This work is motivated to explore the structural stability and electronic and electrochemical pro... more This work is motivated to explore the structural stability and electronic and electrochemical properties of nanocomposites of M 4 Li n (M = Si and Ge)−carbon nanotube (CNT) by employing first-principles density functional theory calculations. By analyzing the structural stability of various M 4 Li n (n = 0−10) clusters, it is revealed that a tetrahedron-shaped M 4 Li 4 Zintl cluster is found to be highly stable. Our study on the interaction between the lithiated clusters and CNT illustrates that the charge transfer from the former to latter plays a pivotal role in stabilizing these nanocomposites. The structural stability of those nanocomposites arises as a consequence of bonding between lithiated clusters and CNT, which is mediated through the cation−π interaction. The strength of the interaction between them is well reflected in electronic structure calculations by shifting the energy levels with respect to the Fermi energy. Further, the electrochemical properties of these nanocomposites are explored by forming an assembly of the cluster-inserted CNT. The calculated average intercalation voltage of the systems is found to be low (maximum ∼1.0 V for M = Si and 1.05 V for M = Ge), which demonstrates their anodic behavior.
Magnetic property transition is essential for α-MnO 2 , since ferromagnets have potential applica... more Magnetic property transition is essential for α-MnO 2 , since ferromagnets have potential applications compared to antiferromagnets. Herein, the role of various substituents in the anion site (F, N) and cation site (Fe, Cr) on α-MnO 2 .0.25 H 2 O is studied using first principle density functional theory calculations. From our calculations, we have shown that cation (Fe and Cr) substitutions are capable of tuning the antiferromagnetic ground state into ferromagnetic state than anion (F and N) substitutions. These results provide key ideas which are an indispensable need for multifunctional usage of this material.
We studied the stability of several borophene layers on an Al(111) surface and found a structure ... more We studied the stability of several borophene layers on an Al(111) surface and found a structure called 9R using ab initio calculations. This layer competes with χ3 and β12 borophene layers and is made up of boron nonagons that form a network of hexagonal boron double chains. Remarkably, it has no B6 hexagon unlike other borophene layers. All three layers lie significantly lower in energy than the honeycomb layer recently reported on the Al(111) surface [W. Li, et al., Sci. Bull., 2018, 63, 282]. We discuss the structural stability and electronic structures of different borophene layers in light of the role of the filling factor f of boron atoms in boron hexagons in a honeycomb layer as well as charge transfer from the Al substrate to the borophene layer as obtained from the Bader charge analysis. The electron localization function shows that the 9R layer has two-center bonding within the nonagon rings and three-center bonding between the rings. Calculations of the phonon spectra sh...
Physical chemistry chemical physics : PCCP, Jan 18, 2018
Capping ligands are vital in stabilizing various nanostructures and semiconductor quantum dots in... more Capping ligands are vital in stabilizing various nanostructures and semiconductor quantum dots in which unusual optical properties, especially white light emission, have been realized. Oleic acid (OA) is a widely used capping ligand. Here, we report blue emission from OA in its free molecular form and further demonstrate this by anchoring OA over the surfaces of Al2O3, ZnAl2O4(ZA), ZnAl2O4:Eu3+ (ZA:Eu3+), and Y2O3:Eu3+. White light emission was observed from OA-modified ZA:Eu3+ nanophosphor due to mixing of broad blue emission of OA and red emission of Eu3+ through energy transfer from OA to Eu3+. A detailed study revealed the characteristic binding modes of OA and their dependence on Eu3+ concentration, structural inversion in ZA, and the optical properties and surface states in the pristine and OA-modified ZA:Eu3+. First principles density functional theory calculations were employed to provide an insight into the HOMO-LUMO levels of OA molecule and, electronic structure of pristi...
