Mihir Sahoo | IIT Bhubaneswar (original) (raw)
Papers by Mihir Sahoo
Oxford Open Materials Science
Metal matrix composites have attracted extensive attention from both the research and industrial ... more Metal matrix composites have attracted extensive attention from both the research and industrial perspective. In this study, we prepared aluminum-reduced graphene oxide (Al–rGO) composites with enhanced thermal conductivity in an easy single-step process. Pristine Al shows a thermal conductivity of 175 Wm−1K−1 (standard deviation <5%), which increases to 293 Wm−1K−1 for an Al–rGO composite with 1% rGO. Analysis of theoretical models shows that a higher percentage of rGO inside the Al matrix creates a continuous network resulting in more available phase space through which heat carrier phonons travel with less scattering, and hence thermal conductivity of the composite increases. Furthermore, Al–rGO composites show an ∼5% increase in microhardness compared with pristine Al. The electrical resistivity of the composite is comparable to that of pristine Al for a narrow weight percentage of rGO, whereas a 70% enhancement in the thermal conductivity of the composite is observed for the...
IOP conference series, Mar 1, 2022
Abstarct. Two dimensional (2D) derivatives of tin (Sn) have obtained special deliberations recent... more Abstarct. Two dimensional (2D) derivatives of tin (Sn) have obtained special deliberations recently due to practical realization of planar, as well as, buckled hexagonal lattice of Sn called stanene. However, it has been observed that proper choice of substrate is very important for growth of stanene like films owing to large core size of Sn that prefers sp 3 hybridization over sp 2. Transition metal dichalcogenides (TMDs) like MoS2 or WS2 with honey comb lattice structure seem to be promising substrate candidates for 2D growth of Sn. In the present work, we report mechanical exfoliation of few layers of WS2 under ultra-high vacuum (UHV) conditions and investigations of growth and local electronic structure by in-situ scanning tunneling microscopy (STM) and spectroscopy (STS) studies. Flat WS2 surface with honeycomb lattice structure in the atomic scale with a lattice constant of 0.34 nm is evident in the STM investigations, whereas, STS measurements reveal local density of states (LDOS) of WS2 with a bandgap of approximately 1.34 eV. Density functional theory (DFT) calculations performed by considering bulk WS2 reveal conduction and valence band states comprised of S p and W d at both sides of the Fermi energy (EF) and an indirect bandgap of 1.38 eV. Experimental observations upon Sn adsorption, reveal commensurate growth of Sn atoms on the sulfur `S’ sites with a buckling height of 40 ±10 pm. STS measurements exhibit local electronic structure of the Sn adsorbed surface with clear evidence of in-gap states. DFT calculations quantify the experimental results demonstrating `S’ sites as the most stable sites for the atomic adsorption of Sn with a buckling height of around 80 pm and reveal signature of in-gap hybridized states comprised of Sn p and W d orbitals.
Materials Today Chemistry, 2021
Abstract In the past few years, Pb-free metal halide perovskites have been recognized as a promis... more Abstract In the past few years, Pb-free metal halide perovskites have been recognized as a promising material for various optoelectronic applications because of some of their unique features, such as direct and tunable bandgap, visible light emission, narrow emission spectra, lower toxicity level, and easy solution processability. Recently, several Bi-based perovskite-like single crystals (SCs) and nanocrystals (NCs) were reported, which are mostly suffering from their poor structural stability and lower emission intensity. Here, we report the growth of millimeter-sized formamidinium bismuth bromide (FA3Bi2Br9) perovskite SCs via slow solvent evaporation method. They crystallized into a trigonal crystal structure and exhibit an indirect bandgap of 2.71 eV. These results are supported by the first-principle density-functional theory studies. We have also synthesized nanometer-sized spherical blue-emitting FA3Bi2Br9 NCs by solvent ligand-assisted reprecipitation method and achieved a maximum photoluminescence quantum yield of 22%. We observe that the addition of excess ligands into the FA3Bi2Br9 NCs solution before the purification step significantly improves the optical and colloidal stability of the NCs.
