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The reaction mechanism of the CH

Synthesis of nanostructured carbon allotropes using CO2 as a cheap carbon source is challenging and usually limited by high temperature activation. Herein, formation of 3D nanostructured carbon allotropes including nano-graphene and single crystalline nanodiamond films is feasible at room temperature on various single crystal metals (e.g., Bi, Ag, Zn, and Co) that were formed under the dynamic CO2 electrochemical reduction reaction environment at relatively low applied potential (−1.1 to −1.6 V vs. Ag/AgCl). The nanocrystalline carbon was obtained as the major products from CO2 (≥96% selectivity, ∼1 μm thickness) without any liquid products. Upon applying the negative potential, nanoclustering of the self-limiting ultrathin metal oxide layers of metal particles on the highly conductive substrate could lead to formation of negatively charged metal clusters, which were well stabilized by the ternary electrolyte system containing [BMIm]+[BF4]-/propylene carbonate/water. This system allows the reduction of CO2 into single atoms C∗ and the subsequently electrocrystallization of C∗ into carbon allotropes on the crystallographic planes of the single crystal metals formed as the building blocks. The CO2-derived Ag–C/epoxy composites show promising thermal conductivity. The results present a breakthrough advancement in the growth of nanostructured carbon allotropes from CO2 by the viable negative CO2 emission approach.

BN1 doped g-C9N10 exhibits superior N2RR activity and selectivity due to the lower UL of the N2RR and weaker H adsorption.

Formation of nanostructured carbon films on nascent Ag clusters during room-temperature electrochemical CO2 reduction.

The interactions of CO2 with terrace, step, and defect or kink sites on Pt surfaces were investigated using temperature-programmed desorption, X-ray photoelectron spectroscopy, and density function...

John Isaac Enriquez, Fahdzi Muttaqien, Masato Michiuchi, Kouji Inagaki, Masaaki Geshi, Ikutaro Hamada, Yoshitada Morikawa, Oxidative etching mechanism of the diamond (100) surface, Carbon, Volume 174, 2021, Pages 36-51, https://doi.org/10.1016/j.carbon.2020.11.057., We performed density functional theory calculations with van der Waals corrections to elucidate diamond oxidation mechanism on the atomic-level which could lead to insights that will advance the improvement of nascent nanofabrication technologies. We developed a comprehensive theory of oxidative etching of the diamond (100) surface, from the adsorption of gas phase O2, including details of metastable adsorption states, intersystem crossing, and induced surface dereconstruction, to the desorption of CO and CO2, complete etching of the top surface layer and its subsequent stabilization. Oxygen adsorption induce C-dimer bond breaking through the formation of carbonyl structures at low surface coverage. At high surface coverage, adjacent carbonyls can transform into the more stable ether chain with small energy barrier requirement. A mix of carbonyl and ether will form in surfaces with defects, and several models of possible structures have been presented. CO desorption creates a point defect that serves as nucleation site for the preferred etching direction along [011], perpendicular to the top layer C-dimer bonds. We obtained a wide range of desorption activation energies, which depend on the existence of point defects and reconstruction of surfaces. C-dimer formation and oxygen adsorption stabilize vacancies and single-atomic-layer-deep trough.

A new-type nitrogen-rich carbon nitride material C3N5 has been synthesized recently, in which the C:N ratio increases from 3:4 in g-C3N4 to 3:5 due to the introduction of azo linkage ( N N ) connecting segments in two C6N7 units. Herein, C3N5 as a photocatalyst for CO2 reduction was investigated by density functional theory methods. The electronic and optical properties indicate that C3N5 has a longer visible-light region with 2.0 eV of band gap in comparison with g-C3N4. The spatial distributions of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) show that the π network of C3N5 is extended by introducing —N N— linkage, which results in much higher photocatalytic efficiency than g-C3N4. The Gibbs free energies for possible CO2 reaction paths on C3N5 were computed. The results show that CO2 can be reduced to CH4 with a low limiting potential of −0.54 V and to CH3CH2OH with a low limiting potential of −0.61 V, which all driven by solar energy. The present work is expected to provide useful guide for new-type nitrogen-rich C3N5 as promising photocatalyst for CO2 reduction reaction (CO2RR).

