| 1. |
- Samantara, Aneeya K., et al.
(author)
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Enhanced Oxygen Evolution Reaction with a Ternary Hybrid of Patronite-Carbon Nanotube-Reduced Graphene Oxide : A Synergy between Experiments and Theory
- 2021
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In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:30, s. 35828-35836
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Journal article (peer-reviewed)abstract
- This work reports the hybridization of patronite (VS4) sheets with reduced graphene oxide and functionalized carbon nanotubes (RGO/FCNT/VS4) through a hydrothermal method. The synergistic effect divulged by the individual components, i.e., RGO, FCNT, and VS4, significantly improves the efficiency of the ternary (RGO/FCNT/VS4) hybrid toward the oxygen evolution reaction (OER). The ternary composite exhibits an impressive electrocatalytic OER performance in 1 M KOH and requires only 230 mV overpotential to reach the state-of-the-art current density (10 mA cm–2). Additionally, the hybrid shows an appreciable Tafel slope with a higher Faradaic efficiency (97.55 ± 2.3%) at an overpotential of 230 mV. Further, these experimental findings are corroborated by the state-of-the-art density functional theory by presenting adsorption configurations, the density of states, and the overpotential of these hybrid structures. Interestingly, the theoretical overpotential follows the qualitative trend RGO/FCNT/VS4 < FCNT/VS4 < RGO/VS4, supporting the experimental findings.
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| 2. |
- Banerjee, Amitava, et al.
(author)
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Scrupulous Probing of Bifunctional Catalytic Activity of Borophene Monolayer : Mapping Reaction Coordinate with Charge Transfer
- 2018
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In: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1:8, s. 3571-3576
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Journal article (peer-reviewed)abstract
- We have envisaged the hydrogen evolution and oxygen evolution reactions (HER and OER) on two-dimensional (2D) noble metal free borophene monolayer based on first-principles electronic structure calculations. We have investigated the effect of Ti functionalization on borophene monolayer from the perspective of HER and OER activities enhancement. We have probed the activities based on the reaction coordinate, which is conceptually related to the adsorption free energies of the intermediates of HER and OER, as well as from the vibrational frequency analysis with the corresponding charge transfer mechanism between the surface and the adsorbate. Tifunctionalized borophene has emerged as a promising material for HER and OER mechanisms. We believe that our probing method, based on reaction coordinate coupled with vibrational analysis that has been validated by the charge transfer mechanism, would certainly become as a robust prediction route for HER and OER mechanisms in coming days.
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| 3. |
- De Adhikari, Amrita, et al.
(author)
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Polyaniline-Stabilized Intertwined Network-like Ferrocene/Graphene Nanoarchitecture for Supercapacitor Application
- 2017
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In: Chemistry - An Asian Journal. - : WILEY-V C H VERLAG GMBH. - 1861-4728 .- 1861-471X. ; 12:8, s. 900-909
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Journal article (peer-reviewed)abstract
- The present work highlights the effective H-p interaction between metallocenes ( ferrocene; Fc) and graphene and their stabilization in the presence of polyaniline ( PANI) through pi-pi interactions. The PANI-stabilized Fc@ graphene nanocomposite ( FcGA) resembled an intertwined network-like morphology with high surface area and porosity, which could make it a potential candidate for energy-storage applications. The relative interactions between the components were assessed through theoretical ( DFT) calculations. The specific capacitance calculated from galvanostatic charging/discharging indicated that the PANI-stabilized ter-nary nanocomposite exhibited a maximum specific capacitance of 960 Fg(-) at an energy density of 85 WhKg(-1) and a current density of 1 Ag-. Furthermore, electrochemical impedance spectroscopy (EIS) analysis confirmed the low internal resistance of the as-prepared nanocomposites, which showed improved charge-transfer properties of graphene after incorporation of Fc and stabilization with PANI. Additionally, all electrodes were found to be stable up to 5000 cycles with a specific capacitance retention of 86%, thus demonstrating the good reversibility and durability of the electrode material.
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| 4. |
- Gadegaard, Ane Riis, et al.
(author)
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Spectroscopy and picosecond dynamics of aqueous NO2
- 2014
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 141:6, s. 064310-
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Journal article (peer-reviewed)abstract
- We investigate the formation of aqueous nitrogen dioxide, NO2 formed through femtosecond photolysis of nitrate, NO3- ( aq) and nitromethane CH3NO2(aq). Common to the experiments is the observation of a strong induced absorption at 1610 +/- 10 cm(-1), assigned to the asymmetric stretch vibration in the ground state of NO2. This assignment is substantiated through isotope experiments substituting N-14 by N-15, experiments at different pH values, and by theoretical calculations and simulations of NO2-D2O clusters.