Journal of Materials Science: Materials in Electronics
Hotspot engineering has the potential to transform the field of Surface-Enhanced Raman Spectrosco... more Hotspot engineering has the potential to transform the field of Surface-Enhanced Raman Spectroscopy (SERS) by enabling ultra-sensitive and reproducible detection of analytes. However, the ability to controllably generate SERS hotspots, with desired location and geometry, over large-area substrates, has remained elusive. In this study, we sculpt artificial edges in monolayer Molybdenum Disulfide (MoS2) by low-power focused laser-cutting. We find that when gold nanoparticles (AuNPs) are deposited on MoS2 by drop-casting, the AuNPs tend to accumulate predominantly along the artificial edges. First-principles density functional theory (DFT) calculations indicate strong binding of AuNPs with the artificial edges due to dangling bonds that are ubiquitous on the un-passivated (laser-cut) edges. The dense accumulation of AuNPs along the artificial edges intensifies plasmonic effects in these regions creating hot spots exclusively along the artificial edges. DFT further indicates that adsorption of AuNPs along the artificial edges prompts a transition from semiconducting to metallic behavior, which can further intensify the plasmonic effect along the artificial edges. These effects are observed exclusively for the sculpted (i.e., cut) edges and not observed for the MoS2 surface (away from the cut edges) or along the natural (passivated) edges of the MoS2 sheet. To demonstrate the practical utility of this concept, we use our substrate to detect Rhodamine B (RhB) with large SERS enhancement (~104) at the hotspots for RhB concentrations as low as ~10-10 M. The single-step laser etching process reported here can be used to controllably generate arrays of SERS hotspots. As such, this concept offers several advantages over previously reported SERS substrates that rely on electro-chemical deposition, e-beam lithography, nanoimprinting or photolithography. While we have focused our study on MoS2, this concept could in principle, be extended to a variety of 2D material platforms.
A universal activity descriptor for catalytic alkaline hydrogen evolution reaction (HER) was unav... more A universal activity descriptor for catalytic alkaline hydrogen evolution reaction (HER) was unavailable, though metal-hydrogen binding energy can be considered as a good such descriptor in acidic medium. Herein, with the help of experimental and first principles density functional theory (DFT) based studies, we have shown that structural changes in the water coordination in electrolytes having high alkalinity can be a possible reason for the reduced catalytic activity of platinum (Pt) in high pH. Studies with polycrystalline Pt electrodes indicate that electrocatalytic HER activity reduces in terms of high overpotential required, high Tafel slope, and high charge transfer resistances in concentrated aqueous alkaline electrolytes (say 6M KOH) in comparison to that in low alkaline electrolytes (say 0.1M KOH), irrespective of the counter cations (Na+, K+ or Rb+) present. The changes in the water structure of bulk electrolytes with concentration are established using Raman, infrared, a...
The Journal of Physical Chemistry C, 2022
Journal of Electronic Materials, 2020
Owing to its high energy density, high specific capacity, and low self-discharge rate, the Li-ion... more Owing to its high energy density, high specific capacity, and low self-discharge rate, the Li-ion battery (LIB) has been implemented in a wide area of applications starting from small electronic devices to large electric vehicles. However, the use of LIBs in electric vehicles has not yet been commercialized on a large scale due to the unavailability of suitable electrolytic solvents for highvoltage LIBs. Recently, fluorinated carbonates have gained much attention as potential high-voltage electrolytes for having desirable physical properties such as low melting points, low flammability, and high electrochemical stability. However, the solvation properties of Li + in electrolytic fluorinated carbonates solvents require detailed investigations. With the first-principles calculations, the present work provides a comparative study of the structural, electronic, thermochemical and solvation properties of Li + solvated by fluoroethylene carbonate (FEC), trifluoropropylene carbonate (TFPC), i.e., Li +-(FEC) n and Li +-(TFPC) n , where n = 1-4. We have found that the structural properties, e.g., bond length C=O (of carbonyl) and associated infrared (IR) frequency, show similar variation for both the fluorinated Li-carbonate complexes. However, higher solvation energy and lower desolvation energy for the TFPC than the FEC show the opposite nature of their respective pristine carbonate counterparts. Our result, i.e., superior solvation energy of TFPC compared to FEC, is in good agreement with the experimentally developed solvating power series. Based on the solvation/desolvation energy, we conclude that TFPC could be a better high-voltage electrolyte for LIBs.
AIP Advances, 2020
A simple yet innovative approach has been made through a powder metallurgy route for the synthesi... more A simple yet innovative approach has been made through a powder metallurgy route for the synthesis of aluminum-graphene (Al-Gr) composite materials for commercially viable solar thermal collectors. The Al-Gr composite (with 1 wt. % of graphene filler content) recorded an enhanced thermal conductivity of ∼280 W/mK, which is higher than that of pristine Al (∼124 W/mK), at room temperature. It has also been found that the prepared composite has a lower coefficient of thermal expansion. The structures and morphologies of the composites have been investigated in detail with the help of X-ray diffraction technique, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, etc. Furthermore, the density measurements showed that the composites retain ∼97.5% of the density of pristine aluminum even after the sintering treatment. X-ray micro-computed tomography revealed the structural integrity and non-porous nature of the samples, free from any defects and deformations. The thermal fusing of Al-based composite materials at 630 ○ C is found to be satisfactory with the required strength, and the composites showed at least ∼125% increase in the thermal conductivity than that of pristine Al. These results suggest that the Al-Gr composites can be deployed as solar thermal collectors and heat sink materials for thermal dissipation.
