Faculty Publications
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Item Improved electrochemical performance of graphene oxide supported vanadomanganate (IV) nanohybrid electrode material for supercapacitors(Elsevier Ltd, 2020) Kumari, S.; Maity, S.; Anandan Vannathan, A.A.; Shee, D.; Das, P.P.; Mal, S.S.Graphene oxide (GO)-supported polyoxometalates (POMs) have been considered as promising electrode materials for energy storage applications due to their ability to undergo fast and reversible redox reactions. Herein, vanadomanganate-GO composites (K7MnIVV13O38.18H2O-GO with 2:1 and 4:1 ratio) were investigated for use as potential electrode materials in supercapacitors (SCs). The K7MnIVV13O38.18H2O (MnV13) was synthesized and anchored on GO through electron transfer interaction and electrostatic interaction to make the composite electrodes for the present study. All synthesized electrode materials were fully characterized by various techniques, e.g., Fourier Transform Infrared (FTIR) Spectroscopy, Powder X-ray Diffraction (XRD), Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy (SEM/EDS) and High Resolution-Transmission Electron Microscopy (HR-TEM). The electrochemical properties of MnV13/GO composites with different MnV13/GO ratios were investigated by two-electrode cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD) in different electrolytes. The MnV13/GO composite of ratio 2:1 in 1 M LiCl electrolyte and that of ratio 4:1 in 1 M Na2SO4 electrolyte showed significant specific capacitance values of 269.15 F/g and 387.02 F/g, respectively and energy density of 37.38 Wh/kg and 53.75 Wh/kg, respectively for a scan rate of 5 mV/s. Interestingly, the 1:1 (MnV13/GO) composite in 1 M Na2SO4 and 1 M LiCl electrolytes showed very low specific capacitance values as the deposition of MnV13 on GO was not sufficient, as indicated by FTIR and SEM. Thus, it is evident that the specific capacitance value of these composite materials depends on the amount of MnV13 deposited on GO and these composite materials exhibit the potential to improve the performance of GO-based SCs. © 2019Item Redox-Active Vanadium-Based Polyoxometalate as an Active Element in Resistive Switching Based Nonvolatile Molecular Memory(Wiley-VCH Verlag info@wiley-vch.de, 2020) Sterin, N.S.; Basu, N.; Cahay, M.; Satyanarayan, M.N.; Mal, S.S.; Das, P.P.Resistive switching (RS)-based random access memory has been envisaged as a viable alternative to existing memory technology due to its nonvolatility, high switching speed, high endurance/retention, and considerably low operating voltage. Herein, a new uniform, repetitive, and stable RS phenomenon is demonstrated based on very low-cost two-terminal metal–insulator–metal stack fabricated using a highly redox-active vanadium-based polyoxometalate (POM) molecular clusters, [V10O28]6?—belonging to polyoxovanadate (POV) family. The RS is observed to be unipolar and nonvolatile in nature, and occur at a fairly low operating bias voltage (less than 2 V), making it suitable for low-power operations. The switching event is attributed to the cycling between formation and rupture of tiny conductive nanofilaments formed due to trapping and detrapping of positively charged ionized oxygen vacancy sites present in the active switching layer of [V10O28]6?. POMs, in their rich abundance, are highly stable early transition-metal oxide nanosized clusters, capable of storing as well as releasing a large number of electrons. In addition, they can undergo fast and reversible redox reactions (both in solid and liquid electrolyte media) in “stepwise” manner—a property that makes them a promising candidate for ultrafast and multi-level nonvolatile molecular memory for high-density data storage. Preliminary investigations on the POV-based memory cells result in device resistance ratio ?25, endurance for more than 200 cycles, and stable retention time around 2200 s, in fully open air condition. © 2020 Wiley-VCH GmbHItem In situ vanadophosphomolybdate impregnated into conducting polypyrrole for supercapacitor(Elsevier Ltd, 2020) Anandan Vannathan, A.A.; Maity, S.; Kella, T.; Shee, D.; Das, P.P.; Mal, S.S.The fast