Understanding the nature of active sites is a non-trivial task, especially when the catalyst is sensitively affected by chemical reactions and environmental conditions. The challenge lies on capturing explicitly the dynamics of catalyst evolution during reactions. Despite the complexity of catalyst reconstruction, we can untangle them into several elementary processes, of which surface diffusion is of prime importance. By applying density functional theory–kinetic Monte Carlo (DFT–KMC) simulation employed with cluster expansion (CE), we investigated the microscopic mechanism of surface diffusion of Cu with defects such as steps and kinks. Based on the result, the energetics obtained from CE have shown good agreement with DFT calculations. Various diffusion events during the step fluctuations are discussed as well. Aside from the adatom attachment, the diffusion along the step edge is found to be the dominant mass transport mechanism, indicated by the lowest activation energy. We also calculated time correlation functions at 300, 400, and 500 K. However, the time exponent in the correlation function does not strictly follow the power law behavior due to the limited step length, which inhibits variation in the kink density.

SrFeO3-δ is known to be an effective oxygen ion conductor and oxygen vacancies are central to its performance. SrFeO3-δ displays four crystallographic structural transitions as it undergoes oxygen reduction over a broad range of operating temperatures. In this work, systematic density functional theory calculations using the Hubbard U correction were performed to understand oxygen vacancy interactions and migration as a function of vacancy concentrations in SrFeO3-δ (δ = 0-0.5). We found strong repulsion between oxygen vacancies at close distance while these oxygen vacancies are stabilized at further distance. We also found that the oxygen migration is highly anisotropic and the calculated effective migration energy for the oxygen migration tends to be high and increases from 0.91 eV to 1.30 eV as δ goes from 0.125 (tetragonal phase) to 0.25 (orthorhombic phase). In the ordered brownmillerite SrFeO2.625, the oxygen migration is restricted in the one-dimensional channel because of the highly anisotropic nature of the crystal structure, resulting in the relatively low effective migration energy of 0.49 eV. This explains the experimental activation energy of 0.55 ± 0.05 eV. These results suggest the importance of regulating the oxygen migration path via the crystal structure design toward development of a SrFeO3-δ based fast oxygen conductor.

Performing bottom-up synthesis by using molecules adsorbed on a surface is an effective method to yield functional polycyclic aromatic hydrocarbons (PAHs) and nanocarbon materials. The intramolecular cyclodehydrogenation of hydrocarbons is a critical process in this synthesis; however, thus far, its elementary steps have not been elucidated thoroughly. In this study, we utilize the metal tip of a low-temperature noncontact atomic force microscope as a manipulable metal surface to locally activate dehydrogenation for PAH-forming cyclodehydrogenation. This method leads to the dissociation of a H atom of an intermediate to yield the cyclodehydrogenated product in a target-selective and reproducible manner. We demonstrate the metal-tip-catalyzed dehydrogenation for both benzenoid and nonbenzonoid PAHs, suggesting its universal applicability as a catalyst for nanographene synthesis.

The interface of π-conjugated organic molecules with metal surfaces plays a crucial role in determining the efficiency of organic-based electronic devices. Because the interface is buried under the...

Synthesis of carbon nanostructures at room temperature and under atmospheric pressure is challenging but it can provide significant impact on the development of many future advanced technologies. Here, the formation and growth characteristics of nanostructured carbon films on nascent Ag clusters during room-temperature electrochemical CO

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We have studied the adsorption of small nitric oxide (NO) clusters [(NO)n (n = 1–3)] on Cu(111), by means of the van der Waals density functional. We have found that a single NO molecule preferably adsorbs in an upright N-down configuration at the fcc-hollow site, whereas all constituent NO molecules of the NO dimer and trimer adsorb at the fcc-hollow sites, in inclined N-down geometries. Among three NO clusters, the NO trimer is the most stable regardless of lateral periodicities, in good agreement with the scanning tunneling microscopy experiment. van der Waals interaction dominates the stabilization of the NO dimer, while the hybridization among 2π* orbitals of NO plays an important role in addition to the van der Waals interaction in the formation of the NO trimer. The relatively weak interaction between the NO and Cu substrate is crucial for the stabilization of the NO trimer. Our vibrational analysis has revealed that the N–O stretching mode is blue-shifted from monomer to trimer, and the latter agr...

Ionic liquids (ILs) with their high dielectric constants (k) are promising dielectrics of organic field-effect transistors (OFETs). However, it is known that interfacial polarizations of dielectric...

