Conduction of Li+ cations in ethylene carbonate (EC) and propylene carbonate (PC): comparative studies using density functional theory

Bhatt, Mahesh Datt,Cho, Maenghyo,Cho, Kyeongjae Springer-Verlag 2012 Journal of solid state electrochemistry Vol.16 No.2

Density functional theory calculations for the interaction of Li⁺ cations and PF₆^- anions with nonaqueous electrolytes

Bhatt, Mahesh Datt,Cho, Maenghyo,Cho, Kyeongjae Canadian Science Publishing 2011 Canadian journal of chemistry Vol.89 No.12

<P> The interaction of lithium (Li<SUP>+</SUP>) cation and hexafluorophosphate (PF6<SUP>-</SUP>) anion with nonaqueous electrolytes is studied by using density functional theory at the B3LYP/6-311++G(d,p) level in the gas phase in terms of the coordination of Li<SUP>+</SUP> and PF6<SUP>-</SUP> with these solvents. Ethylene carbonate (EC) coordinates with Li<SUP>+</SUP> and PF6<SUP>-</SUP> most strongly and reaches the anode and cathode most easily because of its highest dielectric constant among all the solvent molecules, resulting in its preferential reduction on the anode and oxidation on the cathode. For cyclic carbonates EC and propylene carbonate (PC), the structure Li<SUP>+</SUP>(S)4 is found to be the most stable. However, for linear carbonates dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), the formation of PF6<SUP>-</SUP>(S)n=1-3 is not favorable. Such analysis may be useful in applications for lithium ion batteries. </P>

Electronic states at 4,4´-N,N´-dicarbazol-biphenyl (CBP)emetal (Mg, Ag, and Au) interfaces: A joint experimental and theoretical study

Bhatt Mahesh Datt,Akahasi Baba,Takeaki Sakurai,Katsuhiro Akimoto 한국물리학회 2011 Current Applied Physics Vol.11 No.3

We used ultraviolet photoelectron spectroscopy (UPS) to study the electronic structure at the interface between organic semiconductor (CBP) and metals (Mg, Ag, and Au). Controlling the injection of charges at the interface requires a better understanding of the basic mechanism of the formation of interface states. In this context, photoelectron spectroscopy and density functional theory calculations were used to investigate the interaction of CBP with metal (111) surfaces. The position of HOMO relative to the Fermi level and the magnitude of the interface dipole were measured for each interface by UPS measurement. For CBP on Au, interface state (continuous state) was observed near the Fermi level by density functional theory calculations. However, no interface state was observed for CBP on Mg and Ag. It is suggested that the interface state plays an important role in charge transport at the interface. It was analyzed by density functional theory calculations that the interface state is formed due to interaction of CBP with metals and the position of the Fermi level varies strongly with the metal work function. The mechanism of formation of interface states and electrical properties were discussed.

Barrier formation at organic-metal interfaces studied by density functional theory

Bhatt Mahesh Datt,Shugo Suzuki,Takeaki Sakurai,Katsuhiro Akimoto 한국물리학회 2011 Current Applied Physics Vol.11 No.3

The barrier formation at organic-metal interfaces was studied with density functional theory (DFT). We analyzed the induced density of states in the organic molecular gap and showed that it is high enough to control the barrier formation. We calculated the interface Fermi level for contact of BCP with various metals e.g. Ca, Mg, Al, Ag, and Au surfaces. We found our calculated result in consistent with experimental (UPS) result and concluded that the barrier formation is due to the charge transfer between the metal and the states induced in BCP molecular gap.

Density functional theory calculations for ethylene carbonate-based binary electrolyte mixtures in lithium ion batteries

Mahesh Datt Bhatt,Colm O’Dwyer 한국물리학회 2014 Current Applied Physics Vol.14 No.3

The density functional theory (DFT) calculations have been performed to investigate the interaction of Liþ with various organic solvents widely used as Li ion rechargeable battery electrolytes such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC); and their EC-based binary mixtures at the level of B3LYP/6-31G (d). The interaction of Liþ with these solvents has been calculated in terms of electronic structures of clusters of the mixtures of organic solvents including a lithium ion. The main objective of our investigation is to help in understanding a stable and enhancing ionic transfer at graphite/electrolyte interface assisted by the mixtures of the solvents. The calculated results favor the stability of EC-based binary mixtures and high EC-content binary mixture systems. In infrared (IR) vibrational spectra, the IR active modes of the solvent show significant changes due to the cation-solvent interaction.

