Charge-storage mechanism of free-standing MoS 2 /r-GO (r-GO = reduced graphene oxide) hybrid nanoflakes on molybdenum (Mo) foil in Na 2 SO 4 solution is elucidated for realizing a high-performance asymmetric supercapacitor (ASC). Thiourea that acts primarily as sulfur source also helps intercalating ammonium ions, which along with r-GO facilitate in situ exfoliation of MoS 2 , producing hierarchical MoS 2 with expanded interlayer spacing. This interlayer expansion in MoS 2 facilitates Na + -ions intercalation/deintercalation and ensures enhanced capacitance, rate capability, and cycling stability of the capacitor . Besides exhibiting attractive energy-cum-power traits, the 2 V MoS 2 /r-GO//Fe 2 O 3 /MnO 2 ASC shows compelling cycling performance for over 20 000 cycles in an aqueous electrolyte.

A simple wet chemical technique has been employed to fabricate MnO2 nanolayer-coated α-Fe2O3/MnO2 core–shell nanowire heterostructure arrays to prepare unique pseudocapacitor electrodes. The coating of MnO2 on α-Fe2O3 nanowires is triggered by the reduction of KMnO4 solutions by the metallic (Au) film on which the polycrystalline α-Fe2O3 nanowires have been grown electrochemically. This metallic film also acts as the current collector by making direct contact with the arrays of the 1D nanoheterostructures. The as-prepared α-Fe2O3/MnO2 nanoheterostructures are found to exhibit excellent specific capacitance, high energy density, high power density, and long-term cyclic stability as compared with the bare α-Fe2O3 nanowire electrodes. The unique geometry of the 1D nanoheterostructures with high effective surface area to allow faster redox reaction kinetics, the incorporation of two highly redox active materials in the same structure, and the porous surface structures of the heterostructure to allow facile electrolyte diffusion help in the superior electrochemical performance of the α-Fe2O3/MnO2 nanoheterostructures. The maximum specific capacitance of 838 F g–1 (based on pristine MnO2) has been achieved by cyclic voltammetry at a scan rate of 2 mV s–1 in 1 M KOH aqueous solution. The hybrid α-Fe2O3/MnO2 nanocomposite electrodes also exhibit good rate capability with excellent specific energy density of 17 Wh kg–1 and specific power density of 30.6 kW kg–1 at a current density of 50 A g–1 and good long-term cycling stability (only 1.5% loss of its initial specific capacitance after 1000 cycles). These studies indicate that the α-Fe2O3/MnO2 nanoheterostructure architecture is very promising for next-generation high-performance pseudocapacitors.

We report a facile method to design Co3O4-MnO2-NiO ternary hybrid 1D nanotube arrays for their application as active material for high-performance supercapacitor electrodes. This as-prepared novel supercapacitor electrode can store charge as high as ∼2020 C/g (equivalent specific capacitance ∼2525 F/g) for a potential window of 0.8 V and has long cycle stability (nearly 80% specific capacitance retains after successive 5700 charge/discharge cycles), significantly high Coulombic efficiency, and fast response time (∼0.17s). The remarkable electrochemical performance of this unique electrode material is the outcome of its enormous reaction platform provided by its special nanostructure morphology and conglomeration of the electrochemical properties of three highly redox active materials in a single unit.

