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Graphene is thought to be a promising material for many applications. However, pristine graphene is not suitable for most electrochemical devices, where defect engineering is crucial for its performance. We demonstrate how the boron doping of graphene can alter its reactivity, electrical conductivity and potential application for sodium and aluminum storage, with an emphasis on novel metal-ion batteries. Using Density Functional Theory calculations, we investigate both the influence of boron concentration and the oxidation of the material on the mentioned properties. It is demonstrated that the presence of boron in graphene increases its reactivity towards atomic hydrogen and oxygen-containing species; in other words, it makes B-doped graphene more prone to oxidation. Additionally, the presence of these surface functional groups significantly alters the type and strength of the interaction of Na and Al with the given materials. Boron-doping and the oxidation of graphene is found to increase the Na storage capacity of graphene by a factor of up to four, and the calculated sodiation potentials indicate the possibility of using these materials as electrode materials in high-voltage Na-ion batteries., Godkänd;2024;Nivå 0;2024-02-09 (signyg);Funder: Serbian Ministry of Science, Technological Development, and Innovations (451-03-47/2023-01/200146); Serbian Academy of Sciences and Arts (F-190);Full text license: CC BY

Graphene is thought to be a promising material for many applications. However, pristine graphene is not suitable for most electrochemical devices, where defect engineering is crucial for its performance. We demonstrate how the boron doping of graphene can alter its reactivity, electrical conductivity and potential application for sodium and aluminum storage, with an emphasis on novel metal-ion batteries. Using Density Functional Theory calculations, we investigate both the influence of boron concentration and the oxidation of the material on the mentioned properties. It is demonstrated that the presence of boron in graphene increases its reactivity towards atomic hydrogen and oxygen-containing species; in other words, it makes B-doped graphene more prone to oxidation. Additionally, the presence of these surface functional groups significantly alters the type and strength of the interaction of Na and Al with the given materials. Boron-doping and the oxidation of graphene is found to increase the Na storage capacity of graphene by a factor of up to four, and the calculated sodiation potentials indicate the possibility of using these materials as electrode materials in high-voltage Na-ion batteries., Godkänd;2024;Nivå 0;2024-02-09 (signyg);Funder: Serbian Ministry of Science, Technological Development, and Innovations (451-03-47/2023-01/200146); Serbian Academy of Sciences and Arts (F-190);Full text license: CC BY

High-temperature properties of ceria surfaces are important for many applications. Here, we report the temperature dependencies of surface energy for (111) and (110) CeO2 obtained in the framework of the extended two-stage up-sampled thermodynamic integration using Langevin dynamics. The method was used together with machine-learning potentials called moment tensor potentials (MTPs), which were fitted to the results of the ab initio molecular dynamics calculations for (111) and (110) CeO2 at different temperatures. The parameters of MTP training and fitting were tested, and the optimal algorithm for the ceria systems was proposed. We found that the temperature increases from 0 to 2100 K led to the decrease of the Helmholtz free energy of (111) CeO2 from 0.78 to 0.64 J/m2. The energy of (110) CeO2 dropped from 1.19 J/m2 at 0 K to 0.92 J/m2 at 1800 K. We show that it is important to consider anharmonicity, as simple consideration of volume expansion gives the wrong temperature dependencies of the surface energies.

High-temperature properties of ceria surfaces are important for many applications. Here, we report the temperature dependencies of surface energy for (111) and (110) CeO2 obtained in the framework of the extended two-stage up-sampled thermodynamic integration using Langevin dynamics. The method was used together with machine-learning potentials called moment tensor potentials (MTPs), which were fitted to the results of the ab initio molecular dynamics calculations for (111) and (110) CeO2 at different temperatures. The parameters of MTP training and fitting were tested, and the optimal algorithm for the ceria systems was proposed. We found that the temperature increases from 0 to 2100 K led to the decrease of the Helmholtz free energy of (111) CeO2 from 0.78 to 0.64 J/m2. The energy of (110) CeO2 dropped from 1.19 J/m2 at 0 K to 0.92 J/m2 at 1800 K. We show that it is important to consider anharmonicity, as simple consideration of volume expansion gives the wrong temperature dependencies of the surface energies.

The development of new electrochromic materials and devices, like smart windows, has an enormous impact on the energy efficiency of modern society. One of the crucial materials in this technology is nickel oxide. Ni-deficient NiO shows anodic electrochromism, whose mechanism is still under debate. We use DFT+U calculations to show that Ni vacancy generation results in the formation of hole polarons localized at the two oxygens next to the vacancy. In the case of NiO bulk, upon Li insertion or injection of an extra electron into Ni-deficient NiO, one hole gets filled, and the hole bipolaron is converted into a hole polaron well-localized at one O atom, resulting from the transition between oxidized (colored) to reduced (bleached) state. In the case of the Ni-deficient NiO(001) surface, the qualitatively same picture is obtained upon embedding Li, Na, and K into the Ni surface vacancy, reinforcing the conclusion that the electron injection, resulting in the filling of the hole states, is responsible for the modulation of the optical properties of NiO. Hence, our results suggest a new mechanism of Ni-deficient NiO electrochromism not related to the change of the Ni oxidation states, i.e., the Ni2+/Ni3+ transition, but based on the formation and annihilation of hole polarons in oxygen p-states.

