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Ammonia electrooxidation in aqueous solutions can be a highly energy‐efficient process in producing nitrate and nitrite while generating hydrogen under ambient conditions. However, the kinetics of this reaction are slow and the role of catalyst in facilitating ammonia electrooxidation is not well understood. In this study, a high‐performance NiOOH‐Ni catalyst is introduced for converting ammonia into nitrite with Faraday efficiency of up to 90.4% and nitrate production rate of 1 mg h−1 cm−2. By employing Operando techniques, the role of NiOOH catalyst is elucidated in the dynamic electrooxidation of ammonia. Density functional theory (DFT) calculations support experimental observations and reveal the mechanism of the electrochemical oxidation of ammonia to nitrite and nitrate. Overall, this research contributes to the development of a cost‐effective and highly efficient catalyst for large‐scale ammonia electrolysis, while shedding light on the underlying mechanism of the NiOOH catalyst in ammonia electrooxidation. [ABSTRACT FROM AUTHOR]

Electrocatalytic activities for the oxygen reduction reaction (ORR) of Au electrodes modified by as prepared and size selected (0.45–1.0, 0.22–0.45, and 0.1–0.22 µm) h-BN nanosheet (BNNS), which is an insulator, were examined in O2 saturated 0.5M H2SO4 solution. The overpotential was reduced by all the BNNS modifications, and the smaller the size, the smaller the overpotential for ORR, i.e., the larger the ORR activity, in this size range. The overpotential was reduced by as much as ∼330 mV compared to a bare Au electrode by modifying the Au surface by the BNNS of the smallest size range (0.1–0.22 µm). The overpotential at this electrode was only 80 mV more than that at the Pt electrode. Both the rotation disk electrode experiments with Koutecky–Levich analysis and rotating ring disk electrode measurements showed that more than 80% of oxygen is reduced to water via the four-electron process at this electrode. These results strongly suggest and theoretical density functional theory calculations support that the ORR active sites are located at the edges of BNNS islands adsorbed on Au(111). The decrease in size of BNNS islands results in an effective increase in the number of the catalytically active sites and, hence, in the increase in the catalytic activity of the BNNS/Au(111) system for ORR. [ABSTRACT FROM AUTHOR]

The catalytic activity of oxygen functionalized hexagonal boron nitride (h‐BN) with >B−O−O−B< and >B−O−B< active sites at the zigzag edges for oxidative dehydrogenation (ODH) of light alkanes, specifically ethane (C2H6), propane (C3H8), butane (C4H10), and isobutane (HC(CH3)3) is explored. It has been found that the reaction pathway involves two H atom transfer steps with small activation energies. We demonstrate that the synergy of two active sites, >B−O−O−B< and >B−O−B<, is crucial for the first and second H‐transfer, respectively. With the increase in molecular mass of the considered light alkanes, the ODH reaction temperature decreases. In the case of butane and isobutane, the ODH reaction occurs almost at the same temperature indicating that the reaction is independent of the shape of the isomer. The rate‐limiting nature of the first H‐transfer step is predicted. The charge redistribution during H‐transfers and localized oxygen atomic states in the conduction band are explored to suggest possible descriptors for the rational design of new catalysts. The universal action of the >B−O−O−B< and >B−O−B< active sites for ODH of the light alkanes paves the way for metal‐free BN‐based materials for future catalytic applications. [ABSTRACT FROM AUTHOR]

The nature and structure of occupied and empty valence electronic states (molecular orbitals, MOs) of the [Ni(Salen)] molecular complex (NiO2N2C16H14) have been studied by X-ray photoemission and absorption spectroscopy combined with density functional theory (DFT) calculations. As a result, the composition of the high-lying occupied and low-lying unoccupied electronic states has been identified. In particular, the highest occupied molecular orbital (HOMO) of the complex is found to be predominantly located on the phenyl rings of the salen ligand, while the states associated with the occupied Ni 3d-derived molecular orbitals (MOs) are at higher binding energies. The lowest unoccupied molecular orbital (LUMO) is also located on the salen ligand and is formed by the 2pπ orbitals of carbon atoms in phenyl groups of the salen macrocycle. The unoccupied MOs above the LUMO reflect σ- and π-bonding between Ni and its nearest neighbours. All valence states have highly mixed character. The specific nature of the unoccupied Ni 3d-derived σ-MO is a consequence of donor–acceptor chemical bonding in [Ni(Salen)]. [ABSTRACT FROM AUTHOR]

