Formation Of Bridge Bonds Research Articles

Atomic surface achieved through a novel cross-scale model from macroscale to nanoscale.

Chemical mechanical polishing (CMP) is widely used to achieve an atomic surface globally, yet its cross-scale polishing mechanisms are elusive. Moreover, traditional CMP normally employs toxic and corrosive slurries, resulting in potential pollution to the environment. To overcome these challenges, a novel cross-scale model from the millimeter to nanometer scale is proposed, which was confirmed by a newly developed green CMP process. The developed CMP slurry consisted of hydrogen peroxide, sodium carbonate, sodium hydroxycellulose, and silica. Prior to CMP, fused silica was polished by a ceria slurry. After CMP, the surface roughness (Sa) was 0.126 nm, the material-removal rate was 88.3 nm min-1, and the thickness of the damaged layer was 8.8 nm. The proposed model was built by fibers, through integrating Eulerian and Lagrangian models and reactive force field-molecular dynamics. The results predicted by the model were in good agreement with those of CMP experimentally. A model for large-sized fibers revealed that a direct contact area of 11.12% was obtained for a non-woven polishing pad during the CMP experiments. Another model constructed via combining Eulerian and Lagrangian functions showed that the stress at the intersections of the fibers varied mainly from 0.1 to 0.01 MPa and was higher than the stress at other parts. An increase in viscosity led to a decrease in the areas with low stress, demonstrating that viscosity enhanced the stress and facilitated the removal of material. At the microscale and nanoscale, the stress of the abrasive surface exposed to the workpiece changed from 2.21 to 6.43 GPa. Stress at the interface contributed to the formation of bridging bonds, further promoting the removal of material. With increasing the compressive stress, the material-removal form was transformed from a single atom to molecular chains. The proposed model and developed green CMP offer new insights to understand the cross-scale polishing mechanism, as well as for designing and manufacturing novel polishing slurries, pads, and setups.

The disposition of bridge hydrogen bond in the homopolar-diborane and its derivatives

Compounds that comprehend less valence electrons are designated as electron deficient and atoms involved in such compounds occasionally form three-center-two-electron (3c-2e-) bonds to engross all of their available valence orbitals in bonding. Hence, in this study, calculations using M06-2X, MP2, and CCSD(T) method with the inclusion of def2-TZVP basis sets are exploited to reconnoiter the authentic bonding portrayal in diborane (DB) and its derivatives. Molecular electrostatic potential (MEP) analysis on the basis of vSmax and vSmin values indicates that there is a charge transfer between a π-hole that encompasses one monomer and the most negative region of another monomer that results in the formation of bridge bonds between two monomers. QTAIM investigation directed towards the charge depletion at bridging fragment in all the complexes and disclosed the polar covalent nature of bridge hydrogen bond. Additionally, ETS-NOCV examination suggests that charge flow from bridge to boron atom of all the complexes. Additionally, the bonding found to be more through orbital interactions compared to electrostatic interactions.

Bridge-bond formation in aluminum and its alloys under high pressure

Despite being a simple metal in which the free-electron model prevails, aluminum is known to exhibit peculiar bonding characteristics. In this work, we report a hitherto unexplored bonding behavior of Al through extensive first-principles modeling. Starting from liquid Al, we report that upon increasing pressure, electrons tend to localize between two nearest Al neighbors, forming a partitionable electronic center resembling a pseudoparticle that lies between the two Al atoms. This finding is further generalized to binary alloys containing Al under high pressure, as exemplified by an Al-Li intermetallic compound. The emergence of this bridge bonding under pressure is found to profoundly affect the physical properties of the materials, evidenced by anomalous property crossovers systematically explored in the Al-Li alloy. The finding of the anomalous electronic bonding behavior of Al described in this work will lay groundwork for interpreting and predicting physical behavior under extreme conditions.

