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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Spin-orbit-controlled metal–insulator transition in Sr 2 IrO 4

In the context of correlated insulators, where electron–electron interactions (U) drive the localization of charge carriers, the metal–insulator transition is described as either bandwidth- or filling-controlled. Motivated by the challenge of the insulating phase in Sr 2 IrO 4 , a new class of correlated insulators has been proposed, in which spin–orbit coupling (SOC) is believed to renormalize the bandwidth of the half-filled j eff = 1/2 doublet, allowing a modest U to induce a charge-localized phase. Although this framework has been tacitly assumed, a thorough characterization of the ground state has been elusive. Furthermore, direct evidence for the role of SOC in stabilizing the insulating state has not been established, because previous attempts at revealing the role of SOC have been hindered by concurrently occurring changes to the filling. Here, we overcome this challenge by employing multiple substituents that introduce well-defined changes to the signatures of SOC and carrier concentration in the electronic structure, as well as a new methodology that allows us to monitor SOC directly. Specifically, we study Sr 2 Ir 1-x T x O 4 (T = Ru, Rh) by angle-resolved photoemission spectroscopy, combined with ab initio and supercell tight-binding calculations. This allows us to distinguish relativistic and filling effects, thereby establishing conclusively the central role of SOC in stabilizing the insulating state of Sr 2 IrO 4 . Most importantly, we estimate the critical value for SOC in this system to be λ c = 0.42 ± 0.01 eV, and provide the first demonstration of a spin–orbit-controlled metal–insulator transition.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Unconventional Anomalous Hall Effect in Hexagonal Polar Magnet Y 3 Co 8 Sn 4

A rare realization of unconventional anomalous Hall effect (UAHE) both below and above the magnetic transition temperature (T C ) in a hexagonal noncentrosymmetric magnet Y 3 Co 8 Sn 4 , using a combined experimental and ab initio calculations. Occurrence of such UAHE is mainly attributed to the reciprocal ($\mathscr{KS}$) topology (i.e., the presence of topological Weyl points at/near the Fermi level), along with some contribution from the topological magnetic texture (at low temperatures), as inferred from the measured field-dependent ac susceptibility. The effect of UAHE on the measured transport behavior however evolves differently with temperature above and below T C = 53 K, suggesting different physical mechanism responsible in the two phases. A unique planar ferrimagnetic ordering is found to be the most stable state with ab-plane as the easy plane below T C . The simulated net magnetization and the moment per Co atom agrees fairly well with the experimentally measured values. A reasonably large anomalous Hall conductivity (AHC) is also observed in both the phases (above and below T C ) of the present compound, which is again not so ubiquitous. In conclusion, the results underscore the family of R 3 Co 8 Sn 4 (R = rare earth) polar magnets as a compelling backdrop for exploring the synergy of magnetism and topological non-trivial electronic states, pivotal for spintronic applications.

Density functional theory calculations↗
DOE OSTI2023

CoTe 2 : A Quantum Critical Dirac Metal with Strong Spin Fluctuations

Abstract Quantum critical points separating weak ferromagnetic and paramagnetic phases trigger many novel phenomena. Dynamical spin fluctuations not only suppress the long‐range order, but can also lead to unusual transport and even superconductivity. Combining quantum criticality with topological electronic properties presents a rare and unique opportunity. Here, by means of ab initio calculations and magnetic, thermal, and transport measurements, it is shown that the orthorhombic CoTe 2 is close to ferromagnetism, which appears suppressed by spin fluctuations. Calculations and transport measurements reveal nodal Dirac lines, making it a rare combination of proximity to quantum criticality and Dirac topology.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Kinetic Pathways Templated by Low-Temperature Intermediates during Solid-State Synthesis of Layered Oxides

