Sol–gel approach for controllable synthesis and electrochemical properties of NiCo 2O 4 crystals as electrode materials for application in supercapacitors

Abstract

In this work, NiCo 2O 4 coral-like porous crystals, nanoparticles and submicron-sized particles have been systematically prepared via a facile sol–gel method, using citric acid as the chelating ligand and H 2O (H 2O-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 NiCo 2O 4 crystals with distinct morphologies were evaluated by cyclic voltammetry, and galvanostatic charge–discharge cycling techniques. The results show that submicron-sized NiCo 2O 4 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 NiCo 2O 4/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, NiCo 2O 4 crystal is very promising for real application in supercapacitors.