Here, we report the synthesis of TiO 2 /BiFeO 3 nano-heterostructure (NH) arrays by anchoring BiFeO 3 (BFO) nanoparticles on TiO 2 nanotube surface and investigate their pseudocapacitive and photo-electrochemical properties considering their applications in green energy fields. The unique TiO 2 /BFO NHs have been demonstrated both as energy conversion and storage material. Capacitive behavior of the NHs has found to be significantly higher than the pristine TiO 2 NTs which is mainly due to the anchoring of redox active BFO nanoparticles.Specific capacitance of about 440 F g -1 has been achieved for this NHs at a current density of 1.1 Ag -1 with ~ 80% capacity retention at a current density of 2.5 A g -1 . The NHs also exhibit high energy and power performance (energy density of 46.5 Wh kg -1 and power density of 1.2 kW kg -1 at a current density of 2.5 Ag -1 ) with moderate cycling stability (92 % capacity retention after 1200 cycles). Photo-electrochemical investigation reveals that the photo current density of the NHs is almost 480% higher than the corresponding dark current and it shows significantly improved photo switching performance as compared to pure TiO 2 nanotubes which has been demonstrated based the interfacial type-II band alignment between TiO 2 and BFO.INTRODUCTION. Intensive research attention has been focused on the energy storage and conversion from the renewable and clean energy sources in order to deal with the ever-increasing energy consumption and environmental issues. 1, 2 Recently, hybrid supercapacitors (SCs) having high energy and high power density, which can bridge the gap between rechargeable battery and ordinary dielectric capacitor, are being considered to be one of the pioneers in the field of alternative energy storage systems in lieu of the conventional rechargeable battery and fuel-cell to quench the energy-thirst of the battery powered electronic gadgets, hybrid vehicles, mechatronic systems and medical instruments. 3, 4 Among SCs, the pseudocapacitors have gained remarkable attention because of their high theoretical specific capacitance, high energy and power density and long life cycle associated with Faradaic redox reactions compared to the electrical double-layer capacitors (EDLCs). 5-8 Being inspired by the high pseudocapacitance of various transition metal oxides such as MnO 2 , Fe 2 O 3 , NiO, Co 3 O 4 , NiCo 2 O 4 and V 2 O 5 , they have been studied extensively as promising candidates for SC electrodes which are also economical, environment friendly, abundant in nature and can be fabricated using easy, cost-effective routes.suitable band gap of BFO to absorb visible light efficiently and also the type II heterojunction formation due to the interface engineering which helps the generation/separation of free charge carriers (electron-hole pairs) allowing unidirectional current flow. This study indicates that the arrays of TiO 2 /BFO nano-heterostructure with enhanced capacitive and photo-electrochemical performance holds potential for applications in both renewable en...

This study demonstrates a scheme to design and fabricate a novel 1D core/shell Ni/NiO nano-architecture electrode as a pseudocapacitor with significantly improved capacitive performance through hydrogenation. The specific capacitance of the as prepared 1D core/shell Ni/NiO nanoheterostructure (717 F g À1 at a scan rate of 2 mV s À1 ) is nearly 1635 F g À1 after the hydrogenation. The improved pseudocapacitive properties of hydrogenated Ni/NiO nano-heterostructures are attributed to the incorporation of the hydroxyl groups on the NiO surface due to hydrogenation, where the metallic Ni nanowire core of this unique 1D core/shell heterostructure serves as the efficient channel for the fast electron conduction to the current collector. The H-Ni/NiO nanoheterostructures exhibit good rate capability (retaining nearly 60% of their initial charge) and good long-term cycling stability with an excellent specific energy and power density of 49.35 W h kg À1 and 7.9 kW kg À1 , respectively, at a current density of 15.1 A g À1 . This study demonstrates that the H-Ni/NiO nano-heterostructure is very promising for next generation high-performance pseudocapacitors.

Supercapacitor electrodes are fabricated with the self-organized 3D architecture of NiO and hydrogenated NiO (H-NiO) nano-blocks (NBs) grown by the facile electrodeposition and high temperature annealing of the Ni foil on Cu substrate. The unique architecture of H-NiO NBs electrode exhibits excellent cycling stability (only 5.3% loss of its initial specific capacitance after 3000 cycles at current density of 1.1 A g(-1)) along with the high specific and areal capacitance of ∼1272 F g(-1) and 371.8 mF cm(-2), respectively at scan rate of 5 mV s(-1) compared with the pure NiO NBs electrode (∼ 865 F g(-1) and 208.2 mF cm(-2), respectively at scan rate of 5 mV s(-1)). H-NiO NBs electrode also exhibits excellent rate capability; nearly 61% specific capacity retention has been observed when the current density increases from 1.11 to 111.11 A g(-1). This electrode offers excellent energy density of 13.51 Wh kg(-1) and power density of 19.44 kW kg(-1) even at a high current density of 111.11 A g(-1). The superior pseudocapacitive performance of the H-NiO NBs electrode is because of the high electron and ion conductivity of the active material because of the incorporation of hydroxyl groups on the surface of NiO NBs.

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