Department Of Physics
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Item Theoretical investigation of quantum capacitance of Co-doped ?-MnO2 for supercapacitor applications using density functional theory(Royal Society of Chemistry, 2023-09-07T00:00:00) Vijayan, Ariya K.; Sreehari, M.S.; Kour, Simran; Dastider, Saptarshi Ghosh; Mondal, Krishnakanta; Sharma, A.L.The rapid depletion of fossil fuels and ever-growing energy demand have led to a search for renewable clean energy sources. The storage of renewable energy calls for immediate attention to the fabrication of efficient energy storage devices like supercapacitors (SCs). As an electrode material for SCs, MnO2 has gained wide research interest because of its high theoretical capacitance, variable oxidation state, vast abundance, and low cost. However, the low electric conductivity of MnO2 limits its practical application. The conductivity of MnO2 can be enhanced by tuning the electronic states through substitution doping with cobalt. In the present work, first principles analysis based on density functional theory (DFT) has been used to examine the quantum capacitance (CQC) and surface charge (Q) of Co-doped MnO2. Doping enhanced the structural stability, electrical conductivity, potential window, and quantum capacitance of ?-MnO2. The shortened band gap and localized states near the Fermi level improve the CQC of ?-MnO2. For the narrow potential range (?0.4 to 0.4 V), the CQC is observed to increase with doping concentration. The highest CQC value at +0.4 V is observed to be 2412.59 ?F cm?2 for Mn6Co2O16 (25% doping), five times higher than that of pristine MnO2 (471.18 ?F cm?2). Mn6Co2O16 also exhibits better CQC and �Q� at higher positive bias. Hence, it can be used as an anode material for asymmetric supercapacitors. All these results suggest better capacitive performance of Co-doped ?-MnO2 for aqueous SCs and as an anode material for asymmetric supercapacitors. � 2023 The Royal Society of Chemistry.Item Mesoporous carbon/titanium dioxide composite as an electrode for symmetric/asymmetric solid?state supercapacitors(Elsevier Ltd, 2022-08-27T00:00:00) Arya, Anil; Iqbal, Muzahir; Tanwar, Shweta; Sharma, Annu; Sharma, A.L.; Kumar, VijayThis paper reports the successful synthesis of mesoporous carbon/titanium dioxide (MC/TiO2) composite electrodes via the hydrothermal method for supercapacitor (SC) applications. The morphology and structural properties of MC/TiO2 composites were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectra (FTIR). The electrochemical properties were recorded by cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD) with an electrolyte (6 M KOH) in symmetric/asymmetric configuration. The specific capacitance (Cs) evaluated by CV is about 280F/g for composite electrode (95 % capacitance retention after 1000 cycles) and pristine has 150F/g @ 10 mV/s. Enhancement in capacitance is owing to faster charge dynamics within electrode material. The fabricated asymmetric device demonstrates high energy density (30.31 Wh/kg), than the symmetric configuration (?27 Wh/kg). Finally, both symmetric/asymmetric supercapacitors have illuminated a red LED, and strengthens the candidature of composite electrode for energy storage technology. � 2022 Elsevier B.V.Item Nanofiller-assisted Na+-conducting polymer nanocomposite for ultracapacitor: structural, dielectric and electrochemical properties(Springer, 2021-01-04T00:00:00) Kamboj, Vashu; Arya, Anil; Tanwar, Shweta; Kumar, Vijay; Sharma, A.L.We report the preparation of ZrO2 nanofiller-incorporated polymer nanocomposite electrolyte based on the PEO-NaPF6 matrix via standard solution cast method. The structure and morphology of polymeric films have been examined with X-ray diffraction and field emission scanning electron microscopy. Different interactions between the polymer, salt and nanofiller have been examined by Fourier transform infrared technique. The temperature-dependent (40�100��C) electrical conductivity has been examined from complex impedance spectroscopy (CIS). The highest ionic conductivity is exhibited by 5�wt% nanofiller-based electrolyte and recorded ~ 2 � 10�4�S�cm?1 at 100��C. The voltage stability window of polymeric film checked from linear sweep voltammetry is about ~ 4�V, and ion transference number close to unity confirms the major contribution from ion conduction. The dielectric properties have been explored in terms of complex permittivity, loss tangent and complex conductivity. The dielectric plots have been further fitted with an associated equation to evaluate principal dielectric parameters. The optimized polymer electrolyte possesses the lowest relaxation time and the highest dielectric constant that suggests the highest ionic conductivity, which is in good correlation with impedance results. The dc conductivity is also highest for the optimum system, and relaxation time decreases with an increase in temperature. The thermal stability of polymer electrolytes is about 200��C, as examined by thermogravimetric analysis (TGA). The ion transport parameters n, ?, D have been evaluated via FTIR, impedance spectroscopy and Bandara and Mellander (B�M) approach. Finally, the optimized polymer nanocomposite film has been used as an electrolyte-cum-separator for the fabrication of a solid-state symmetric supercapacitor. The electrochemical parameters specific capacitance, energy density, power density have been examined from cyclic voltammetry and galvanostatic charge�discharge technique. It may be concluded that nanofiller incorporation is an effective strategy to enhance the properties of electrolyte and has the potential to adopt as an electrolyte-cum-separator for ultracapacitor. � 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature.Item Structural, microstructural and electrochemical properties of dispersed-type polymer nanocomposite films(Institute of Physics Publishing, 2018) Arya, A.; Sharma, A.L.Free-standing solid polymer nanocomposite (PEO-PVC) + LiPF6-TiO2 films have been prepared through a standard solution-cast technique. The improvement in structural, microstructural and electrochemical properties has been observed on the dispersion of nanofiller in polymer salt complex. X-ray diffraction studies clearly reflect the formation of complex formation, as no corresponding salt peak appeared in the diffractograms. The Fourier transform infrared analysis suggested clear and convincing evidence of polymer-ion, ion-ion and polymer-ion-nanofiller interaction. The highest ionic conductivity of the prepared solid polymer electrolyte (SPE) films is ?5 10-5 S cm-1 for 7 wt.% TiO2. The linear sweep voltammetry provides the electrochemical stability window of the prepared SPE films, about ?3.5 V. The ion transference number has been estimated, t ion = 0.99 through the DC polarization technique. Dielectric spectroscopic studies were performed to understand the ion transport process in polymer electrolytes. All solid polymer electrolytes possess good thermal stability up to 300 ?C. Differential scanning calorimetry analysis confirms the decrease of the melting temperature and signal of glass transition temperature with the addition of nanofiller, which indicates the decrease of crystallinity of the polymer matrix. An absolute correlation between diffusion coefficient (D), ion mobility (?), number density (n), double-layer capacitance (C dl), glass transition temperature, melting temperature (T m), free ion area (%) and conductivity (?) has been observed. A convincing model to study the role of nanofiller in a polymer salt complex has been proposed, which supports the experimental findings. The prepared polymer electrolyte system with significant ionic conductivity, high ionic transference number, and good thermal and voltage stability could be suggested as a potential candidate as electrolyte cum separator for the fabrication of a rechargeable lithium-ion battery system. ? 2018 IOP Publishing Ltd.