Cyclo‐dehydrogenation is of importance to induce the planarization of molecules on noble surfaces upon annealing. In contrast to a number of successful syntheses of polycyclic aromatic hydrocarbons by forming carbon–carbon bonds, it is still rare to conduct conjugation and cleavage of carbon–nitrogen bonds in molecules. Here, we present a systematic transformation of the C−N bonds in11,11,12,12‐tetraphenyl‐1,4,5,8‐tetraazaanthraquinodimethane as well as three other derivatives on Au(111). With bond‐resolved scanning tunneling microscopy, we discovered novel the "heterocyclic segregation" reaction of one pyrazine ring with two nitrogen atoms to form two quinoline rings with one nitrogen each. Density functional theory calculations showed that the intramolecular ring‐forming and ‐opening of N‐heterocycles are strongly affected by the initial hydrogen–substrate interaction. [ABSTRACT FROM AUTHOR]

The mechanism of dissociative D2 adsorption on Ti2O4−, which serves as a model for an oxygen vacancy on a titania surface, is studied using infrared photodissociation spectroscopy in combination with density functional theory calculations and a recently developed single-component artificial force induced reaction method. Ti2O4− readily reacts with D2 under multiple collision conditions in a gas-filled ion trap held at 16 K forming a global minimum-energy structure (DO–Ti–(O)2–Ti(D)–O)−. The highly exergonic reaction proceeds quasi barrier-free via several intermediate species, involving heterolytic D2-bond cleavage followed by D-atom migration. We show that, compared to neutral Ti2O4, the excess negative charge in Ti2O4− is responsible for the substantial lowering of the D2 dissociation barrier, but does not affect the molecular D2 adsorption energy in the initial physisorption step. [ABSTRACT FROM AUTHOR]

In this Personal Account, we review the work of our group in the area of environmental and energy-related nanocatalysis over the past seven years. We focus on understanding the fundamental mechanisms that control the properties of atomic clusters and nanoparticles - a form of matter that is intermediate between atoms and their bulk counterpart. The emphasis is on the theoretical design of effective catalysts based on cheap and abundant elements. The main idea that stands behind our work is that even catalytically inactive or completely inert materials can be functionalized at the nanoscale via the size, structure, morphology, and support effects. Such an approach opens up new ways to design catalytically active systems based on materials never before considered as catalysts. In particular, we demonstrate that hexagonal boron nitride ( h-BN), which has been traditionally considered an inert material, can be functionalized and become active for a number of catalytic reactions involving oxygen activation, oxidation by molecular oxygen, and the oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

Molecular and dissociative adsorption of O2 on Au atoms supported on the regular and defected hexagonal boron nitride (h-BN) surface has been studied theoretically using density functional theory. It is shown that even weak interaction of Au with the defect-free h-BN support has an unusually strong influence on the binding and catalytic activation of the molecular oxygen. The strong interaction of Au with vacancy point defects on the h-BN surface is accompanied by the large charge transfer to/from the adsorbate which can considerably affect the catalytic activity of the supported Au. It is demonstrated that activation of the molecular O2 and barriers for O2 dissociation on the supported Au atom can be affected by the interaction of Au with the pristine or defected h-BN support. Therefore, the h-BN surface cannot be considered as an absolutely inert support for Au. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

This work is devoted to the elucidation of the applicability of the jellium model to the description of alkali cluster properties. We compare the jellium model results with those derived within ab initio theoretical approaches and with experiments. On the basis of Hartree–Fock and local-density approximations we have calculated the binding energies per atom, ionization potentials, deformation parameters and optimized values of the Wigner–Seitz radii for neutral and singly charged sodium clusters with the number of atoms N ≤ 20. The characteristics calculated within the framework of the deformed jellium model are compared with the results derived from ab initio simulations of cluster electronic and ionic structure based on density functional theory and systematic post Hartree–Fock many-body perturbation theory accounting for all electrons in the system. The comparison performed demonstrates the great role of the cluster shape deformations in the formation cluster properties and quite reasonable level of applicability of the deformed jellium model. This elucidates the similarities of atomic cluster physics with the physics of atomic nuclei. [ABSTRACT FROM AUTHOR]

