This journal is © The Royal Society of Chemistry 2014 Chem. Commun. Cite this: DOI: 10.1039/c3cc48773c Facile synthesis of nanostructured CuCo 2 O 4 as a novel electrode material for high-rate supercapacitors† Afshin Pendashteh, a Mohammad S. Rahmanifar, b Richard B. Kaner c and Mir F. Mousavi* ac CuCo 2 O 4 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 À1 ) and desirable cycling stability at di fferent current densities. With demand growing every day for electric energy storage for electrical vehicles and portable devices, electrochemical capacitors or supercapacitors (SCs) have stimulated extensive research interest due to their high-power density, high-rate capability and long cycle life. 1 The charge storage mechanism in SCs is based on either non- Faradaic electrochemical double layer capacitance (EDLC) or fast, reversible Faradaic redox reactions (pseudocapacitance). 2 Transi- tion metal oxides have been extensively investigated as pseudo- capacitive materials due to their potentially higher capacitance compared to EDLCs, mainly ascribed to their multiple oxidation states. 3 However, they suffer from intrinsically low electrical con- ductivity and the fact that fast Faradaic reactions only occur at the surface of the electrode. 4 These disadvantages hinder their applica- tion in high-rate supercapacitors. Therefore, novel materials or strategies to improve the performance of the electrode materials for high-power applications, including fabrication of nano-engineered structures or utilizing synergistic effects of hybrid materials, are needed. 5,6 Among the many transition metal oxides, Co 3 O 4 has been widely studied in pseudocapacitors, and has demonstrated promising performance. 7 Complete or partial substitution of Co with low-cost and benign elements to form the spinel structure could prove to be even better. 8 Recently, CuCo 2 O 4 nanostructures have been investigated as an anode material in Li-ion batteries, showing high Li-ion storage capacities, 8,9 suggesting that they can offer high-charge storage capacity through redox reactions. In this communication, a simple urea combustion method is combined with a post annealing process to synthesize nanostructured CuCo 2 O 4 particles in the shape of cauliflower- like structures. The electrochemical behavior of the sample as a novel material for supercapacitor electrodes was evaluated using different electrochemical techniques including cyclic voltammetry (CV), chronopotentiometry (CP), and electrochemical impedance spectroscopy (EIS). CuCo 2 O 4 nanostructures were synthesized via a combustion route using the corresponding nitrate salts as precursors and urea as fuel. The detailed preparation procedure can be found in the ESI. † Moreover, a sample comprised of CuCo 2 O 4 microparticles was also synthesized via the co-precipitation method (see ESI†). The as-prepared samples were structurally characterized by means of powder X-ray diffraction (XRD). The XRD patterns of both samples can be entirely indexed to a cubic spinel copper cobaltite structure with the lattice parameter a = 8.039 Å, belonging to the Fd3m space group (Fig. 1a, and Fig. S4A, ESI†), which is well matched with the JCPDS file no. 001-1155. These features are also in good agreement with previous reports. 8,9 For clarity, the hkl lines are ascribed to the corresponding peaks. Broadened di ffracted peaks for the nanostructured sample illuminate the fine crystalline size of the Fig. 1 XRD pattern (a), and FESEM of CuCo 2 O 4 nanostructures magnified 30 000Â (b) and 100 000Â (c). a Department of Chemistry, Tarbiat Modares University, Tehran, Iran b Faculty of Basic Sciences, Shahed University, Tehran, Iran c Department of Chemistry and Biochemistry and California NanoSystems Institute, University of California, Los Angeles (UCLA), Los Angeles, CA 90095, USA. E-mail: mousavim@modares.ac.ir, mousavi@chem.ucla.edu † Electronic supplementary information (ESI) available: Details of the experi- mental procedure. See DOI: 10.1039/c3cc48773c Received 17th November 2013, Accepted 16th December 2013 DOI: 10.1039/c3cc48773c www.rsc.org/chemcomm ChemComm COMMUNICATION Published on 17 December 2013. Downloaded by University of California - Los Angeles on 13/01/2014 04:38:28. View Article Online View Journal