Highly effective yet affordable non-noble metal catalysts are a key component for advances in hydrogen generation via electrolysis. The synthesis of catalytic heterostructures containing established Ni in combination with surface NiO, Ni(OH)(2), and NiOOH domains gives rise to a synergistic effect between the surface components and is highly beneficial for water splitting and the hydrogen evolution reaction (HER). Herein, the intrinsic catalytic activity of pure Ni and the effect of partial electrochemical oxidation of ultra-smooth magnetron sputter-deposited Ni surfaces are analyzed by combining electrochemical measurements with transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. The experimental investigations are supplemented by Density Functional Theory and Kinetic Monte Carlo simulations. Kinetic parameters for the HER are evaluated while surface roughening is carefully monitored during different Ni film treatment and operation stages. Surface oxidation results in the dominant formation of Ni(OH)(2), practically negligible surface roughening, and 3-5 times increased HER exchange current densities. Higher levels of surface roughening are observed during prolonged cycling to deep negative potentials, while surface oxidation slows down the HER activity losses compared to as-deposited films. Thus, surface oxidation increases the intrinsic HER activity of nickel and is also a viable strategy to improve catalyst durability., Validerad;2023;Nivå 2;2023-09-26 (hanlid);Funder: Montanuniversität Leoben; Science Fund of the Republic of Serbia (PROMIS project Ratio-CAT); Ministry of Science, Technological Development; Innovations of the Republic of Serbia (451-03-47/2023-01/200146); Austrian Science Fund (FWF) (Y1236-N37)

High-temperature properties of ceria surfaces are important for many applications. Here, we report the temperature dependencies of surface energy for (111) and (110) CeO2 obtained in the framework of the extended two-stage up-sampled thermodynamic integration using Langevin dynamics. The method was used together with machine-learning potentials called moment tensor potentials (MTPs), which were fitted to the results of the ab initio molecular dynamics calculations for (111) and (110) CeO2 at different temperatures. The parameters of MTP training and fitting were tested, and the optimal algorithm for the ceria systems was proposed. We found that the temperature increases from 0 to 2100 K led to the decrease of the Helmholtz free energy of (111) CeO2 from 0.78 to 0.64 J/m2. The energy of (110) CeO2 dropped from 1.19 J/m2 at 0 K to 0.92 J/m2 at 1800 K. We show that it is important to consider anharmonicity, as simple consideration of volume expansion gives the wrong temperature dependencies of the surface energies.

Highly effective yet affordable non-noble metal catalysts are a key component for advances in hydrogen generation via electrolysis. The synthesis of catalytic heterostructures containing established Ni in combination with surface NiO, Ni(OH)(2), and NiOOH domains gives rise to a synergistic effect between the surface components and is highly beneficial for water splitting and the hydrogen evolution reaction (HER). Herein, the intrinsic catalytic activity of pure Ni and the effect of partial electrochemical oxidation of ultra-smooth magnetron sputter-deposited Ni surfaces are analyzed by combining electrochemical measurements with transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. The experimental investigations are supplemented by Density Functional Theory and Kinetic Monte Carlo simulations. Kinetic parameters for the HER are evaluated while surface roughening is carefully monitored during different Ni film treatment and operation stages. Surface oxidation results in the dominant formation of Ni(OH)(2), practically negligible surface roughening, and 3-5 times increased HER exchange current densities. Higher levels of surface roughening are observed during prolonged cycling to deep negative potentials, while surface oxidation slows down the HER activity losses compared to as-deposited films. Thus, surface oxidation increases the intrinsic HER activity of nickel and is also a viable strategy to improve catalyst durability., Validerad;2023;Nivå 2;2023-09-26 (hanlid);Funder: Montanuniversität Leoben; Science Fund of the Republic of Serbia (PROMIS project Ratio-CAT); Ministry of Science, Technological Development; Innovations of the Republic of Serbia (451-03-47/2023-01/200146); Austrian Science Fund (FWF) (Y1236-N37)

High-temperature properties of ceria surfaces are important for many applications. Here, we report the temperature dependencies of surface energy for (111) and (110) CeO2 obtained in the framework of the extended two-stage up-sampled thermodynamic integration using Langevin dynamics. The method was used together with machine-learning potentials called moment tensor potentials (MTPs), which were fitted to the results of the ab initio molecular dynamics calculations for (111) and (110) CeO2 at different temperatures. The parameters of MTP training and fitting were tested, and the optimal algorithm for the ceria systems was proposed. We found that the temperature increases from 0 to 2100 K led to the decrease of the Helmholtz free energy of (111) CeO2 from 0.78 to 0.64 J/m2. The energy of (110) CeO2 dropped from 1.19 J/m2 at 0 K to 0.92 J/m2 at 1800 K. We show that it is important to consider anharmonicity, as simple consideration of volume expansion gives the wrong temperature dependencies of the surface energies.

High-temperature properties of ceria surfaces are important for many applications. Here, we report the temperature dependencies of surface energy for (111) and (110) CeO2 obtained in the framework of the extended two-stage up-sampled thermodynamic integration using Langevin dynamics. The method was used together with machine-learning potentials called moment tensor potentials (MTPs), which were fitted to the results of the ab initio molecular dynamics calculations for (111) and (110) CeO2 at different temperatures. The parameters of MTP training and fitting were tested, and the optimal algorithm for the ceria systems was proposed. We found that the temperature increases from 0 to 2100 K led to the decrease of the Helmholtz free energy of (111) CeO2 from 0.78 to 0.64 J/m2. The energy of (110) CeO2 dropped from 1.19 J/m2 at 0 K to 0.92 J/m2 at 1800 K. We show that it is important to consider anharmonicity, as simple consideration of volume expansion gives the wrong temperature dependencies of the surface energies.