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| 5. |
- Gond, Ritambhara, et al.
(author)
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Enabling the Electrochemical Activity in Sodium Iron Metaphosphate [NaFe(PO3)(3)] Sodium Battery Insertion Material : Structural and Electrochemical Insights
- 2017
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In: Inorganic Chemistry. - : AMER CHEMICAL SOC. - 0020-1669 .- 1520-510X. ; 56:10, s. 5918-5929
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Journal article (peer-reviewed)abstract
- Sodium-ion batteries are widely pursued as an economic alternative to lithium-ion battery technology, where Fe- and Mn-based compounds are particularly attractive owing to their elemental abundance. Pursuing phosphate-based polyanionic chemistry, recently solid-state prepared NaFe(PO3)(3) metaphosphate was unveiled as a novel potential sodium insertion material, although it was found to be electrochemically inactive. In the current work, employing energy-savvy solution combustion synthesis, NaFe2+(PO3)(3) was produced from low-cost Fe3+ precursors. Owing to the formation of nanoscale carbon-coated product, electrochemical activity was enabled in NaFe(PO3)(3) for the first time. In congruence with the first principles density functional theory (DFT) calculations, an Fe3+/Fe2+ redox activity centered at 2.8 V (vs Na/Na+) was observed. Further, the solid-solution metaphosphate family Na(Fe1-xMnx)(PO3)(3) (x = 0-1) was prepared for the first time. Their structure and distribution of transition metals (TM = Fe/Mn) was analyzed with synchrotron diffraction, X-ray photoelectron spectroscopy, and Mossbauer spectroscopy. Synergizing experimental and computational tools, NaFe(PO3)(3) metaphosphate is presented as an electrochemically active sodium insertion host material.
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| 6. |
- Jena, Naresh K., et al.
(author)
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Atomic level simulations of the interaction of asphaltene with quartz surfaces : role of chemical modifications and aqueous environment
- 2017
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In: Materials and Structures. - : Kluwer Academic Publishers. - 1359-5997 .- 1871-6873. ; 50:1
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Journal article (peer-reviewed)abstract
- Understanding the properties of bitumen and its interaction with mineral aggregates is crucial for future strategies to improve roads and highways. Knowledge of basic molecular and electronic structures of bitumen, one out of the two main components of asphalt, poses a major step towards achieving such a goal. In the present work we employ atomistic simulation techniques to study the interaction of asphaltenes, a major constituent of bitumen, with quartz surfaces. As an effective means to tune adhesion or cohesion properties of asphaltenes and mineral surfaces, we propose chemical modification of the pristine asphaltene structure. By the choice of substituent and site of substitution we find that adhesion between the asphaltene molecule and the quartz surface can easily be improved at the same time as the cohesive interaction between the asphaltene units is reduced, while other substituents may lead to the opposite effect. We also provide insight at the molecular level into how water molecules affect interactions between asphaltenes and quartz. Our approach emphasizes a future role for advanced atomistic modeling to understand the properties of bitumen and suggest further improvements.
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| 7. |
- Jena, Naresh K., et al.
(author)
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Borophane as a Benchmate of Graphene : A Potential 2D Material for Anode of Li and Na-Ion Batteries
- 2017
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In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 9:19, s. 16148-16158
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Journal article (peer-reviewed)abstract
- Borophene, single atomic-layer sheet of boron (Science 2015, 350, 1513), is a rather new entrant into the burgeoning class of 2D materials. Borophene exhibits anisotropic metallic properties whereas its hydrogenated counterpart borophane is reported to be a gapless Dirac material lying on the same bench with the celebrated graphene. Interestingly, this transition of borophane also rendered stability to it considering the fact that borophene was synthesized under ultrahigh vacuum conditions on a metallic (Ag) substrate. On the basis of first-principles density functional theory computations, we have investigated the possibilities of borophane as a potential Li/Na-ion battery anode material. We obtained a binding energy of -2.58 (-1.08 eV) eV for Li (Na)-adatom on borophane and Bader charge analysis revealed that Li(Na) atom exists in Li+(Na+) state. Further, on binding with Li/Na, borophane exhibited metallic properties as evidenced by the electronic band structure. We found that diffusion pathways for Li/Na on the borophane surface are anisotropic with x direction being the favorable one with a barrier of 0.27 and 0.09 eV, respectively. While assessing the Li-ion anode performance, we estimated that the maximum Li content is Li0.445B2H2, which gives rises to a material with a maximum theoretical specific capacity of 504 mAh/g together with an average voltage of 0.43 V versus Li/Li+. Likewise, for Na-ion the maximum theoretical capacity and average voltage were estimated to be 504 mAh/g and 0.03 V versus Na/Na+, respectively. These findings unambiguously suggest that borophane can be a potential addition to the map of Li and Na-ion anode materials and can rival some of the recently reported 2D materials including graphene.