Focusing on the electric double layer formed at aqueous solution/graphite electrode interfaces, we investigated the relationship between the mobility of interfacial water and its hydrogen bonding networks by using molecular dynamics simulations. We focused on the mobility of the first hydration layer constructed nearest to the electrode. The mobility was determined by calculating the diffusion coefficient which showed an opposite trend to that of the applied potential polarity. The mobility decreased upon positive potentials while showing an increase upon negative potentials, which is rationalized by the strength of the interfacial hydrogen bonding networks.

Understanding gas–surface reaction dynamics, such as the rupture and formation of bonds in vibrationally and translationally excited (‘hot’) molecules, is important to provide mechanistic insight into heterogeneous catalytic processes. Although it has been established that such excitation can affect the reactions occurring via dissociative mechanisms, for associative mechanisms—in which the gas-phase reactant collides directly with a surface-adsorbed species—only translational excitation has been observed to affect reactivity. Here we report a bond-formation reaction that is driven by the vibrational energy of reactant molecules and occurs via an (associative) Eley–Rideal-type mechanism, in which the reaction takes place in a single collision. Hot CO2 in a molecular beam is found to react with pre-adsorbed hydrogen atoms directly on cold Cu(111) and Cu(100) surfaces to form formate adspecies. The vibrational energy of CO2 is more effective at promoting the reaction than translational energy, the reaction rate is independent of the surface temperature and the experimental results are consistent with density functional theory calculations. Vibrational and translational energies have previously been observed to promote reactions at surfaces occurring via dissociative mechanisms. Now, it has been shown that the reaction of CO2 with surface-adsorbed atomic hydrogen—which occurs via an associative (Eley–Rideal-type) mechanism—can be driven by vibrationally exciting CO2.

The reaction of nitric oxide (NO) on Cu(100) is studied by scanning tunneling microscopy, electron energy loss spectroscopy and density functional theory calculations. The NO molecules adsorb mainly as monomers at 64 K, and react and dissociate to yield oxygen atoms on the surface at ∼70 K. The temperature required for the dissociation is significantly low for Cu(100), compared to those for Cu(111) and Cu(110). The minimum energy pathway of the reaction is via (NO)2 formation, which converts into a flat-lying ONNO and then dissociates into N2O and O with a considerably low activation energy. We propose that the formation of (NO)2 and flat-lying ONNO is the key to the exceptionally high reactivity of NO on Cu(100).

We investigate the polymeric adsorption of formic acid (HCOOH) on the Cu(111) surface by means of density functional theory. We present structural models for the polymeric form of HCOOH on Cu(111) and characterize their stability, electronic, and vibrational properties. Based on the energetics and dynamics, as well as simulated scanning tunneling microscopy and atomic force microscopy images, we propose that the $\ensuremath{\alpha}$ polymorph is likely to be formed on the Cu(111) surface and can explain the experimental findings. We also study the initial step of the catalytic dehydrogenation of HCOOH and find that the O-H bond dissociation at the edge of the polymer is facilitated, rather than that forming hydrogen bonding, agreeing well with the experiments.

β12 borophene has received great attention because of its intriguing mechanical and electronic properties. One of the possible applications of borophene is gas sensing. However, the interaction between common gases and β12 borophene remains to be clarified. In this work, we study the interactions of β12 borophene towards five hazardous gases, namely, CO, NO, NH3, NO2, and CO2 using various non-empirical van der Waals density functionals and provide an insight into the adsorption behavior of borophene. The adsorption mechanism and molecular vibrations are discussed in great detail. Among the gases considered, CO2 is physisorbed while other gases are chemically bonded to β12 borophene. We also demonstrate that the deformation at the ridge of borophene enables its active pz orbital to strongly hybridize with frontier orbitals of the studied polar gases. Consequently, borophene is predicted to interact strongly with CO, NO, NH3, and especially NO2, making it a sensitive sensing material for toxic gases.