modernization and advancement in lifestyle increase the consumption of power daily due to all innovative technologies, e.g., hybrid vehicles, solar cells, smart power grid, communication devices, artificial hearts, etc. Conducting organic polymer-based energy storage devices had attracted much attention due to the conductive nature for a long time. However, its application has been restricted because of swelling and shrinking capability during the charge and discharge cycle. The combination of redox-active inorganic metal oxides, such as polyoxometalates (multi-metal oxide cluster) with conduction polymers, could enhance the material's stability due to its fast multi-electron redox property. Here, we report the two polypyrroles combined vanadophosphomolybdates, namely PPy-H4[PVMo11O40] and PPy-H5[PV2Mo10O40] nanohybrid electrode materials. The PPy-H5[PV2Mo10O40] electrode material behaves as pseudocapacitance and can deliver an excellent capacitance of 561.1 F/g in 0.1 M H2SO4 electrolyte solution at a 0.2 A/g current density, indicating capacitive composite material. The electrochemical impedance spectroscopy (EIS) reveals that PPy-H5[PV2Mo10O40] is more capacitive than PPy-H4[PVMo11O40] and PPy with equivalent series resistance (ESR) of 5.74 ?. The cell capacitance of PPy-H5[PV2Mo10O40] and PPy-H4[PVMo11O40] are found to be 5.38 and 9.15 mF, stipulating in small SC cell application. Likewise, the PPy-H5[PV2Mo10O40] nanohybrid electrode shows better responsive behavior with a relaxation time of 0.16 ms. Furthermore, the PPy-H5[PV2Mo10O40] electrode exhibits outstanding cycle stability, retaining ~95% of its capacitance after 4500 cycles as compare to PPy-H4[PVMo11O40] (~91%) electrode. © 2020Item Activated carbon- supported Vanado-nickelate (IV) based hybrid materials for energy application(Elsevier Ltd, 2021) Maity, S.; BM, N.; Kella, T.; Shee, D.; Das, P.P.; Mal, S.S.The rapid development of supercapacitor (SC) technology leads to increased demand for nanofabrication of novel and effective electroactive hybrid materials for next-generation energy storage devices. Herein, nickel tetradecavanadate, K2H5[NiV14O40](NiV14), is doped into porous activated carbon (AC), for the first time, in different wt.% in order to investigate the homogeneous loading of the inorganic metal-oxide component on the AC matrix. The resulting complex, AC-NiV14, is found to have possessed an enhanced electrochemical characteristic (for both symmetric and asymmetric SC cell), which operates at a significantly higher potential of 1.2 V. The combination of the double-layer capacitance (EDLC) and the redox-active polyoxometalate cluster leads to an intrinsic increase in specific capacitance (capacity) (from 45.3 Fg?1 (54.4 Cg?1) for AC to 316 Fg?1 (379.2 Cg?1) for 15 wt.% AC-NiV14 at a current density of 1 Ag?1). It was also observed that there is an increase of 20% in the operating voltage compared to conventional AC supercapacitors with acidic aqueous electrolytes. Firstly, symmetric supercapacitor's electrochemical performances of various wt.% of NiV14 composition were studied in acidic aqueous electrolyte (0.5 M H2SO4) solution. We observed that the 15 wt.% of AC-NiV14 hybrid electrode showed remarkable specific energy value (~63.2 Wh kg?1) compared with pristine AC and NiV14 electrodes, separately. Besides, the asymmetric layout (AC//AC-NiV14) increased the potential window up to 1.5 V and enhanced the specific energy and power values (90.1 Whkg?1 and 2400 Wkg?1, respectively), with 98% coulombic efficiency. Meanwhile, the AC-NiV14//NiV14 asymmetric cell possesses a specific capacitance (capacity) of 375 Fg?1 (450 Cg?1) with a maximum power of 3140 Wkg?1 at the high current density of 2 Ag?1. © 2021 Elsevier LtdItem Investigations of redox-active polyoxomolybdate embedded polyaniline-based electrode material for energy application(Springer Science and Business Media Deutschland GmbH, 2022) Anandan Vannathan, A.A.; Kella, T.; Shee, D.; Mal, S.S.Higher capacitance supercapacitors have received considerable attention, including their massive power density, high stability, and long cycle life. On the other hand, polymers have been known