Girish S. Gund

Temperature influence on morphological progress of Ni(OH)2 thin films and its subsequent effect on electrochemical supercapacitive properties

The temperature dependent morphological evolution and its effect on the electrochemical supercapacitive properties of Ni(OH)2 thin films have been systematically investigated. A temperature dependent growth mechanism model is proposed for the changes in microstructure. Different nanostructures of Ni(OH)2 thin films such as nanoplates, stacked nanoplates, nanobelts and nanoribbons have been fabricated by varying the deposition temperature. An X-ray diffraction study discloses the orientations of different nanostructures and the formation of nanocrystalline β-Ni(OH)2. Further, these Ni(OH)2 nanostructures demonstrate excellent surface properties like uniform surface morphology, good surface area, pore volume and uniform pore size distribution. The electrochemical supercapacitive properties of Ni(OH)2 nanostructures have been investigated by cyclic voltammetry, charge–discharge and electrochemical impedance spectroscopy techniques. The electrochemical studies of the Ni(OH)2 samples show an obvious influence of surface properties on the pseudocapacitance. The maximum specific capacitance of 357 F g−1 was evaluated for nanoplates at a scan rate of 5 mV s−1. Furthermore, all these Ni(OH)2 samples show good long-term cycling performances in KOH electrolyte. The Ragone plots ascertain good power and energy densities of all Ni(OH)2 nanostructured samples. Subsequently, electrochemical impedance measurements for the different nanostructures of Ni(OH)2 electrodes are assessed indicating that the Ni(OH)2 nanoplates structured electrodes are suitable for good capacity electrochemical supercapacitors.

Architectured morphologies of chemically prepared NiO/MWCNTs nanohybrid thin films for high performance supercapacitors.

The preparation of nanostructured metal oxide decorated on multiwalled carbon nanotubes (MWCNTs) nanohybrid films through simple, scalable, additive-free, binderless, and cost-effective route has fascinated significant attention not only in fundamental research areas but also its commercial applications, in order to reduce the growing environmental pollution and the cost of electrode fabrication. Here, we report the fabrication of highly flexible electrode with NiO/MWCNTs nanohybrid thin films directly on stainless steel substrate using successive ionic layer adsorption and reaction (SILAR) method. The impact of ratio of adsorption and reaction cycles on structural, surface areas and electrochemical properties of NiO/MWCNTs nanohybrids was investigated. X-ray diffraction measurements confirm the hybridization and face centered cubic (FCC) crystal structure of NiO in NiO/MWCNTs nanohybrids. In addition, these nanohybrids exhibit excellent surface properties such as uniform surface morphology, good surface area, pore volume, and uniform pore size distribution. The electrochemical tests demonstrate the highest specific capacitance of 1727 F g(-1) at 5 mA cm(-2) of current density with 91% capacitance retention after 2000 cycles. In addition, the Ragone plot confirms the better power and energy densities for all NiO/MWCNTs nanohybrids. The attractive electrochemical capacitive activity revealed by NiO/MWCNTs nanohybrid electrode proposes that it is an auspicious respondent for future energy storage application.

Low-cost flexible supercapacitors with high-energy density based on nanostructured MnO2 and Fe2O3 thin films directly fabricated onto stainless steel.

The facile and economical electrochemical and successive ionic layer adsorption and reaction (SILAR) methods have been employed in order to prepare manganese oxide (MnO2) and iron oxide (Fe2O3) thin films, respectively with the fine optimized nanostructures on highly flexible stainless steel sheet. The symmetric and asymmetric flexible-solid-state supercapacitors (FSS-SCs) of nanostructured (nanosheets for MnO2 and nanoparticles for Fe2O3) electrodes with Na2SO4/Carboxymethyl cellulose (CMC) gel as a separator and electrolyte were assembled. MnO2 as positive and negative electrodes were used to fabricate symmetric SC, while the asymmetric SC was assembled by employing MnO2 as positive and Fe2O3 as negative electrode. Furthermore, the electrochemical features of symmetric and asymmetric SCs are systematically investigated. The results verify that the fabricated symmetric and asymmetric FSS-SCs present excellent reversibility (within the voltage window of 0–1 V and 0–2 V, respectively) and good cycling stability (83 and 91%, respectively for 3000 of CV cycles). Additionally, the asymmetric SC shows maximum specific capacitance of 92 Fg−1, about 2-fold of higher energy density (41.8 Wh kg−1) than symmetric SC and excellent mechanical flexibility. Furthermore, the “real-life” demonstration of fabricated SCs to the panel of SUK confirms that asymmetric SC has 2-fold higher energy density compare to symmetric SC.