Density functional theory was used to investigate the effects of doping alkaline earth metal atoms (beryllium, magnesium, calcium and strontium) on graphene. Electron transfer from the dopant atom to the graphene substrate was observed and was further probed by a combined electron localization function/non-covalent interaction (ELF/NCI) approach. This approach demonstrates that predominantly ionic bonding occurs between the alkaline earth dopants and the substrate, with beryllium doping having a variant characteristic as a consequence of electronegativity equalization attributed to its lower atomic number relative to carbon. The ionic bonding induces spin-polarized electronic structures and lower workfunctions for Mg-, Ca-, and Sr-doped graphene systems as compared to the pristine graphene. However, due to its variant bonding characteristic, Be-doped graphene exhibits non-spin-polarized p-type semiconductor behavior, which is consistent with previous works, and an increase in workfunction relative to pristine graphene. Dirac half-metal-like behavior was predicted for magnesium doped graphene while calcium doped and strontium doped graphene were predicted to have bipolar magnetic semiconductor behavior. These changes in the electronic and magnetic properties of alkaline earth doped graphene may be of importance for spintronic and other electronic device applications.

The electronic structures of $\mathrm{La}\mathrm{Ni}{\mathrm{O}}_{3}$ thin films with an oxygen vacancy on a $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ substrate are investigated using first-principles calculations. We find that the oxygen vacancy induces the insulator-metal transition as the film thickness is increased. For a 1.0-unit-cell-thick $\mathrm{La}\mathrm{Ni}{\mathrm{O}}_{3}$ film, an insulating state with an energy gap of 1.2 eV is formed as a result of the large exchange and Coulomb interactions between Ni $3d$ orbitals, whereas a negative charge transfer energy causes restoration of the metallic state in films with a 2.0-unit-cell or larger thickness. Thermodynamic study reveals that an oxygen vacancy induced insulating film may be the preferable structure during the initial stage of film deposition. The low calculated formation energy of 0.26 eV for the oxygen vacancy indicates that the nonstoichiometric and insulating film may survive even the annealing process. Finally, work functions for films with various surfaces are discussed.

A new-type nitrogen-rich carbon nitride material C

The adsorption of CO on ${\mathrm{Pt}}_{4}$ clusters supported on graphene with lattice vacancies is studied theoretically using the first-principles calculation. Our results show that the electronic structure of the graphene-supported ${\mathrm{Pt}}_{4}$ clusters is significantly modified by the interaction with carbon dangling bonds. As a result the adsorption energy of CO at a Pt site decreases almost linearly with the lowering of the Pt $d$-band center, in analogy with the linear law previously reported for CO adsorption on various Pt surfaces. An exceptional behavior is found for ${\mathrm{Pt}}_{4}$ supported on graphene with a tetravacancy, where CO adsorption is noticeably weaker than predicted by the shift in the $d$-band center. Detailed electronic structure analyses reveal that the deviation from the linear scaling can be attributed to lack of Pt $d$ states near the Fermi level that hybridize with CO molecular orbitals. The weakening of CO adsorption on the ${\mathrm{Pt}}_{4}$ clusters is considered as a manifestation of the support effect of graphene, and leads to the enhancement of CO poisoning tolerance that is crucial for developing high-performance Pt cluster catalysts.

This work presents an interpretation of the origin of changes in absorption spectra upon one-electron oxidation and reduction of two ruthenium polypyridyl complexes based on a combination of UV-Vis spectroelectrochemical experiments and theoretical calculations using the Gaussian 09 program. A bis-chelating ligand containing a p-bromobenzoylthiourea unit connected to 1,10-phenanthroline (phen-p-BrBT) has been prepared. Complexation of phen-p-BrBT to ruthenium bis-diimine centres, Ru(N-N)2 [N-N = 2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen)], affords octahedral Ru(ii) tris-diimine complexes that are synthesised and structurally characterised. The two complexes exhibit similar MLCT bands and electronic energy levels owing to the similar electronic structures of the bpy and phen ligands. However, [Ru(phen)2(phen-p-BrBT)]2+ exhibits a slightly broader visible region MLCT (metal-to-ligand-charge transfer) band than [Ru(bpy)2(phen-p-BrBT)]2+ as expected from a slightly more delocalised π-electron system in the phen diimine ligands. In addition, the π→π* absorption in the UV is blue-shifted for [Ru(phen)2(phen-p-BrBT)]2+ relative to that for [Ru(bpy)2(phen-p-BrBT)]2+, because of greater stabilisation of the bpy HOMO relative to that of phen. The extra C-C bond in phen produces greater delocalisation of electron density leading to a blue-shift in the π→π* transition. The MLCT band is blue-shifted and diminished in intensity upon oxidation due to stabilisation of the Ru d-orbitals by removal of one electron. A new broad absorption band appears in the UV region upon reduction. The new transition is attributed to a blue-shift of the first MLCT transition for [Ru(bpy)2(phen-p-BrBT)]2+ and a red-shift of the second MLCT transition for [Ru(phen)2(phen-p-BrBT)]2+. The new transitions originate from destabilisation or stabilisation of the ligand LUMO orbitals relative to the Ru d-orbitals. A red-shift of the UV band in the initial complex also contributes to the new band produced upon reduction of [Ru(bpy)2(phen-p-BrBT)]2+. The new band does not involve an n(C[double bond, length as m-dash]S) →π* transition. Although both complexes show subtle differences in behaviour, their spectral changes are distinct, and the origin of changes in their absorption spectra upon oxidation and reduction is successfully interpreted.