Layered oxides have been the dominant cathodes in lithium-ion batteries, and among them, high-nickel (Ni) systems are attractive because of their high capacity. For practical use, synthetic control of stoichiometry and structural ordering is crucial but has been nontrivial due to the complexity inherent to synthesis reactions, which often proceed via nonequilibrium pathways. In this paper, we report here a combined in situ synchrotron X-ray diffraction and ab initio study of solid-state synthesis of layered oxides starting from acetate precursors for LiCoO 2 and LiNiO 2 and their solid solution LiNi 0.8 Co 0.2 O 2 . While all three systems ultimately evolve into the same thermodynamically stable layered phase ($R\overline{3}m$), each chemistry involves distinct metastable intermediates. We explain the phase progressions using a structural template model, demonstrating that during the synthesis of LiCoO 2 , the formed metastable spinel polymorph (Li 2 Co 2 O 4 ; $Fd\overline{3}m$) is a kinetically facile lithiation product of spinel Co 3 O 4 —the low-temperature (LT) intermediate from the decomposed Co-acetate. Similarly, in the Ni-based systems, the acetate decomposition products, rocksalts (Ni,Co)O, topotactically template the kinetic pathways of forming disordered rocksalts (Li x (Ni,Co) 2–x O 2 ; $Fm\overline{3}m$), consequently leading to off-stoichiometric Li x (Ni,Co)O 2 with undesired high Li/Ni mixing. These findings highlight new opportunities for engineering precursors to form LT intermediates that template the synthesis of target phases and structural properties.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Unusual dynamics of tetrahedral liquids caused by the competition between dynamic heterogeneity and structural heterogeneity

Tetrahedral liquids exhibit intriguing thermodynamic and transport properties because of the various ways tetrahedra can be packed and connected. Recently, an unusual temperature dependence of the stretching exponent β in a model tetrahedral liquid ZnCl 2 from T m + 85 K to T m + 35 K has been reported using neutron-spin echo spectroscopy. This discovery stands in sharp contrast to other glass-forming liquids. In this study, we conducted neural network force field driven molecular dynamic simulations of ZnCl 2 . We found a non-monotonic temperature dependence of β from liquid to supercooled liquid temperatures. Further structural decomposition and dynamic analysis suggest that this unusual dynamic behavior is a result of the competition between the decrease in the diversity of tetrahedra motifs (structural heterogeneity) and the increase in glassy dynamic heterogeneity. Furthermore, this result may contribute to new understandings of the structural relaxation of other network liquids.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Peierls transition, ferroelectricity, and spin-singlet formation in monolayer VOI 2

Using ab initio density functional theory and single-orbital Hubbard model calculations via the density matrix renormalization group method, we systematically studied the monolayer VOI 2 with a 3d 1 electronic configuration. Our phonon calculations indicate that the orthorhombic Pmm2 FE-II phase is the most likely ground state, involving a ferroelectric (FE) distortion along the a axis and V-V dimerization along the b axis. Specifically, the “pseudo Jahn-Teller” effect caused by the coupling between empty V (d xz/yz and d 3z 2 -r 2 ) and O 2p states is proposed as the mechanism that stabilizes the FE distortion from the paraelectric phase. Moreover, the half-filled metallic d xy band displays a Peierls instability along the b axis, inducing a V-V dimerization. Additionally, we found very short-range antiferromagnetic coupling along the V-V chain due to the formation of nearly decoupled spin singlets in the ground state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Thermodynamics of Plutonium Monocarbide from Anharmonic and Relativistic Theory

Thermodynamics of plutonium monocarbide is studied from first-principles theory that includes relativistic electronic structure and anharmonic lattice vibrations. Density-functional theory (DFT) is expanded to include orbital-orbital coupling in addition to the relativistic spin-orbit interaction for the electronic structure and it is combined with anharmonic, temperature dependent, lattice dynamics derived from the self-consistent ab initio lattice dynamics (SCAILD) method. The obtained thermodynamics are compared to results from simpler quasi-harmonic theory and experimental data. Formation enthalpy, specific heat, and Gibbs energy calculated from the anharmonic model are validated by direct comparison with a calculation of phase diagram (CALPHAD) assessment of PuC and sub-stochiometric PuC0.896. Overall, the theory reproduces CALPHAD results and measured data for PuC rather well, but the comparison is hampered by the sub-stoichiometric nature of plutonium monocarbide. It was found that a bare theoretical approach that ignores spin-orbit and orbital-orbital coupling (orbital polarization) of the plutonium 5f electrons promotes too soft phonons and Gibbs energies that are incompatible with that of the CALPHAD assessment of the experimental data. The investigation of PuC suggests that the electronic structure is accurately described by plutonium 5f electrons as “band like” and delocalized, but correlate through spin polarization, orbital polarization, and spin-orbit coupling, in analogy to previous findings for plutonium metal.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Vacancy-Induced Tunable Kondo Effect in Twisted Bilayer Graphene