Using ab initio calculations, we demonstrate the strong influence of valence electron concentrati... more Using ab initio calculations, we demonstrate the strong influence of valence electron concentration (VEC) on the local atomic structure and electronic properties of Mo 6 S 9−x I x (x = 0−9) nanowires (NWs). We find new atomic models of the NWs with unique decoration of S/I atoms that are more stable than reported earlier. The electronic and mechanical properties of these NWs are in good agreement with experiments. Further we tuned VEC by either varying the number of I atoms or adding S/Li atoms to obtain
Nano-structures of MO-S are useful for removal of S in petroleum industry, as solid state lubrica... more Nano-structures of MO-S are useful for removal of S in petroleum industry, as solid state lubricants in space technology, and in Pt-free fuel cell research. We study by first principles density functional calculations Mo-S nanoclusters, nanowires, their assemblies, and triangular nano-platetlets all of which have been produced in laboratory. Mo-S clusters have Mo polyhedral structures and sulfur atoms cap this metal polyhedron. These structures have high stability due to strong Mo-Mo and Mo-S bonding. Some of the polyhedral clusters have non-zero magnetic moments due to the partially occupied 4d states in Mo atoms. Mo6S8 octahedral cluster has ultra-high stability and it could be condensed to form Mo-S nanowire or nanorod. However, for high S contents, we show that triangular platelets become more stable. The Mo-S nanowires are good electronic conductors and are interesting for miniature devices. Assembly of nanowires stabilizes in a hexagonal structure with vdW interactions. The tr...
Using first-principles calculations with ultrasoft pseudopotential formalism and the generalized ... more Using first-principles calculations with ultrasoft pseudopotential formalism and the generalized gradient approximation for the exchange-correlation functional, we study the stability of MonSm (n =1-6 and m ranging from n to 3n) clusters and obtain the optimal stoichiometry for each n corresponding to the magic cluster. It is found that in this size range, the lowest-energy structures favor a core of metal atoms, which is covered by sulfur. In particular, we observe that for Mo6S14 isolated clusters, a 3D structure is significantly lower in energy as compared to platelet structures found recently on Au (111) surface. The composition ratio between S and Mo in the magic clusters is less than 2 for n=3 and greater than 2 for n<3. The structural stability of the magic clusters arises from the optimization of the Mo-Mo and Mo- S bonding as well as the symmetry of the cluster. Addition of a terminal sulfur in a magic cluster generally lowers its binding energy. The presence of partially occupied d-orbitals in Mo atoms contributes to Mo-Mo bonding and for higher S concentration it leads to sulfur-sulfur bond formation. The variation in energy due to a change in the sulfur composition suggests that sulfurization of the magic clusters is generally more favorable than desulfurization.
Based on first-principles density functional calculations, a general approach for determining and... more Based on first-principles density functional calculations, a general approach for determining and analyzing the degree of spin polarization (P) in ferromagnets is presented. The approach employs the so-called tetrahedron method to evaluate the Fermi surface integrations of P in both ballistic and diffusive regimes. The validity of the method is examined by comparing the calculated P values for Fe and Ni with the experiment. The method is shown to yield highly accurate results with minimal computational effort. Within our approach, it is also possible to systematically analyze the contributions of various types of electronic states to the spin induced transport. As a case study, the transport properties of the soft-ferromagnet CeMnNi4 are investigated in order to explain the origin of the existing difference between the experimental and theoretical values of P in this intermetallic compound.