Using x-ray photoelectron spectroscopy of the oxygen 1s core level, the ratio between intact (D2O) and dissociated (OD) water in the hydrated stoichiometric TiO2 (110) surface is determined at varying coverage and temperature. In the submonolayer regime, both the D2O:OD ratio and the core-level binding energy of D2O (Delta BE) decrease with temperature. The observed variations in Delta BE are shown with density functional theory to be governed crucially and solely by the local hydrogen bonding environment, revealing a generally applicable classification and details about adsorption motifs.

Using x-ray photoelectron spectroscopy of the oxygen 1s core level, the ratio between intact (D2O) and dissociated (OD) water in the hydrated stoichiometric TiO2 (110) surface is determined at varying coverage and temperature. In the submonolayer regime, both the D2O:OD ratio and the core-level binding energy of D2O (Delta BE) decrease with temperature. The observed variations in Delta BE are shown with density functional theory to be governed crucially and solely by the local hydrogen bonding environment, revealing a generally applicable classification and details about adsorption motifs.

W18O49 has been studied by means of ab initio techniques in the framework of the density functional theory using the onsite Hubbard-U correction applied to the W-d states as well as using the hybrid potential. The existence of bipolarons is found to be an intrinsic feature of this oxide resulting in the presence of different oxidation states of W atoms (W6+ and W5+) and in the co-existence of localized and delocalized electrons. We also discuss possible switching from the W6+ to W5+ and from the W5+ to W4+ oxidation states in the presence of an O vacancy. It appears that O vacancy formation does not cause any additional charge localization at W sites but solely contributes to delocalized electrons. The calculated absorption and reflection coefficients manifest a transparency window in the visible region. At the same time, sizable absorption, occurring due to the presence of free carriers, is detected in the far and mid infrared regions. Additionally, in the near infrared region we confirm and explain an experimentally observed shielding effect originating from transitions involving the localized bipolaronic states.

Single layer low-dimensional materials are presently of emerging interest, including in the context of magnetism. In the present report, on-surface supramolecular architecturing was further developed and employed to create surface supported two-dimensional binary spin arrays on atomically clean non-magnetic Au(111). By chemical programming of the modules, different checkerboards were produced combining phthalocyanines containing metals of different oxidation and spin states, diamagnetic zinc, and a metal-free 'spacer'. In an in-depth, spectro-microscopy and theoretical account, we correlate the structure and the magnetic properties of these tunable systems and discuss the emergence of 2D Kondo magnetism from the spin-bearing components and via the physico-chemical bonding to the underlying substrate. The contributions of the individual elements, as well as the role of the electronic surface state in the bottom substrate, are discussed, also looking towards further in-depth investigations.

Here, we evaluate three different noble metal co-catalysts (Pd, Pt, and Au) that are present as single atoms (SAs) on the classic benchmark photocatalyst, TiO2. To trap the single atoms on the surface, we introduced controlled surface vacancies (Ti3+-Ov) on anatase TiO2 nanosheets by a thermal reduction treatment. After anchoring identical loadings of single atoms of Pd, Pt, and Au, we measure the photocatalytic H-2 generation rate and compare it to the classic nanoparticle co-catalysts on the nanosheets. While nanoparticles yield the well-established the hydrogen evolution reaction activity sequence (Pt > Pd > Au), for the single atom form, Pd radically outperforms Pt and Au. Based on density functional theory (DFT), we ascribe this unusual photocatalytic co-catalyst sequence to the nature of the charge localization on the noble metal SAs embedded in the TiO2 surface.

Single atom catalysts (SACs) present the ultimate level of catalyst utilization, which puts them in the focus of current research. Using density functional theory calculations, model SACs consisting of nine metals (Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au) on four different supports (pristine graphene, N- and B-doped graphene and graphene with single vacancy) are analyzed. Only graphene with a single vacancy enables the formation of SACs, which are stable in terms of aggregation and dissolution under electrochemical conditions. Reactivity of models SACs is probed using atomic (hydrogen and A = C, N, O, and S) and molecular adsorbates (AH(x), x = 1, 2, 3, or 4, depending on A). Scaling relations between adsorption energies of A and AH(x) on model SACs are confirmed. However, the scaling is broken for CH3. There is also an evident scaling between adsorption energies of atomic and molecular adsorbates on metals SAs supported by pristine, N-doped and B-doped graphene, which originates from similar electronic structures of SAs on these supports. Using the obtained data, the authors analyze the hydrogen evolution on the model SACs. Only M@graphene vacancy systems (excluding Ag and Au) are stable under hydrogen evolution conditions in highly acidic solutions.

