[en] The rapidly increasing demand for sustainable energy has inspired researchers to develop efficient electrochemical energy storage devices. Considering this, binary transition metal oxides with high surface area have attracted great interest as a new class of porous materials due to their structural tunability and porosity for application in energy storage devices. With this inspiration, we herein report a simple one-step facile approach for the synthesis of cobalt nickel oxide (CoNi₂O₄). The material was subjected to thorough physicochemical characterizations, which revealed distinct crystal characteristics, ideal elemental composition, and highly porous unique microstructure. Electrochemical studies of the CoNi₂O₄ as electrode material revealed good redox kinetics, pseudocapacitive charge-discharge behavior, minimal charge transfer and solution resistance. Additionally, the fabricated all-solid-state asymmetric supercapacitor device assembled with CoNi₂O₄ and nitrogen-doped reduced graphene oxide (N−rGO) as the positive and negative electrode materials, respectively, showed good kinetic reversibility, pseudocapacitive charge-discharge behavior with low charge transfer and total series resistance. The solid-state asymmetric supercapacitor device (CoNi₂O₄||N−rGO) showed energy density (~31 W h kg−1) of a rechargeable battery and power density (~9358 W kg−1) of a supercapacitor. Therefore, the CoNi₂O₄ material can be an excellent choice to fabricate ultra-efficient all-solid-state asymmetric supercapacitor devices. (author)

[en] 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.