Using first principles calculations with ultrasoft pseudopotentials, we study the thick dependenc... more Using first principles calculations with ultrasoft pseudopotentials, we study the thick dependence of the atomic and electronic structures of ͑110͒ slabs of TiO 2 rutile having one to five layers. Thin slabs with an even and odd number of layers show significantly different structural characteristics and electronic properties that can affect photocatalysis as well as the catalytic behavior of supported clusters. We discuss the origin of the oscillating band gap for both an even and odd number of layers and the effects on the atomic, electronic, and magnetic properties of octahedral M 6 and icosahedral M 13 ͑M=Pd,Rh͒ clusters deposited on stoichiometric slabs with two and three layers. Calculations have also been carried out for a Pd atom deposited on different sites of a two layer slab. These results show that the bridging oxygen atoms are most reactive and preferred for adsorption. The adsorption energy of a Pd atom on the bridging site has only a weak dependence on the thickness of the slab. However, the adsorption energy of a cluster supported on a three-layer slab is significantly higher than the value for a two-layer slab due to significant structural differences and this alters the magnetic and electronic properties of the supported clusters. The magnetic moments of Pd clusters are reduced after interaction with the support. However, for Rh clusters there is an increase in the magnetic moment. In general we find that the cluster-support interactions affect mainly the cluster and support atoms that are in contact at the interface. The variation in the band gap with slab thickness can, however, lead to metallic character of the slab after cluster adsorption and this could have important consequences for catalysis.
First-principles calculations on stoichiometric Mo n S 2n and W n S 2n ͑n =1-8͒ clusters show tha... more First-principles calculations on stoichiometric Mo n S 2n and W n S 2n ͑n =1-8͒ clusters show that their lowest energy atomic structures are dominated by a central core of metal atoms while the S atoms cap this core. We discuss in detail terminal, edge, and face capping of tetrahedral and octahedral Mo clusters by sulfur atoms for off-stoichiometric compositions also. Capping on the terminal sites is found to be least favorable. Edge capped Mo 4 S 6 and face capped Mo 6 S 8 clusters have high symmetries and high stability among all the clusters we have studied. We find that magnetic isomers are lowest in energy for some clusters though bulk MS 2 ͑M = Mo and W͒ is nonmagnetic. Our results on Mo 6 S 8+p ͑p =0-6͒ clusters further show that Mo 6 S 12 is magic with 4 B magnetic moment. The origin of magnetism and bonding nature in these clusters is discussed. Our finding could lead to the possibility of magnetic clusters of a variety of nonmagnetic transition-metal compounds and their interesting assemblies.
... The addition of F atoms makes four nearest neighbors around each such carbon atom and the loc... more ... The addition of F atoms makes four nearest neighbors around each such carbon atom and the local bonding character changes from predominantly sp 2 to sp 3 type, as well as the CC bonds elongate in the range of 1.51.6 Å. ...
... a Institute for Materials Research (IMR), Tohoku University, Aoba-ku, Sendai 980-8577, Japan.... more ... a Institute for Materials Research (IMR), Tohoku University, Aoba-ku, Sendai 980-8577, Japan. b Dr. Vijay Kumar Foundation, 45 Bazaar Street, KK Nagar (West), Chennai-600 078, India. ... A non-planar isomer with three O E and three O T atoms on an Mo 3 triangle (shown in Fig. ...
The large variation in specific heats with concentration between temperatures 50 K and 200 K for ... more The large variation in specific heats with concentration between temperatures 50 K and 200 K for AI-Si and AI-Ge alloys are analysed in detail by lattice dynamical and Monte Carlo approaches. The large deviation from linearity at low temperatures does not seem to be due to the Debye's low temperature contribution. It is shown that an anharmonic vibration in the above solid solutions, particularly at 200 K, is the cause for the small variation in the specific heat.
Theoretical studies are carried out to ascertain the dominant mechanism of Si diffusion in GaAs. ... more Theoretical studies are carried out to ascertain the dominant mechanism of Si diffusion in GaAs. Lattice dynamical model calculations have shown that the most probable diffusion mechanism is through a single vacancy even though several experiments cannot fix the mechanism as substitutional, substitutionalinterstitial pair or neutral defect pair.