AIP Conference Proceedings, 2018
Li-ion battery has wide area of application starting from low power consumer electronics to high ... more Li-ion battery has wide area of application starting from low power consumer electronics to high power electric vehicles. However, their large scale application in electric vehicles requires further improvement due to their low specific power density which is an essential parameter and is closely related to the working potential windows of the battery system. Several studies have found that these parameters can be taken care of by considering different cathode/anode materials and electrolytes. Recently, a unique approach has been reported on the basis of cluster size in which the use of Li3 cluster has been suggested as a potential component of the battery electrode material. The cluster based approach significantly enhances the working electrode potential up to ~0.6V in the acetonitrile solvent. In the present work, using ab-initio quantum chemical calculation and the dielectric continuum model, we have investigated various dielectric solvent medium for the suitable electrolyte for the potential component Li3 cluster. This study suggests that high dielectric electrolytic solvent (ethylene carbonate and propylene carbonate) could be better for lithium cluster due to improvement in the total electrode potential in comparison to the other dielectric solvent.Li-ion battery has wide area of application starting from low power consumer electronics to high power electric vehicles. However, their large scale application in electric vehicles requires further improvement due to their low specific power density which is an essential parameter and is closely related to the working potential windows of the battery system. Several studies have found that these parameters can be taken care of by considering different cathode/anode materials and electrolytes. Recently, a unique approach has been reported on the basis of cluster size in which the use of Li3 cluster has been suggested as a potential component of the battery electrode material. The cluster based approach significantly enhances the working electrode potential up to ~0.6V in the acetonitrile solvent. In the present work, using ab-initio quantum chemical calculation and the dielectric continuum model, we have investigated various dielectric solvent medium for the suitable electrolyte for the potential componen...
AIP Conference Proceedings, 2018
Due to high in-plane charge carrier mobility with high electron velocity and long spin diffusion ... more Due to high in-plane charge carrier mobility with high electron velocity and long spin diffusion length, graphene guarantees as a completely unique material for devices with various applications. Unaffected 2pz orbitals of carbon atoms in graphene can be highly influenced by substrates and leads to tuning in electronic properties. We report here a density functional calculation of graphene monolayer based on metallic substrate like nickel surfaces. Band-gap of graphene near K points opens due to interactions between 2pz and d-orbitals of nickel atoms and the gap modulation can be done with the increasing number of layers of substrates.
Ceramics International, 2019
Urchin-like microsphere of NiCo 2 O 4 /NIC sample was synthesized by hydrothermal method, followe... more Urchin-like microsphere of NiCo 2 O 4 /NIC sample was synthesized by hydrothermal method, followed by post annealing treatment at 400°C for 3 h. The phase confirmation and surface morphology was analyzed by XRD, FESEM and Raman spectroscopy, which shows that cubic spinel structure with Fd3m space group supporting the microstructure. The elemental mappings were characterized by EDS analysis. The electrochemical performance revealed that the prepared NIC sample exhibits specific capacitance of 295Fg-1 at 20 mV −1 owing to its high surface area; consist of interconnection of nanopores between the subunit of nanoneedle inside the urchin like microsphere. The optical band gap energy was estimated by using Tauc plot, are 2.17eV and 3.5eV respectively. This result well consistent with the theoretical investigation by using DFT calculation. Furthermore a significant M-H loop revealed that, NIC system shows ferromagnetic behavior at RT. Hence all the combined experimental and theoretical results provide to design synergetic microstructure of NIC system for multifunctional application.
