Faculty Publications
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Item Nano ZnO-activated carbon composite electrodes for supercapacitors(2010) Muthu, M.S.; Bhat, D.K.; Aggarwal, A.; Prahladh Iyer, S.; Sravani, G.A symmetrical (p/p) supercapacitor has been fabricated by making use of nanostructured zinc oxide (ZnO)-activated carbon (AC) composite electrodes for the first time. The composites have been characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction analysis (XRD). Electrochemical properties of the prepared nanocomposite electrodes and the supercapacitor have been studied using cyclic voltammetry (CV) and AC impedance spectroscopy in 0.1 M Na2SO4 as electrolyte. The ZnO-AC nanocomposite electrode showed a specific capacitance of 160 F/g for 1:1 composition. The specific capacitance of the electrodes decreased with increase in zinc oxide content. Galvanostatic charge-discharge measurements have been done at various current densities, namely 2, 4, 6 and 7 mA/cm2. It has been found that the cells have excellent electrochemical reversibility and capacitive characteristics in 0.1 M Na2SO4 electrolyte. It has also been observed that the specific capacitance is constant up to 500 cycles at all current densities. © 2010 Elsevier B.V. All rights reserved.Item Molecular dynamics investigation of dipeptide - Transition metal salts in aqueous solutions(American Chemical Society service@acs.org, 2010) Santosh, M.S.; Lyubartsev, A.; Mirzoev, A.; Bhat, D.K.Molecular dynamics (MD) simulations of glycylglycine dipeptide with transition metal ions (Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+) in aqueous solutions have been carried out to get an insight into the solvation structure, intermolecular interactions, and salt effects in these systems. The solvation structure and hydrogen bonding were described in terms of radial distribution function (RDF) and spatial distribution function (SDF). The dynamical properties of the solvation structure were also analyzed in terms of diffusion and residence times. The simulation results show the presence of a well-defined first hydration shell around the dipeptide, with water molecules forming hydrogen bonds to the polar groups of the dipeptide. This shell is, however, affected by the strong electric field of divalent metal ions, which at higher ion concentrations lead to the shift in the dipeptide-water RDFs. Higher salt concentrations lead also to increased residence times and slower diffusion rates. In general, smaller ions (Cu2+, Zn2+) demonstrate stronger binding to dipeptide than the larger ones (Fe2+, Mn 2+). Simulations do not show any stronger association of peptide molecules indicating their dissolution in water. The above results may be of potential interest to future researchers on these molecular interactions. © 2010 American Chemical Society.Item Zn: a versatile resonant dopant for SnTe thermoelectrics(Elsevier Ltd, 2019) Bhat, D.K.; Shenoy, U.S.SnTe-based materials have been receiving increasing heed in the field of thermoelectrics (TEs) because of their tunable electronic structure. Until now, only In and Bi are reported to introduce resonance level in SnTe. In this work, for the very first time, we report Zn as a resonant dopant in SnTe using first-principles density functional theory calculations. We show that the resonant states introduced by Zn raises the heavy hole valence sub-band above light hole valence sub-band leading to both record high room temperature Seebeck coefficient (~127 ?VK?1 at 300 K) and figure of merit, ZT (~0.28 at 300 K) for SnTe-based materials. The transport properties calculated using Boltzmann transport equations predicts Zn-doped SnTe to be a promising TE material, further confirmed by experimental ZTmaximum of ~1.49 at 840 K and ZTaverage of ~0.78 with 300 K and 840 K as cold and hot ends, respectively. © 2019 Elsevier LtdItem Bi and Zn co-doped SnTe thermoelectrics: Interplay of resonance levels and heavy hole band dominance leading to enhanced performance and a record high room temperature: ZT(Royal Society of Chemistry, 2020) Shenoy, U.S.; Bhat, D.K.Lead free SnTe with a tunable electronic structure has become the front runner in eco-friendly thermoelectrics. Herein, we show through first-principles density functional theory calculations that Bi and Zn doping introduces a resonance level in SnTe. The dominance of the heavy hole valence band at room temperature in Bi-Zn co-doped SnTe leads to a record high room temperature ZT of ?0.3 (at 300 K) for SnTe based materials. The increase in the Seebeck coefficient value due to the interaction between the resonance states and formation of the nanoprecipitates leading to an appreciably low lattice thermal conductivity of 0.68 W m-1 