Carbon supported PdCo catalysts in varying atomic ratios of Pd to Co, namely 1 : 1, 2 : 1 and 3 :... more Carbon supported PdCo catalysts in varying atomic ratios of Pd to Co, namely 1 : 1, 2 : 1 and 3 : 1, were prepared. The oxygen reduction reaction (ORR) was studied on commercial carbonsupported Pd and carbon-supported PdCo nanocatalysts in aqueous 0.1 M KOH solution with and without methanol. The structure, dispersion, electrochemical characterization and surface area of PdCo/C were determined by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Cyclic Voltammetry (CV), respectively. The electrochemical activity for ORR was evaluated from Linear Sweep Voltammograms (LSV) obtained using a rotating ring disk electrode. The catalysts were evaluated for their electrocatalytic activity towards oxygen reduction reaction (ORR) in Alkaline Polymer Electrolyte Membrane Fuel Cells (APEMFCs). PdCo(3 : 1)/C gives higher performance (85 mW cm À2) than PdCo(1 : 1)/C, PdCo(2 : 1)/C and Pd/C. The maximum electrocatalytic activity for ORR in the presence of methanol was observed for PdCo(3 : 1)/C. First principles calculations within the framework of density functional theory were performed to understand the origin of its catalytic activity based on the energy of adsorption of an O 2 molecule on the cluster, structural variation and charge transfer mechanism.
The atomic structural stability and electronic properties of LinSn4–carbon nanotube (CNT) and Lin... more The atomic structural stability and electronic properties of LinSn4–carbon nanotube (CNT) and LinSn4–graphene nanocomposites were studied by first principles calculations. Results on isolated LinSn4 clusters, with n ¼ 0–10, revealed that the tetrahedron shaped Li4Sn4 Zintl cluster is the most stable owing to it having high symmetry as well as a largest highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gap. This LinSn4 cluster weakly interacted with CNT as well as graphene for n # 4, whereas a strong cation–p interaction is observed between them for n > 4 which significantly reduces the Li clustering. The interaction between the Sn cluster and CNT or graphene is mediated only through Li ions whose absence destabilizes the Sn–C composite. These results were further confirmed by electronic density of states and band structure calculations. In addition, our calculations on hexagonal assembly of LinSn4–CNT imply that the volume change is minimal during...
This work is motivated to explore the structural stability and electronic and electrochemical pro... more This work is motivated to explore the structural stability and electronic and electrochemical properties of nanocomposites of M 4 Li n (M = Si and Ge)−carbon nanotube (CNT) by employing first-principles density functional theory calculations. By analyzing the structural stability of various M 4 Li n (n = 0−10) clusters, it is revealed that a tetrahedron-shaped M 4 Li 4 Zintl cluster is found to be highly stable. Our study on the interaction between the lithiated clusters and CNT illustrates that the charge transfer from the former to latter plays a pivotal role in stabilizing these nanocomposites. The structural stability of those nanocomposites arises as a consequence of bonding between lithiated clusters and CNT, which is mediated through the cation−π interaction. The strength of the interaction between them is well reflected in electronic structure calculations by shifting the energy levels with respect to the Fermi energy. Further, the electrochemical properties of these nanocomposites are explored by forming an assembly of the cluster-inserted CNT. The calculated average intercalation voltage of the systems is found to be low (maximum ∼1.0 V for M = Si and 1.05 V for M = Ge), which demonstrates their anodic behavior.
Magnetic property transition is essential for α-MnO 2 , since ferromagnets have potential applica... more Magnetic property transition is essential for α-MnO 2 , since ferromagnets have potential applications compared to antiferromagnets. Herein, the role of various substituents in the anion site (F, N) and cation site (Fe, Cr) on α-MnO 2 .0.25 H 2 O is studied using first principle density functional theory calculations. From our calculations, we have shown that cation (Fe and Cr) substitutions are capable of tuning the antiferromagnetic ground state into ferromagnetic state than anion (F and N) substitutions. These results provide key ideas which are an indispensable need for multifunctional usage of this material.