ACS Applied Materials & Interfaces, 2019
The Journal of Physical Chemistry C, 2018
Journal of Magnetism and Magnetic Materials, 2019
High in-plane charge carrier mobility and long spin diffusion length makes graphene a unique mate... more High in-plane charge carrier mobility and long spin diffusion length makes graphene a unique material for spin-based devices. However, in a vertical graphene junction, the 2p z orbitals of carbon atoms in graphene can be tuned via suitable magnetic substrates; this would affect the spin injection into graphene. Here, a vertical spin switch has been designed by embedding a single layer of graphene as a tunnel layer between the Ni (111) substrate. Periodic density functional approach in conjunction with Julliere's model is used to calculate the tunnel magnetoresistance (TMR). Further, single-layered hexagonal Boron Nitride (h-BN) is sandwiched between the graphene and Ni (111) substrate to understand the role of hybridization at the interface on TMR. Our calculation shows that in contrast to the graphene junction, a much higher TMR value is obtainable in the case of the graphene/h-BN multi-tunnel junction (MTJ). The TMR in graphene junction is found to decrease with the increase of an externally applied electric field, and drops to zero for a field greater than equal to 0.16 eV/Å. Similar phenomenon was observed in the case of h-BN/graphene MTJ, where TMR value remains unchanged for electric field up to 0.1 eV/Å beyond which it drops to zero. The change in hybridization and charge-carrier-population at the interface modifies the magnetic exchange interaction and magnetic anisotropy resulting in a spin flip at interface, leads to rapid drop in TMR after a threshold electric field. The high and tunable TMR value suggests h-BN assisted high performance graphene based vertical spin switch.
ChemistrySelect, 2019
The donor-acceptor orbital interaction between the unoccupied orbital of Li + and the lone pair o... more The donor-acceptor orbital interaction between the unoccupied orbital of Li + and the lone pair of oxygen atoms in the carbonyl group of Li +-carbonate complexes shows significant decrease on fluorination. This has been investigated through molecular orbital formalism based density functional theory. The fluorination process lowers the binding energy (reduced up to 13.8 kcal/mol), and widens the HOMO-LUMO gap (enhanced up to 0.7 eV), which is essential for achieving electrolytes with high potential window in Li-ion battery. Furthermore, the impact of fluorination on few critical factors has been observed, i. e. dipole moment (drastic enhancement), IR spectra (most affected C=O vibrational mode shows blue shift in the spectra) and Raman active mode (carbonyl group stretching mode doublet (n C<C¼>O) shifted to higher frequency) which have been probed by vibrational frequency analysis.
ACS Catalysis, 2018
Enhancing the intrinsic activity of a benchmarked electrocatalyst such as platinum (Pt) is highly... more Enhancing the intrinsic activity of a benchmarked electrocatalyst such as platinum (Pt) is highly intriguing from fundamental as well as applied perspectives. In this work, hydrogen evolution reaction (HER) activity of Pt electrodes, benchmarked HER catalysts, modified with ultrathin sheets of hexagonal boron nitride (h-BN) is studied in acidic medium (Pt/h-BN), and augmented HER performance, in terms of the overpotential at a 10 mA cm–2 current density (10 mV lower than that of Pt nanoparticles) and a lower Tafel slope (29 ± 1 mV/decade), of the Pt/h-BN system is demonstrated. The effects of h-BN surface modification of bulk Pt as well as Pt nanoparticles are studied, and the origin of such an enhanced HER activity is probed using density functional theory-based calculations. The HER charge transfer resistance of h-BN-modified Pt is found to be drastically reduced, and this enhances the charge transfer kinetics of the Pt/h-BN system because of the synergistic interaction between h-BN and Pt. An enormous ...
Carbon, 2018
We have investigated here, the electronic and magnetic properties of graphene-nickel system by ti... more We have investigated here, the electronic and magnetic properties of graphene-nickel system by tight-binding mean-field approach. Strong hybridization between the 2p z orbital of graphene and 3d z2 orbital of nickel occurs when monolayer graphene is placed over a single layer of ferromagnetically ordered Ni (111) metal due to the excellent lattice matching between the two layers. This hybridization greatly affects the electronic and magnetic properties of the bilayer system, resulting in a significantly reduced local magnetic moment of the nickel layer and an enhanced induced spin polarization on the graphene layer. The calculated Hamiltonian revealed critical information regarding the first-, second-and third-nearest-neighbor hopping integrals of electrons ofgraphene besides the Coulomb correlation of electrons in nickel-(111). The Hubbard type Coulomb interactions present in nickel lattices were treated within the mean-field approximation. Zubarev's technique was employed to calculate electronic Green's functions and subsequent investigation of the temperature dependent ferromagnetic magnetization of nickel (111)was carried out through self-consistent calculation. Further calculations regarding the induced magnetization in the graphene, total magnetization in bilayer layer system, electronic band dispersion, spin resolved density of states (DOS)and spin polarization efficiency have been carried out. The results were corroborated by experimental observations.