The mechanism of CO oxidation by O2 on Au atoms supported on the pristine and defected hexagonal boron nitride (h-BN) surface has been studied theoretically using density functional theory. It is found that O2 binds stronger than CO on an Au atom supported on the defect free h-BN surface and h-BN surface with nitrogen vacancy (VN@h-BN), but weaker than CO on a free Au atom or Au trapped by a boron vacancy (VB@h-BN). The excess of the positive or negative charge on Au can considerably change its catalytic properties and enhance activation of the adsorbed O2. Coadsorption of CO and O2 on Au, Au/VN@h-BN, and Au/VB@h-BN results in additional charge transfer to O2. Various pathways of the CO oxidation reaction by molecular oxygen are studied. We found two different pathways for CO oxidation: a two-step pathway where two CO2 molecules are formed independently, and a self-promotion pathway where oxidation of the first CO molecule is promoted by the second CO molecule. Interaction of Au with the defect-free and defected h-BN surface considerably affects the CO oxidation reaction pathways and barriers. Therefore, Au supported on the h-BN surface (pristine or defected) cannot be considered as pseudo-free atom and support effects have to be taken into account, even when the interaction of Au with the support is weak. [ABSTRACT FROM AUTHOR]

We report an observation of a quantum tunneling effect in a proton-transfer (PT) during potential-induced transformation of dioxygen on a platinum electrode in a low overpotential (η) region at 298 K. However, this quantum process is converted to the classical PT scheme in the high η region. Therefore, there is a quantum-to-classical transition of the PT (QCT-PT) process as a function of the potential, which is confirmed by theoretical analysis. This observation indicates that the quantum tunneling governs the multistep electron-proton-driven transformation of dioxygen in the low η condition. [ABSTRACT FROM AUTHOR]

Review: 62 refs. [ABSTRACT FROM AUTHOR]

Overpotential for oxygen reduction reaction (ORR) at Au electrode is reported to be reduced by 0.27 V by the modification with boron nitride nanosheet (BNNS) but oxygen is reduced only to H 2 O 2 by 2-electron process at Au electrode. Here we demonstrate that the decoration of BNNS with gold nanoparticles (AuNP) not only reduces the overpotential for ORR further by ca. 50 mV, but also opens a 4-electron reduction route to water. Both rotating disk electrode experiments with Koutecky–Levich analysis and rotating ring disk electrode measurements show that more than 50% of oxygen is reduced to water via 4-electron process at Au–BNNS/Au electrode while less than 20 and 10% of oxygen are reduced to water at the BNNS/Au and bare Au electrodes, respectively. Theoretical analysis of free energy profiles for ORR at the BN monolayer with and without Au 8 cluster placed on Au(111) shows significant stabilization of adsorbed oxygen atom by the Au 8 cluster, opening a 4-electron reduction pathway. [ABSTRACT FROM AUTHOR]

Molecular passivation is a prominent approach for improving the performance and operation stability of halide perovskite solar cells (HPSCs). Herein, we reveal discernible effects of diammonium molecules with either an aryl or alkyl core onto Methylammonium-free perovskites. Piperazine dihydriodide (PZDI), characterized by an alkyl core-electron cloud-rich-NH terminal, proves effective in mitigating surface and bulk defects and modifying surface chemistry or interfacial energy band, ultimately leading to improved carrier extraction. Benefiting from superior PZDI passivation, the device achieves an impressive efficiency of 23.17% (area ~1 cm 2 ) (low open circuit voltage deficit ~0.327 V) along with superior operational stability. We achieve a certified efficiency of ~21.47% (area ~1.024 cm 2 ) for inverted HPSC. PZDI strengthens adhesion to the perovskite via -NH 2 I and Mulliken charge distribution. Device analysis corroborates that stronger bonding interaction attenuates the defect densities and suppresses ion migration. This work underscores the crucial role of bifunctional molecules with stronger surface adsorption in defect mitigation, setting the stage for the design of charge-regulated molecular passivation to enhance the performance and stability of HPSC., (© 2024. The Author(s).)