In single sheets of graphene, vacancy-induced states have been shown to host an effective spin-1/2 hole that can be Kondo screened at low temperatures. Here, we show how these vacancy-induced impurity states survive in twisted bilayer graphene (TBG), which thus provides a tunable system to probe the critical destruction of the Kondo effect in pseudogap hosts. Ab initio calculations and atomic-scale modeling are used to determine the nature of the vacancy states in the vicinity of the magic angle in TBG, demonstrating that the vacancy can be treated as a quantum impurity. Utilizing this insight, we construct an Anderson impurity model with a TBG host that we solve using the numerical renormalization group combined with the kernel polynomial method. We determine the phase diagram of the model and show how there is a strict dichotomy between vacancies in the AA/BB versus AB/BA tunneling regions. In AB/BA vacancies, the Kondo temperature at the magic angle develops a broad distribution with a tail to vanishing temperatures due to multifractal wave functions at the magic angle. Finally, we argue that scanning tunneling microscopy in the vicinity of the vacancy can act as a probe of both the critical single-particle states and the underlying many-body ground state in magic-angle TBG.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Directed gas phase preparation of ethynylallene (H 2 CCCHCCH; X 1 A') via the crossed molecular beam reaction of the methylidyne radical (CH; X 2 Π) with vinylacetylene (H 2 CCHCCH; X 1 A')

The gas-phase bimolecular reaction of the methylidyne (CH; X 2 Π) radical with vinylacetylene (H 2 CCHCCH; X 1 A') was conducted at a collision energy of 20.3 kJ mol –1 under single collision conditions exploiting the crossed molecular beam experimental results merged with ab initio electronic structure calculations and ab initio molecular dynamics (AIMD) simulations. The laboratory data reveal that the bimolecular reaction proceeds barrierlessly via indirect scattering dynamics through long-lived C 5 H 5 reaction intermediate(s) ultimately dissociating to C 5 H 4 isomers along with atomic hydrogen with the latter predominantly originating from the vinylacetylene reactant as confirmed by the isotopic substitution experiments in the D1-methylidyne–vinylacetylene reaction. Combined with ab initio calculations of the potential energy surface (PES) and statistical Rice–Ramsperger–Kassel–Marcus (RRKM) calculations, the experimental determined reaction energy of –146 ± 26 kJ mol –1 along with the distribution minimum of T(θ) at 90° and isotopic substitution experiments suggest ethynylallene (p1; ΔrG = –230 ± 4 kJ mol –1 ) as the dominant product. The ethynylallene (p1) may be formed with extensive rovibrational excitation, which would result in a lower maximum translational energy. Further, AIMD simulations reveal that the reaction dynamics leads to p1 (ethynylallene, 75%) plus atomic hydrogen with the dominant initial complex being i1 formed by methylidyne radical addition to the double C[double bond, length as m-dash]C bond in vinylacetylene. Altogether, combining the crossed molecular beam experimental results with ab initio electronic structure calculations and ab initio molecular dynamics (AIMD) simulations, ethynylallene (p1) is expected to represent the dominant product in the reaction of the methylidyne (CH; X 2 Π) radical with vinylacetylene (H 2 CCHCCH; X 1 A').