Effect of doping on metal doped semiconductor

Bhatt Mahesh Datt,Shugo Suzuki,Takeaki Sakurai,Katsuhiro Akimoto 한국물리학회 2011 Current Applied Physics Vol.11 No.2

The effect of doping on position of interface states for metal doped bathocuproine (BCP) was studied with density functional theory (DFT). The doping of Ca atoms with BCP induces the formation of interface states with shift in their relative positions from Fermi level and approximately no shift in HOMO position of BCP molecule. The shift in the position of interface states towards higher binding energy was believed to be due to the presence of doping excess electrons from Ca at the interface. The analysis of modification in intensity of LUMO or EF or interface states, suggests the formation of multiply charged anions in heavily doped film. It clearly gives the direct evidence for the origin of the doping interface states in organic molecules. The effects of Ca doping on electrical properties were discussed.

Density Functional Theory (DFT) Calculations for Oxygen Reduction Reaction Mechanisms on Metal-, Nitrogen- co-doped Graphene (M-N₂-G (M=Ti, Cu, Mo, Nb and Ru)) Electrocatalysts

Bhatt, Mahesh Datt,Lee, Geunsik,Lee, Jae Sung Pergamon Press 2017 Electrochimica Acta Vol. No.

<P><B>Abstract</B></P> <P>The density functional theory (DFT) calculations are performed to study the oxygen reduction reaction (ORR) on M-N<SUB>2</SUB>-G (M=Ti, Cu, Mo, Nb and Ru) electrocatalyst surfaces. In order to explain catalytic properties of M-N<SUB>2</SUB>-G (M=Ti, Cu, Mo, Nb and Ru) electrocatalysts, adsorption properties of all six intermediates O<SUB>2</SUB>, O, OOH, OH, H<SUB>2</SUB>O and H<SUB>2</SUB>O<SUB>2</SUB> are analyzed. We also calculate the adsorption property of ORR intermediates on Cu-N<SUB>2</SUB>-G (for example, an ideal catalyst) with the presence of H<SUB>3</SUB>O<SUP>+</SUP> ion (acid), OH<SUP>−</SUP> ion (base) and water molecule. After analysis, we can see clearly that the stable adsorption site for ORR intermediates in presence of acid, base and water is atop. Moreover, the adsorption properties of ORR intermediates in acid are quantitatively more stable than in base and water respectively. The catalytic activity of the ORR intermediates is found to be enhanced with the increase in the concentration of acid and base, but not of water. Our calculated results reveal that the ORR via a 4 electron transfer mechanism is energetically favorable on the M-N<SUB>2</SUB>-G (M=Ti, Mo, Nb and Ru) electrocatalyst surfaces to form two water molecules, while Cu-N<SUB>2</SUB>-G catalyst surface favors 2 electron transfer pathway to form unwanted hydrogen peroxide. Such types of electrocatalysts will be useful in the practical applications of polymer electrolyte fuel cells.</P>

Oxygen reduction reaction (ORR) kinetics through different solvents of the non-aqueous electrolyte in Li-air (O₂) batteries in both the gas and solution phases: A DFT study

Bhatt, Mahesh Datt,Lee, Jin Yong Elsevier 2018 Journal of Molecular Liquids Vol.271 No.-

<P><B>Abstract</B></P> <P>We performed DFT calculations to investigate the role of solvent of the non-aqueous electrolytes for the oxygen reduction reaction (ORR) kinetics in Li-air batteries. The calculated results on structural, thermodynamic and vibrational properties revealed that dimethyl sulfoxide (DMSO) is the most stable solvent among DME, DMSO, and MeCN of non-aqueous electrolytes. The LiCF<SUB>3</SUB>SO<SUB>3</SUB>/DMSO electrolyte was primarily assumed to be the most favorable for ORR kinetics from the IR analysis. We calculated thermodynamic properties of the ORR reactions held during the formation of superoxide (O<SUB>2</SUB> <SUP>−</SUP>) ion and the sole discharge products lithium peroxide (Li<SUB>2</SUB>O<SUB>2</SUB>), and lithium oxide (Li<SUB>2</SUB>O) to study the ORR kinetics of the stable salt LiCF<SUB>3</SUB>SO<SUB>3</SUB> with three solvents namely dimethoxyethane (DME), dimethyl sulfoxide (DMSO), and acetonitrile (MeCN). The thermodynamic properties of the ORR reaction signified the best role of LiCF<SUB>3</SUB>SO<SUB>3</SUB>/DMSO electrolyte compared to LiCF<SUB>3</SUB>SO<SUB>3</SUB>/DME and LiCF<SUB>3</SUB>SO<SUB>3</SUB>/MeCN both in the gas and solution (water) phases.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The role of solvent of non-aqueous electrolyte in Li-air batteries was studied theoretically. </LI> <LI> The LiCF<SUB>3</SUB>SO<SUB>3</SUB>/DMSO electrolyte was primarily assumed to be the most favorable for ORR kinetics from the IR analysis. </LI> <LI> The thermodynamic properties of the ORR reactions including the (O<SUB>2</SUB> <SUP>−</SUP>) ion and Li<SUB>2</SUB>O<SUB>2</SUB> and Li<SUB>2</SUB>O </LI> <LI> Improved ORR kinetics was due to the key role of LiCF<SUB>3</SUB>SO<SUB>3</SUB>/DMSO electrolyte compared to LiCF<SUB>3</SUB>SO<SUB>3</SUB>/DME and LiCF<SUB>3</SUB>SO<SUB>3</SUB>/MeCN. </LI> </UL> </P>