Effects of slurry pH on chemical and mechanical actions during chemical mechanical polishing of YAG

Yttrium aluminum garnet (YAG) single crystal has become a promising substrate for the high-power solid-state laser. It needs to be processed into a defect-free surface by chemical mechanical polishing (CMP). The preparation of polishing slurry is critical for the material removal efficiency and surface quality, which relies on understanding the removal mechanism of polished materials. In this study, the impacts of slurry pH on the chemical and mechanical actions of YAG in CMP process are investigated. Chemical reaction mechanisms are revealed by X-ray photoelectron spectroscopy analysis. And mechanical actions of abrasives are analyzed by the theory of Derjaguin–Landau–Verwey–Overbeek and the measured coefficient of friction. The results indicate that the material removal depends on the formation of bridge bonds at the interface and the dissociation of work surface bonds when the slurry pH is below 12. In comparison, it is based on forming a softer reaction layer and removed mechanically at pH 13. More abrasives interact with YAG under the acidic condition and it contributes to elevating the material removal rate. The colloidal silica at pH 6 is preferred for CMP of YAG. This study helps to understand the material removal mechanism and optimize the polishing process.

INVESTIGATION OF THE PROCESS OF GELATION OF GALACTOMANNAN ISOLATED FROM THE SEEDS OF STYPHNOLOBIUM JAPONICUM (FABACEAE)

This article is devoted to the study of the structuring of galactomannan isolated from Sophora japonica with borate ions. Based on the galactomannan isolated from the seeds of Sophora japonica (lat. Styphnolobium japonicum), a basis for a soft dosage form has been developed. It has been suggested that the network structures of gel systems are formed due to the formation of bridge bonds between the functional groups of the galactomannan and boron ions. Studied the rheological properties of the resulting jelly. The study of the process of gelation of galactomannan showed that the dynamic viscosity depends on the pH, the concentration of the crosslinking agent and the concentration of the solution of galactomannan. The gel was plasticized and it was assumed that the presence of glycerol destroys chemical crosslinking, due to the formation of a complex compound with sodium tetraborate. A soft dosage form has been developed with the addition of 10% propylene glycol as a plasticizer and a preservative solution – 0.1%. As a result of further research developed soft dosage forms revealed that after 6–12 months of storage in vivo at a temperature of +20±5 °C, the studied gel remained stable. These studies made it possible to apply the studied gel in medicine as the basis for a soft dosage form.

Competitive polycondensation of model compound melamine-urea-formaldehyed (MUF) resin system by 13C NMR

Melamine-urea-formaldehyde (MUF) resin is an excellent adhesive in the field of wood adhesives, however the competition mechanism is questionable which affects the structure control and performance optimization of the resin. In this study, the competitive resin synthesis polycondensation reaction of MUF system under alkaline condition was studied based on the model compound 1,3-dihydroxymethyl urea (UF2) and melamine (M) system, and the competitive reaction mechanism in the system was deduced by 13C NMR quantitative analysis. The results show that the energy barrier of hydroxymethylation of melamine is lower than that of urea, and the priority of hydroxymethylation is lower; the addition of melamine results in a large amount of hydrolysis of UF2, and the formed free formaldehyde, resulting in hydroxymethylation of melamine; there is obvious polycondensation reaction in UF2+M system, mainly from the relationship between hydroxymethylurea and melamine or hydroxymethylmelamine. The type I bridge bond structure of polycondensation mainly comes from the reaction of UF2 and M, which is difficult to form the type II bridge bond. At low molar ratio, the formation of bridge bond is superior to that of ether bond. With the increase of molar ratio, the formation of ether bond shows advantages, but there is obvious competition between them. There may be competitive presence of the UF self-condensation products, melamine-formaldehyde (MF) self-condensation products and MUF co-condensed products after the polycondensation reaction.

Закрепление нетоксичных антипиренов на поверхности полиэфирных волокон

Установлены режимы формирования в спиртовых растворах хлорида олова реакционноспособных коллоидных наноразмерных частиц, обеспечивающих прочную привязку к полиэфирной матрице азот-фосфорсодержащего ингибитора горения. Установлено наличие химического взаимодействия компонентов антипирена с адгезионным подслоем соединений олова с формированием новых соединений и мостиковых связей.