Journal of Cluster Science, 2017
Oxford Open Materials Science
Metal matrix composites have attracted extensive attention from both the research and industrial ... more Metal matrix composites have attracted extensive attention from both the research and industrial perspective. In this study, we prepared aluminum-reduced graphene oxide (Al–rGO) composites with enhanced thermal conductivity in an easy single-step process. Pristine Al shows a thermal conductivity of 175 Wm−1K−1 (standard deviation <5%), which increases to 293 Wm−1K−1 for an Al–rGO composite with 1% rGO. Analysis of theoretical models shows that a higher percentage of rGO inside the Al matrix creates a continuous network resulting in more available phase space through which heat carrier phonons travel with less scattering, and hence thermal conductivity of the composite increases. Furthermore, Al–rGO composites show an ∼5% increase in microhardness compared with pristine Al. The electrical resistivity of the composite is comparable to that of pristine Al for a narrow weight percentage of rGO, whereas a 70% enhancement in the thermal conductivity of the composite is observed for the...
IOP conference series, Mar 1, 2022
Abstarct. Two dimensional (2D) derivatives of tin (Sn) have obtained special deliberations recent... more Abstarct. Two dimensional (2D) derivatives of tin (Sn) have obtained special deliberations recently due to practical realization of planar, as well as, buckled hexagonal lattice of Sn called stanene. However, it has been observed that proper choice of substrate is very important for growth of stanene like films owing to large core size of Sn that prefers sp 3 hybridization over sp 2. Transition metal dichalcogenides (TMDs) like MoS2 or WS2 with honey comb lattice structure seem to be promising substrate candidates for 2D growth of Sn. In the present work, we report mechanical exfoliation of few layers of WS2 under ultra-high vacuum (UHV) conditions and investigations of growth and local electronic structure by in-situ scanning tunneling microscopy (STM) and spectroscopy (STS) studies. Flat WS2 surface with honeycomb lattice structure in the atomic scale with a lattice constant of 0.34 nm is evident in the STM investigations, whereas, STS measurements reveal local density of states (LDOS) of WS2 with a bandgap of approximately 1.34 eV. Density functional theory (DFT) calculations performed by considering bulk WS2 reveal conduction and valence band states comprised of S p and W d at both sides of the Fermi energy (EF) and an indirect bandgap of 1.38 eV. Experimental observations upon Sn adsorption, reveal commensurate growth of Sn atoms on the sulfur `S’ sites with a buckling height of 40 ±10 pm. STS measurements exhibit local electronic structure of the Sn adsorbed surface with clear evidence of in-gap states. DFT calculations quantify the experimental results demonstrating `S’ sites as the most stable sites for the atomic adsorption of Sn with a buckling height of around 80 pm and reveal signature of in-gap hybridized states comprised of Sn p and W d orbitals.
Materials Today Chemistry, 2021
Abstract In the past few years, Pb-free metal halide perovskites have been recognized as a promis... more Abstract In the past few years, Pb-free metal halide perovskites have been recognized as a promising material for various optoelectronic applications because of some of their unique features, such as direct and tunable bandgap, visible light emission, narrow emission spectra, lower toxicity level, and easy solution processability. Recently, several Bi-based perovskite-like single crystals (SCs) and nanocrystals (NCs) were reported, which are mostly suffering from their poor structural stability and lower emission intensity. Here, we report the growth of millimeter-sized formamidinium bismuth bromide (FA3Bi2Br9) perovskite SCs via slow solvent evaporation method. They crystallized into a trigonal crystal structure and exhibit an indirect bandgap of 2.71 eV. These results are supported by the first-principle density-functional theory studies. We have also synthesized nanometer-sized spherical blue-emitting FA3Bi2Br9 NCs by solvent ligand-assisted reprecipitation method and achieved a maximum photoluminescence quantum yield of 22%. We observe that the addition of excess ligands into the FA3Bi2Br9 NCs solution before the purification step significantly improves the optical and colloidal stability of the NCs.