Isolated nickel-doped aluminum oxide cations (NiO m )(Al 2 O 3 ) n (AlO) + with m = 1-2 and n = 1-3 are investigated by infrared photodissociation (IRPD) spectroscopy in combination with density functional theory and the single-component artificial force-induced reaction method. IRPD spectra of the corresponding He-tagged cations are reported in the 400-1200 cm -1 spectral range and assigned based on a comparison to calculated harmonic IR spectra of low-energy isomers. Simulated spectra of the lowest energy structures generally match the experimental spectra, but multiple isomers may contribute to the spectra of the m = 2 series. The identified structures of the oxides ( m = 1) correspond to inserting a Ni-O moiety into an Al-O bond of the corresponding (Al 2 O 3 ) 1-3 (AlO) + cluster, yielding either a doubly or triply coordinated Ni 2+ center. The m = 2 clusters prefer similar structures in which the additional O atom either is incorporated into a peroxide unit, leaving the oxidation state of the Ni 2+ atom unchanged, or forms a biradical comprising a terminal oxygen radical anion Al-O •- and a Ni 3+ species. These clusters represent model systems for under-coordinated Ni sites in alumina-supported Ni catalysts and should prove helpful in disentangling the mechanism of selective oxidative dehydrogenation of alkanes by Ni-doped catalysts.

A great variety of two-dimensional (2D) boron allotropes (borophenes) were extensively studied in the past decade in the quest for graphene-like materials with potential for advanced technological applications. Among them, the 2D honeycomb boron is of specific interest as a structural analogue of graphene. Recently it has been synthesized on the Al(111) substrate; however it remains unknown to what extent does honeycomb boron behave like graphene. Here we elucidate the structural and electronic properties of this unusual 2D material with a combination of core-level X-ray spectroscopies, scanning tunneling microscopy, and DFT calculations. We demonstrate that in contrast to graphene on lattice-mismatched metal surfaces, honeycomb boron cannot wiggle like a blanket on Al(111), but rather induces reconstruction of the top metal layer, forming a stoichiometric AlB 2 sheet on top of Al. Our conclusions from theoretical modeling are fully supported by X-ray absorption spectra showing strong similarity in the electronic structure of honeycomb boron on Al(111) and thick AlB 2 films. On the other hand, a clear separation of the electronic states of the honeycomb boron into π- and σ-subsystems indicates an essentially 2D nature of the electronic system in both one-layer AlB 2 and bulk AlB 2 .

Cyclo-dehydrogenation is of importance to induce the planarization of molecules on noble surfaces upon annealing. In contrast to a number of successful syntheses of polycyclic aromatic hydrocarbons by forming carbon-carbon bonds, it is still rare to conduct conjugation and cleavage of carbon-nitrogen bonds in molecules. Here, we present a systematic transformation of the C-N bonds in11,11,12,12-tetraphenyl-1,4,5,8-tetraazaanthraquinodimethane as well as three other derivatives on Au(111). With bond-resolved scanning tunneling microscopy, we discovered novel the "heterocyclic segregation" reaction of one pyrazine ring with two nitrogen atoms to form two quinoline rings with one nitrogen each. Density functional theory calculations showed that the intramolecular ring-forming and -opening of N-heterocycles are strongly affected by the initial hydrogen-substrate interaction., (© 2021 Wiley-VCH GmbH.)