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| 8. |
- Jena, Naresh K., et al.
(author)
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Solvent-Dependent Conformational States of a [2]Rotaxane-Based Molecular Machine : A Molecular Dynamics Perspective
- 2013
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:47, s. 25059-25068
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Journal article (peer-reviewed)abstract
- Motion is an essential and fundamental feature of any living organism. The evolved organisms have developed sophisticated and perfect machineries and highly delicate mechanisms to carry out directional and coordinated movements which eventually lead to motion at the macroscopic length scale. By mimicking these natural machineries, attempts to design and synthesize similar molecular motors are made in relevance to their applications in drug delivery, data storage, and molecular sensing. It is highly desirable to establish the rules for controlling the conformational states of molecular motors by tuning some of the external variables which can be used for the design strategies. We contribute to this subject by looking into the solvent influence on the conformational states of a synthetic molecular rotor, namely, diketopyrrolopyrrole (DPP) based [2]rotaxane, using the force-field molecular dynamics approach. We study this system in three different solvents, and we report a strong solvent dependence in the population of three different translational isomers. In chloroform solvent we report the dominant population of the 2-P isomer which is in excellent agreement with experimental results based on H NMR spectra (Org. Lett. 2013, 15, 1274). However, there is a striking difference seen in the population of translational isomers in DMSO solvent, and we attribute these features to negligence of solvent hydrogen bonding induced upfield and downfield effects in the interpretation of experimental proton NMR spectra. In addition, we also report a solvent-polarity-induced fully unstretched to folded conformational transition in the [2]rotaxane system. On the basis of the molecular mechanics Poisson-Boltzmann (and generalized Born) surface area approach, we identify the driving force for the formation of the supramolecular guest-host [2]rotaxane system. Finally, we calculate the relative binding free energies for the macrocycle at different binding sites of the DPP skeleton using the molecular dynamics simulations performed for the macrocycle-rotaxane system in water solvent which suggests the increased stability of the 2-O isomer in polar solvent.
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| 9. |
- Ji, Cheng, et al.
(author)
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Stability of Ar(H2)2 to 358 GPa
- 2017
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In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 114:14, s. 3596-3600
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Journal article (peer-reviewed)abstract
- "Chemical precompression" through introducing impurity atoms into hydrogen has been proposed as a method to facilitate metallization of hydrogen under external pressure. Here we selected Ar(H-2)(2), a hydrogen-rich compound with molecular hydrogen, to explore the effect of "doping" on the intermolecular interaction of H-2 molecules and metallization at ultrahigh pressure. Ar(H-2)(2) was studied experimentally by synchrotron X-ray diffraction to 265 GPa, by Raman and optical absorption spectroscopy to 358 GPa, and theoretically using the density-functional theory. Our measurements of the optical bandgap and the vibron frequency show that Ar(H-2)(2) retains 2-eV bandgap and H-2 molecular units up to 358 GPa. This is attributed to reduced intermolecular interactions between H-2 molecules in Ar(H-2)(2) compared with that in solid H-2. A splitting of the molecular vibron mode above 216 GPa suggests an orientational ordering transition, which is not accompanied by a change in lattice symmetry. The experimental and theoretical equations of state of Ar(H-2)(2) provide direct insight into the structure and bonding of this hydrogen-rich system, suggesting a negative chemical pressure on H-2 molecules brought about by doping of Ar.
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| 10. |
- Lindblad, Rebecka, et al.
(author)
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Electronic Structure of CH3NH3PbX3 Perovskites : Dependence on the Halide Moiety
- 2015
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In: The Journal of Physical Chemistry C. - American Chemical Society : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:4, s. 1818-1825
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Journal article (peer-reviewed)abstract
- A combination of measurements using photoelectron spectroscopy and calculations using density functional theory (DFT) was applied to compare the detailed electronic structure of the organolead halide perovskites CH3NH3PbI3 and CH3NH3PbBr3. These perovskite materials are used to absorb light in mesoscopic and planar heterojunction solar cells. The Pb 4f core level is investigated to get insight into the chemistry of the two materials. Valence level measurments are also included showing a shift of the valence band edges where there is a higher binding energy of the edge for the CH3NH3PbBr3 perovskite. These changes are supported by the theoretical calculations which indicate that the differences in electronic structure are mainly caused by the nature of the halide ion rather than structural differences. The combination of photoelectron spectroscopy measurements and electronic structure calculations is essential to disentangle how the valence band edge in organolead halide perovskites is governed by the intrinsic difference in energy levels of the halide ions from the influence of chemical bonding.
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