We combined the hybrid density functional theory (DFT) calculations and X-ray absorption spectroscopy (XAS) experiments in the study of the local atomic structure around Ir ions in ZnO thin films with different iridium content. This was then used in the first principles analysis of the thermoelectric properties of material. The emphasis has been put on the conditions for a positive Seebeck coefficient and p-type electrical conductivity as the functions of the Fermi level. We studied both computationally and experimentally several possible IrOx polyhedra (complexes) with a different number of surrounding oxygens and Ir oxidation states, including those with the formation of peroxide ions (O-2(2-)). In particular, octahedral coordination of iridium ions was identified by reverse Monte Carlo (RMC) simulations of the Ir L-3-edge EXAFS spectra of ZnO:Ir thin films as the predominant complex, which is supported by the calculated lowest interstitial oxygen incorporation energies. All the calculated IrOx (x = 4, 5, 6) complexes, regardless of Ir the oxidation state, demonstrate potential for p-type conduction if the Fermi level (mu(F)) falls in the range of 0-0.8 eV from the valence band maximum (VBM) and the Ir concentration is high enough (12.5% in the present DFT calculations). Even though the corresponding calculated Seebeck coefficient (S) around 80-89 mu V K-1 slightly exceeds the experimental values, we emphasise the presence of an important plateau in the dependence of S on mu(F) in this range for two complexes with the formation of peroxide ions (O-2(2-)). We predicted also that peroxide ions O-2(2-) are characterized by the calculated phonon frequencies of 810-942 cm(-1) in agreement with our previous Raman experimental results. In this light, we discuss the high sensitivity of calculated S(mu(F)) dependences to the atomic and electronic structure.

Here, we evaluate three different noble metal co-catalysts (Pd, Pt, and Au) that are present as single atoms (SAs) on the classic benchmark photocatalyst, TiO2. To trap the single atoms on the surface, we introduced controlled surface vacancies (Ti3+-Ov) on anatase TiO2 nanosheets by a thermal reduction treatment. After anchoring identical loadings of single atoms of Pd, Pt, and Au, we measure the photocatalytic H-2 generation rate and compare it to the classic nanoparticle co-catalysts on the nanosheets. While nanoparticles yield the well-established the hydrogen evolution reaction activity sequence (Pt > Pd > Au), for the single atom form, Pd radically outperforms Pt and Au. Based on density functional theory (DFT), we ascribe this unusual photocatalytic co-catalyst sequence to the nature of the charge localization on the noble metal SAs embedded in the TiO2 surface.

Single layer low-dimensional materials are presently of emerging interest, including in the context of magnetism. In the present report, on-surface supramolecular architecturing was further developed and employed to create surface supported two-dimensional binary spin arrays on atomically clean non-magnetic Au(111). By chemical programming of the modules, different checkerboards were produced combining phthalocyanines containing metals of different oxidation and spin states, diamagnetic zinc, and a metal-free 'spacer'. In an in-depth, spectro-microscopy and theoretical account, we correlate the structure and the magnetic properties of these tunable systems and discuss the emergence of 2D Kondo magnetism from the spin-bearing components and via the physico-chemical bonding to the underlying substrate. The contributions of the individual elements, as well as the role of the electronic surface state in the bottom substrate, are discussed, also looking towards further in-depth investigations.

Here, we evaluate three different noble metal co-catalysts (Pd, Pt, and Au) that are present as single atoms (SAs) on the classic benchmark photocatalyst, TiO2. To trap the single atoms on the surface, we introduced controlled surface vacancies (Ti3+-Ov) on anatase TiO2 nanosheets by a thermal reduction treatment. After anchoring identical loadings of single atoms of Pd, Pt, and Au, we measure the photocatalytic H-2 generation rate and compare it to the classic nanoparticle co-catalysts on the nanosheets. While nanoparticles yield the well-established the hydrogen evolution reaction activity sequence (Pt > Pd > Au), for the single atom form, Pd radically outperforms Pt and Au. Based on density functional theory (DFT), we ascribe this unusual photocatalytic co-catalyst sequence to the nature of the charge localization on the noble metal SAs embedded in the TiO2 surface., QC 20210915

Single layer low-dimensional materials are presently of emerging interest, including in the context of magnetism. In the present report, on-surface supramolecular architecturing was further developed and employed to create surface supported two-dimensional binary spin arrays on atomically clean non-magnetic Au(111). By chemical programming of the modules, different checkerboards were produced combining phthalocyanines containing metals of different oxidation and spin states, diamagnetic zinc, and a metal-free 'spacer'. In an in-depth, spectro-microscopy and theoretical account, we correlate the structure and the magnetic properties of these tunable systems and discuss the emergence of 2D Kondo magnetism from the spin-bearing components and via the physico-chemical bonding to the underlying substrate. The contributions of the individual elements, as well as the role of the electronic surface state in the bottom substrate, are discussed, also looking towards further in-depth investigations., QC 20210921

Here, we evaluate three different noble metal co-catalysts (Pd, Pt, and Au) that are present as single atoms (SAs) on the classic benchmark photocatalyst, TiO2. To trap the single atoms on the surface, we introduced controlled surface vacancies (Ti3+-Ov) on anatase TiO2 nanosheets by a thermal reduction treatment. After anchoring identical loadings of single atoms of Pd, Pt, and Au, we measure the photocatalytic H-2 generation rate and compare it to the classic nanoparticle co-catalysts on the nanosheets. While nanoparticles yield the well-established the hydrogen evolution reaction activity sequence (Pt > Pd > Au), for the single atom form, Pd radically outperforms Pt and Au. Based on density functional theory (DFT), we ascribe this unusual photocatalytic co-catalyst sequence to the nature of the charge localization on the noble metal SAs embedded in the TiO2 surface.