The oscillatory electro-oxidation of formic acid: Insights on the adsorbates involved from time-resolved ATR-SEIRAS and UV reflectance experiments

Galvanostatic potential oscillations during the oxidation of formic acid were studied by time-resolved Surface-Enhanced Infrared Absorption Spectroscopy in the attenuated total reflection configuration (ATR-SEIRAS) and reflectance measurements in the ultraviolet (UV) region. ATR-SEIRAS allowed monitoring oscillations in the coverage of adsorbed CO (COad) and adsorbed bridge-bonded formate (HCOObi), while UV reflectance revealed oscillations in the coverage by specifically adsorbed anions (namely, adsorbed sulfate). The potential oscillations and the coverage of all these species are strongly interconnected, and an analysis of their correlation provides detailed insight into the autocatalytic loop responsible for the emergence of non-linear dynamics.

Dynamics of the Interaction of Formic Acid with a Polycrystalline Pt Film Electrode: a Time-Resolved ATR-FTIR Spectroscopy Study at Low Potentials and Temperatures

Aiming at more insights into the interaction of formic acid with a Pt electrode, we have studied the dynamics of formic acid interaction with a polycrystalline Pt film electrode in the potential range around the onset of the reaction, from 0.0 to 0.4 V (reversible hydrogen electrode (RHE)), by a combination of electrochemical and in situ IR spectroscopy transient measurements. The measurements were performed under well-defined mass transport conditions; IR spectra were acquired in an attenuated total reflection (ATR) configuration with a time resolution of up to 25 ms (rapid scan mode). To slow down the reaction kinetics and thus stabilize short-living adsorbed intermediates, measurements were performed at ambient and low reaction temperatures (3 °C). Kinetic H/D isotope effects, introduced by using deuterated formic acid, were explored to learn more about the contribution of C–H bond splitting in the rate-determining step in formic acid dehydration (COad formation). Rapid scan ATR-FTIRS measurements show no measurable time delay between the appearance of the bands related to adsorbed bridge-bonded formate species and adsorbed CO at higher potentials (>0.1 V) and no detectable formate signals at low potentials (≤0.1 V), although COad is still formed even at 0.0 V. Adsorption of HCOOH species at low potentials (0.0–0.1 VRHE) is indicated by a band developing at around 1720 cm−1, which is isotope shifted upon deuteration of the C–H bond. Consequences of these and other observations, including the observation of a bell-shaped potential dependence of the initial rate for COad formation in the potential range 0.0–0.4 V or distinct kinetic H/D isotope effects in the rate constants for COad formation, on the mechanistic understanding of the formic acid–Pt interaction are discussed.

Promotion effects of potassium on the activity and selectivity of Pt/zeolite catalysts for reverse water gas shift reaction

Catalytic hydrogenation of carbon dioxide to CO by reverse water gas shift reaction plays a vital role in the recycling of the abundant carbon source. Here, the reaction over a series of zeolite L-supported platinum catalysts was systematically investigated to study the promoting role of potassium. The results of activity tests showed that controlled addition of potassium promoter to Pt/L catalyst was beneficial for the catalytic activity and selectivity. It was observed that cage encapsulation by zeolite pores could stabilize Pt nano-particles even at severe reaction conditions. Furthermore, X-ray absorption near edge structure and X-ray photoelectron spectra results demonstrated that the chemical state of platinum was altered by the additional potassium promoter, providing evidence for the formation of Pt-O(OH)-K interfacial sites. Thereafter, the Pt-O(OH)-K interfaces, acting as main active sites to adsorb CO2 and produce bridge-bonded formate intermediates, were identified by a set of in-situ diffuse reflectance Fourier transform infrared spectroscopy and microcalorimetry measurements. This finding provides new insights into the use of a variety of zeolite as carriers for highly dispersed noble metal in catalytic CO2 reduction.