We studied the stability of several borophene layers on an Al(111) surface and found a structure ... more We studied the stability of several borophene layers on an Al(111) surface and found a structure called 9R using ab initio calculations. This layer competes with χ3 and β12 borophene layers and is made up of boron nonagons that form a network of hexagonal boron double chains. Remarkably, it has no B6 hexagon unlike other borophene layers. All three layers lie significantly lower in energy than the honeycomb layer recently reported on the Al(111) surface [W. Li, et al., Sci. Bull., 2018, 63, 282]. We discuss the structural stability and electronic structures of different borophene layers in light of the role of the filling factor f of boron atoms in boron hexagons in a honeycomb layer as well as charge transfer from the Al substrate to the borophene layer as obtained from the Bader charge analysis. The electron localization function shows that the 9R layer has two-center bonding within the nonagon rings and three-center bonding between the rings. Calculations of the phonon spectra sh...
Physical chemistry chemical physics : PCCP, Jan 18, 2018
Capping ligands are vital in stabilizing various nanostructures and semiconductor quantum dots in... more Capping ligands are vital in stabilizing various nanostructures and semiconductor quantum dots in which unusual optical properties, especially white light emission, have been realized. Oleic acid (OA) is a widely used capping ligand. Here, we report blue emission from OA in its free molecular form and further demonstrate this by anchoring OA over the surfaces of Al2O3, ZnAl2O4(ZA), ZnAl2O4:Eu3+ (ZA:Eu3+), and Y2O3:Eu3+. White light emission was observed from OA-modified ZA:Eu3+ nanophosphor due to mixing of broad blue emission of OA and red emission of Eu3+ through energy transfer from OA to Eu3+. A detailed study revealed the characteristic binding modes of OA and their dependence on Eu3+ concentration, structural inversion in ZA, and the optical properties and surface states in the pristine and OA-modified ZA:Eu3+. First principles density functional theory calculations were employed to provide an insight into the HOMO-LUMO levels of OA molecule and, electronic structure of pristi...
Using ab initio calculations, we demonstrate the strong influence of valence electron concentrati... more Using ab initio calculations, we demonstrate the strong influence of valence electron concentration (VEC) on the local atomic structure and electronic properties of Mo 6 S 9−x I x (x = 0−9) nanowires (NWs). We find new atomic models of the NWs with unique decoration of S/I atoms that are more stable than reported earlier. The electronic and mechanical properties of these NWs are in good agreement with experiments. Further we tuned VEC by either varying the number of I atoms or adding S/Li atoms to obtain
Nano-structures of MO-S are useful for removal of S in petroleum industry, as solid state lubrica... more Nano-structures of MO-S are useful for removal of S in petroleum industry, as solid state lubricants in space technology, and in Pt-free fuel cell research. We study by first principles density functional calculations Mo-S nanoclusters, nanowires, their assemblies, and triangular nano-platetlets all of which have been produced in laboratory. Mo-S clusters have Mo polyhedral structures and sulfur atoms cap this metal polyhedron. These structures have high stability due to strong Mo-Mo and Mo-S bonding. Some of the polyhedral clusters have non-zero magnetic moments due to the partially occupied 4d states in Mo atoms. Mo6S8 octahedral cluster has ultra-high stability and it could be condensed to form Mo-S nanowire or nanorod. However, for high S contents, we show that triangular platelets become more stable. The Mo-S nanowires are good electronic conductors and are interesting for miniature devices. Assembly of nanowires stabilizes in a hexagonal structure with vdW interactions. The tr...
Using first-principles calculations with ultrasoft pseudopotential formalism and the generalized ... more Using first-principles calculations with ultrasoft pseudopotential formalism and the generalized gradient approximation for the exchange-correlation functional, we study the stability of MonSm (n =1-6 and m ranging from n to 3n) clusters and obtain the optimal stoichiometry for each n corresponding to the magic cluster. It is found that in this size range, the lowest-energy structures favor a core of metal atoms, which is covered by sulfur. In particular, we observe that for Mo6S14 isolated clusters, a 3D structure is significantly lower in energy as compared to platelet structures found recently on Au (111) surface. The composition ratio between S and Mo in the magic clusters is less than 2 for n=3 and greater than 2 for n<3. The structural stability of the magic clusters arises from the optimization of the Mo-Mo and Mo- S bonding as well as the symmetry of the cluster. Addition of a terminal sulfur in a magic cluster generally lowers its binding energy. The presence of partially occupied d-orbitals in Mo atoms contributes to Mo-Mo bonding and for higher S concentration it leads to sulfur-sulfur bond formation. The variation in energy due to a change in the sulfur composition suggests that sulfurization of the magic clusters is generally more favorable than desulfurization.