Journal of Materials Science: Materials in Electronics
Hotspot engineering has the potential to transform the field of Surface-Enhanced Raman Spectrosco... more Hotspot engineering has the potential to transform the field of Surface-Enhanced Raman Spectroscopy (SERS) by enabling ultra-sensitive and reproducible detection of analytes. However, the ability to controllably generate SERS hotspots, with desired location and geometry, over large-area substrates, has remained elusive. In this study, we sculpt artificial edges in monolayer Molybdenum Disulfide (MoS2) by low-power focused laser-cutting. We find that when gold nanoparticles (AuNPs) are deposited on MoS2 by drop-casting, the AuNPs tend to accumulate predominantly along the artificial edges. First-principles density functional theory (DFT) calculations indicate strong binding of AuNPs with the artificial edges due to dangling bonds that are ubiquitous on the un-passivated (laser-cut) edges. The dense accumulation of AuNPs along the artificial edges intensifies plasmonic effects in these regions creating hot spots exclusively along the artificial edges. DFT further indicates that adsorption of AuNPs along the artificial edges prompts a transition from semiconducting to metallic behavior, which can further intensify the plasmonic effect along the artificial edges. These effects are observed exclusively for the sculpted (i.e., cut) edges and not observed for the MoS2 surface (away from the cut edges) or along the natural (passivated) edges of the MoS2 sheet. To demonstrate the practical utility of this concept, we use our substrate to detect Rhodamine B (RhB) with large SERS enhancement (~104) at the hotspots for RhB concentrations as low as ~10-10 M. The single-step laser etching process reported here can be used to controllably generate arrays of SERS hotspots. As such, this concept offers several advantages over previously reported SERS substrates that rely on electro-chemical deposition, e-beam lithography, nanoimprinting or photolithography. While we have focused our study on MoS2, this concept could in principle, be extended to a variety of 2D material platforms.
A universal activity descriptor for catalytic alkaline hydrogen evolution reaction (HER) was unav... more A universal activity descriptor for catalytic alkaline hydrogen evolution reaction (HER) was unavailable, though metal-hydrogen binding energy can be considered as a good such descriptor in acidic medium. Herein, with the help of experimental and first principles density functional theory (DFT) based studies, we have shown that structural changes in the water coordination in electrolytes having high alkalinity can be a possible reason for the reduced catalytic activity of platinum (Pt) in high pH. Studies with polycrystalline Pt electrodes indicate that electrocatalytic HER activity reduces in terms of high overpotential required, high Tafel slope, and high charge transfer resistances in concentrated aqueous alkaline electrolytes (say 6M KOH) in comparison to that in low alkaline electrolytes (say 0.1M KOH), irrespective of the counter cations (Na+, K+ or Rb+) present. The changes in the water structure of bulk electrolytes with concentration are established using Raman, infrared, a...
The Journal of Physical Chemistry C, 2022
Journal of Electronic Materials, 2020
Owing to its high energy density, high specific capacity, and low self-discharge rate, the Li-ion... more Owing to its high energy density, high specific capacity, and low self-discharge rate, the Li-ion battery (LIB) has been implemented in a wide area of applications starting from small electronic devices to large electric vehicles. However, the use of LIBs in electric vehicles has not yet been commercialized on a large scale due to the unavailability of suitable electrolytic solvents for highvoltage LIBs. Recently, fluorinated carbonates have gained much attention as potential high-voltage electrolytes for having desirable physical properties such as low melting points, low flammability, and high electrochemical stability. However, the solvation properties of Li + in electrolytic fluorinated carbonates solvents require detailed investigations. With the first-principles calculations, the present work provides a comparative study of the structural, electronic, thermochemical and solvation properties of Li + solvated by fluoroethylene carbonate (FEC), trifluoropropylene carbonate (TFPC), i.e., Li +-(FEC) n and Li +-(TFPC) n , where n = 1-4. We have found that the structural properties, e.g., bond length C=O (of carbonyl) and associated infrared (IR) frequency, show similar variation for both the fluorinated Li-carbonate complexes. However, higher solvation energy and lower desolvation energy for the TFPC than the FEC show the opposite nature of their respective pristine carbonate counterparts. Our result, i.e., superior solvation energy of TFPC compared to FEC, is in good agreement with the experimentally developed solvating power series. Based on the solvation/desolvation energy, we conclude that TFPC could be a better high-voltage electrolyte for LIBs.
AIP Advances, 2020
A simple yet innovative approach has been made through a powder metallurgy route for the synthesi... more A simple yet innovative approach has been made through a powder metallurgy route for the synthesis of aluminum-graphene (Al-Gr) composite materials for commercially viable solar thermal collectors. The Al-Gr composite (with 1 wt. % of graphene filler content) recorded an enhanced thermal conductivity of ∼280 W/mK, which is higher than that of pristine Al (∼124 W/mK), at room temperature. It has also been found that the prepared composite has a lower coefficient of thermal expansion. The structures and morphologies of the composites have been investigated in detail with the help of X-ray diffraction technique, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, etc. Furthermore, the density measurements showed that the composites retain ∼97.5% of the density of pristine aluminum even after the sintering treatment. X-ray micro-computed tomography revealed the structural integrity and non-porous nature of the samples, free from any defects and deformations. The thermal fusing of Al-based composite materials at 630 ○ C is found to be satisfactory with the required strength, and the composites showed at least ∼125% increase in the thermal conductivity than that of pristine Al. These results suggest that the Al-Gr composites can be deployed as solar thermal collectors and heat sink materials for thermal dissipation.