FEATURES OF GAS-SENSIBILITY OF DYES ON THE BASE OF 4-VALENCE STANNUM COMPLEXES

Aim: Regularity detecting of possible sensitivity of nanoparticles ensemble of dyes on the base of 4-valence stannum complexes to presence of ammonia or HCl vapour in environment.Research methods: Analysis of photoluminescence spectra of specimens with posterior summarizing of obtained experimental results and using the literary data and analogies with results of previous researching.Results of researching: It’s found, that the nanoparticles ensemble of dyes containing the benzoyl type amine substituent in the hydrazone fragment sharp and stably decreases its luminescence intensity about in half after placing into ammonia atmosphere. The initial luminescence intensity may be restored after annealing only. Probably this result is connected with formation of bridge bonds inside the pores of matrix by ammonia molecules. On the other hand, the nanoparticles ensemble of dyes containing the hydroxyl type amine substituent is sensitive to the HCl vapour. They reduce their luminescence intensity about three times due to redistribution of negative charge in system. However, specified changes have a place with some latent period. The initial luminescence intensity also may be restored after annealing in this case.Conclusion: There is certain selectivity of gas sensitivity of investigated dyes. The dyes containing amine substituent are sensitive to ammonia and insensitive to HCl vapour. The dyes containing hydroxyl substituent are sensitive to HCl vapour and insensitive to ammonia. So it’s promise to use as an indicated luminescence gas sensor both systems simultaneously. If it will need, every one snaps into action to appropriate gas.

New Insights on Formic Acid Electrooxidation at a Polycrystalline Au Film Electrode: Simultaneous in Situ ATR-Ftirs and Online Dems Measurements

