Sol-gel approach for controllable synthesis and electrochemical properties of NiCo2O4 crystals as electrode materials for application in supercapacitors

In this work, NiCo2O4 coral-like porous crystals, nanoparticles and submicron-sized particles have been systematically prepared via a facile sot-gel method, using citric acid as the chelating ligand and H2O (H2O-DMF) as solvent. The experimental results reveal that the initial molar concentration of reactants, reaction time and solvent species involved are crucial for preparing the target products. The as-obtained samples were characterized by means of XRPD, FESEM, HRTEM, EDS and SAED techniques. Finally, the electrochemical performances of NiCo2O4 crystals with distinct morphologies were evaluated by cyclic voltammetry, and galvanostatic charge-discharge cycling techniques. The results show that submicron-sized NiCo2O4 particles exhibit the best capacitive properties with high specific capacitance and excellent cycle stability. At a high mass loading (5.6 mg cm(-2)), specific capacitance value of submicron-sized NiCo2O4/Ni electrode reaches as much as 217 F g(-1), and 96.3% of which can be still maintained after 600 charge-discharge cycles. Therefore, NiCo2O4 crystal is very promising for real application in supercapacitors. (C) 2011 Elsevier Ltd. All rights reserved.