Ab Initio Thermodynamics Study Research Articles

Why alloying with noble metals does not decrease the oxidation of platinum: a DFT-based ab initio thermo-dynamics study.

Despite its well-known nobility, even platinum is subject to corrosion under the harsh conditions that many technical applications require. Based on the assumption that the platinum loss is mainly caused by the formation of volatile PtO2, alloying is a promising strategy to reduce it. This investigation explores the bulk stability of Pt-Au, Pt-Ir, Pt-Re, Pt-W, Pt-Ag, Pt-Rh, Pt-Cu, Pt-Ni and Pt-Co, as well as their oxides, utilizing density functional theory, as well as ab initio and literature thermodynamic data. The alloy model combines special-quasi random structures with thermodynamic properties interpolated from the constituting metals, which are complemented by the configuration entropy. The results suggest that reducing platinum oxidation by alloying decreases the overall nobility of the alloy, since platinum- and oxygen affinity of the alloying metal are related to each other. Despite this limitation, copper was identified as a promising candidate for stabilizing the platinum catalyst in the Ostwald process.

Ab Initio Thermodynamics Insight into the Structural Evolution of Working IrO2 Catalysts in Proton-Exchange Membrane Electrolyzers

At the cell voltages required to reach technologically viable current densities in proton-exchange membrane (PEM) electrolyzers, IrO2 catalysts are suspected to undergo a transformation to an amorphous hydrous form. Here, we present a systematic ab initio thermodynamics study analyzing the shape and stability of IrO2 nanoparticles in this potential range. Our results confirm a thermodynamic instability of the rutile crystal structure induced by the stabilization of highly oxidized O species at the surface already at onset potentials for the oxygen evolution reaction (OER). Intriguingly, this is preceded by a transformation of the equilibrium shape at even lower potentials. Instead of the well-studied IrO2(110) facets, this shape is dominated by IrO2(111) facets that have hitherto barely received attention. Our findings highlight the need to extend detailed characterization studies to this high-potential range, not the least to establish more suitable active-site models for the OER that may then serve as t...

Electronic structural, optical and phonon lattice dynamical properties of pure- and La-doped SrTiO3: An ab initio thermodynamics study

To better understand the electronic, optical, and thermodynamic behaviors of lanthanum doped strontium titanate (La-STO) with different doping levels at high temperature, ab initio thermodynamics have been employed to investigate their electronic structures and thermodynamic evolutions versus temperatures. The results show that with increasing La-doping level, the corresponding structures of La-STO become less stable with an increasing number of phonon soft modes. The calculated thermodynamic properties show that with increasing La-doping levels, the free energy and enthalpy changes of La-STOs are decreased at given temperature. For all La-STOs with different La-doping levels investigated, we found that in three cases doping with 25%, 37.5% and 75% La substituted for Sr, the diagonal elements of their dielectric constant matrix are not all equal, which means these crystal structures are uniaxial and anisotropic. Our results indicate that doping La into STO could alter the optical properties of pure STO to be birefringent.

Ab initio thermodynamic study on two-dimensional atomic nucleation on ZnO polar surfaces

Structures of the two-dimensional atomic nuclei on ZnO (0001)-Zn and (0001¯)-O polar surfaces were studied by first principles density functional theory. The polarity-dependent nucleation dynamics was investigated by simulating two-dimensional (2D) nuclei consisting of 1-8 ZnO monomers on both polar surfaces. According to total energy calculations, average binding energy per ZnO monomer of the surface nuclei was analyzed to investigate if the nucleation and growth will proceed reasonably in physics. We found nucleation on (0001)-Zn surface was easier than that on (0001¯)-O surface. By using atomistic thermodynamics analysis, we calculated the Gibbs free energy of formation of these nuclei and made a comparison between the two polar surfaces. On (0001)-Zn surface, the critical Gibbs free energy of formation is much lower than that on (0001¯)-O surface under the same supersaturation, which leads to a much larger ZnO growth rate and rougher morphology, in accordance with experimental results. In addition, energetic analysis of nucleation at real thermodynamic conditions was achieved by introducing the temperature- and pressure-dependent chemical potentials of ZnO precursors.

Toward Atomic-Scale Patterned Atomic Layer Deposition: Reactions of Al2O3 Precursors on a Si(001) Surface with Mixed Functionalizations

In this paper, we use density functional theory (DFT) calculations to investigate the initial surface reactions involved in the atomic layer deposition (ALD) of Al2O3 from H2O and Al(CH3)3 (trimethylaluminum, TMA) molecular precursors on the Si(001)-(2×1) reconstructed surface with different chemical terminations. Our results for the kinetic barriers and adsorption energies of both Al and oxygen precursors along different reaction pathways show the dependence of the ALD nucleation rate on the surface defects (Si dangling bonds or dimer trench) and how it can be modified with suitable p-doping. Finally, our ab initio thermodynamics study clearly determines the relation between typical ALD working conditions and the different chemical functionalizations of the Si(001) surface with the growth properties of Al2O3 nanofilms.

Ab initio thermodynamic study of the SnO2(110) surface in an O2 and NO environment: a fundamental understanding of the gas sensing mechanism for NO and NO2.