Based on first-principles density functional calculations, a general approach for determining and... more Based on first-principles density functional calculations, a general approach for determining and analyzing the degree of spin polarization (P) in ferromagnets is presented. The approach employs the so-called tetrahedron method to evaluate the Fermi surface integrations of P in both ballistic and diffusive regimes. The validity of the method is examined by comparing the calculated P values for Fe and Ni with the experiment. The method is shown to yield highly accurate results with minimal computational effort. Within our approach, it is also possible to systematically analyze the contributions of various types of electronic states to the spin induced transport. As a case study, the transport properties of the soft-ferromagnet CeMnNi4 are investigated in order to explain the origin of the existing difference between the experimental and theoretical values of P in this intermetallic compound.
Using first principles calculations with ultrasoft pseudopotentials, we study the thick dependenc... more Using first principles calculations with ultrasoft pseudopotentials, we study the thick dependence of the atomic and electronic structures of ͑110͒ slabs of TiO 2 rutile having one to five layers. Thin slabs with an even and odd number of layers show significantly different structural characteristics and electronic properties that can affect photocatalysis as well as the catalytic behavior of supported clusters. We discuss the origin of the oscillating band gap for both an even and odd number of layers and the effects on the atomic, electronic, and magnetic properties of octahedral M 6 and icosahedral M 13 ͑M=Pd,Rh͒ clusters deposited on stoichiometric slabs with two and three layers. Calculations have also been carried out for a Pd atom deposited on different sites of a two layer slab. These results show that the bridging oxygen atoms are most reactive and preferred for adsorption. The adsorption energy of a Pd atom on the bridging site has only a weak dependence on the thickness of the slab. However, the adsorption energy of a cluster supported on a three-layer slab is significantly higher than the value for a two-layer slab due to significant structural differences and this alters the magnetic and electronic properties of the supported clusters. The magnetic moments of Pd clusters are reduced after interaction with the support. However, for Rh clusters there is an increase in the magnetic moment. In general we find that the cluster-support interactions affect mainly the cluster and support atoms that are in contact at the interface. The variation in the band gap with slab thickness can, however, lead to metallic character of the slab after cluster adsorption and this could have important consequences for catalysis.
First-principles calculations on stoichiometric Mo n S 2n and W n S 2n ͑n =1-8͒ clusters show tha... more First-principles calculations on stoichiometric Mo n S 2n and W n S 2n ͑n =1-8͒ clusters show that their lowest energy atomic structures are dominated by a central core of metal atoms while the S atoms cap this core. We discuss in detail terminal, edge, and face capping of tetrahedral and octahedral Mo clusters by sulfur atoms for off-stoichiometric compositions also. Capping on the terminal sites is found to be least favorable. Edge capped Mo 4 S 6 and face capped Mo 6 S 8 clusters have high symmetries and high stability among all the clusters we have studied. We find that magnetic isomers are lowest in energy for some clusters though bulk MS 2 ͑M = Mo and W͒ is nonmagnetic. Our results on Mo 6 S 8+p ͑p =0-6͒ clusters further show that Mo 6 S 12 is magic with 4 B magnetic moment. The origin of magnetism and bonding nature in these clusters is discussed. Our finding could lead to the possibility of magnetic clusters of a variety of nonmagnetic transition-metal compounds and their interesting assemblies.
