Pine-cone morphology and pseudocapacitive behavior of nanoporous nickel oxide

Nanoporous pine-cone structured NiO powder was prepared by hydrothermally heated homogeneous precipitation method using cetyltrimethylammonium bromide surfactant (CTAB) as a template and urea as hydrolysis controlling agent. The NiO powder sample was characterized by thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), Brunauer–Emmet–Teller (BET) isotherm, scanning electron microscopy (SEM) and electrochemical measurements. The prepared NiO was found to be crystalline and highly porous in nature with high specific surface area and pore volume. The pseudocapacitance behavior of this material was investigated using cyclic voltammetry, chronopotentiometry and impedance spectroscopic studies employing a three-electrode system in the single cell mode. The SEM analysis reveals hierarchically porous pine-cone morphology for NiO which shows good specific capacitance (∼337 F g −1) measured by cyclic voltammetry. The galvanostatic charge–discharge cycles obtained in chronopotentiometric measurements indicate that the NiO sample exhibits good electrochemical stability. The columbic efficiency of NiO was found to be about 99% after 100 galvanostatic charge–discharge cycles. The impedance spectroscopic studies confirmed that the pseudocapacitance behavior of the porous NiO was a result of OH − ion diffusion processes in the system. In this study, a correlation has been made between the specific capacitance values and physicochemical properties as well as the unique surface morphology of NiO.