Browsing by Author "Gupta, Asha"

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    Effect of strontium doping on the electrochemical pseudocapacitance of Y1?xSrxMnO3?? perovskites
    (Royal Society of Chemistry, 2022) Singh, Abhay Narayan; Nigam, Krishna Gopal; Mondal, Rakesh; Kushwaha, Vishal; Gupta, Asha; Rath, Chandana; Singh, Preetam
    Grid-scale bulk energy storage solutions are needed to utilize the full potential of renewable energy technologies. Pseudocapacitive electrochemical energy storage can play a vital role in developing efficient energy storage solutions. The use of perovskites as anion intercalation-type pseudocapacitor electrodes has received significant attention in recent years. In this study, Sr-doped YMnO3i.e. Y1?xSrxMnO3?? perovskite was prepared by the solid-state ceramic route and studied for electrochemical pseudocapacitance in aqueous KOH electrolyte. Microstructures, morphologies, and electrochemical properties of these materials were investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance method. The formation of the mostly cubic phase, with 50% strontium doped YMnO3 (YSMO-50) provides an equivalent three-dimensional network and superior conductivity due to Mn3+-O2?-Mn4+ hopping conduction. YSMO-50 exhibited low intrinsic resistance, 1.45 ? cm?2, and the highest specific capacity, 259.83 F g?1 at a current density of 1 A g?1 in 2 M KOH aqueous electrolyte. Redox-mediated interconversion of oxide to hydroxide (M2+O2? + H2O + e? ? M+OH? + OH?) in aqueous media is shown to be the reason behind the high capacitance of YSMO-50. The excellent electrochemical performance of YSMOs was attributed to the reversible interconversion of oxide-ion into hydroxide ion coupled with surface redox reaction of Mn2+/Mn3+ and Mn3+/Mn4+ occurring during the charge-discharge process. The maximum energy density of 65.13 W h kg?1 was achieved at a power density of 0.45 kW kg?1 for an asymmetric mode, in which YSMO serves as a negative electrode and Activated carbon (AC) as a positive electrode in the PVA-KOH gel electrolyte. Our study reveals that the doping of low valence atom (Sr) at the A-site in perovskite manganites (YMnO3) may be an effective tool to enhance the pseudocapacitive performance of perovskite-based electrodes. � 2023 The Royal Society of Chemistry.
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    Fabrication and electrochemical performance of pseudocapacitive ABO2-type AgFeO2@C
    (Elsevier Ltd, 2023) Singh, Abhay Narayan; Yadav, Akhilesh Kumar; Gupta, Asha; Rath, Chandana; Singh, Preetam
    To make effective utilization of renewable energy sources, a highly efficient large-scale energy storage solution is needed that can fill the gap between the batteries (high energy density) and the capacitors (high power density). Supercapacitors are being a bridge between batteries and capacitors, suffer from low energy density, and need to be further upgradation for utilization as a grid-level energy storage solution. A higher energy density can be achieved by constructing an asymmetric cell (ASC) in which both, the electrodes (positive and negative) are worked in a separate potential window. Pseudocapacitive ABO2-type electrode in the form of an asymmetric cell (ASC), AgFeO2@C//K0.4MnO2. xH2O is envisaged here as high high-performing battery-type supercapacitor cell to develop large-scale energy storage solutions. Herein, crystallites of K0.4MnO2. xH2O were successfully grown via a facile chemical flux method that gives a birnessite-type layered structure having a lateral dimension in the range of 2�5 ?m. Thus, the incorporation of birnessite- K0.4MnO2. xH2O as a positive electrode (cathode), and the thin carbon layer coated AgFeO2 as a negative electrode (anode) in aqueous 1 M Na2SO4 electrolyte in the form of ASC exhibited high energy density as well as power density with excellent cycle life up to cell voltages close to 1.8 V. The presented battery-type supercapacitor cell can deliver a maximum energy density equivalent to 61.51 Wh kg?1 and a power density of 450 W kg?1 at a current density of 0.5 A g?1, which is substantially larger than the previously reported aqueous electrolyte-based asymmetric supercapacitor devices. The newly developed high-voltage aqueous asymmetric battery-type supercapacitors device has a low-cost and enviro-friendly, that can replace currently market-available hazardous lead-acid batteries for fast energy storage applications. � 2023
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    Investigation of the Role of Sr and Development of Superior Sr-Doped Hexagonal BaCoO3-?Perovskite Bifunctional OER/ORR Catalysts in Alkaline Media
    (American Chemical Society, 2022) Mondal, Rakesh; Ratnawat, Himanshu; Mukherjee, Soham; Gupta, Asha; Singh, Preetam
    Superior electrocatalytic activity of catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) enhances the reversible energy storage efficiency of metal-air batteries and electrochemical water splitting performances to produce hydrogen. Sr incorporation in the BaCoO3-?lattice in the form of 2H-type Ba1-xSrxCoO3-?(0 ? x ? 0.5) perovskites enhances both ORR and OER activities. A relatively low overpotential of 395 mV at 10 mA/cm2, lower Tafel slope of 64.95 mV dec-1, and good stability up to 500 cycles (10% reduction of current density and overpotential shift to a 0.04 V higher value) in a 0.1 M KOH electrolyte were obtained for the Ba0.5Sr0.5CoO3-?electrode. Incorporation of Sr in the BaCoO3-?lattice decreases the Co-O-Co bond angle that results in a superior orbital overlap between Co(3d) and O(2p) orbitals and a decrease in lattice parameters that generates lower surface oxygen separation pathways and a large number of active sites on the (011) planes, making Ba0.5Sr0.5CoO3-?a superior catalyst with increased OER/ORR activity. The formation of oxygen-vacant CoO5octahedra containing surface oxygen vacancies, the presence of Co3+/4+valence states, and the superior overlap between O(2p)-Co(3d) bands (covalency increases) result in a higher electronic conductivity, a lower flat band potential, and improved OER and ORR activities. The key highlight of this work is the matching of the onset potential with the calculated flat band (Efb) potential from the Mott-Schottky plot. The Mott-Schottky plot was utilized to calculate the flat band potential (Efb) that indicates the basic information about the electrochemical interface potential between the electrode and the electrolyte, and in the case of Ba0.5Sr0.5CoO3-?, it matches very well with the onset potential for the OER activity of the catalyst. � 2022 American Chemical Society. All rights reserved.
