Browsing by Author "Mondal, Rakesh"

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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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    Electrochemical Performance of Delafossite, AgFeO2: A Pseudo-Capacitive Electrode in Neutral Aqueous Na2SO4Electrolyte
    (IOP Publishing Ltd, 2021) Singh, Abhay Narayan; Mondal, Rakesh; Rath, Chandana; Singh, Preetam
    Layered delafossite AgFeO2 with open channel structure is envisaged as a pseudo capacitor electrode using Fe2+/Fe3+ redox couple. A simple co-precipitation method was employed for the phase formation of delafossite AgFeO2 resulting in a mixture of 2H and 3R-phase. Phase tuning of 2H phase was done by controlling the calcination conditions and characterizing by powder XRD, FT-IR, and Raman methods. 2H AgFeO2 was used to synthesize as a majority phase because it have the larger inter layer spacing than 3R phase shown. HRTEM study confirms the formation 2H phase in majority. All of the synthesized samples exhibit predominantly faradic battery-type redox behavior along with surface charge storage. Flower like microarchitectures of AgFeO2 show outstanding electrochemical performance with high specific capacity of 110.4 F g-1 at 1 A g-1 current density, that retained up to 89% after 2000th times charge/discharge in 1 M Na2SO4 electrolyte. In an asymmetric device mode, AFO-400//AC full cell exhibits superior electrochemical performance by delivering high energy density (33.5 Wh kg-1) and high power density (454.3 W kg-1) with excellent cycling stability (86% retention after 2000th cycles). The results clearly demonstrate that the synthesized delafossite AgFeO2 containing mixture of 2H and 3R-phases have remarkable potential to be used as a negative electrode material for supercapacitor and other energy storage technologies. � 2021 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.
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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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    NiC2O4 ? 2H2O Nanoflakes: A Novel Redox-mediated Intercalative Pseudocapacitive Electrode for Supercapacitor Applications in Aqueous KOH and Neutral Na2SO4 electrolytes
    (John Wiley and Sons Inc, 2022) Mishra, Neeraj Kumar; Singh, Abhijeet Kumar; Mondal, Rakesh; Singh, Preetam
    Pseudocapacitors with the accessibility of different oxidation states for redox-mediated charge storage can achieve higher energy density compared to EDLC.�NiC2O4 ? 2H2O is envisaged here as a potential pseudocapacitive electrode that works with the accessibility of the Ni2+/3+�redox couple in the flexible structural network due to the presence of planar oxalate anions (C2O42?) supported by the 3-dimensional hydrogen bonding network of crystal water. The NiC2O4 ? 2H2O electrode showed a superior specific capacitance equivalent to 990 F/g in the potential window of 0 to 0.45 V observed in aqueous KOH electrolyte and 440 F/g in 1 M neutral Na2SO4�electrolyte in the potential window of 0 to 0.85 V. Predominant intercalative mechanism seems to play an important role behind the high charge storage capacity of NiC2O4 ? 2H2O electrode and the interactive contribution was found to be ?84 % and surface contribution was found to be ?16 % respectively. Further, in full cell asymmetric supercapacitor (AAS) mode in KOH electrolyte, in which NiC2O4 ? 2H2O is made as the positive electrode and Activated Carbon (AC) is made as the negative electrode, the highest specific energy of 141.5 Wh/kg and specific power of ?559 W/kg at 0.2 A/g current density was obtained with superior cyclic stability. The detailed electrochemical studies confirm high cyclic stability and stable performance that makes NiC2O4 ? 2H2O a potential pseudocapacitive electrode for large-scale energy storage applications. � 2022 Wiley-VCH GmbH.
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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.
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    Synthesis, characterizations and electrochemical performances of anhydrous CoC2O4nanorods for pseudocapacitive energy storage applications
    (Royal Society of Chemistry, 2021) Mishra, Neeraj Kumar; Mondal, Rakesh; Singh, Preetam
    To overcome the environmental challenges caused by utilization of fossil fuel based energy technologies and to utilize the full potential of renewable energy sources such as solar, wind and tidal, high power and high energy density containing large scale electrochemical energy storage devices are a matter of concern and a need of the hour. Pseudocapacitors with accessibility to multiple oxidation states for redox charge transfer can achieve a higher degree of energy storage density compared to electric double layer capacitors (EDLC) and the hybrid supercapacitor is one of the prominent electrochemical capacitors that can resolve the low energy density issues associated with EDLCs. Due to its open pore framework structure with superior structural stability and accessibility of Co2+/3+/4 redox states, porous anhydrous CoC2O4 nanorods are envisaged here as a potential energy storage electrode in a pseudo-capacitive mode. Superior specific capacitance equivalent to 2116 F g-1 at 1 A g-1 in the potential window of 0.3 V was observed for anhydrous CoC2O4 nanorods in aqueous 2 M KOH electrolyte. A predominant pseudo-capacitive mechanism seems to be operative behind the high charge storage at electrodes as intercalative (Inner) and surface (outer) charge storage contributions were found to be 75% and 25% respectively. Further, in full cell asymmetric supercapacitor (ASC) mode in which porous anhydrous CoC2O4 nanorods were used as positive electrodes and activated carbon (AC) was utilised as negative electrodes within an operating potential window of 1.3 V, a highest specific energy of W h kg-1 and specific power of ?647 W kg-1 at 0.5 A g-1 current density were obtained with superior cycling stability. High cycling stability coupled with superior electrochemical storage properties make anhydrous CoC2O4 nanorods potential pseudo-capacitive electrodes for large scale energy storage applications. This journal is � The Royal Society of Chemistry.