Jin H. Kim

Langmuir–Blodgett self organized nanocrystalline tungsten oxide thin films for electrochromic performance

We explore a novel method to synthesize pebble-like nanocrystalline WO3 thin films for the first time by thermal decomposition of a multilayer Langmuir–Blodgett film of an octadecylamine–tungsten complex. The resulting film was thoroughly characterized by various characterization techniques. The electrochromic performance was evaluated in Li+ as a charge-balancing ion. The WO3 thin film displays a state-of-the-art performance with respect to optical modulation of 25.94% at λ630 nm with a very rapid coloration and bleaching time of 3.57 s and 3.14 s, respectively and a high coloration efficiency of 71.26 cm2 C−1. The excellent electrochromic performance can be attributed to the high size uniformity of WO3 nanoparticles, whose crystalline nature offer more active sites for Li+ diffusion and control the diffusion path length. Thus, the Langmuir–Blodgett WO3 film contributes to high energy conversion devices.

An innovative concept of use of redox-active electrolyte in asymmetric capacitor based on MWCNTs/MnO2 and Fe2O3 thin films

In present investigation, we have prepared a nanocomposites of highly porous MnO2 spongy balls and multi-walled carbon nanotubes (MWCNTs) in thin film form and tested in novel redox-active electrolyte (K3[Fe(CN)6] doped aqueous Na2SO4) for supercapacitor application. Briefly, MWCNTs were deposited on stainless steel substrate by “dip and dry” method followed by electrodeposition of MnO2 spongy balls. Further, the supercapacitive properties of these hybrid thin films were evaluated in hybrid electrolyte ((K3[Fe(CN)6 doped aqueous Na2SO4). Thus, this is the first proof-of-design where redox-active electrolyte is applied to MWCNTs/MnO2 hybrid thin films. Impressively, the MWCNTs/MnO2 hybrid film showed a significant improvement in electrochemical performance with maximum specific capacitance of 1012 Fg−1 at 2 mA cm−2 current density in redox-active electrolyte, which is 1.5-fold higher than that of conventional electrolyte (Na2SO4). Further, asymmetric capacitor based on MWCNTs/MnO2 hybrid film as positive and Fe2O3 thin film as negative electrode was fabricated and tested in redox-active electrolytes. Strikingly, MWCNTs/MnO2//Fe2O3 asymmetric cell showed an excellent supercapacitive performance with maximum specific capacitance of 226 Fg−1 and specific energy of 54.39 Wh kg−1 at specific power of 667 Wkg−1. Strikingly, actual practical demonstration shows lightning of 567 red LEDs suggesting “ready-to sell” product for industries.

Highly energetic flexible all-solid-state asymmetric supercapacitor with Fe2O3 and CuO thin films

In the present investigation, the applicability of Fe2O3 and CuO thin films as anode and cathode electrodes respectively in supercapacitors has been systematically studied. Fe2O3 and CuO thin films are synthesized by simple and cost effective chemical methods and further more all-solid-state symmetric (Fe2O3/Fe2O3, CuO/CuO) and asymmetric (CuO//Fe2O3) supercapacitor devices are fabricated. The electrochemical properties (cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), electrochemical impedance spectroscopy (ESR), etc.) of these devices are studied using two electrodes system. The asymmetric supercapacitor shows improved performance with maximum operating potential window of 2.0 V and specific capacitance of 79 F g−1 at 2 mA cm−2 current density. The maximum energy density and power density of 23 W h kg−1 and 19 kW kg−1 are obtained for asymmetric supercapacitor. In addition, the asymmetric supercapacitor demonstrates the excellent flexibility with capability retention of 89% over bending at an angle of 180°.

Fabrication of high performance flexible all-solid-state asymmetric supercapacitors with a three dimensional disc-like WO3/stainless steel electrode

Presently, significant attention has been paid towards the rational synthesis of nanostructured anode and cathode electrode materials for assembling high-performance supercapacitors. Despite significant progress being achieved in designing cathode electrode materials, anode electrode materials with high capacitance are hardly investigated. In the present article, a tungsten oxide (WO3) thin film is prepared on a flexible stainless steel substrate by a wet chemical method and used as an anode electrode to fabricate a flexible asymmetric supercapacitor (ASC). An electrochemical investigation of the WO3 thin film shows a maximum specific capacitance of 530 F g−1 at 1 mA cm−2 in a potential window of 0 to −0.8 V in 1 M Na2SO4 electrolyte. In addition, a highly energetic, flexible ASC device is assembled using a WO3 thin film as an anode, a MnO2 thin film as a cathode and polymer gel as an electrolyte. The as-assembled MnO2//WO3 ASC device exhibited a stable electrochemical potential window of 1.8 V and better cycling stability. Whats more, the flexible MnO2//WO3 ASC device achieves a high specific capacitance of 115 F g−1 with an acceptable specific energy of 52 W h kg−1 at a current density of 3 mA. Hence, the proposed flexible MnO2//WO3 ASC device creates one more option for anode materials to develop flexible energy storage devices.

