The search for faster, safer, and more efficient energy storage systems continues to inspire researchers to develop new energy storage materials with ultrahigh performance. Mesoporous nanostructures are interesting for supercapacitors because of their high surface area, controlled porosity, and large number of active sites, which promise the utilization of the full capacitance of active materials. Herein, highly ordered mesoporous CuCo2O4 nanowires have been synthesized by nanocasting from a silica SBA-15 template. These nanowires exhibit superior pseudocapacitance of 1210 F g–1 in the initial cycles. Electroactivation of the electrode in the subsequent 250 cycles causes a significant increase in capacitance to 3080 F g–1. An asymmetric supercapacitor composed of mesoporous CuCo2O4 nanowires for the positive electrode and activated carbon for the negative electrode demonstrates an ultrahigh energy density of 42.8 Wh kg–1 with a power density of 15 kW kg–1 plus excellent cycle life. We also show that two asymmetric devices in series can efficiently power 5 mm diameter blue, green, and red LED indicators for 60 min. This work could lead to a new generation of hybrid supercapacitors to bridge the energy gap between chemical batteries and double layer supercapacitors.

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CuCo2O4 nanostructures were synthesized through a facile solution combustion method. Electrochemical investigations demonstrate a novel electrode material for supercapacitors with remarkable performance including high-rate capability, high-power density (22.11 kW kg(-1)) and desirable cycling stability at different current densities.

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The incorporation of redox-active counter anions (anthraquinone and nitroxide groups) into poly(ionic liquid)s broadens the scope of applications to different energy storage technologies such as lithium, metal-air or redox-flow batteries.

Supercapacitors capable of providing high voltage, energy and power density but yet light, low volume occupying, flexible and mechanically robust are highly interesting and demanded for portable applications. Herein, freestanding flexible hybrid electrodes based on MnO2 nanoparticles grown on macroscopic carbon nanotube fibers (CNTf-MnO2) were fabricated, without the need of any metallic current collector. The CNTf, a support with excellent electrical conductivity, mechanical stability, and appropriate pore structure, was homogeneously decorated with porous akhtenskite ɛ-MnO2 nanoparticles produced via electrodeposition in an optimized organic-aqueous mixture. Electrochemical properties of these decorated fibers were evaluated in different electrolytes including a neutral aqueous solution and a pure 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid (PYR14TFSI). This comparison helps discriminate the various contributions to the total capacitance: (surface) Faradaic and non-Faradaic processes, improved wetting by aqueous electrolytes. Accordingly, symmetric supercapacitors with PYR14TFSI led to a high specific energy of 36 Wh·kg MnO 2 −1 (16 Wh·kg -1 including the weight of CNTf) and real specific power of 17 kW·kg MnO 2 −1 (7.5 kW·kg -1 ) at 3.0 V with excellent cycling stability. Moreover, flexible all solid-state supercapacitors were fabricated using PYR14TFSIbased polymer electrolyte, exhibiting maximum energy density of 21 Wh·kg -1 and maximum power density of 8 kW·kg -1 normalized by total active material.

Demand for more efficient energy storage systems stimulates research efforts to 9 seek and develop new energy materials with promising properties. In this regard, binary metal 10 oxides have attracted great attention due to their better electrochemical performance as compared 11 to their single oxide analogues. Herein, nanostructured porous wires of FeCo 2 O 4 have been 12 grown on nickel foam via a facile hydrothermal route and were employed as binder/additive-free 13 electrodes to investigate the electrochemical behavior of FeCo 2 O 4 as electrode materials for 14 supercapacitors. The FeCo 2 O 4 sample exhibits a high specific capacitance of 407 F g -1 at a scan 15 rate of 10 mV s -1 in initial cycling. After cycling for 2000 cycles, electro-activation of material 16 results in subsequent increase in capacitance up to 610 F g -1 , showing promising characteristics 17 of this material for energy storage. The performance of the prepared FeCo 2 O 4 sample is found to 18 2be much better than the corresponding single oxides. Furthermore, porous nanostructured 1 FeCo 2 O 4 //AC asymmetric supercapacitors were assembled and could achieve a high energy 2 density of 23 Wh kg -1 and a maximum power density of 3780 W kg -1 .3