Porous CuO nanosheet clusters prepared by a surfactant assisted hydrothermal method for high performance supercapacitors

This investigation demonstrates the surfactant assisted fabrication of nanosheet clusters of caddice clew, yarn ball and cabbage slash-like microstructures of copper oxide (CuO) in thin film form directly grown onto a stainless steel substrate using a binder free hydrothermal approach. The impact of organic surfactants such as Triton X-100 (TRX) and polyvinyl alcohol (PVA) on the structural, morphological, surface area and electrochemical properties of CuO is investigated. The X-ray diffraction study reveals the structure-directing ability of the organic surfactants and confirms the nanocrystalline nature of the CuO thin films. Additionally, these CuO microstructures show excellent surface properties like uniform surface morphology, good surface area and a uniform pore size distribution. The electrochemical tests manifest a high specific capacitance of 535 F g−1 at a scan rate of 5 mV s−1 with 90% capacitive retention after 1000 cycles and low dissolution and charge transfer resistance of the yarn ball-like structured CuO thin film. This approach renders a plain picture of the process–structure–property relationship in thin film synthesis and provides significant schemes to boost the performance of supercapacitor electrodes.

Alcohol mediated growth of α-MnO2 thin films from KMnO4 precursor for high performance supercapacitors

Energy storage devices, with low cost, high energy density, high power density, and long cycle life, have prime importance in order to solve the problem of interrupted power supply of renewable generation systems. In the present work, MnO2 thin films have been deposited by a simple, scalable, additive-free, binder-less, low cost, low temperature and eco-friendly chemical bath deposition method. The impact of three different alcohols (methanol, ethanol, 2-propenol) as reducing agents on the morphological, structural and electrochemical properties of MnO2 thin film is investigated. The MnO2 thin film prepared with the methanol as the reducing agent exhibits high specific surface area with excellent electrochemical features such as high specific capacitance of 633 F g−1 and high energy density of 65.9 W h kg−1 at current density of 1 mA cm−2 along with a good cycling stability of 95% after 2000 CV cycles. Such leading electrochemical properties suggest that MnO2 thin film prepared with methanol as the reducing agent using chemical bath deposition is a significant method to prepare reliable electrode material for future energy storage devices.

Cost effective facile synthesis of TiO2 nanograins for flexible DSSC application using rose bengal dye

Synthesis of titanium dioxide (TiO2) nanograins using economical successive ionic layer adsorption and reaction (SILAR) method has been carried out. TiO2 thin films are studied for their structural, compositional, optical and morphological properties. A layer by layer process leads to the formation of 2.4 μm thick nanocrystalline TiO2 film. The heat treated TiO2 thin films are hydrophilic in nature with contact angle of 67°. The interconnected nanograins are employed for dye sensitized solar cells (DSSC) using inexpensive Rose Bengal (RB) dye. RB dye sensitization resulted into shifting of absorption peak from UV to visible region. The photoresponce of the dye sensitized solar cell is evaluated in the polyiodide electrolyte (0.1 M KI + 0.01 M I2) at 40 mWcm−2 illumination intensity. The TiO2 nanograins accompanied with RB sensitizer showed the conversion efficiency (η) of 0.89%. These results depict the strong assurance of TiO2 nanograins for DSSC application.

Diamond-coated silicon nanowires for enhanced micro-supercapacitor with ionic liquids

Silicon nanowires (SiNWs) and diamond-coated SiNWs (D@SiNWs) on highly n-doped silicon wafer substrates were prepared through standard chemical vapor deposition (CVD) method as electrodes for micro-supercapacitors. The surface of electrodes exhibited uniform distribution of SiNWs on silicon wafer and continuous diamond coating on SiNWs. Electrochemical measurements were carried out in order to test the combined effect of using Ionic Liquid electrolytes and diamond coating on SiNWs on energy storage performance. Optimal values of areal capacitance, energy density and power densities were 317 μF cm-2, 0.13 μWh cm-2 and 150 μW cm-2, respectively. So, the work reported here confirms the suitability and compatibility of D@SiNWs electrode materials and ionic liquid electrolytes for the fabrication of high-performing and robust micro-supercapacitors.