... The addition of F atoms makes four nearest neighbors around each such carbon atom and the loc... more ... The addition of F atoms makes four nearest neighbors around each such carbon atom and the local bonding character changes from predominantly sp 2 to sp 3 type, as well as the CC bonds elongate in the range of 1.51.6 Å. ...
... a Institute for Materials Research (IMR), Tohoku University, Aoba-ku, Sendai 980-8577, Japan.... more ... a Institute for Materials Research (IMR), Tohoku University, Aoba-ku, Sendai 980-8577, Japan. b Dr. Vijay Kumar Foundation, 45 Bazaar Street, KK Nagar (West), Chennai-600 078, India. ... A non-planar isomer with three O E and three O T atoms on an Mo 3 triangle (shown in Fig. ...
The large variation in specific heats with concentration between temperatures 50 K and 200 K for ... more The large variation in specific heats with concentration between temperatures 50 K and 200 K for AI-Si and AI-Ge alloys are analysed in detail by lattice dynamical and Monte Carlo approaches. The large deviation from linearity at low temperatures does not seem to be due to the Debye's low temperature contribution. It is shown that an anharmonic vibration in the above solid solutions, particularly at 200 K, is the cause for the small variation in the specific heat.
Theoretical studies are carried out to ascertain the dominant mechanism of Si diffusion in GaAs. ... more Theoretical studies are carried out to ascertain the dominant mechanism of Si diffusion in GaAs. Lattice dynamical model calculations have shown that the most probable diffusion mechanism is through a single vacancy even though several experiments cannot fix the mechanism as substitutional, substitutionalinterstitial pair or neutral defect pair.
Carbon supported PdCo catalysts in varying atomic ratios of Pd to Co, namely 1 : 1, 2 : 1 and 3 :... more Carbon supported PdCo catalysts in varying atomic ratios of Pd to Co, namely 1 : 1, 2 : 1 and 3 : 1, were prepared. The oxygen reduction reaction (ORR) was studied on commercial carbonsupported Pd and carbon-supported PdCo nanocatalysts in aqueous 0.1 M KOH solution with and without methanol. The structure, dispersion, electrochemical characterization and surface area of PdCo/C were determined by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Cyclic Voltammetry (CV), respectively. The electrochemical activity for ORR was evaluated from Linear Sweep Voltammograms (LSV) obtained using a rotating ring disk electrode. The catalysts were evaluated for their electrocatalytic activity towards oxygen reduction reaction (ORR) in Alkaline Polymer Electrolyte Membrane Fuel Cells (APEMFCs). PdCo(3 : 1)/C gives higher performance (85 mW cm À2) than PdCo(1 : 1)/C, PdCo(2 : 1)/C and Pd/C. The maximum electrocatalytic activity for ORR in the presence of methanol was observed for PdCo(3 : 1)/C. First principles calculations within the framework of density functional theory were performed to understand the origin of its catalytic activity based on the energy of adsorption of an O 2 molecule on the cluster, structural variation and charge transfer mechanism.
The atomic structural stability and electronic properties of LinSn4–carbon nanotube (CNT) and Lin... more The atomic structural stability and electronic properties of LinSn4–carbon nanotube (CNT) and LinSn4–graphene nanocomposites were studied by first principles calculations. Results on isolated LinSn4 clusters, with n ¼ 0–10, revealed that the tetrahedron shaped Li4Sn4 Zintl cluster is the most stable owing to it having high symmetry as well as a largest highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gap. This LinSn4 cluster weakly interacted with CNT as well as graphene for n # 4, whereas a strong cation–p interaction is observed between them for n > 4 which significantly reduces the Li clustering. The interaction between the Sn cluster and CNT or graphene is mediated only through Li ions whose absence destabilizes the Sn–C composite. These results were further confirmed by electronic density of states and band structure calculations. In addition, our calculations on hexagonal assembly of LinSn4–CNT imply that the volume change is minimal during...
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Papers by P. Murugan