Screening of Oxygen-Reduction-Reaction-Efficient Electrocatalysts Based on Ag–M (M = 3d, 4d, and 5d Transition Metals) Nanoalloys: A Density Functional Theory Study

Bhatt, Mahesh Datt,Lee, Geunsik,Lee, Jae Sung American Chemical Society 2017 Energy & fuels Vol.31 No.2

<P>As a result of the high cost and scarcity of Pt and. Pt-based materials as electrocatalysts with high oxygen reduction reaction (ORR) performance at the carbon-supported oxygen cathode of polymer electrolyte membrane fuel cells (PEMFCs), we perform a screening of ORR-efficient electrocatalysts based on Ag-M nanoalloys, where M is a 3d, 4d, or 5d transition metal using density functional theory (DFT) methods. We consider atomic oxygen adsorption energy E-ads(O) as a descriptor to explore the cheap and ORR-efficient Ag M(1 1 1) (M = 3d, 4d, and Sd transition metal's) surfaces in various suballoying configurations compared to the Pt(1 1 1) surface. Our calculated results reveal that the Ag-shelled catalysts by subsurface alloying with all 3d, 4d, and Sd transition metals are more stable than pure Ag(1 1 1) by analyzing the surface energy and surface segregation energy of Ag M alloys and consistent with Pt M alloys suballoying with 3d transition metals. Moreover, the d-band center of the same Ag M alloy with different suballoying configurations is found to be in the order of Ag M skin < Ag M subsurface < Ag3M mixing < pure Pt < Ag M overlayer in Ag-shelled catalysts suballoying with all 3d, 4d, and Sd transition metals. We finally propose that Mn, Fe, and Co (3d), Zr, Mo, Nb and Ru and Ta and W (Sd) are suitable catalysts for ORE. on Ag3M mixing surfaces and Mn, Fe, and Co (3d) and Ta and W (5d) are suitable catalysts for ORR on Ag M overlayer surfaces based on the fact that any catalyst with the strength of atomic oxygen reduction higher (but not very high) than that of pure Pt would be a suitable catalyst for enhanced ORR, which should be confirmed by further investigating ORR mechanisms on these catalyst surfaces in alkaline media both experimentally and theoretically. Moreover, the trends of oxygen reduction activity plotted against O binding energy, relative adsorption energies of ORR intermediates, and scaling relations between ORR intermediates (O, OH, and OOH) also stress our proposition illustrated above. Such a type of DFT investigation may open room for the researchers working in this direction.</P>

Photocatalytic properties of intrinsically defective undoped bismuth vanadate (BiVO₄) photocatalyst: A DFT study

Bhatt, Mahesh Datt,Lee, Jin Yong Elsevier 2018 Journal of electroanalytical chemistry Vol.828 No.-

<P><B>Abstract</B></P> <P>Monoclinic clinobisvanite BiVO<SUB>4</SUB> is one of the most promising photocatalyst due to its stability, low cost, narrow band gap, and suitable valence band maximum (VBM) position. The valence band maximum of about −7.10 eV at vacuum level was observed, which is well below the redox potential of water. However, the conduction band minimum, CBM of about −4.86 eV at vacuum level, which was responsible for its low efficiency. The presence of metal (Bi or V) vacancy changed the charge density and VBM of pristine BiVO<SUB>4</SUB>. Our calculated results revealed that 0.04% of the intrinsic Bi or V defects enhanced p-type conductivity and hence improved photocatalytic activity than O-interstitial in pristine BiVO<SUB>4</SUB>. The optical properties of both pristine and intrinsically defective BiVO<SUB>4</SUB> were calculated and analyzed with perspective of their photocatalytic properties. Conclusively, the role of Bi or V (metal) vacancies in pristine BiVO<SUB>4</SUB> was found to be significant than O interstitials in enhancing the photocatalytic properties regarding the solar water splitting.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The electronic structure of pristine and intrinsically defective BiVO4 was investigated by DFT. </LI> <LI> The CBM of BiVO<SUB>4</SUB> was calculated to be -4.86 eV at vacuum level, which is responsible for its low efficiency. </LI> <LI> Bi or V vacancies enhanced p-type conductivity and hence improved photocatalytic activity than O-interstitial in BiVO<SUB>4</SUB>. </LI> </UL> </P>