AIP Conference Proceedings, 2018
Li-ion battery has wide area of application starting from low power consumer electronics to high ... more Li-ion battery has wide area of application starting from low power consumer electronics to high power electric vehicles. However, their large scale application in electric vehicles requires further improvement due to their low specific power density which is an essential parameter and is closely related to the working potential windows of the battery system. Several studies have found that these parameters can be taken care of by considering different cathode/anode materials and electrolytes. Recently, a unique approach has been reported on the basis of cluster size in which the use of Li3 cluster has been suggested as a potential component of the battery electrode material. The cluster based approach significantly enhances the working electrode potential up to ~0.6V in the acetonitrile solvent. In the present work, using ab-initio quantum chemical calculation and the dielectric continuum model, we have investigated various dielectric solvent medium for the suitable electrolyte for the potential component Li3 cluster. This study suggests that high dielectric electrolytic solvent (ethylene carbonate and propylene carbonate) could be better for lithium cluster due to improvement in the total electrode potential in comparison to the other dielectric solvent.Li-ion battery has wide area of application starting from low power consumer electronics to high power electric vehicles. However, their large scale application in electric vehicles requires further improvement due to their low specific power density which is an essential parameter and is closely related to the working potential windows of the battery system. Several studies have found that these parameters can be taken care of by considering different cathode/anode materials and electrolytes. Recently, a unique approach has been reported on the basis of cluster size in which the use of Li3 cluster has been suggested as a potential component of the battery electrode material. The cluster based approach significantly enhances the working electrode potential up to ~0.6V in the acetonitrile solvent. In the present work, using ab-initio quantum chemical calculation and the dielectric continuum model, we have investigated various dielectric solvent medium for the suitable electrolyte for the potential componen...
AIP Conference Proceedings, 2018
Due to high in-plane charge carrier mobility with high electron velocity and long spin diffusion ... more Due to high in-plane charge carrier mobility with high electron velocity and long spin diffusion length, graphene guarantees as a completely unique material for devices with various applications. Unaffected 2pz orbitals of carbon atoms in graphene can be highly influenced by substrates and leads to tuning in electronic properties. We report here a density functional calculation of graphene monolayer based on metallic substrate like nickel surfaces. Band-gap of graphene near K points opens due to interactions between 2pz and d-orbitals of nickel atoms and the gap modulation can be done with the increasing number of layers of substrates.
Ceramics International, 2019
Urchin-like microsphere of NiCo 2 O 4 /NIC sample was synthesized by hydrothermal method, followe... more Urchin-like microsphere of NiCo 2 O 4 /NIC sample was synthesized by hydrothermal method, followed by post annealing treatment at 400°C for 3 h. The phase confirmation and surface morphology was analyzed by XRD, FESEM and Raman spectroscopy, which shows that cubic spinel structure with Fd3m space group supporting the microstructure. The elemental mappings were characterized by EDS analysis. The electrochemical performance revealed that the prepared NIC sample exhibits specific capacitance of 295Fg-1 at 20 mV −1 owing to its high surface area; consist of interconnection of nanopores between the subunit of nanoneedle inside the urchin like microsphere. The optical band gap energy was estimated by using Tauc plot, are 2.17eV and 3.5eV respectively. This result well consistent with the theoretical investigation by using DFT calculation. Furthermore a significant M-H loop revealed that, NIC system shows ferromagnetic behavior at RT. Hence all the combined experimental and theoretical results provide to design synergetic microstructure of NIC system for multifunctional application.