Single layer low-dimensional materials are presently of emerging interest, including in the context of magnetism. In the present report, on-surface supramolecular architecturing was further developed and employed to create surface supported two-dimensional binary spin arrays on atomically clean non-magnetic Au(111). By chemical programming of the modules, different checkerboards were produced combining phthalocyanines containing metals of different oxidation and spin states, diamagnetic zinc, and a metal-free 'spacer'. In an in-depth, spectro-microscopy and theoretical account, we correlate the structure and the magnetic properties of these tunable systems and discuss the emergence of 2D Kondo magnetism from the spin-bearing components and via the physico-chemical bonding to the underlying substrate. The contributions of the individual elements, as well as the role of the electronic surface state in the bottom substrate, are discussed, also looking towards further in-depth investigations.

Using x-ray photoelectron spectroscopy of the oxygen 1s core level, the ratio between intact (D2O) and dissociated (OD) water in the hydrated stoichiometric TiO2 (110) surface is determined at varying coverage and temperature. In the submonolayer regime, both the D2O:OD ratio and the core-level binding energy of D2O (Delta BE) decrease with temperature. The observed variations in Delta BE are shown with density functional theory to be governed crucially and solely by the local hydrogen bonding environment, revealing a generally applicable classification and details about adsorption motifs.

By means of ab-initio techniques we have investigated changes in the structure and electronic properties of alkaline-earth metal silicide (Ca2Si, Mg2Si and MgCaSi) nanotubes caused by the curvature-induced effects. It is revealed that the curvature-induced effects can: 1) stabilize Mg2Si nanotubes in a phase, which is metastable for the parent 2D Mg2Si; 2) lead to an energy gain as a result of 2D to nanotube structural transformation in the case of ternary MgCaSi nanotubes; 3) modify the band dispersion and band gaps for nanotubes with the diameters less than 30 angstrom. In addition, Mg2Si and MgCaSi nanotubes are found to be direct band-gap (0.5-1.2 eV) materials with appreciable oscillator strength of the first direct transitions.

Problems associated with carbon support corrosion under operating fuel cell conditions require the identification of alternative supports for platinum-based nanosized electrocatalysts. Platinum supported on manganese vanadate (Pt/MnV2O6 ) was prepared by microwave irradiation method and characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy with energy dispersive spectroscopy, and transmission electron microscopy. The borohydride oxidation reaction (BOR) on Pt/MnV2O6 was studied in highly alkaline media using voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. BOR electrocatalytic activity of Pt/MnV2O6 was also compared with that of commercial Pt/C (46 wt% Pt) electrocatalyst. The apparent activation energy of BOR at Pt/MnV2O6 was estimated to be 32 kJ mol(-1) and the order of reaction to be 0.51, indicating that borohydride hydrolysis proceeds in parallel with its oxidation. Long-term stability of Pt/MnV2O6 under BOR typical conditions was observed. A laboratory-scale direct borohydride fuel cell assembled with a Pt/MnV2O6 anode reached a specific power of 274 W g(-1). Experimental results on Pt/MnV2O6 were complemented by DFT calculations, which indicated good adherence of Pt to MnV2O6, beneficial for electrocatalyst stability.

Using x-ray photoelectron spectroscopy of the oxygen 1s core level, the ratio between intact (D2O) and dissociated (OD) water in the hydrated stoichiometric TiO2 (110) surface is determined at varying coverage and temperature. In the submonolayer regime, both the D2O:OD ratio and the core-level binding energy of D2O (Delta BE) decrease with temperature. The observed variations in Delta BE are shown with density functional theory to be governed crucially and solely by the local hydrogen bonding environment, revealing a generally applicable classification and details about adsorption motifs.

Here, we evaluate three different noble metal co-catalysts (Pd, Pt, and Au) that are present as single atoms (SAs) on the classic benchmark photocatalyst, TiO2. To trap the single atoms on the surface, we introduced controlled surface vacancies (Ti3+-Ov) on anatase TiO2 nanosheets by a thermal reduction treatment. After anchoring identical loadings of single atoms of Pd, Pt, and Au, we measure the photocatalytic H-2 generation rate and compare it to the classic nanoparticle co-catalysts on the nanosheets. While nanoparticles yield the well-established the hydrogen evolution reaction activity sequence (Pt > Pd > Au), for the single atom form, Pd radically outperforms Pt and Au. Based on density functional theory (DFT), we ascribe this unusual photocatalytic co-catalyst sequence to the nature of the charge localization on the noble metal SAs embedded in the TiO2 surface.

Single layer low-dimensional materials are presently of emerging interest, including in the context of magnetism. In the present report, on-surface supramolecular architecturing was further developed and employed to create surface supported two-dimensional binary spin arrays on atomically clean non-magnetic Au(111). By chemical programming of the modules, different checkerboards were produced combining phthalocyanines containing metals of different oxidation and spin states, diamagnetic zinc, and a metal-free 'spacer'. In an in-depth, spectro-microscopy and theoretical account, we correlate the structure and the magnetic properties of these tunable systems and discuss the emergence of 2D Kondo magnetism from the spin-bearing components and via the physico-chemical bonding to the underlying substrate. The contributions of the individual elements, as well as the role of the electronic surface state in the bottom substrate, are discussed, also looking towards further in-depth investigations.

Using x-ray photoelectron spectroscopy of the oxygen 1s core level, the ratio between intact (D2O) and dissociated (OD) water in the hydrated stoichiometric TiO2 (110) surface is determined at varying coverage and temperature. In the submonolayer regime, both the D2O:OD ratio and the core-level binding energy of D2O (Delta BE) decrease with temperature. The observed variations in Delta BE are shown with density functional theory to be governed crucially and solely by the local hydrogen bonding environment, revealing a generally applicable classification and details about adsorption motifs.