Formic acid oxidation to CO2 on a gold electrode was proposed recently to occur via dimers of adjacent bridge-bonded adsorbed formates [1]. A systematic theoretical study of different pathways for formic acid electro-oxidation at a Au(111) electrode [2] indicates that the reaction path depends on the potential and formate coverage (via single formate, direct path, complex of formate and formic acid, formate dimers), which is difficult to address experimentally.In the present work, formic acid oxidation on a polycrystalline Au thin film electrode was studied using simultaneous in situ ATR-FTIRS, online DEMS and electrochemical measurements [3] in both potentiodynamic and potentiostatic modes in a thin-layer flow cell configuration under well-defined mass transport conditions, and compared to the mass transport controlled bulk CO and oxalic acid oxidation. In addition, oxalic acid oxidation was studied as a model reaction for in situ sensing of adsorbed oxalates [4]. These may be plausible intermediates in the formic acid oxidation, resulting from the dimerization of neighboring adsorbed formate species. Simultaneous in situ ATR-FTIRS and online DEMS measurements were employed to address the relation between the oxidation current, the CO2 formation rate, and the appearance of the adsorbed formate during formic acid oxidation. The kinetic H/D isotope effect (kH/kD) in formic acid oxidation was studied by DEMS as a function of Au electrode potential to discriminate between adsorption of formate (C-H bond remains intact, kH/kD = 1), or oxidation to CO2 (C-H bond rupture, kH/kD > 1). A thin (~50 nm) Au film was electrolessly deposited on the top plane of a hemi-cylindrical Si prism, which was subsequently annealed in a butane flame in a N2 stream to improve the stability of the Au film. The IR spectra were acquired using p-polarized IR radiation at 1 s-1 time resolution and 4 cm-1 spectral resolution using a Cary 680 FTIR spectrometer (Agilent Technologies). A quadrupole mass spectrometer QMS 422 (Pfeiffer Vacuum) was used for online monitoring of CO2 at m/z = 44. Potentials were controlled and currents acquired by an AFRDE 5 (Pine Instruments) potentiostat.The onset of CO2 formation during formic acid oxidation during the potentiodynamic scan is significantly delayed compared to the onset of the Faradaic current, while in bulk CO oxidation and in oxalic electrooxidation they increase in parallel. In contrast, the bridge-bonded adsorbed formate species appear instantaneously with the current increase, indicating that at low potentials the Faradaic current results from adsorption of formate species under these conditions. At higher potentials (>0.9 V), the coverage of bridge-bonded formate still increases, while the overall Faradaic current saturates. A steep increase in formic acid oxidation rate at potentials positive of 1.25 V correlates with the appearance of a band at ca. 1250 cm-1, which was detected also in oxalic acid oxidation and assigned to adsorbed oxalate [4]. Accordingly, we postulate that at these potentials adsorbed oxalates are formed by dimerization of adsorbed formates. Although we cannot decide whether these species subsequently decompose to CO2, it is clear that at 1.25 V a new reaction pathway is activated. The kH/kD, found from the Faradaic currents in HCOOH and DCOOH potentiodynamic oxidation is close to one at the onset of formic acid oxidation, which indicates the C-H bond remains intact, as could be expected for the selective formic acid oxidation to adsorbed formate, in agreement with a low current efficiency for CO2 formation under these conditions. In contrast, the kH/kD, as found from the corresponding CO2 formation currents, is close to 5 at the onset of CO2 formation, approaching ca. 4 at potentials, where the current efficiency for CO2 formation is 100%, indicating that C-H bond splitting is the rate determining step of CO2 formation.Overall, the present findings demonstrate that at very low potentials formic acid oxidation starts by adsorption of formate species, followed by CO2 formation at potentials > 0.4 V. First spectroscopic evidence was provided for the dimerization of adsorbed formates to form adsorbed oxalate at high potentials. The present work shows the role of the adsorbed formate in formic acid oxidation to depend on the reaction conditions [2]. Acknowledgement. This work was supported by the Deutsche Forschungsgemeinschaft (Research unit FOR 1376, JU 2781/2-2) [1] A. Cuesta, G. Cabello, F.W. Hartl, M. Escudero-Escribano, C. Vaz-Domínguez, L.A. Kibler, M. Osawa, C. Gutiérrez, Cat. Tod. 202, 79 (2013). [2] W. Gao, E.H. Song, Q. Jiang, T. Jacob, Chem. Eur. J. 20, 11005 (2014).[3] M. Heinen, Y.X. Chen, Z. Jusys, R.J. Behm, Electrochim. Acta 52, 5634 (2007).[4] A. Berná, J.M. Delgado, J.M. Orts, A. Rodes, J.M. Feliu, Langmuir 22, 7192 (2006).

Formic Acid Electrooxidation on Au Electrode Studied By Potential Step and a Fast Scan ATR-FTIR Spectroscopy

