 1Ag−1 in the potential range of −0.7 to 0V, which is twice higher than that of the host MPC. The capacitance only decreases about 9% when the discharge current density increases from 1 to 20Ag−1, indicative of excellent rate capability. Therefore, the composites are very promising for the application as electrode materials in supercapacitors, especially as materials for negative electrode in hybrid supercapacitors. [ABSTRACT FROM AUTHOR]