Here, we evaluate three different noble metal co-catalysts (Pd, Pt, and Au) that are present as single atoms (SAs) on the classic benchmark photocatalyst, TiO2. To trap the single atoms on the surface, we introduced controlled surface vacancies (Ti3+-Ov) on anatase TiO2 nanosheets by a thermal reduction treatment. After anchoring identical loadings of single atoms of Pd, Pt, and Au, we measure the photocatalytic H-2 generation rate and compare it to the classic nanoparticle co-catalysts on the nanosheets. While nanoparticles yield the well-established the hydrogen evolution reaction activity sequence (Pt > Pd > Au), for the single atom form, Pd radically outperforms Pt and Au. Based on density functional theory (DFT), we ascribe this unusual photocatalytic co-catalyst sequence to the nature of the charge localization on the noble metal SAs embedded in the TiO2 surface.

Single layer low-dimensional materials are presently of emerging interest, including in the context of magnetism. In the present report, on-surface supramolecular architecturing was further developed and employed to create surface supported two-dimensional binary spin arrays on atomically clean non-magnetic Au(111). By chemical programming of the modules, different checkerboards were produced combining phthalocyanines containing metals of different oxidation and spin states, diamagnetic zinc, and a metal-free 'spacer'. In an in-depth, spectro-microscopy and theoretical account, we correlate the structure and the magnetic properties of these tunable systems and discuss the emergence of 2D Kondo magnetism from the spin-bearing components and via the physico-chemical bonding to the underlying substrate. The contributions of the individual elements, as well as the role of the electronic surface state in the bottom substrate, are discussed, also looking towards further in-depth investigations.

Using x-ray photoelectron spectroscopy of the oxygen 1s core level, the ratio between intact (D2O) and dissociated (OD) water in the hydrated stoichiometric TiO2 (110) surface is determined at varying coverage and temperature. In the submonolayer regime, both the D2O:OD ratio and the core-level binding energy of D2O (Delta BE) decrease with temperature. The observed variations in Delta BE are shown with density functional theory to be governed crucially and solely by the local hydrogen bonding environment, revealing a generally applicable classification and details about adsorption motifs.

Hydrogen evolution reaction (HER) is one of the most important reactions in electrochemistry. This is not only because it is the simplest way to produce high purity hydrogen and the fact that it is the side reaction in many other technologies. HER actually shaped current electrochemistry because it was in focus of active research for so many years (and it still is). The number of catalysts investigated for HER is immense, and it is not possible to overview them all. In fact, it seems that the complexity of the field overcomes the complexity of HER. The aim of this review is to point out some of the latest developments in HER catalysis, current directions and some of the missing links between a single crystal, nanosized supported catalysts and recently emerging, single-atom catalysts for HER.

Developing ultraefficient electrocatalytic materials for the hydrogen evolution reaction (HER) with low content of expensive platinum group metals (PGMs) via low-energy-input procedures is the key to the successful commercialization of green water electrolysis technologies for sustainable production of high-purity hydrogen. In this study, we report a facile room-temperature synthesis of ultrafine metallic Ir nanoparticles on conductive, proton-intercalated TiO2 nanotube (H-TNT) arrays via galvanic displacement. A series of experiments demonstrate that a controlled transformation of the H-TNT surface microstructure from neat open-top tubes to disordered nanostripe bundles ("nanograss") is highly beneficial for providing an abundance of exposed Ir active sites. Consequently, for nanograss-engineered composites, outstanding HER activity metrics are achieved even at very low Ir(iii) precursor concentrations. An optimum Ir@TNT cathode loaded with 5.7 mu g(Ir) cm(-2) exhibits an overpotential of -63 mV at -100 mA cm(-2) and a mass activity of 34 A mg(Ir)(-1) at -80 mV under acidic conditions, along with excellent catalytic durability and structural integrity. Density functional theory (DFT) simulations reveal that the hydrogen-rich TiO2 surface not only stabilizes the deposited Ir and weakens its H binding strength to a moderate intensity, but also actively takes part in the HER mechanism by refreshing the Ir catalytic sites near the Ir|H-TiO2 interface, thus substantially promoting H-2 generation. The comprehensive characterization combined with theory provides an in-depth understanding of the electrocatalytic behavior of H-TNT supported PGM nanoparticles and demonstrates their high potential as competitive electrocatalyst systems for the HER.

Understanding the reactions in M-O-2 cells (M = Li or Na) is of great importance for further advancement of this promising technology. Computational modelling can be helpful along this way, but an adequate approach is needed to model such complex systems. We propose a new scheme for modelling processes in M-O-2 cells, where reference energies are obtained from high-level theory, CCSD(T), while the interactions of reaction intermediates with catalyst surfaces are extracted from computationally less expensive DFT. The approach is demonstrated for the case of graphene-based surfaces as model catalysts in Li-O-2 and Na-O-2 cells using the minimum viable mechanism. B-doped graphene was identified as the best catalyst amongst considered surfaces, while pristine graphene performs poorly. Moreover, we show that the inclusion of dispersion corrections for DFT has a significant impact on calculated discharge and charge potentials and suggests that long-range dispersion interactions should always be considered when graphene-based materials are modelled as electrocatalysts. Finally, we offer general guidelines for designing new ORR catalysts for M-O-2 cells in terms of the optimization of the interactions of catalyst surface with reaction intermediates.