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Metastable piezoelectric group-IV monochalcogenide monolayers with a buckled honeycomb structure

Multiple two-dimensional materials are being naïvely termed stable on the grounds of displaying phonon dispersions with no negative frequencies and of not collapsing on molecular dynamics calculations at fixed volume. But, if these phases do not possess the smallest possible structural energy, how does one understand and establish their actual meta stability? To answer this question, twelve two-dimensional group-IV monochalcogenide monolayers (SiS, SiSe, SiTe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbS, PbSe, and PbTe) with a buckled honeycomb atomistic structure—belonging to symmetry group P3m1—displaying an out-of-plane intrinsic electric polarization are shown to be metastable by three independent methods. First, we uncover a coordination-preserving structural transformation from the low-buckled honeycomb structure onto the lower-energy Pnm2 1 (or Pmmn for PbS, PbSe, and PbTe) phase to estimate energy barriers E B that must be overcome during such structural transformation. Using the curvature of the local minima and E B as inputs to Kramers escape formula, large escape times are found, implying the structural metastability of the buckled honeycomb phase (with the exception of PbS and PbSe, these phases display escape times ranging from 700 years to multiple times the age of the universe and can be considered “stable” for practical purposes in that relative sense). The second demonstration is provided by phonon dispersion relations that include the effect of long-range Coulomb forces and display no negative vibrational modes. The third and final demonstration of structural metastability is furnished by room-temperature ab initio molecular dynamics for selected compounds. Here, the magnitude of the electronic band gap evolves with chemical composition. Different from other binary two-dimensional compounds such as transition metal dichalcogenide monolayers and hexagonal boron nitride monolayers which only develop an in-plane piezoelectric response, the twelve group-IV monochalcogenide monolayers with a buckled honeycomb structure also display out-of-plane piezoelectric properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Lattice dynamics and thermodynamics for δ -plutonium from density functional theory

Here, we present results from density functional theory (DFT) calculations of the lattice dynamics (phonons) and thermodynamics for δ-phase plutonium. The fully relativistic electronic structure is calculated assuming a three-dimensional noncollinear magnetic structure in conjunction with DFT and the general gradient approximation for the electron exchange and correlation interactions. The electronic-structure model is further enhanced by addressing strong orbital-orbital coupling via the conventional orbital-polarization (OP) scheme as has been successfully done for plutonium. The temperature dependence of the phonons is calculated within the self-consistent ab initio lattice dynamics approach. The obtained phonons compare very well with measurements although a modest overestimation of the transverse L-point [ξξξ] phonon is acknowledged. Calculated thermal vibration amplitudes and the associated Debye-Waller temperatures are close to experiments. Lattice, electronic, and magnetic contributions to the heat capacity are predicted and consistent to a few percent with that deduced from experimental data. Good agreement is only achieved when a magnetic contribution to the specific heat is recognized. The parameter-free DFT+OP electronic model is thus capable of predicting phonon properties and thermodynamic behavior of δ-phase plutonium rather accurately.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Role of Surface Features on the Initial Dissolution of CH 3 NH 3 PbI 3 Perovskite in Liquid Water: An Ab Initio Molecular Dynamics Study

In this study, the degradation of CH 3 NH 3 PbI 3 (MAPbI 3 ) hybrid organic inorganic perovskite (HOIP) by water has been the major issue hampering its use in commercial perovskites solar cells (PSCs) as MAPbI 3 HOIP have been known to easily degrade in the presence of water molecules. However, even though there have been numerous studies investigating this phenomenon, there is still no consensus on the mechanisms of initial stages of dissolution. Here, we attempt to consolidate differing mechanistic interpretations previously reported in the literature through the use of the first-principles constrained ab-initio molecular dynamics (AIMD) to study the mechanisms, kinetics, and thermodynamics that accompany the degradation of MAPbI 3 HOIP in liquid water. We consider not only the dissolution of the species found on the pristine MAPbI 3 HOIP surfaces, but also the dissolution from defect sites to imitate the successive degradation steps, and propose a sequence of events in the initial phase of MAPbI 3 HOIP dissolution. By comparing the dissolution free energy barrier between surface species of different surficial types, we find that the dominant dissolution mechanisms of surface species varies widely based on the specific surface features adjacent to the dissolving ion. The high sensitivity of dissolution mechanism to surface features has contributed to the many dissolution mechanisms proposed in the literature. In contrast, the dissolution free energy barriers are mainly determined by the dissolving species rather than the type of surfaces, and the type of surfaces the ions are dissolving from are inconsequential toward the dissolution free energy barrier. However, the presence of surface defects such as vacancy sites are found to significantly lower the dissolution free energy barriers. Based on the estimated dissolution free energy barriers from different types of surfaces that we investigated in this study, we proposed that the dissolution of MAPbI 3 HOIP in liquid water originates from surface defect sites that propagate laterally along the surface layer of the MAPbI 3 HOIP crystal.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Synthesis and thermophysical property determination of NaCl-PuCl3 salts

