A.C. Lokhande

Bath temperature controlled phase stability of hierarchical nanoflakes CoS2 thin films for supercapacitor application

In the present study, CoS2 thin-film electrodes are synthesized at different bath temperatures using a simple chemical bath deposition (CBD) method. The bath temperature controls the phase stability of the CoS2 thin film along the in-plane direction up to 353 K. However, at 363 K, an oxide phase is included in the film. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies showed enhanced crystallinity of CoS2 as the bath temperature increased and evolution in surface morphology from immature nanoflakes to well-grown aligned mature nanoflakes. A specific capacitance of 800 F g−1 is obtained from cyclic voltammetry measurements by utilizing the 83.6 m2 g−1 surface area of CoS2 nanoflakes synthesized at 353 K. The hierarchical distribution of pores gives rise to a high specific energy and specific power of 40.74 W h kg−1 and 3333 W kg−1, respectively, as a result of utilization of the high electrochemically active surface area. Furthermore, good long-term cycling stability of CoS2 nanoflakes has been observed in a 2 M KOH electrolyte. A low impedance value suggests that the CoS2 nanoflake electrode prepared by a facile CBD method is a potential candidate for supercapacitor application.

The synthesis of multifunctional porous honey comb-like La2O3 thin film for supercapacitor and gas sensor applications

The porous honey comb-like La2O3 thin films have been synthesized using one step spray pyrolysis method. The influence of sprayed solution quantity on properties of La2O3 thin films is studied using X-ray diffraction, Fourier transform spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, optical absorption and Brunauer-Emmett-Teller techniques. Morphology of La2O3 electrode is controlled with sprayed solution quantity. The supercapacitive properties of La2O3 thin film electrode are investigated using cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance techniques. The La2O3 film electrode exhibited the specific capacitance of the 166Fg-1 with 85% stability for the 3000 cycles. The La2O3 film electrode exhibited sensitivity of 68 at 523K for 500ppm CO2 gas concentration. The possible CO2 sensing mechanism is discussed.

Ionically conducting PVA-LiClO4 gel electrolyte for high performance flexible solid state supercapacitors.

The synthesis of polymer gel electrolyte having high ionic conductivity, excellent compatibility with active electrode material, mechanical tractability and long life is crucial to obtain majestic electrochemical performance for flexible solid state supercapacitors (FSS-SCs). Our present work describes effect of different polymers gel electrolytes on electrochemical properties of MnO2 based FSS-SCs device. It is revealed that, MnO2-FSS-SCs with polyvinyl alcohol (PVA)-Lithium perchlorate (LiClO4) gel electrolyte demonstrate excellent electrochemical features such as maximum operating potential window (1.2V), specific capacitance of 112Fg(-1) and energy density of 15Whkg(-1) with extended cycling stability up to 2500CV cycles. Moreover, the calendar life suggests negligible decrease in the electrochemical performance of MnO2-FSS-SCs after 20days.

Chemically deposited nano grain composed MoS2 thin films for supercapacitor application

Low temperature soft chemical synthesis approach is employed towards MoS2 thin film preparation on cost effective stainless steel substrate. 3-D semispherical nano-grain composed surface texture of MoS2 film is observed through FE-SEM technique. Electrochemical supercapacitor performance of MoS2 film is tested from cyclic voltammetry (CV) and galvanostatic charge discharge (GCD) techniques in 1M aqueous Na2SO4 electrolyte. Specific capacitance (Cs) of 180Fg-1 with CV cycling stability of 82% for 1000 cycles is achieved. Equivalent series resistance (Rs) of 1.78Ωcm-2 observed through Nyquist plot shows usefulness of MoS2 thin film for charge conduction in supercapacitor application.

Supercapacitive properties of nanoporous oxide layer formed on 304 type stainless steel.

The nanoporous oxide layer is formed on the surface of 304 type stainless steel (SS) by chemical oxidation method. The characterization of the oxide layer is carried out using X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), contact angle and energy-dispersive X-ray spectroscopy (EDS) techniques. The supercapacitive properties of oxide layer are studied using cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy techniques.

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 sensitive CO2 sensor based on microrods-like La2O3 thin film electrode

In this paper, microrods-like La2O3 thin films are successfully prepared by a chemical bath deposition method. The structural, morphological, wettability and compositional properties of La2O3 thin films are studied using X-ray diffraction (XRD), Fourier transform Raman (FT-Raman) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) and X-ray photo-electron spectrum (XPS) techniques. The La2O3 thin film shows highest selectivity 48% toward CO2 gas as compared to other gases with response and recovery time periods of 50 and 73 s, respectively at a concentration of 350 ppm.

Ultrathin nickel sulfide nano-flames as an electrode for high performance supercapacitor; comparison of symmetric FSS-SCs and electrochemical SCs device

Metal sulfides have received well deserved attention due to their excellent electrical conductivity and thermal stability, as compared to metal oxides, allowing them to achieve a high capacitance and energy density for portable energy storage devices. In this study, the preparation of highly porous nano-flames composed of nickel sulfide (NiS) thin film on a cost effective, flexible stainless steel substrate through a trouble free, inexpensive and simple chemical bath deposition (CBD) method is reported. The prepared nano-flames composed of a NiS thin film demonstrates the excellent electrochemical features with a maximum specific capacitance (Cs) of 750.6 F g−1 at a scan rate of 5 mV s−1 in a three electrode system. Furthermore, the portable symmetric flexible solid state supercapacitor (FSS-SC) and electrochemical supercapacitor (SC) are fabricated and tested. In comparison with the symmetric electrochemical SC, the symmetric FSS-SC shows an excellent electrochemical performance with a high Cs of 104 F g−1 at 5 mV s−1 with a good electrochemical stability of 85.3% over 3000 CV cycles. This study constitutes the first comparison of symmetric FSS-SCs and electrochemical SCs formed with NiS nano-flames. Such an impressive symmetric FSS-SC is predicted to be an exceptionally promising candidate for energy storage systems.

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°.

Cobalt Iron Hydroxide as a Precious Metal-Free Bifunctional Electrocatalyst for Efficient Overall Water Splitting

Highly efficient and stable electrocatalysts from inexpensive and earth-abundant elements are emerging materials in the overall water splitting process. Herein, cobalt iron hydroxide nanosheets are directly deposited on nickel foam by a simple and rapid electrodeposition method. The cobalt iron hydroxide (CoFe/NF) nanosheets not only allow good exposure of the highly active surface area but also facilitate the mass and charge transport capability. As an anode, the CoFe/NF electrocatalyst displays excellent oxygen evolution reaction catalytic activity with an overpotential of 220 mV at a current density of 10 mA cm-2 . As a cathode, it exhibits good performance in the hydrogen evolution reaction with an overpotential of 110 mV, reaching a current density of 10 mA cm-2 . When CoFe/NF electrodes are used as the anode and the cathode for water splitting, a low cell voltage of 1.64 V at 10 mA cm-2 and excellent stability for 50 h are observed. The present work demonstrates a possible pathway to develop a highly active and durable substitute for noble metal electrocatalysts for overall water splitting.