We have studied the dissociation process of nitric oxide (NO) on Cu(110) and the influence of the hydrogen bond with water by means of density functional theory calculations. We have found that an upright NO adsorbed at a short-bridge site and a side-on NO at a hollow site connecting two short-bridge sites are the two most stable molecularly adsorbed states, and the latter is the precursor for the dissociation process. Various NO dissociation pathways under the influences of the hydrogen bonds with water have been investigated. We have found that hydrogen bonds efficiently reduce the activation energy of NO dissociation by the introductions of a water dimer to O and water dimers to both sides of the side-on NO, respectively. More importantly, the promoting effect of water molecules on NO dissociation is dominant only when one of water molecules in a water dimer forms a hydrogen bond with O of the side-on NO. Our results provide a physical insight into the promoting effect of hydrogen bonds with water, whi...

Pentacene, one of the most studied organic semiconductors, crystallizes in different structures depending on the growth conditions. The structure is usually classified into one of the three polymorphs, the so-called single crystal phase, bulk phase, and thin film phase. In this report, we show that epitaxial crystalline pentacene thin films on Bi(0001), which have been believed to be the bulk phase, have a distinct molecular orientation in the same crystal lattice as the bulk phase. The calculated band structures are clearly different from those of the bulk phase and show an excellent agreement with the experimental data for the bandwidth.(21) A tight-binding model indicates that one of the two main intermolecular interactions is almost identical to that of the single crystal phase, while the other one is almost identical to that of the bulk phase. The results implies that polymorphs in the same crystal lattice can be formed by a molecular-substrate interaction.

The elucidation of the oxygen ionic transport mechanism in atomic scale is important for finding the essential element of the higher efficiency and the wider oxygen content range in the application...

Spectro-photoelectron holography method combined with first-principles simulations determined the local three-dimensional atomic structures of arsenic (As) atoms doped into a silicon (Si) crystal. As 3d core level photoelectron spectroscopy demonstrated the presence of three types of As atoms, denoted as BEH, BEM, and BEL. The As atoms of BEH corresponded to electrically active As occupying substitutional sites, while those of BEM corresponded to electrically inactive As embedded in the As n V (n = 2–4) type clusters, and those of BEL were assigned to electrically inactive As in locally disordered structures.

Using the density functional method, we investigated the crystal and electronic structures and the electrochemical properties of NaxVOPO4 (x = 0, 1) and explored the diffusion mechanism of Na ions in these materials. The van der Waals interaction was also taken into account to include the non-local electron correlation in the calculation of structural parameters and voltage. The diffusion of Na ions is treated as a process of the Na vacancy–positive small polaron complex in NaVOPO4 and the Na ion–negative small polaron complex in VOPO4, respectively. During the charging (discharging) process, the removal (insertion) of a Na ion would result in the formation of a positive (negative) small polaron at one of the two first nearest vanadium sites to the Na vacancy. Three elementary diffusion processes, including the single, crossing and parallel diffusion processes, are explored. It is found that the [010] direction is preferable for Na ion diffusion in both the charging and discharging processes. The influence of small polaron migration on Na ion diffusion in the charging state is negligible, whereas such effect is considerably strong in the discharging process. Moreover, while three elementary diffusion processes in NaVOPO4 require the same energy, the parallel diffusion process in VOPO4 is not preferred. The diffusion of Na vacancy accompanied by a positive polaron in the full charging process requires an activation energy of 395 meV, while the diffusion of Na ion accompanied by a negative polaron in the discharging state, VOPO4, has a higher activation energy of 627 meV. With a voltage and activation barrier similar to that of the olivine phosphate LiFePO4, these sodium-based materials are expected to be promising cathode materials for sodium ion batteries.