ACS Applied Materials & Interfaces, 2019
The Journal of Physical Chemistry C, 2018
Journal of Magnetism and Magnetic Materials, 2019
High in-plane charge carrier mobility and long spin diffusion length makes graphene a unique mate... more High in-plane charge carrier mobility and long spin diffusion length makes graphene a unique material for spin-based devices. However, in a vertical graphene junction, the 2p z orbitals of carbon atoms in graphene can be tuned via suitable magnetic substrates; this would affect the spin injection into graphene. Here, a vertical spin switch has been designed by embedding a single layer of graphene as a tunnel layer between the Ni (111) substrate. Periodic density functional approach in conjunction with Julliere's model is used to calculate the tunnel magnetoresistance (TMR). Further, single-layered hexagonal Boron Nitride (h-BN) is sandwiched between the graphene and Ni (111) substrate to understand the role of hybridization at the interface on TMR. Our calculation shows that in contrast to the graphene junction, a much higher TMR value is obtainable in the case of the graphene/h-BN multi-tunnel junction (MTJ). The TMR in graphene junction is found to decrease with the increase of an externally applied electric field, and drops to zero for a field greater than equal to 0.16 eV/Å. Similar phenomenon was observed in the case of h-BN/graphene MTJ, where TMR value remains unchanged for electric field up to 0.1 eV/Å beyond which it drops to zero. The change in hybridization and charge-carrier-population at the interface modifies the magnetic exchange interaction and magnetic anisotropy resulting in a spin flip at interface, leads to rapid drop in TMR after a threshold electric field. The high and tunable TMR value suggests h-BN assisted high performance graphene based vertical spin switch.
ChemistrySelect, 2019
The donor-acceptor orbital interaction between the unoccupied orbital of Li + and the lone pair o... more The donor-acceptor orbital interaction between the unoccupied orbital of Li + and the lone pair of oxygen atoms in the carbonyl group of Li +-carbonate complexes shows significant decrease on fluorination. This has been investigated through molecular orbital formalism based density functional theory. The fluorination process lowers the binding energy (reduced up to 13.8 kcal/mol), and widens the HOMO-LUMO gap (enhanced up to 0.7 eV), which is essential for achieving electrolytes with high potential window in Li-ion battery. Furthermore, the impact of fluorination on few critical factors has been observed, i. e. dipole moment (drastic enhancement), IR spectra (most affected C=O vibrational mode shows blue shift in the spectra) and Raman active mode (carbonyl group stretching mode doublet (n C<C¼>O) shifted to higher frequency) which have been probed by vibrational frequency analysis.
ACS Catalysis, 2018
Enhancing the intrinsic activity of a benchmarked electrocatalyst such as platinum (Pt) is highly... more Enhancing the intrinsic activity of a benchmarked electrocatalyst such as platinum (Pt) is highly intriguing from fundamental as well as applied perspectives. In this work, hydrogen evolution reaction (HER) activity of Pt electrodes, benchmarked HER catalysts, modified with ultrathin sheets of hexagonal boron nitride (h-BN) is studied in acidic medium (Pt/h-BN), and augmented HER performance, in terms of the overpotential at a 10 mA cm–2 current density (10 mV lower than that of Pt nanoparticles) and a lower Tafel slope (29 ± 1 mV/decade), of the Pt/h-BN system is demonstrated. The effects of h-BN surface modification of bulk Pt as well as Pt nanoparticles are studied, and the origin of such an enhanced HER activity is probed using density functional theory-based calculations. The HER charge transfer resistance of h-BN-modified Pt is found to be drastically reduced, and this enhances the charge transfer kinetics of the Pt/h-BN system because of the synergistic interaction between h-BN and Pt. An enormous ...
Carbon, 2018
We have investigated here, the electronic and magnetic properties of graphene-nickel system by ti... more We have investigated here, the electronic and magnetic properties of graphene-nickel system by tight-binding mean-field approach. Strong hybridization between the 2p z orbital of graphene and 3d z2 orbital of nickel occurs when monolayer graphene is placed over a single layer of ferromagnetically ordered Ni (111) metal due to the excellent lattice matching between the two layers. This hybridization greatly affects the electronic and magnetic properties of the bilayer system, resulting in a significantly reduced local magnetic moment of the nickel layer and an enhanced induced spin polarization on the graphene layer. The calculated Hamiltonian revealed critical information regarding the first-, second-and third-nearest-neighbor hopping integrals of electrons ofgraphene besides the Coulomb correlation of electrons in nickel-(111). The Hubbard type Coulomb interactions present in nickel lattices were treated within the mean-field approximation. Zubarev's technique was employed to calculate electronic Green's functions and subsequent investigation of the temperature dependent ferromagnetic magnetization of nickel (111)was carried out through self-consistent calculation. Further calculations regarding the induced magnetization in the graphene, total magnetization in bilayer layer system, electronic band dispersion, spin resolved density of states (DOS)and spin polarization efficiency have been carried out. The results were corroborated by experimental observations.
Journal of Cluster Science, 2017