In nanocatalysis, growing attention has recently been given to investigation of energetically low-lying structural isomers of atomic clusters, because some isomers can demonstrate better catalytic activity than the most stable structures. In this study, we present a comparative investigation of catalytic activity for NO dissociation of a pair of the energetically degenerated isomers of Cu 13 cluster having C 2 and C s symmetries. It is shown that although these isomers have similar structural, electronic, and optical properties, they can possess very different catalytic activities. The effect of isomerization between cluster isomers is considered using state-of-the-art automated reaction pathway search techniques such as an artificial force induced reaction (AFIR) method as a part of a global reaction route mapping (GRRM) strategy. This method allows effectively to locate a large number of possible reaction pathways and transition states (TSs). In total, 12 TSs for NO dissociation were obtained for Cu 13 , of C 2 , C s , as well as I h isomers. Sparse modeling analysis shows that LUMO is strongly negatively correlated with total energy of TSs. For most TSs, LUMO has the antibonding character of NO, consisting of the interaction between π* of NO and SOMO of Cu 13 . Therefore, an increase in the strength of interaction between NO molecule and Cu 13 cluster causes the rise in energy of the LUMO, resulting in lowering of the TS energy for NO dissociation. The combination of the automated reaction pathway search technique and sparse modeling represents a powerful tool for analysis and prediction of the physicochemical properties of atomic clusters, especially in the regime of structural fluxionality, where traditional methods based on random geometry search analyses are difficult.

We report an observation of a quantum tunneling effect in a proton-transfer (PT) during potential-induced transformation of dioxygen on a platinum electrode in a low overpotential (η) region at 298 K. However, this quantum process is converted to the classical PT scheme in the high η region. Therefore, there is a quantum-to-classical transition of the PT (QCT-PT) process as a function of the potential, which is confirmed by theoretical analysis. This observation indicates that the quantum tunneling governs the multistep electron-proton-driven transformation of dioxygen in the low η condition.

The mechanism of dissociative D 2 adsorption on Ti 2 O 4 - , which serves as a model for an oxygen vacancy on a titania surface, is studied using infrared photodissociation spectroscopy in combination with density functional theory calculations and a recently developed single-component artificial force induced reaction method. Ti 2 O 4 - readily reacts with D 2 under multiple collision conditions in a gas-filled ion trap held at 16 K forming a global minimum-energy structure (DO-Ti-(O) 2 -Ti(D)-O) - . The highly exergonic reaction proceeds quasi barrier-free via several intermediate species, involving heterolytic D 2 -bond cleavage followed by D-atom migration. We show that, compared to neutral Ti 2 O 4 , the excess negative charge in Ti 2 O 4 - is responsible for the substantial lowering of the D 2 dissociation barrier, but does not affect the molecular D 2 adsorption energy in the initial physisorption step.

The material choice for efficient electrocatalysts is limited because it is necessary to be highly active as well as highly stable. One direction to solve this issue is to understand elementary steps of electrode processes and build an unconventional strategy for a conversion of inert and, therefore, stable materials into efficient catalysts. Herein, we propose a simple concept for obtaining catalysts from inert and hence stable materials by forming their heterojunctions, namely, covering inert Au with corrugated carbon-nitrogen-based two-dimensional porous frameworks. It shows more than 10 times better activity for the hydrogen evolution reaction than for the pure Au surface, and it also demonstrates the high catalytic activity for the oxygen reduction reaction (ORR) via an effective four-electron reduction mechanism, which is different from the usual two-electron reduction typical for ORR on Au surfaces. This activity induced by formation of a heterojunction was analyzed by a conjugation of computational and experimental methods and found to originate from alternative efficient reaction pathways that emerged by the corrugated porous framework and the Au surface. This work provides not only the method for creating active surface but also the knowledge on elementary steps of such complicated multielectron transfer reactions, thereby leading to intriguing strategies for developing energy conversion reactions based on materials which had never been considered as catalysts before.