In pursuit of the ideal photocatalyst, cheap and stable semiconductor TiO(2)is considered to be a good choice if one is able to reduce its band gap and decrease the recombination rate of charge carriers. The approach that offers such improvements for energy conversion applications is the modification of TiO(2)with nitrogen and noble metals. However, the origin of these improvements and possibilities for further design of single-atom catalysts are not always straightforward. To shed light on the atomic-scale picture, we modeled the nitrogen-doped (001) anatase TiO(2)surface as a support for palladium and platinum single-atom deposition. The thermodynamics of various synthesis routes for Pd/Pt deposition and nitrogen doping is considered based on density functional theory (DFT)-calculated energies, highlighting the effect of nitrogen doping on metal dimer formation and metal-support interaction. XPS analysis of the valence band of the modified TiO(2)nanocrystals, and the calculated charge transfer and electronic structure of single-atom catalysts supported on the (001) anatase TiO(2)surface provide an insight into modifications occurring in the valence zone of TiO(2)due to nitrogen doping and Pd/Pt deposition at the surface. DFT results also show that substitutional nitrogen doping significantly increases metal-support interaction, while interstitial nitrogen doping promotes only Pt-support interaction.

For carbon-based materials, in contrast to metal surfaces, a general relationship between strain and reactivity is not yet established, even though there are literature reports on strained graphene. Knowledge of such relationships would be extremely beneficial for understanding the reactivity of graphene-based surfaces and finding optimisation strategies which would make these materials more suitable for targeted applications. Here we investigate the effects of compressive and tensile strain (up to +/- 5%) on the structure, electronic properties and reactivity of pure, N-doped and P-doped graphene, using DFT calculations. We demonstrate the possibility of tuning the topology of the graphene surface by strain, as well as by the choice of the dopant atom. The reactivity of (doped) strained graphene is probed using H and Na as simple adsorbates of great practical importance. Strain can both enhance and weaken H and Na adsorption on (doped) graphene. In case of Na adsorption, a linear relationship is observed between the Na adsorption energy on P-doped graphene and the phosphorus charge. A linear relationship between the Na adsorption energy on flat graphene surfaces and strain is found. Based on the adsorption energies and electrical conductivity, potentially good candidates for hydrogen storage and sodiumion battery electrodes are discussed.

We present the results of an extended theoretical study of the structure, phonon, electronic and optical properties of 2D alkaline-earth metal silicides, germanides and stannides (2D Me2X, where Me=Mg, Ca, Sr, Ba and X=Si, Ge, Sn). The performed analysis has shown the occurrence of the pseudo passivation effect and ionic chemical bonding in these 2D Me2X. In addition, the preformed investigation of their phonon spectra has shown the absence of imaginary frequencies indicating the stability of these 2D structures. The band structure calculations performed using the hybrid functional have revealed that all 2D Me2X are semiconductors with the gap varying from 0.12 to 1.01 eV. Among them Mg- and Ca-based 2D materials are direct band-gap semiconductors with the first direct transition having appreciable oscillator strength. We also propose to consider ternary 2D silicides, germanides and stannides with different Me atoms as a feasible way to modify properties of parent 2D Me2X.

We present the ab initio study of different phases of Nb12O29, which has been done in the framework of density functional theory using the onsite Hubbard-U correction applied to the Nb-d states. We vary the U parameter in between 0 and 7 eV and suggest U = 3.7–5.0 eV to be most appropriate for the description of Nb12O29. We show that one cannot get any adequate description of this oxide using the crystallographic unit cell but at least 3 times larger supercell is needed increased along the shortest lattice parameter b to accommodate lattice distortions associated with polaron formation. Our results obtained for the enlarged cells show the possibility of simultaneous co-existence of localized states (polaron formation) and delocalized states providing metal-like properties of Nb12O29, in qualitative agreement with available experimental data.

Hydrogen evolution reaction (HER) is one of the most important reactions in electrochemistry. This is not only because it is the simplest way to produce high purity hydrogen and the fact that it is the side reaction in many other technologies. HER actually shaped current electrochemistry because it was in focus of active research for so many years (and it still is). The number of catalysts investigated for HER is immense, and it is not possible to overview them all. In fact, it seems that the complexity of the field overcomes the complexity of HER. The aim of this review is to point out some of the latest developments in HER catalysis, current directions and some of the missing links between a single crystal, nanosized supported catalysts and recently emerging, single-atom catalysts for HER.

In pursuit of the ideal photocatalyst, cheap and stable semiconductor TiO2 is considered to be a good choice if one is able to reduce its band gap and decrease the recombination rate of charge carriers. The approach that offers such improvements for energy conversion applications is the modification of TiO2 with nitrogen and noble metals. However, the origin of these improvements and possibilities for further design of single-atom catalysts are not always straightforward. To shed light on the atomic-scale picture, we modeled the nitrogen-doped (001) anatase TiO2 surface as a support for palladium and platinum single-atom deposition. The thermodynamics of various synthesis routes for Pd/Pt deposition and nitrogen doping is considered based on density functional theory (DFT)-calculated energies, highlighting the effect of nitrogen doping on metal dimer formation and metal-support interaction. XPS analysis of the valence band of the modified TiO2 nanocrystals, and the calculated charge transfer and electronic structure of single-atom catalysts supported on the (001) anatase TiO2 surface provide an insight into modifications occurring in the valence zone of TiO2 due to nitrogen doping and Pd/Pt deposition at the surface. DFT results also show that substitutional nitrogen doping significantly increases metal-support interaction, while interstitial nitrogen doping promotes only Pt-support interaction. © the Owner Societies.