K-1 results in a peak ZT of ?1.6 at 840 K. A record high ZTaverage of ?0.86 with 300 K and 840 K as cold and hot ends, respectively, makes Bi-Zn co-doped SnTe a potential material for thermoelectric applications. This strategy of using two resonant dopants, to not only improve the room temperature ZT but also high temperature values, can very well be extended to other systems. This journal is © The Royal Society of Chemistry.Item SnTe thermoelectrics: Dual step approach for enhanced performance(Elsevier Ltd, 2020) Bhat, D.K.; Shenoy, U.S.Doping of SnTe to achieve desirable properties has been a wide spread approach in the recent past to enhance its thermoelectric performance. Herein, we apply a dual approach: Pb doping for reduction of thermal conductivity and Zn doping for improving the power factor. The theoretical prediction of enhanced Seebeck due to increase in the band gap, introduction of the resonance levels by Zn and dominance of the heavy hole valence band, is realized experimentally as improved power factor throughout the temperature range. The accompanying reduction in the thermal conductivity by co-doping Pb and Zn leads to a record high room temperature figure of merit, ZT of 0.35 (@ 300K) and ZT of 1.66 at 840 K. The ZTaverage of ?0.9 with 300 K as cold end and 840 K as hot end sets a new record for SnTe based materials. © 2020 Elsevier B.V.Item Resonance levels in GeTe thermoelectrics: Zinc as a new multifaceted dopant(Royal Society of Chemistry, 2020) Bhat, D.K.; Shenoy, U.S.Recently doping has been widely used in enhancing the thermoelectric properties of lead-free GeTe. But much of the work has been concentrated on carrier concentration tuning or phonon scattering. Until now, only indium has been reported to be the best resonant dopant in cubic GeTe. Herein, for the first time we introduce zinc as a resonant dopant to the cubic GeTe family. We show that zinc in GeTe not only introduces resonance states but also increases the band gap and raises the heavy hole valence band above the light hole valence band leading to enhanced Seebeck values. This multifunctional dopant incorporation in GeTe leads to enhanced transport properties as predicted by Boltzmann transport properties calculations based on first principles density functional theory electronic structure calculations. This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.Item Electronic structure modulation of Pb0.6Sn0.4Te via zinc doping and its effect on the thermoelectric properties(Elsevier Ltd, 2021) Shenoy, U.S.; Bhat, D.K.Striking a balance between the high performance and detrimental environmental toxicity of PbTe materials in thermoelectrics (TE) has become a necessity in the current situation. In this context, improving the performance of materials with lower lead content to the level of PbTe is crucial. Herein, we engineer the electronic structure of Pb0.6Sn0.4Te, a well-known TCI but a poor TE material by doping Zn. The first principles calculation reveal that Zn doping introduces multiple electronic valleys while simultaneously opening the band gap of Pb0.6Sn0.4Te. Higher power factor with lower thermal conductivity is predicted by the transport property calculations in the doped material. The resonance level introduced along with features of hyper-convergence of the valence bands leads to improved Seebeck co-efficient throughout the studied temperature range. An experimental figure of merit, ZT of ~1.57 at 840 K promises us a TE material applicable for a broad temperature range for future energy applications. © 2021 Elsevier B.V.Item Selective co-doping improves the thermoelectric performance of SnTe: An outcome of electronic structure engineering(Elsevier Ltd, 2022) Shenoy, U.S.; Bhat, D.K.Thermoelectric materials which exhibit high performance throughout a range of temperature is required for successful scavenging of waste heat to generate electricity. Herein, we tailor the electronic structure of SnTe by co-doping Zn with three elements namely Ag, Ca and Mg. We observe that the dopants play complementary roles and improve the thermoelectric performance throughout the studied temperature range. Zn introduces resonance level and causes hyper-convergence to increase the Seebeck at low temperatures while M (M = Ag, Ca, Mg) enlarges the band gap preventing bipolar transport and also helps in the band convergence improving the performance at higher temperatures. The enhanced thermoelectric properties predicted by theoretical calculations is supported by experimental results. For the same concentration of doping, AgZn co-doped SnTe exhibits higher performance compared to the other two with an impressive ZT of ~1.54 at 840 K and average ZT of ~0.97 between 500 K and 840 K. © 2021 Elsevier B.V.