Faculty Publications
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Item Capacitance and impedance spectroscopy studies of polymer light emitting diodes based on MEH-PPV:BT blends(Elsevier Ltd, 2019) K M, N.K.; Sterin, N.S.; Das, P.P.; Umesh, G.; Satyanarayan, M.N.Light emitting polymer poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) is blended with a wide bandgap electron transport material benzothiadiazole (BT) and its effect on the electronic properties has been studied by capacitance and impedance spectroscopy (IS) in PLEDs. The impedance data is fitted using equivalent circuit models and the minimum parallel resistance (Rp) at zero bias have been obtained for 1:3 ratio of MEH-PPV:BT blended devices. The negative capacitance (NC) shows the occurrence of the trap-assisted non-radiative recombination mechanism at low frequencies in the unblended MEH-PPV PLEDs. Further, this behavior is seen to be reduced in PLEDs with MEH-PPV:BT blends. This clearly suggests that the blending of MEH-PPV and BT at different weight ratios results in the suppression of trap-assisted recombination. This can be attributed to the elimination of trap states due to the dilution of semiconductor material on account of the addition of wide bandgap host material. Moreover, the blended devices have shown a significant improvement in the conductivity at small bias voltages. © 2019 Elsevier B.V.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 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 Enhanced Power Density of Graphene Oxide–Phosphotetradecavanadate Nanohybrid for Supercapacitor Electrode(Springer, 2021) Maity, S.; Anandan Vannathan, A.A.; Kumar, K.; Das, P.P.; Mal, S.S.Successful exploration of supercapacitor (SC) material to integrate with high energy and high power density storage device still remains a daunting challenge. Conducting carbon nanostructures have been primarily used for this purpose; however, most of their surface area remains unutilized throughout the storage process. Herein, a new type of hybrid material has been reported by effectively using active sides of carbon nanostructures. Insertion of faradaic-type polyoxometalates (POMs), namely phosphotetradecavanadate (Na7[H2PV14O42], hereafter described as PV14), into the graphene oxide (GO) matrix creates a novel hybrid material for SC applications. Owing to the formation of nanohybrid, it can store charges both electrostatically and electrochemically. PV14/GO composite’s electrochemical behavior in different electrolyte (acidic/neutral) solutions shows different types of characteristics. The PV14/GO composite as a working electrode exhibits a high galvanostatic capacitance of 139 F/g while maintaining at a power density of 97.94 W/kg in 0.25 M H2SO4 electrolyte. The specific energy density was also found out to be around 56.58 Wh/kg at a 5 mV/s scan rate for the same electrolyte. Furthermore, in 1 M Na2SO4 solution, PV14/GO composite demonstrates a specific capacitance of 85.4 F/g at a scan rate of 5 mV/s. The equivalent series resistance for the device was found to be approximately 0.51 ? with a circuit resistance of 3.881 ?, using electrochemical impedance spectroscopy. The cell capacitance, employing the Nyquist plot, was calculated to be around 2.78 mF. © 2021, ASM International.Item 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 Electrochemical performance of activated carbon-supported vanadomolybdates electrodes for energy conversion(Elsevier Ltd, 2021) Maity, S.; Anandan Vannathan, A.; Kella, T.; Shee, D.; Das, P.P.; Mal, S.Reinforcing polyoxomolybdates (POMs) into the activated carbon (AC) template engenders a nanohybrid electrode material for high-performance supercapacitor applications. Herein, a first-time novel integration of two polyoxometalates ([PVMo11O40]4-, [PV2Mo10O40]5-) with AC has been demonstrated, and their structural and electrochemical performances were analyzed. AC-VMo11 composite displayed an enhanced capacitance of 450 Fg-1 with an improved energy density of 59.7 Whkg-1. Furthermore, the symmetric supercapacitor cell for AC-VMo11 and AC-V2Mo10 showed high cell capacitances of 38.8 and 20.01 mF, respectively, alongside 99.99% capacitance retention of over 5000 cycles. In addition, the influence of ionic liquid as an electrolyte on AC-V2Mo10 based supercapacitor cell was investigated in tetrabutylammonium bromide (TBAB) electrolyte solution. © 2021 Elsevier Ltd and Techna Group S.r.l.Item Polyoxomolybdate-Polypyrrole-Graphene Oxide Nanohybrid Electrode for High-Power Symmetric