Currently, a knowledge gap exists in the available data and understanding of thermophysical properties relating to fresh fuel salts, especially those containing plutonium. These data are necessary for designing, constructing, and licensing future commercial molten-salt reactors. Thermophysical properties, such as melting temperature, salt stability, density, and heat capacity were ascertained using NaCl-PuCl3 (36 mol% PuCl3) and a more sodium rich composition containing 25 mol% PuCl3. The NaCl-PuCl3 salt mixture was synthesized for this study and contained 63.4 mol% NaCl, 36.3 mol% PuCl3 and was 99.7% pure. Upon heating, the NaCl–PuCl3 eutectic was stable at temperatures up to 800 °C. The onset of melting occurred at 451 ± 3 °C, and the enthalpy of fusion was determined to be 23.0 ± 1.4 kJ/mol. Heat capacity measurements in the liquid phase ranged from 107.7 to 91.3 J/mol.K, with an average value of 104.6 ± 11.4 J/mol.K between 500 and 650 °C. Three independent trials of the molten NaCl-PuCl3 salt found the density to be ?(T) = 3.8589 – 9.5342·10-4 T(°C). In addition, ab initio molecular dynamic simulations to calculate density and heat capacity values are included.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2026

Effect of Solvent on the Local Structure, Dynamics, and Vibrational Density of States in Sn-BEA Zeolite

Lewis acid zeolites are attractive catalysts for epoxidation and biomass valorization, as they are highly active and selective in the liquid phase and can operate at or near ambient conditions. While a rich experimental literature exists on liquid-phase Lewis acid zeolite catalysis, our understanding of the molecular organization and solvent dynamics in the vicinity of Lewis acid sites with differing metal site speciation remains limited. In this work, we investigate the molecular coordination and diffusion of two common solvents (methanol and water) around the closed and open Sn-BEA zeolite active sites using molecular dynamics simulations with a machine-learned interatomic potential trained on ab initio molecular dynamics trajectories. Molecular dynamics simulations reveal that introducing active sites significantly enhances local order in the first and second solvation shells compared to the pure silica case. For methanol, both closed and open active sites are singly coordinated, while more than two water molecules coordinate the open site. In contrast to methanol, we observed that water molecules dissociate, leading to the formation of additional Sn-OH and silanol groups away from the active site. The diffusion coefficients of water and methanol are functions of the solvent population in the pore. Here, our work provides insights into how active site speciation in Lewis acid zeolites affects solvent coordination, diffusion, and vibrational signature. This information is foundational for catalyst design and optimization of liquid-phase catalytic processes in zeolites. It also demonstrates the suitability of machine-learned interatomic potentials for modeling reactive systems, enabling sufficiently long trajectories for appropriate statistical averaging.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Ab initio calculations for void swelling bias in α - and δ -plutonium

Void swelling can develop in materials under persistent irradiation when nonequilibrium vacancy and self-interstitial populations migrate under sufficiently asymmetric interaction biases. In conventional metals, the propensity is determined to the first approximation by comparing point-defect relaxation strains. We thus present DFT-based calculations of structures and formation energies and volumes of point defects in the α and the δ phases of plutonium. Here we discuss the pros and cons of various levels of electronic structure theory: spin polarization, spin-orbit coupling, and orbital polarization. Our results show that lattice defects in δ-Pu, in contrast to most fcc metals, have surprisingly small formation volumes. Equally unexpected are the large defect formation volumes found in the low-symmetry α-Pu phase. Both these unusual properties can be satisfactorily explained from defect-induced spin/orbital moment formation and destruction in the Pu phases. Surprisingly, the point defects in α-Pu are found to induce far larger transformation of the local electronic structure than in δ-Pu. When we use the calculated defect properties to estimate the classic void swelling bias in each of the phases, we find it to be unusually small in δ-Pu but likely much larger in α-Pu. Hence, swelling rates and mechanisms can diverge dramatically between the different phases of Pu. Especially in the transient regime before the formation of large defect clusters, the swelling rate of α-Pu can reliably be expected to be much larger than δ-Pu. However, accurate forecasts over longer times will require the conventional void-swelling theory to be modified to handle the complexities presented by the different Pu phases. As a case in point, we show the possible anomalous temperature dependence of vacancy properties in δ-Pu, caused by entropic contributions from defect-induced spin-lattice fluctuations. Such complications may affect defect-defect interactions and thus alter the void swelling bias.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Thermodynamics and Magnetism of YCo5 Compound Doped with Fe and Ni: An Ab Initio Study