Investigations on Chemo-Mechano Stabilities of the Molybdenum Thin Films Deposited by DC-Sputter Technique

Abstract This paper reports the chemical and mechanical stability of Molybdenum (Mo) thin films deposited by direct current magnetron sputtering technique onto soda lime glass substrates. Mo thin films were deposited at various Ar (working) gas pressures to get optimized structural, morphological, adhesive and electrical properties. Mo thin films were further characterized by field emission scanning electron microscope (FE-SEM), X-ray diffraction, Hall measurements and the cross hatch tape test. To study their chemical stability the prepared Mo thin films were further dipped in acetic acid and ammonia solution for 6 h. Mechanical stability of Mo thin films was tested by high speed ultrasonication for an hour. Both the chemical and mechanical stability studies showed that Mo thin films were highly stable since morphology, adhesion and electrical properties did not alter significantly. FE-SEM results showed that the grain size of the chemo-mechano stability tested Mo thin films remained significantly similar with an unimportant effect on the film thickness. Electrical properties showed that electrical resistivity and hall mobility for as-deposited Mo thin films were 2.7 · 10–5 Ω cm and 5.1 cm2/Vs, respectively and remained nearly stable regardless of chemical and mechanical treatment. All of the films passed the cross hatch tape test and showed an excellent adhesion with glass substrates. The wettability investigations showed that all the Mo thin films were hydrophilic in nature and having contact angles in the range of 35○ to 40○.

Rapid synthesis of CdS nanowire mesh via a simplistic wet chemical route and its NO2 gas sensing properties

In this report, 1-D interconnected CdS nanowires were prepared rapidly via a wet chemical route at relatively low temperature, using cadmium sulphate, thiourea and ammonia as raw materials. The formation of a CdS nanowire mesh (CdS NW mesh) and its structural, optical, surface morphological properties and elemental composition were studied by various characterization techniques. The cubic crystal structure of the CdS interconnected nanowire mesh was confirmed via X-ray diffraction and field emission scanning electron microscopy analysis. The photoluminescence spectroscopy measurements reveal the presence of defects in the as synthesized CdS NW mesh. However, the defect states are beneficial for the gas sensing behavior. Therefore, the gas sensing properties of the CdS NW mesh were studied using NO2 as an analyte gas at moderate operating temperature. The nanowire mesh and inter-wire space were observed to play a crucial role in determining the gas sensing performance of the devices. The as synthesized CdS NW mesh shows a gas response of about 1850% to 100 ppm NO2 gas. In particular, our CdS based gas sensor showed a fifty fold better gas response towards NO2 gas than the earlier reports in the literature. Due to the high value of gas sensitivity, the reported CdS NW mesh could be a suitable candidate for NO2 sensing.

Chemically synthesized PbS Nano particulate thin films for a rapid NO2 gas sensor

Abstract Rapid NO2 gas sensor has been developed based on PbS nanoparticulate thin films synthesized by Successive Ionic Layer Adsorption and Reaction (SILAR) method at different precursor concentrations. The structural and morphological properties were investigated by means of X-ray diffraction and field emission scanning electron microscope. NO2 gas sensing properties of PbS thin films deposited at different concentrations were tested. PbS film with 0.25 M precursor concentration showed the highest sensitivity. In order to optimize the operating temperature, the sensitivity of the sensor to 50 ppm NO2 gas was measured at different operating temperatures, from 50 to 200 °C. The gas sensitivity increased with an increase in operating temperature and achieved the maximum value at 150 °C, followed by a decrease in sensitivity with further increase of the operating temperature. The sensitivity was about 35 % for 50 ppm NO2 at 150 °C with rapid response time of 6 s. T90 and T10 recovery time was 97 s at this gas concentration.

Facile green synthesis of In2O3 bricks and its NO2 gas sensing properties

Recently, metal oxide semiconductor based gas sensors have been used to monitor and maintain amount of toxic gases in environment. Use of In2O3 nano/microstructures have been increased as a heterogeneous catalyst for gas sensing due to its high response, good selectivity, short response and recovery time. In the present work, synthesis of In2O3 bricks was carried by a hydrothermal method using biomolecule as green product. The effect of precursor concentrations of In2O3 thin film was studied in this particular work. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Photoluminescence (PL), scanning electron microscope (SEM), Field emission scanning electron microscope (FE-SEM) and Brunauer–Emmett–Teller (BET) analyses were used for structural, optical, morphological and surface analysis characterizations. The In2O3 thin film displays high sensitivity and selectivity due to its active sites present on sensing layer. The results assures that optimized In2O3 thin films exhibit a high response with very low response and recovery time about 600 for NO2 gas.

Synthesis and characterization of chemically deposited ZnO nanorods for NO 2 gas sensing applications

Zinc oxide (ZnO) nanorod arrays were deposited on to the soda-lime glass substrates by wet chemical route using zinc acetate as precursor. The structural and surface morphological properties of the ZnO nanorod arrays (ZNAs) were investigated by X-ray diffraction (XRD), and scanning electron microscopy (SEM) respectively. The XRD pattern revealed wurtzite crystal structures of ZNAs, preferentially orienting in the (002) direction. Depending on the length of nanorod, the intensity of the (002) plane was found to be varied. SEM micrographs show the vertical alignment of ZNAs perpendicular to the substrate and increase in rod length with increase in deposition time. The Gas sensing device was prepared by using ZNAs and tested for NO2 gas at different temperatures, concentrations and size of nanorods. Response increased with gas concentration as well as temperature. It was revealed that ZNAs gas sensor operating at 150 0C temperature could detect NO2 at low concentration (100ppm) with very high sensitivity (90 %).