The role of adsorbed formates in the electro-oxidation of formic acid on Pt electrodes was widely debated [1-3]; on a gold electrode formic acid oxidation was assumed to proceed via dimers of contiguously adsorbed bridge-bonded formates [4]. In the present work, formic acid oxidation on Au thin film electrode was studied by simultaneous in situ ATR-FTIRS and electrochemical measurements in both potentiodynamic and potential step mode with a fast IR spectra acquisition in a thin-layer flow cell configuration under well-defined mass transport conditions [2], to address the impact of adsorbed spectator species (perchlorate) and adsorbed bridge-bonded formate on the formic acid electrooxidation rate. 0.1 M HCOOH and DCOOH were used to i) assess the kinetic H/D isotope effect in formic acid oxidation on Au electrode; ii) identify the adsorbed species and follow their temporal development and the potential dependence. A thin (~30 nm) Au film was electrolessly deposited onto the top plane of a hemi-cylindrical Si prism, which was subsequently carefully annealed in a butane flame in nitrogen atmosphere to improve the adhesion and thus the stability of the Au film under enforced hydrodynamic conditions and large repetitive perturbations of the working electrode potential (from 0.0 up to 1.65 V vs. RHE). This gold thin film electrode exhibited an unprecedented sensitivity of DR/R ~ 0.03 for the linearly adsorbed CO band in CO saturated supporting electrolyte at 0.0 V (reference spectrum acquired in CO-free electrolyte at 0.0 V). The IR spectra were acquired applying p-polarized IR radiation at 0.025 s-1 time resolution, 16 cm-1 spectral resolution and 75 kHz frequency employing a Cary 680 FTIR spectrometer (Agilent Technologies) equipped with a step scan accessory, and operated in a dual scan / quad compute mode. A EG&G 273A (PAR) potentiostat was used for potentiodynamic (100 mV s-1) and multistep (from 0.0 V to desired oxidation potential) experiments. A base CV in 1M HClO4 supporting electrolyte revealed a clean Au film electrode as confirmed by in situ IR spectroscopy measurements, which exhibit only the potential dependent bipolar bands at 3610 / 3455 and 1654 / 1515 cm-1 related to adsorbed water, and a unipolar band at ca. 1125 cm-1 of adsorbed perchlorate. Formic acid oxidation starts at about 0.5 V, approaches a plateau from 0.9 to 1.2 V (HCOOH) and from 0.9 to 1.3 V (DCOOH), and then passes through a maximum at around 1.45 V, which is about three times higher for HCOOH than for DCOOH, due to kinetic isotope effects. The corresponding IR spectra show pronounced potential dependent HCOOad and DCOOad bands at 1326 and 1303 cm-1, respectively. Plots of the integrated adsorbed formate band intensity vs. the potential are qualitatively similar to those of the perchlorate band in supporting electrolyte. Perchlorate adsorption is suppressed by adsorbed formate, due to competitive adsorption of the more strongly adsorbing anion. When stepping the potential from 0.0 V to the respective oxidation potential, the integrated band intensities for both adsorbed bridge bonded formate and perchlorate increased instanta­neously (within 25 ms) and remained constant over the step duration (1 s). A similar behavior is observed for adsorbed perchlorate, a clear spectator species. The integrated intensity of adsorbed formate at constant potentials increases with the adsorption potential up to 1.0 V, similar to that of adsorbed perchlorate in pure supporting electrolyte. The development of adsorbed formate reduces the perchlorate adsorption at higher potentials, compared to pure supporting electrolyte, indicating a competitive adsorption of formate and perchlorate. Overall, the data reveal an adsorption behavior of the adsorbed bridge-bonded formate species, which is identical to that of other anions that are known to act as spectator species. Although the participation of adsorbed bridge-bonded formate as active intermediate in formic acid oxidation on a Au electrode [4] cannot be ruled out based on the present data, they are at least equally consistent with a model proposing reaction via coadsorbing formate anions and formic acid species [5]. Acknowledgement. This work was supported by the Deutsche Forschungsgemeinschaft (Research unit FOR 1376, JU 2781/2-2) [1] G. Samjeské, A. Miki, S. Ye, M. Osawa, J. Phys. Chem. B 110, 16559 (2006). [2] Y.X. Chen, M. Heinen, Z. Jusys, R.J. Behm, Angew. Chem. Int. Ed. 45, 981 (2006). [3] W. Gao, J.A. Keith, J. Anton, T. Jacob, J. Am. Chem. Soc. 132, 18378 (2010). [4] A. Cuesta, G. Cabello, F.W. Hartl, M. Escudero-Escribano, C. Vaz-Domínguez, L.A. Kibler, M. Osawa, C. Gutiérrez, Cat. Tod. 202, 79 (2013). [5] S. Brimaud, J. Solla-Gullón, I. Weber, J.M. Feliu, R.J. Behm, ChemElectroChem 1, 1075 (2014).