for their energy storage device application because of the pseudocapacitance behavior resulting from the extended conjugation over the polymer backbone. Here, we report a simple chemical bath deposition method for the synthesis of two polyoxometalates (H4[PVMo11O40] and H5[PV2Mo10O40]) impregnated polyaniline (PAni) composite (PVMo11@PAni and PV2Mo10@PAni) for electrochemical supercapacitors. Various analytical methods characterized the electrode materials, e.g., Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD) method, and the morphological features of those electrodes were acquired by field emission scanning microscopy (FESEM). The exceptionally high average capacitance of 1371 F g−1 was obtained for the composite PVMo11@PAni electrode at a 3 A g−1 current density and 1 V potential window with an energy density of 137.5 W h kg−1. The PVMo11@PAni composite electrode showed almost 4.3 times the higher energy density than pure PAni and 2.3 times higher than PV2Mo10@PAni. In contrast, PV2Mo10@PAni composite showed 1.9 times more energy density than pure PAni composite electrode. Interestingly, high average capacitance, charge–discharge rates, and high energy density with high-level power delivery make them promising electrode candidates for supercapacitors. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.Item Vanadomanganate as a synergistic component in high-performance symmetric supercapacitor(Elsevier Ltd, 2022) Maity, S.; Anandan Vannathan, A.A.; Chandewar, P.R.; Shee, D.; Das, P.P.; Mal, S.S.Supercapacitor devices fabricated from capacitive and battery-type hybrid electrodes have been projected as a promising energy storage system because of their ability to produce high specific power and energy simultaneously. In this work, we have demonstrated a facile method of impregnation of faradaic type manganese (III) polyoxovanadate, [MnV14O40]−6 on the high surface area substrate of activated carbon (AC) as well as graphene oxide (GO). Materials and electrochemical characterizations data confirm the successful incorporation of capacitive and faradaic type manganese (III) polyoxovanadate into the nanohybrid electrode material. Furthermore, the synergic effect between the carbonaceous nanostructures (AC/GO) and redox-active oxometalate (MnV14) provides a better pathway for ion transport to the interface resulting in enhancement of the conductivity, diffusion ability of the nanohybrid. Moreover, the battery-type MnV14 clusters disperse in the micro/mesopores of AC, whereas the oxygen-containing functional groups in GO act as active sites for anchoring of MnV14 clusters. Thus, the surface modification with MnV14 clusters enhances the specific capacitance of nanohybrid with remarkable electrical and mechanical stability. The AC/MnV14 nanohybrid exhibits an enhanced specific capacitance of 547 F g−1 with specific energy and power of 76 Wh kg−1 and 1600 W kg−1, respectively, at 0.8 A g−1 current density. Additionally, GO/MnV14 shows a specific capacitance of 330 F g−1 with improved specific energy and power of 30 Wh kg−1 and 1276 W kg−1, respectively, at the same current density. Moreover, both the nanohybrids possess excellent cycle stability by retaining 92% (AC/MnV14) and 90.6% (GO/MnV14) of initial capacitance even after 5000 sweeping cycles. © 2021 Elsevier B.V.Item Development of a cholesterol biosensor and energy storage system based on polypyrrole coated polyoxometalate(Elsevier Ltd, 2025) Biradar, B.R.; Thathron, N.; Hanchate, A.; Das, P.P.; Mal, S.S.Designing sustainable and environmentally acceptable multifunctional electrode materials is vital for various purposes, such as energy storage and healthcare. The redox property of polyoxometalates is attractive for different electrochemistry fields, such as sensors, energy storage, catalysis, etc. In this study, potassium 9-tungsto-2-molybdo-1-vanadosilicate K5[?