Hydrogen evolution reaction (HER) is one of the most important reactions in electrochemistry. This is not only because it is the simplest way to produce high purity hydrogen and the fact that it is the side reaction in many other technologies. HER actually shaped current electrochemistry because it was in focus of active research for so many years (and it still is). The number of catalysts investigated for HER is immense, and it is not possible to overview them all. In fact, it seems that the complexity of the field overcomes the complexity of HER. The aim of this review is to point out some of the latest developments in HER catalysis, current directions and some of the missing links between a single crystal, nanosized supported catalysts and recently emerging, single-atom catalysts for HER.

Hydrogen evolution reaction (HER) is one of the most important reactions in electrochemistry. This is not only because it is the simplest way to produce high purity hydrogen and the fact that it is the side reaction in many other technologies. HER actually shaped current electrochemistry because it was in focus of active research for so many years (and it still is). The number of catalysts investigated for HER is immense, and it is not possible to overview them all. In fact, it seems that the complexity of the field overcomes the complexity of HER. The aim of this review is to point out some of the latest developments in HER catalysis, current directions and some of the missing links between a single crystal, nanosized supported catalysts and recently emerging, single-atom catalysts for HER.

In pursuit of the ideal photocatalyst, cheap and stable semiconductor TiO2 is considered to be a good choice if one is able to reduce its band gap and decrease the recombination rate of charge carriers. The approach that offers such improvements for energy conversion applications is the modification of TiO2 with nitrogen and noble metals. However, the origin of these improvements and possibilities for further design of single-atom catalysts are not always straightforward. To shed light on the atomic-scale picture, we modeled the nitrogen-doped (001) anatase TiO2 surface as a support for palladium and platinum single-atom deposition. The thermodynamics of various synthesis routes for Pd/Pt deposition and nitrogen doping is considered based on density functional theory (DFT)-calculated energies, highlighting the effect of nitrogen doping on metal dimer formation and metal-support interaction. XPS analysis of the valence band of the modified TiO2 nanocrystals, and the calculated charge transfer and electronic structure of single-atom catalysts supported on the (001) anatase TiO2 surface provide an insight into modifications occurring in the valence zone of TiO2 due to nitrogen doping and Pd/Pt deposition at the surface. DFT results also show that substitutional nitrogen doping significantly increases metal-support interaction, while interstitial nitrogen doping promotes only Pt-support interaction. © the Owner Societies.

Hydrogen evolution reaction (HER) is one of the most important reactions in electrochemistry. This is not only because it is the simplest way to produce high purity hydrogen and the fact that it is the side reaction in many other technologies. HER actually shaped current electrochemistry because it was in focus of active research for so many years (and it still is). The number of catalysts investigated for HER is immense, and it is not possible to overview them all. In fact, it seems that the complexity of the field overcomes the complexity of HER. The aim of this review is to point out some of the latest developments in HER catalysis, current directions and some of the missing links between a single crystal, nanosized supported catalysts and recently emerging, single-atom catalysts for HER.

Hydrogen evolution reaction (HER) is one of the most important reactions in electrochemistry. This is not only because it is the simplest way to produce high purity hydrogen and the fact that it is the side reaction in many other technologies. HER actually shaped current electrochemistry because it was in focus of active research for so many years (and it still is). The number of catalysts investigated for HER is immense, and it is not possible to overview them all. In fact, it seems that the complexity of the field overcomes the complexity of HER. The aim of this review is to point out some of the latest developments in HER catalysis, current directions and some of the missing links between a single crystal, nanosized supported catalysts and recently emerging, single-atom catalysts for HER.

We demonstrate electrodeposition as a synthesis method for fabrication of Al coatings, up to 10 μm thick, containing a high density of genuine growth twins. This has not been expected since the twin boundary energy of pure Al is very high. TEM methods were used to analyze deposited Al and its nanoscaled twins. DFT methods confirmed that the influence of the substrate is limited to the layers close to the interface. Our findings are different from those achieved by sputtering of Al coatings restricted to a thickness less than 100 nm with twins dominated by epitaxial effects. We propose that in the case of electrodeposition, a high density of twins arises because of fast nucleation and is additionally promoted by a monolayer of adsorbed hydrogen originating from water impurities. Therefore, electrodeposition is a viable approach for tailoring the structure and properties of thicker, deposited Al coatings reinforced by twins.

Multipolaron solutions were studied in the framework of the Holstein one-dimensional molecular crystal model. The study was performed in the continuous limit where the crystal model maps into the nonlinear Schrödinger equation for which a new periodic dnoidal solution was found for the multipolaron system. In addition, the stability of the multi-polaron solutions was examined, and it was found that cnoidal and dnoidal solutions stabilize in different ranges of the parameter space. Moreover, the model was studied under the influence of nonlocal effects and the polaronic dynamics was described in terms of internal solitonic modes.

By means of ab initio calculations, we have estimated stability of 2D Me2X (Me = Mg, Ca, Sr, Ba and X = Si, Ge, Sn) in the T and Td phases, which are similar to the ones of 2D transition metal chalcogenides, in addition to their phonon spectra. The T phase is found to be more stable for 2D Ca2X, Sr2X and Ba2X, whereas the Td phase is predicted to be the ground state for 2D Mg2X. We have also discussed that imaginary frequencies in the calculated phonon spectra of 2D Me2X, which appeared in the vicinity of the Gamma point, were not necessarily associated with the dynamic instability.