Bottom-up strategies can be effectively implemented for the fabrication of atomically precise graphene nanoribbons. Recently, using 10,10'-dibromo-9,9'-bianthracene (DBBA) as a molecular precursor to grow armchair nanoribbons on Au(111) and Cu(111), we have shown that substrate activity considerably affects the dynamics of ribbon formation, nonetheless without significant modifications in the growth mechanism. In this paper we compare the on-surface reaction pathways for DBBA molecules on Cu(111) and Cu(110). Evolution of both systems has been studied via a combination of core-level X-ray spectroscopies, scanning tunneling microscopy, and theoretical calculations. Experimental and theoretical results reveal a significant increase in reactivity for the open and anisotropic Cu(110) surface in comparison with the close-packed Cu(111). This increased reactivity results in a predominance of the molecular-substrate interaction over the intermolecular one, which has a critical impact on the transformations of DBBA on Cu(110). Unlike DBBA on Cu(111), the Ullmann coupling cannot be realized for DBBA/Cu(110) and the growth of nanoribbons via this mechanism is blocked. Instead, annealing of DBBA on Cu(110) at 250 °C results in the formation of a new structure: quasi-zero-dimensional flat nanographenes. Each nanographene unit has dehydrogenated zigzag edges bonded to the underlying Cu rows and oriented with the hydrogen-terminated armchair edge parallel to the [1-10] direction. Strong bonding of nanographene to the substrate manifests itself in a high adsorption energy of -12.7 eV and significant charge transfer of 3.46e from the copper surface. Nanographene units coordinated with bromine adatoms are able to arrange in highly regular arrays potentially suitable for nanotemplating.

A new theoretical approach to find metal-cluster-catalyzed single bond activation pathways is introduced. The proposed approach combines two automated reaction path search techniques: the anharmonic downward distortion following (ADDF) and the artificial force induced reaction (AFIR) methods, developed in our previous works [Maeda, S.; Ohno, K.; Morokuma, K. Phys. Chem. Chem. Phys. 2013, 15, 3683-3701]. A simple model reaction of the H-H bond activation catalyzed by Aun (n = 7, 8) clusters is considered as an example. We have automatically found 33 and 20 transition-state (TS) structures for H2 dissociation on Au7 and Au8 clusters, respectively, and successfully identified the best dissociation pathways with the lowest barrier. Systematic analysis of the structure-dependent reactivity of small gold clusters is performed. It is demonstrated that the most stable structures of the gold clusters are not always highly reactive and several isomeric structures must be taken into account for adequate description of the reaction rates at finite temperatures. The proposed approach can serve as a promising tool for investigation of the chemical reactions catalyzed by small metal clusters.

The catalytic activity for the oxygen reduction reaction (ORR) of both the pristine and defect-possessing hexagonal boron nitride (h-BN) monolayer and H-terminated nanoribbon have been studied theoretically using density functional theory. It is demonstrated that an inert h-BN monolayer can be functionalized and become catalytically active by nitrogen doping. It is shown that the energetics of adsorption of O(2), O, OH, OOH, and H(2)O on N atom impurities in the h-BN monolayer (N(B)@h-BN) is quite similar to that known for a Pt(111) surface. The specific mechanism of destructive and cooperative adsorption of ORR intermediates on the surface point defects is discussed. It is demonstrated that accounting for entropy and zero-point energy (ZPE) corrections results in destabilization of the ORR intermediates adsorbed on N(B)@h-BN, while solvent effects lead to their stabilization. Therefore, entropy, ZPE and solvent effects partly cancel each other and have to be taken into account simultaneously. Analysis of the free energy changes along the ORR pathway allows us to suggest that a N-doped h-BN monolayer can demonstrate catalytic properties for the ORR under the condition that electron transport to the catalytically active center is provided.

The specific role played by small gold nanoparticles supported on the rutile TiO2( 110) surface in the processes of adsorption and dissociation of H2 is discussed. It is demonstrated that the molecular and dissociative adsorption of H2 on Au(n) clusters containing n = 1, 2, 8 and 20 atoms depends on cluster size, geometry structure, cluster flexibility and the interaction with the support material. Rutile TiO2(110) support energetically promotes H2 dissociation on gold clusters. It is demonstrated that the active sites towards H2 dissociation are located at corners and edges on the surface of the gold nanoparticle in the vicinity of the support. The low coordinated oxygen atoms on the TiO2(110) surface play a crucial role for H2 dissociation. Therefore the catalytic activity of a gold nanoparticle supported on the rutile TiO2(110) surface is proportional to the length of the perimeter interface between the nanoparticle and the support.