-SiMo2VW9O40].10H2O (hereafter acronym as SiMo2VW9) embedded on polypyrrole (PPy), which acts as a nanohybrid, was synthesized for supercapacitor and biosensor applications. The electrochemical analysis for both applications was carried out using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The PPy-SiMo2VW9 nanohybrid showed the highest specific capacitance of 174.5 F g?1 with power and energy densities of 799.94 W kg?1 and 15.51 Wh kg?1, respectively, at 0.5 M H2SO4 electrolytic medium. The nanohybrid showed the diffusion-dominant charge storage mechanism with 92.24 % at a 5 mV s?1 scan rate, which refers to the battery-type material. Furthermore, electrochemical sensing for cholesterol was also carried out using the cyclic voltammetry approach in the range of 0.03–0.58 mM cholesterol concentration. The PPy-SiMo2VW9 nanohybrid showed a sensitivity of 7.97 mAm M cm?2 with limit-of-detection (LOD) and limit-of-quantification (LOQ) of 0.06 and 0.2 mM, respectively. The outcomes show that PPy-SiMo2VW9 nanohybrid material is promising in sensing and supercapacitor studies. © 2025 Elsevier B.V.Item Polyoxometalate Integrated with Conducting Polymer Nanocomposites for Supercapacitor and Biological Sensor Applications(American Chemical Society, 2025) Puniyanikkottil, M.A.; Mal, S.S.Nanostructured redox-active composite electrode materials have been developed for energy storage applications to address conventional carbon-based supercapacitor’s limited electrochemical performance. Polyoxometalates (POMs) and conducting polymers (CP) have significantly enhanced the pseudocapacitive activity of these electrode materials. In this study, we synthesized H4[PVW11O40]·xH2O (PVW11) and combined it with polypyrrole (PPy) and polyaniline (PAni) separately to improve energy performance and conduct electrochemical analysis. The PVW11-PPy outperformed the PVW11-PAni composite, achieving an energy density of 49.07 W h kg-1 and a specific capacitance of 405.16 F g-1. The supercapacitor cells showed a cyclic retention of 85.13% and 99.99% Coulombic efficiency after 6000 galvanostatic charge-discharge (GCD) cycles. The PVW11-PPy composite was fabricated into a supercapacitor device that powered a set of 10 LED bulbs for 2 min using an active mass of 76 mg. Additionally, the PVW11-PPy composite material was employed to sense glucose solutions with concentrations ranging from 0.04 to 0.4 mM, providing a sensitivity of 0.325 mA mM-1 cm-2, with limits of detection (LOD) and quantification (LOQ) of 0.381 mM and 1.270 mM, respectively. © 2025 American Chemical Society.Item Dual oxygen reservoir model for nonpolar resistive switching in nickel tetradecavanadate based molecular switch(Elsevier B.V., 2025) Thathron, N.; Biradar, B.R.; Pandey, S.K.; Mal, S.S.; Das, P.P.The data explosion and computing limitations of traditional computer systems have led researchers to find alternate data storage devices. Resistive random access memory devices have been accepted as a promising candidate to meet the growing demand for multi-bit memory storage and unconventional computing applications. In this report, we provide a comprehensive mechanistic insight into the multistate nonpolar resistive switching in nickel-embedded polyoxovanadate molecules, K2H5[NiV14O40] based memory device having the architecture Al/K2H5[NiV14O40]/ITO. Such molecular cluster belongs to a larger group of polyoxometalate family. The formation and rupture of multiple conductive filaments made up of oxygen vacancies and their lateral widening with different compliance currents allow the device to exhibit multiple resistance states. The resistance states are likely to be modulated by the multiple redox reactions of Ni and V centers of the active switching layer. The coexistence of two unipolar and two bipolar modes of resistive switching suggests that the device can be modeled as having a dual oxygen reservoir structure where both thermochemical and electrochemical mechanisms of filament theory for resistive switching coexist in the same memory cell. The observation of quantized steps in the conductance plot confirms the conductive filament based resistive switching. The enhancement and reduction in conductance with the increase in the number of pulses can mimic the potentiation and depression in biological synapses. This promises that the polyoxometalate based resistive switching devices can connect memory with neuromorphic applications. © 2025 Elsevier B.V.