For the purpose of elucidating the gas sensing mechanism of SnO2 for NO and NO2 gases, we determine the phase diagram of the SnO2(110) surface in contact with an O2 and NO gas environment by means of an ab initio thermodynamic method. Firstly we build a range of surface slab models of oxygen pre-adsorbed SnO2(110) surfaces using (1 × 1) and (2 × 1) surface unit cells and calculate their Gibbs free energies considering only oxygen chemical potential. The fully reduced surface containing the bridging and in-plane oxygen vacancies under oxygen-poor conditions, while the fully oxidized surface containing the bridging oxygen atom and the oxygen dimer under oxygen-rich conditions, and the stoichiometric surface in between, was proved to be most stable. Using the selected plausible NO-adsorbed surfaces, we then determine the surface phase diagram of SnO2(110) surfaces in (ΔμO, ΔμNO) space. Under NO-rich conditions, the most stable surfaces were those formed by NO adsorption on the most stable surfaces in contact with only oxygen gas. Through the analysis of electronic charge transfer and density of states during NOx adsorption on the surface, we provide a meaningful understanding about the gas sensing mechanism.

First-Principles Investigation of Mercury Adsorption on the α-Fe2O3(11̅02) Surface

Theoretical investigations using density functional theory (DFT) have been carried out to understand the interaction between mercury (Hg) and hematite (α-Fe2O3), both of which are released during the coal combustion processes. A clean α-Fe2O3(1102) surface was chosen as a representative hematite model in this study based upon a previous ab initio thermodynamics study showing the high stability of this surface in the temperature range of typical flue gases. In order to determine the effect of chlorine (Cl) during Hg adsorption, the most probable adsorption sites of Hg, Cl, and HgCl on the clean α-Fe2O3 surface termination were found based on adsorption energy calculations, and the oxidation states of the adsorbates were determined by Bader charge analysis. Additionally, the projected density of states (PDOS) analysis characterizes the surface–adsorbate bonding mechanism. The adsorption energy of −0.103 eV indicates that Hg physisorbs to the clean α-Fe2O3 surface, and the subsequent Bader analysis confirms...

CO- and NO-Induced Disintegration and Redispersion of Three-Way Catalysts Rhodium, Palladium, and Platinum: An ab Initio Thermodynamics Study

Disintegration of supported nanoparticles (NPs) in the presence of reactants can lead to catalyst deactivation or be exploited to redisperse sintered catalysts. To better understand the stability of TiO2(110)-supported three-way catalysts Rh, Pd, and Pt NPs during NOx and CO reduction, we present an ab initio thermodynamics study of the feasibility for these NPs to disintegrate into adatom-reactant complexes across a large parameter space of temperatures, pressures, and sizes. The tendencies for disintegration and redispersion between supported Rh, Pd, and Pt NPs are established. Compared to both Pd and Pt, Rh NPs are found to be more susceptible to either NO- or CO-induced disintegration, due to the large and exothermic formation energy of the Rh adatom complexes. Moreover, NO is a more efficient reactant for particle redispersion than CO. These findings provide valuable insights for how to either prevent reactant-induced NP disintegration or facilitate reactant-induced redispersion of sintered catalysts.

An ab initio thermodynamics study of cobalt surface phases under ethanol steam reforming conditions

A combination of DFT and ab initio atomistic thermodynamics study illustrated the surface structure evolution of Co0/Co2+ catalysts under ethanol steam reforming conditions.

Correction to “Nature of Ptn/TiO2(110) Interface under Water-Gas Shift Reaction Conditions: A Constrained ab Initio Thermodynamics Study”

Correction to “Nature of Pt_<i>n</i>/TiO₂(110) Interface under Water-Gas Shift Reaction Conditions: A Constrained ab Initio Thermodynamics Study”

Ab initio thermodynamic study of the reaction of CF 2Cl 2 and CHF 2Cl CFCs species with OH radical

We report ab initio calculations up to the CCSD(T)/aug-cc-pVQZ and MP4(SDTQ)/aug-cc-pV5Z levels for the OH radical reaction with CF 2Cl 2 and CHF 2Cl CFCs species, aiming to assess the level of calculation required to reproduce experimental thermodynamic data: (I) CF 2Cl 2 + OH → CF 2Cl + HOCl; (II) CHF 2Cl + OH → CF 2Cl + H 2O; (III) CF 2Cl 2 + OH → CFCl 2 + HOF. We found that reaction enthalpies and Gibbs free energies can be evaluated at the CCSD(T)/aug-cc-pVQZ//MP2/aug-cc-pVDZ level, with deviations from experiment of 3%, 5%, 6%, respectively. These results can also be relevant to other studies involving CFCs interactions in large systems.

First-Principles Study of NOx and SO2 Adsorption onto SnO2 ( 110 )

An ab initio study of the adsorption of and onto surfaces is presented and related to gas-sensing applications. Using first-principles calculations density functional theory–generalized gradient approximation (DFT-GGA), the most relevant and adsorptions were analyzed by estimating their adsorption energies. The resulting values were compared to experimental desorption temperatures for and . The adsorption of the poisoning agent was also analyzed. Optimum working temperatures for minimum poisoning in sensing applications are discussed from the perspective of adsorption. In all cases, we observed that the surface reduction state has dramatic consequences on adsorption strength. An ab initio thermodynamics study is presented to analyze the stability of several surface oxygen configurations with respect to the ambient oxygen partial pressure and the temperature of the material.