1-Cyano-1′-ethynyl-ferrocene: Synthesis and reaction chemistry

Abstract Several consecutive synthetic methodologies for the preparation of Fe(η5-C5H4C N)(η5-C5H4C CH) (3) are described. Ferrocene Fe(η5-C5H4C N)(η5-C5H4C(O)Me) (1) reacts under typical Vilsmeier conditions to give as the main product Fe(η5-C5H4C N)(η5-C5H4CCl CH2) (2) and in minor yield Fe(η5-C5H4C N)(η5-C5H4CCl CHC(O)H) (4). Compound 2 could be directly converted to 3 by addition of KOtBu. The title compound is also accessible by the gradual reaction of 4 with NaOH to give Fe(η5-C5H4C(O)NH2)(η5-C5H4C CH) (5), which upon treatment with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and P(O)Cl(OEt)2 produced 3. Organometallic 3 could be homo-coupled to [Fe(η5-C5H4C N)(η5-C5H4C C)]2 (7) in an Eglinton coupling upon addition of [Cu(OAc)2]. With [CuI] and NEt2H in dichloromethane, compound Fe(η5-C5H4C N)(η5-C5H4C CCH2NEt2) (6) was produced by copper-catalyzed three-component coupling. The structures of 3–5 in the solid state were determined by single crystal X-ray structure analysis. While the X-ray structures of 3 and 4 show no peculiarities, the structure of 5 possesses a network structure due to hydrogen bridge bond formation. The electrochemical behavior of 3, 6 and 7 was studied by cyclic voltammetry. It could be shown that 3 possesses a reversible redox event at 550 mV (ΔE = 65 mV), while in homo-coupled 7 two consecutive redox processes at 524 and 680 mV were found indicating that the ferrocenyl units in 7 can be oxidized in a stepwise manner to 7+ and 72+, respectively. The redox separation ΔE with 156 mV implies a possible electron transfer in the mixed-valent species 7+, which was confirmed by spectroelectrochemical studies. From these studies, 7 could be classified as a weakly coupled class II system according to Robin and Day.

Modeling of Potential Oscillation during Galvanostatic Electrooxidation of Formic Acid at Platinum Electrode

Oscillation during electrocatalytic oxidation of formic acid at Pt electrode under galvanostatic conditions in acidic electrolyte has been simulated based on a chemical model that involves three reaction pathways: (i) the indirect pathway via COad formation (formic acid dehydration) and oxidation; (ii) a formate pathway, involving adsorption–desorption of bridged adsorbed formate and its oxidation; and (iii) a direct pathway with successive cutting of O–H and C–H bonds. We found that only when the contribution of formate oxidation to the total formic acid oxidation current is negligible do the simulated results reproduce well the experimentally observed oscillatory patterns for electrode potential and the coverage of COad and bridge-bonded formate. It is found that the fast adsorption–desorption of both formate and OHad are responsible for the hidden negative impedance; the slow COad formation and its fast oxidation at higher potentials lead to a positive impedance. The simulated results further support the conclusion that bridge-bonded formate is not the reactive intermediate for the major pathway of formic acid oxidation at Pt electrode.

Progress in Understanding of the Interactions between Functionalized Polyolefins and Organo‐Layered Double Hydroxides

The dispersion of organo‐layered double hydroxides (O‐LDH) in functionalized polyolefins (POs) is investigated. Two different polyethylene matrices (maleic anhydride (MAH) and diethyl maleate functionalized) are tested and a hydrogenated fatty acid modified LDH is used. The attention is focused on evidencing the interaction between the functional groups of the polymer and the O‐LDH through FT‐IR. Moreover, a combination of solvent fractionation, morphological, and rheological characterizations enables to gain a deeper insight into the structure of these composites. In particular, the formation of bridging bonds between the particles and MAH functionalized macromolecules is assumed, possibly due to the formation of ionic clusters, characteristics of ionomers, with formation of crosslinked/aggregated structures.

Different behavior of adsorbed bridge-bonded formate from that of current in the oxidation of formic acid on platinum

Clarification has been made whether or not adsorbed bridge-bonded formate (HCOOB) is the reactive intermediate in the direct path during oxidation of formic acid, using surface-enhanced infrared absorption spectroscopy (SEIRAS) simultaneously with electrochemical measurement. With a decrease in the sweep rate of cyclic voltammetry, the potential of the maximum current in the positive-going sweep decreases from 0.9 to 0.6V, while that of the maximum HCOOB band intensity in the positive-going sweep is almost constant at approximately 0.9V. When the potential is held at 0.7V after a potential increase or decrease, the current monotonically decreases, while the HCOOB band intensity keeps constant. In the absence of adsorbed CO, the current presents a maximum at approximately 0.5V, while the HCOOB band intensity does at approximately 0.9V. All these results clearly show that HCOOB is not the reactive intermediate. The second order kinetics for the decomposition of HCOOB has also been discussed.