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    La1-xK xFeO3-?: An Anion Intercalative Pseudocapacitive Electrode for Supercapacitor Application
    (American Chemical Society, 2021) Mondal, Rakesh; Mishra, Neeraj Kumar; Maiyalagan, Thandavarayan; Gupta, Asha; Singh, Preetam
    The green energy alternative to a fossil fuel-based economy can be provided only by coupling renewable energy solution solutions such as solar or wind energy plants with large-scale electrochemical energy storage devices. Enabling high-energy storage coupled with high-power delivery can be envisaged though high-capacitive pseudocapacitor electrodes. A pseudocapacitor electrode with multiple oxidation state accessibility can enable more than 1e- charge/transfer per molecule to facilitate superior energy storage. K-doped LaFeO3 (La1-xKxFeO3-?) is presented here as an electrode having a high pseudocapacitance storage, equivalent to 1.32e- charge/transfer per molecule, resulting in a capacity equivalent of 662 F/g at 1 mV/s scan rate by introduction of a layered potential over the Fe-ion octahedral to utilize higher redox state energies (Fe4+? Fe2+). La/K ordering in orthorhombic perovskite (La1-xKxFeO3-?) made the Fe4+ oxidation state accessible, and a systematic shift in the redox energies of Fe4+/3+ and Fe3+/2+ redox couples was observed with K+ ion doping in the A site of the LaFeO3 perovskite, which resulted in a high faradic contribution to the capacitance, coupled with anionic intercalation of H2O/OH- in the host perovskite lattice. The surface capacitive and diffusion control contributions for capacitance are about 42 and 58%, respectively, at-0.6 V, with a scan rate of 1 mV/s. A high gravimetric capacitance, equivalent to 619, 347, 188, 121, and 65 F/g, respectively, at 1, 2, 3, 5, and 10 A/g constant current, was observed for the La0.5K0.5FeO3-? electrode. Up to 88.9% capacitive retention and 97% Coulombic efficacy were obtained for continuous 5000 cycles of charge/discharge for the La0.5K0.5FeO3-? electrode. The gravimetric capacitance values of ASCs (activated carbon//La0.5K0.5FeO3-?) are 348, 290, 228, and 147 F/g at current densities of 1, 2, 3, and 5 A/g, respectively. A maximum specific power of ?3594 W/kg was obtained when the specific energy reached ?117 Wh/kg at 5 A/g of current density. � 2021 The Authors. Published by American Chemical Society.
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    Perovskite La1?xKxCoO3?? (0 ? x ? 0.5): a novel bifunctional OER/ORR electrocatalyst and supercapacitive charge storage electrode in a neutral Na2SO4 electrolyte
    (Royal Society of Chemistry, 2022) Mondal, Rakesh; Mishra, Neeraj Kumar; Singh, Mahatim; Gupta, Asha; Singh, Preetam
    The as-prepared La1?xKxCoO3?? (0 ? x ? 0.5) showed superior pseudocapacitive charge storage capacity in a neutral 0.5 M Na2SO4 electrolyte and superior electrocatalytic activities for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in a 1 M KOH electrolyte. 30% K doped p-type La0.7K0.3CoO3?? presents superior OER activity with an overpotential of ?335 mV at 10 mA cm?2 current rate in a 1 M KOH electrolyte. Additionally, La1?xKxCoO3?? (0 ? x ? 0.5) presents an excellent charge-storage capacitance in a neutral 0.5 M Na2SO4 electrolyte resulting in a gravimetric capacitance of the La0.5K0.5CoO3?? electrode equivalent to 378 F g?1, 282 F g?1, 221 F g?1, 163 F g?1, and 74 F g?1 at a current density of 1 A g?1, 2 A g?1, 3 A g?1, 5 A g?1, and 10 A g?1, respectively. After 2500 continuous cycles of charge/discharge, the La0.5K0.5CoO3??//AC cell exhibits higher stability, capacitive retention (94%) and coulombic efficiency (97%). The gravimetric charge storage capacity of ASCs (La0.5K0.5CoO3??//AC) in the full cell mode showed capacitance equivalent to 308 F g?1, 287 F g?1, 238 F g?1, 209 F g?1 and 162 F g?1 at current densities of 1 A g?1, 2 A g?1, 3 A g?1, 5 A g?1 and 10 A g?1 in a neutral 0.5 M Na2SO4 electrolyte respectively. Maximum specific power equivalent to ?6884 W kg?1 was observed at a current density of 10 A g?1 when the specific energy reached ?57 W h kg?1 for the full cell. The double exchange mechanism coupled with stoichiometric oxygen defects present in the perovskite lattice seems to be operative behind the enhanced electrocatalytic OER properties, and additionally, it improves the charge storage kinetics of the La1?xKxCoO3?? (0 ? x ? 0.5) electrode in a neutral Na2SO4 electrolyte for supercapacitor application. This work presents a rational strategy for introducing facile oxygen ion defects into perovskite structured La1?xKxCoO3?? (0 ? x ? 0.5) to develop multifunctional electrode materials for a supercapacitor and energy conversion (OER/ORR) electrode of metal-air batteries. � 2022 The Royal Society of Chemistry.