Highly Ordered Mesoporous CuCo 2 O 4 Nanowires, a Promising Solution for High-Performance Supercapacitors Afshin Pendashteh, †,‡ Seyyed Ebrahim Moosavifard, † Mohammad S. Rahmanifar, § Yue Wang, ⊥ Maher F. El-Kady, ⊥,∥ Richard B. Kaner,* ,⊥ and Mir F. Mousavi* ,†,⊥ † Department of Chemistry, Tarbiat Modares University, Tehran 14115-175, Iran ‡ IMDEA Energy Institute, ECPU, Avenida Ramon de la Sagra 3, 28935 Mostoles, Madrid, Spain § Faculty of Basic Science, Shahed University, Tehran 18151-159, Iran ∥ Department of Chemistry, Faculty of Science, Cairo University, Giza 12613, Egypt ⊥ Department of Chemistry and Biochemistry, California NanoSystems Institute, University of California, Los Angeles (UCLA), Los Angeles, California 90095, United States * S Supporting Information ABSTRACT: 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 CuCo 2 O 4 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 CuCo 2 O 4 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. ■ INTRODUCTION The rapidly growing demand for electric vehicles and portable electronics has stimulated a great deal of research to develop high-performance electric energy storage devices. 1−3 Super- capacitors, also known as ultracapacitors or electrochemical capacitors, are considered one of the most reliable energy storage devices mainly due to their capability of providing quick bursts of energy and long lifespan. Current supercapacitors use carbon- based materials and store charge through non-Faradaic electric double layers (EDL). Capitalizing on Faradaic redox reactions, 4,5 metal oxide- or conducting polymer-based pseudocapacitors 6,7 show considerably higher specific capacitances than carbon- based supercapacitors. 8 Transition metal oxides are considered especially promising as electrode materials for the next genera- tion of supercapacitors due to their multiple oxidation states. 9 However, their poor electrical conductivity and cycling stability have so far hindered practical applications. 10 Therefore, it is a great challenge to boost the electrochemical performance of pseudoca- pacitive materials by carefully controlling their structure at the nanoscale and by designing the cell structure. 11−15 Since only the surface of metal oxides can effectively contribute to the total capacitance, the preparation of porous metal oxide nanostructures represents a promising solution toward harvest- ing their full capacitance. 16 In addition, pore sizes and their distribution directly affect the ability of a material to function effectively as a supercapacitor. Therefore, development of nano- porous materials, especially metal oxides (consisting of micro- pores, <2 nm; mesopores, 2−50 nm; and macropores, >50 nm) with an extended range of pore sizes, can provide a promising method to enhance the capacitive performance due to enhanced surface area and short electron-/ion-transport pathways. 11 From a wide range of pseudocapacitive materials, spinel structures containing binary or ternary mixtures of metal oxides are of great interest for energy storage applications. 17−19 Among the various types of these structures, spinel cobaltites (MCo 2 O 4 ) are promising because of the presence of mixed valence metal cations that provide higher electronic conductivity and electro- chemical activity in comparison with single-component oxides. 18−20 This makes MCo 2 O 4 a promising electrode material not only for supercapacitors but also for Li-ion batteries. 20−23 Received: February 23, 2015 Revised: April 16, 2015 Published: April 20, 2015 Article pubs.acs.org/cm © 2015 American Chemical Society 3919 DOI: 10.1021/acs.chemmater.5b00706 Chem. Mater. 2015, 27, 3919−3926