Density functional theory study of MnO2, TiO2 and VO2 (original) (raw)
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Formation energies of rutile metal dioxides using density functional theory
Physical Review B, 2009
We apply standard density functional theory at the generalized gradient approximation ͑GGA͒ level to study the stability of rutile metal oxides. It is well known that standard GGA exchange and correlation in some cases is not sufficient to address reduction and oxidation reactions. Especially the formation energy of the oxygen molecule and the electron self-interaction for localized d and f electrons are known shortcomings. In this paper we show that despite the known problems, it is possible to calculate the stability of a wide range of rutile oxides MO 2 , with M being Pt, Ru, Ir, Os, Pb, Re, Mn, Se, Ge, Ti, Cr, Nb, W, Mo, and V, using the electrochemical series as reference. The mean absolute error of the formation energy is 0.29 eV using the revised Perdew-Burke-Ernzerhof ͑PBE͒ GGA functional. We believe that the reason for the success is due to the reference level being H 2 and H 2 O and not O 2 and due to a more accurate description of exchange for this particular GGA functional compared to PBE. Furthermore, we would expect the self-interaction problem to be largest for the most localized d orbitals; that means the late 3d metals and since Co, Fe, Ni, and Cu do not form rutile oxides they are not included in this study. We show that the variations in formation energy can be understood in terms of a previously suggested model separating the formation energy into a metal deformation contribution and an oxygen binding contribution. The latter is found to scale with the filling of the d band.
Composition and electronic structure of Mn3O4 and Co3O4 cathodes in zinc/air batteries: a DFT study
The surface structures of promising cathode materials for zinc-air batteries, Mn3O4 and Co3O4, have been systematically studied under operating conditions by density functional theory calculations. The environment has been taken into account using grand-canonical schemes both for gas-phase and electrochemical conditions. By analysing the structures appearing in the calculated phase diagrams and Pourbaix diagrams in detail, we derive the factors underlying their stability in the gas phase and under electrochemical conditions. Changes in charge, oxidation states and spin states of the metal cations on the surface are discussed and their feasibility as active centers for the oxygen evolution and reduction reaction is thoroughly analyzed.
First Principles Analysis of the Stability and Diffusion of Oxygen Vacancies in Metal Oxides
Physical Review Letters, 2004
Oxygen vacancies in metal oxides are known to determine their chemistry and physics. The properties of neutral oxygen vacancies in metal oxides of increasing complexity (MgO, CaO, -Al 2 O 3 , and ZnO) have been studied using density functional theory. Vacancy formation energies, vacancy-vacancy interaction, and the barriers for vacancy migration are determined and rationalized in terms of the ionicity, the Madelung potential, and lattice relaxation. It is found that the Madelung potential controls the oxygen vacancy properties of highly ionic oxides whereas a more complex picture arises for covalent ZnO.
SINERGI
It is obvious to harness the intermittent renewable energy resources, energy storage applications, such as a lithium-ion battery, are very important. α‒type MnO2 is considered as an attractive cathode material for lithium-ion battery due to its relatively large (2 × 2) tunnel structure, remarkable discharge capacity, low cost, and environmental benignity. However, low intrinsic electronic conductivity of α‒type MnO2 limits its full utilization as a cathode for a lithium-ion battery. Therefore, studies to enhance the α‒type MnO2 properties are undoubted of great interest. While previous computational studies have been focused on pristine α‒type MnO2, in the present report, we present the theoretical research on potassium-intercalated α‒type MnO2 using first principle Density Functional Theory calculations for the first time. Our results showed that potassium-intercalated α‒type MnO2 improved the electronic conductivity which beneficial for energy storage application. The structural t...
MATEC Web of Conferences
In metal air battery, oxygen reacts with lithium ions on the cathode side of the cell which makes it much lighter than conventional cathodes used in Li-ion batteries. Density functional theory (DFT) study is employed in order to investigate the surfaces of, (Rutile) R-MnO2, TiO2 and VO2 (MO2), which act as catalysts in metal-air batteries. Adsorption and co-adsorption of metal K and oxygen on (110) β-MO2 surface is investigated, which is important in the discharging and charging of K- air batteries. Only five values of (gamma) are possible due to the size of the supercell and assuming that oxygen atoms occupy bulk-like positions around the surface metal atoms. The manganyl, titanyl and vanadyl terminated surface are not the only surfaces that can be formed with Γ= +2, oxygen can be adsorbed also as peroxo species (O2)2-, with less electron transfer from the surface vanadium atoms to the adatoms than in the case of manganyl, titanyl or vanadyl formation. MnO2 promotes formation of KO...