Role of Bridge-bonded Formate in Formic Acid Dehydration to CO at Pt Electrode: Electrochemial in-situ Infrared Spectroscopic Study

Formic acid (HCOOH) decomposition at Pt film electrode has been studied by electrochemical in situ FTIR spectroscopy under attenuated-total-reflection configuration, in order to clarify whether bridge-bonded formate (HCOOb) is the reactive intermediate for COad formation from HCOOH molecules. When switching from HCOOH-free solution to HCOOH-containing solution at constant potential (E=0.4 V vs. RHE), we found that immediately upon solution switch COad formation rate is the highest, while surface coverage of formate is zero, then after COad formation rate decreases, while formate coverage reaches a steady state coverage quickly within ca. 1 s. Potential step experiment from E=0.75 V to 0.35 V, reveals that formate band intensity drops immediately right after the potential step, while the COad signal develops slowly with time. Both facts indicate that formate is not the reactive intermediate for formic acid dehydration to CO.

Infrared Spectroelectrochemical Study of Dissociation and Oxidation of Methanol at a Palladium Electrode in Alkaline Solution

The dissociative adsorption and electrooxidation of CH(3)OH at a Pd electrode in alkaline solution are investigated by using in situ infrared spectroscopy with both internal and external reflection modes. The former (ATR-SEIRAS) has a higher sensitivity of detecting surface species, and the latter (IRAS) can easily detect dissolved species trapped in a thin-layer-structured electrolyte. Real-time ATR-SEIRAS measurement indicates that CH(3)OH dissociates to CO(ad) species at a Pd electrode accompanied by a "dip" at open circuit potential, whereas deuterium-replaced CH(3)OH doesn't, suggesting that the breaking of the C-H bond is the rate-limiting step for the dissociative adsorption of CH(3)OH. Potential-dependent ATR-SEIRAS and IRAS measurements indicate that CH(3)OH is electrooxidized to formate and/or (bi)carbonate, the relative concentrations of which depend on the potential applied. Specifically, at potentials negative of ca. -0.15 V (vs Ag/AgCl), formate is the predominant product and (bi)carbonate (or CO(2) in the thin-layer structure of IRAS) is more favorable at potentials from -0.15 to 0.10 V. Further oxidation of the CO(ad) intermediate species arising from CH(3)OH dissociation is involved in forming (bi)carbonate at potentials above -0.15 V. Although the partial transformation from interfacial formate to (bi)carbonate may be justified, no bridge-bonded formate species can be detected over the potential range under investigation.

On the mechanism of the direct pathway for formic acid oxidation at a Pt(111) electrode

In order determine whether formate is a reaction intermediate of the direct pathway for formic acid oxidation at a Pt electrode, formic acid (HCOOH) oxidation at a Pt(111) electrode has been studied by normal and fast scan voltammetry in 0.1 M HClO4 solutions with different HCOOH concentrations. The relationship between the HCOOH oxidation current density (j(ox)) and formate coverage (θ(formate)) is quantitatively analyzed. The kinetic simulation reveals that the previously proposed formate pathway, with decomposition of the bridge-bonded formate (HCOO(B)) as a rate determining step (rds), cannot be the main pathway responsible for the majority of the current for HCOOH oxidation. Instead, a kinetic model based on a mechanism with formic acid adsorption [structure: see text], along with simultaneous C-H bond activation as the rds for the direct pathway, explains the measured data well. It was found for the relatively slow rate of formic acid oxidation, that adsorption-desorption of the formate is faster, which competes for the surface sites for formic acid oxidation.