YCo5 permanent magnet exhibits high uniaxial magnetocrystalline anisotropy energy and has a high Curie temperature. These are good properties for a permanent magnet, but YCo5 has a low energy product, which is notably insufficient for a permanent magnet. In order to improve the energy product in YCo5, we suggest replacing cobalt with iron, which has a much bigger magnetic moment. With a combination of density-functional-theory calculations and thermodynamic CALculation of PHAse Diagrams (CALPHAD) modeling, we show that a new magnet, YFe3(Ni1-xCox)2, is thermodynamically stable and exhibits an improved energy product without significant detrimental effects on the magnetocrystalline anisotropy energy or the Curie temperature.

anisotropy↗
DOE OSTI2025

Experimental and theoretical investigation into the high pressure deflagration products of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105)

Diamond anvil cell (DAC) laser ignition experiments and reactive ab initio molecular dynamics (AIMD) simulations were performed on the high explosive (HE) LLM-105 to investigate its high pressure (HP) deflagration chemistry. Raman and optical spectroscopy measurements reveal LLM-105 reacts into an opaque carbonaceous product at 4–25 GPa. At pressures >~ 27 GPa, the reaction product consists of an amorphous optically transparent solid and nitrogen (N 2 ) in the solid phase. While not a one-to-one comparison due to the small time and length scales, the HP AIMD simulations show that some of the product is molecular N 2 , in qualitative agreement with experiment, while above 20 GPa most of the product consists of large amorphous C x H y N z O k clusters. Clustering is enhanced with pressure and reduces with temperature. In the experiments with initial sample pressure >~ 25 GPa, the pressure within the DAC decreases with minimal change in DAC cavity area. At initial sample pressures of 43.9 GPa, when quenched to 0 K, simulations predict a product experiencing a lower pressure consistent with the experimental measurement at lower load pressures. In conclusion, the results are important for understanding the HP deflagration chemistry of LLM-105.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

First-principle investigation on catalytic hydrogenation of benzaldehyde over Pt-group metals

We report that understanding the hydrogenation of organic compounds in the aqueous phase has always been fundamentally important for improving carbon neutral pathways to fuels and value-added chemicals. In this study, we investigated both thermodynamic and kinetic profiles of benzaldehyde hydrogenation over the Pd(111) and Pt(111) metal surfaces using density functional theory (DFT) and ab initio molecular dynamic (AIMD) simulations. The adsorption of H 2 shows the mixed preference of H adsorption sites on the Pt(111), while the fcc adsorption site is dominant for H on the Pd(111). When benzaldehyde is added to the systems, we observe a strong reduction of benzaldehyde on charged Pd (111) surface compared with that on neutral surface. In contrast, charged state of the Pt(111) surface does not change their interaction. Subsequent hydrogenation reaction of benzaldehyde over Pd(111), proceeding via Langmuir-Hinshelwood mechanism, is affected by two major factors: the presence of H 2 O solvent and surface charge. The presence of H 2 O solvent greatly reduces the activation energy of C-H and O-H bond formation during the hydrogenation process. Furthermore, the hydrogenation step via C-H bond formation is preferred thermodynamically and kinetically over O-H bond formation during thermocatalytic hydrogenation, while the opposite trend holds true during electrocatalytic hydrogenation.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