Supercapacitors(American Chemical Society, 2021) Maity, S.; Je, M.; Biradar, B.R.; Chandewar, P.R.; Shee, D.; Das, P.P.; Mal, S.Supercapacitors have emerged as one of the most promising candidates for high-performance, safe, clean, and economical routes to store and release of nonfossil energy. Designing hybrid materials by integrating double-layer and pseudocapacitive materials is crucial to achieving high-power and high-energy storage devices simultaneously. Herein, we synthesized a polyoxomolybdate-polypyrrole-graphene oxide nanohybrid via a one-pot reaction. The inclusion of polypyrrole enables a uniform distribution of the polyoxomolybdate clusters; it also confines the restacking of graphene oxide nanosheets. The structural and morphological analysis to unveil the nanohybrid architecture implies excellent interfacial contact, enabling fast redox reaction of polyanions, and a quick transfer of charge to the interfaces. Electrochemical characteristics tested under a two-electrode system exhibit the highest capacitance of 354 F g-1 with significantly high specific energy and power of 49.16 Wh kg-1 and 999.86 W kg-1, respectively. In addition, the cell possesses a high-rate capability and long cycle life by maintaining 96% of its capacitance over 5000 sweeping cycles. The highest specific power of ?10 »000 W kg-1 was computed with Coulombic efficiency of 92.30% at 5 A g-1 current density. Electrochemical impedance spectroscopy additionally reveals enhanced redox charge transfer due to double hybridization. Furthermore, it also demonstrates the impedance and capacitive behavior of supercapacitor cells over a definite frequency regime. ©Item Decavanadate-graphene oxide nanocomposite as an electrode material for electrochemical capacitor(Taylor and Francis Ltd., 2022) Maity, S.; Das, P.P.; Mal, S.We have synthesized new electrode material for the supercapacitor application. Polyoxovanadates (POVs) have been used for energy storage electrode materials due to their fast multi-electron redox properties. The formation of SDV/GO composites was confirmed using various analytical methods, e.g., Fourier transforms infrared spectroscopy (FTIR) and powder X-ray diffraction (XRD), followed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composite electrode’s electrochemical behavior was studied using a neutral 1 M sodium sulphate (Na2SO4) solution in three-electrode cyclic voltammetry (CV) system. The SDV/GO composite electrode showed a specific capacitance of 306 F/g for a scan rate of 5 mV/s and a corresponding energy density of 42.4 Wh/Kg. Galvanostatic charge/discharge exhibits a specific capacitance of 310 F/g with energy densities of 43.08 Wh/kg. Electrochemical impedance spectroscopy (EIS), which was used to investigate interface property, yielded a considerably higher power density of 172.41 KW/kg with an equivalent series resistance of 5 ?. © 2021 Informa UK Limited, trading as Taylor & Francis Group.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 DFT Calculations for Temperature Stable Quantum Capacitance of VS2 Based Electrodes for Supercapacitors(Institute of Electrical and Electronics Engineers Inc., 2024) Yadav, A.K.; Shreevathsa, N.S.; Singh, R.; Das, P.P.; Garg, V.; Pandey, S.K.Using density functional theory calculations, we demonstrate the quantum capacitance of the VS2 electrode which can be improved by doping with non-metallic elements such as nitrogen (N), phosphorus (P), and arsenic (As) atoms. The radius, charge, and morphology of these non-metallic elements help to improve the performance of VS2 material as electrodes of supercapacitors. The As-doped VS2 monolayer demonstrated the maximum quantum capacitance of 31.2369 μF/cm2 at 300 K. At 1200 K, quantum capacitance reaches the value of 25.2149 μF/cm2, showing the inconsiderable change in value for this wide range of temperature variation. Additionally, the other important properties of undoped and doped VS2 monolayers such as density of states, energy band structure, electrical conductivity, thermal conductivity, and the Seebeck coefficient were also computed and examined in detail. The band structure of the P and As-doped VS2 monolayers showed a metallic nature, which is suitable for electrode application. In the case of As-doped VS2 material, a high figure of merit of 3.536 was observed by using DFT-D2 calculations, due to the large Seebeck coefficient and significant electrical conductivity. Our findings will be helpful in further exploring the suitability of VS2 monolayers as electrodes of supercapacitors. © 2002-2012 IEEE.