Rutile (β-)MnO2 Surfaces and Vacancy Formation for High Electrochemical and Catalytic Performance
Journal of the American Chemical Society, 2014
MnO 2 is a technologically important material for energy storage and catalysis. Recent investigations have demonstrated the success of nanostructuring for improving the performance of rutile MnO 2 in Li-ion batteries and supercapacitors and as a catalyst. Motivated by this we have investigated the stability and electronic structure of rutile (β-)MnO 2 surfaces using density functional theory. A Wulff construction from relaxed surface energies indicates a rod-like equilibrium morphology that is elongated along the c-axis, and is consistent with the large number of nanowire-type structures that are obtainable experimentally. The (110) surface dominates the crystallite surface area. Moreover, higher index surfaces than considered in previous work, for instance the (211) and (311) surfaces, are also expressed to cap the rod-like morphology. Broken coordinations at the surface result in enhanced magnetic moments at Mn sites that may play a role in catalytic activity. The calculated formation energies of oxygen vacancy defects and Mn reduction at key surfaces indicate facile formation at surfaces expressed in the equilibrium morphology. The formation energies are considerably lower than for comparable structures such as rutile TiO 2 and are likely to be important to the high catalytic activity of rutile MnO 2 .
Surface studies and catalytic properties of the bifunctional bulk MoO2 system
Surface and Interface Analysis, 2002
X-ray photoelectron spectroscopy measurements of commercial bulk MoO2 revealed the presence of MoO3 and Mo2O5 phases in the sample surface region. In situ hydrogen reduction at different temperatures up to 650 K enabled to be reduced Mo6+ and Mo5+ to Mo4+. Bulk MoO2 as prepared by hydrogen reduction of the initial samples showed very interesting catalytic properties in terms of isomerization reactions of alkanes. This catalytic activity was attributed to the MoO2 phase on the surface, which had both metallic and acidic functions (bifunctional mechanism). In addition, inelastic mean free paths in MoO2 catalyst were measured experimentally by elastic peak electron spectroscopy (EPES). Copyright © 2002 John Wiley & Sons, Ltd.
Structural and mechanical properties in rutile (tetragonal) phases of SnO 2 and TiO 2 are investigated by performing first-principle density functional theory (DFT) calculations. Generalized Gradient Approximation (GGA) potentials of electronic exchange and correlation part parameterized by Perdew-Burke-Ernzerhof (PBE) are used. Second order elastic stiffness constants, bulk modulus, first-derivative of bulk modulus, and pressure behavior of these mechanical properties are studied up to pressure of 10 GPa. Structural properties and elastic constants of SnO 2 and TiO 2 calculated in this study are compatible with experimental and other available theoretical studies. Electronic band gap energies of these semiconductors are also calculated. As expected, the calculated values by standard DFT calculations are underestimated in comparison to experimental values.
ACS Applied Materials & Interfaces
Sodium-ion batteries (SIBs) can develop costeffective and safe energy storage technology for substantial energy storage demands. In this work, we have developed manganese oxide (α-MnO 2) nanorods for SIB applications. The crystal structure, which is crucial for high-performance energy storage, is examined systematically for the metal oxide cathode. The intercalation of sodium into the α-MnO 2 matrix was studied using the theoretical density functional theory (DFT) studies. The DFT studies predict Na ions' facile diffusion kinetics through the MnO 2 lattice with an attractively low diffusion barrier (0.21 eV). When employed as a cathode material for SIBs, MnO 2 showed a moderate capacity (109 mAh•g −1 at C/20 current rate) and superior life cyclability (58.6% after 800 cycles) in NaPF 6 /EC+DMC (5% FEC) electrolyte. It shows a much higher capacity of 181 mAh•g −1 (C/20 current rate) in NaClO 4 /PC (5% FEC) electrolyte, though it suffers fast capacity fading (11.5% after 800 cycles). Our findings show that high crystallinity and hierarchical nanorod morphology of the MnO 2 are responsible for better cycling performance in conjunction with fast and sustained charge-discharge behaviors.