研究甲酸在多孔Pt上吸附质的性质以及它与CO的相互作用

应用现场红外反射光谱和微分电化学质谱研究了甲到在多孔Ｐｔ上吸附质的性质。伏安结果显示了甲酸在多孔Ｐｔ上吸附质的氧经与吸附电位和吸附时间有关。在线质谱结果表明从甲酸吸附质氧化成二氧化碳所需要的电子数（ｎｅ）与吸附电位无关。显著地ｎｅ＝２．２说明了甲酸吸附质是由ＣＯ和ＣＯＨ组成，而不是只有单一的ＣＯ或者ＣＯＨ，另一方面，在１２６２ｃｍ＾－１和２０４８ｃｍ＾－１出现的现场红外光谱带证实了甲酸在多孔Ｐｔ上     

Revealing structural effects: electrochemical reactions of butanols on platinum

Spectroelectrochemical studies on the reactivity of butanol isomers on Pt electrodes in perchloric acid medium led to the observation of structural effects that result from the different arrangements of atoms in the organic molecules. The use of differential electrochemical mass spectrometry (DEMS) to detect volatile products showed that all four isomers react on the electrode, though different product yields were observed for each compound. In spite of the differences in the electrochemical behaviour of the butanol isomers, a series of general processes accounts for the results obtained. The formation of strongly adsorbed residues by a dehydration process leading to the formation of a C=C bond was proposed for all isomers. Electroreduction of the adsorbates produces C(4) and C(3) alkanes, and the latter reveal the existence of a fragmentation process. The C(4) hydrocarbons can be formed by hydrogenation of these residues and by hydrogenolysis of alcohol molecules in the bulk solution which react at the electrode with adsorbed hydrogen. On the other hand, CO(2) is formed during electrooxidation of the adsorbed species. Partial-oxidation products containing a carbonyl group were detected from 0.2 M solutions of 1-butanol, isobutyl alcohol and sec-butyl alcohol. The tertiary alcohol tert-butyl alcohol only reacts in its adsorbed state.     

Analysis of time-dependent kinetics for the oxidation of methanol on a platinum electrode and reaction mechanism

The reaction kinetics for the oxidation of methanol on a platinum electrode have been examined under precisely controlled conditions. The Tafel relations at constant surface coverages of the strongly adsorbed species show the existence of two potential regions where the predominant reaction path is different. The surface reaction of the strongly adsorbed species with OH(a) is rate determining at E > ca. 0.55 V, while the oxidative adsorption of methanol to form a reactive intermediate becomes the rate-determining step at E < ca. 0.55 V. In the latter potential region, the strongly adsorbed species is not oxidized so that its accumulation on the surface decreases the rate of the oxidative adsorption and thereby the total oxidation rate.     

An investigation of the oxidation of formaldehyde on noble metal electrodes in alkaline solutions by electrochemically modulated infrared spectroscopy (emirs)

In-situ spectroscopy was used to detect adsorbed species formed during the oxidation of formaldehyde at polycrystalline Au, Pt, Rh and Ir electrodes in alkaline solution. At the gold electrode, the spectra showed the oxidation of the gem-diol form of formaldehyde and the formation of an adsorbed formate species. At platinum, rhodium and iridium, adsorbed CO was observed in the hydrogen adsorption region where the oxidation of formaldehyde is strongly inhibited on these metals. Alternative routes for producing the poison are discussed.     

Voltammetry of basal plane platinum electrodes in acetonitrile electrolytes: effect of the presence of water

The first part of this report studies the electrochemical properties of single-crystal platinum electrodes in acetonitrile electrolytes by means of cyclic voltammetry. Potential difference infrared spectroscopy in conjunction with linear voltammetry was used to obtain a molecular-level picture of this interface. The second part of this report studies the hydrogen evolution and the hydrogen oxidation reactions on the three low-index faces of Pt electrodes in acetonitrile electrolytes. The data (CVs and IR spectra) strongly suggest that acetonitrile and CN(-) molecules are adsorbed on single-crystal platinum electrodes in the range of -1.5 to 0.3 V versus Ag/AgCl. Those species block part of the adsorption sites for hydrogen adatoms, and they decompose on the surface in the presence of water. The nature of the cation and the presence of water strongly affect the onset of acetonitrile electrolysis and the kinetics and stability of the adsorbed species on the electrode. Finally, the hydrogen evolution and the hydrogen oxidation reactions on platinum single-crystal surfaces in acetonitrile electrolytes are strongly affected by the surface-energy state of Pt electrodes.     

In situ radiotracer study of thiourea adsorption on n-Si (100) and p-Si (100) electrodes

The application of a radiotracer method to in situ studies of the adsorption of thiourea labelled with either C-14 or S-35 nuclides on smooth n-type and p-type Si (100) electrodes and on rough p-Si electrodes is described. The adsorption takes place over the whole potential range studied, i.e. −0.5 to 1.2 V. It was found that during the interaction of thiourea with the silicon surface, two different products are formed. The dependence of the surface concentration of the adsorbates on the electrode potential and on the bulk concentration of thiourea was determined. Two different species are proposed to be present on the electrode surface as a result of surface processes: physically adsorbed thiourea molecules and sulphur atoms which are chemically bonded to the surface. Different activities of smooth and rough silicon electrodes towards the adsorption of thiourea were demonstrated.     

Effects of Thermal Activation on the El ectrocatalysis of the Ru(O001) Surface

Variable-temperature in-situ FTIR spectroscopy has been used as the primary tool to investigate the effects of temperature (10 to 50 C ) on formaldehyde dissociative adsorption and electro-oxidation on the Ru (0001) electrode in perchloric acid solution, and the results were interpreted in terms of the surface chemistry of the Ru (0001) electrode and compared to those obtained during our previous studies on the adsorption of CO under the same conditions. It was found that formaldehyde did undergo dissociative adsorption, even at -200 mV vs. Ag/AgCl, to form linear (COL) and 3-fold-hollow(COH) binding CO adsorbates. In contrast to the adsorption of .CO, it was found that increasing the temperature to 50℃ markedly increased the amount of CO adsorbates formed on the Ru(0001) surface from the adsorption of formaldehyde. On increasing the potential, the electrooxidation of the CO adsorbates to CO2 took place via reaction with the active (1×1)-O oxide. A significant increase in the surface reactivity was observed on the RuO2(100) phase formed at higher potentials. Formic acid was detected as a partial oxidation product during formaldehyde electro-oxidation. The data obtained at 50℃are markedly different from those collected at 10 and 25℃ in terms of the amount of both CO2 and formic acid formed and the adsorbed COL and COH species observed. These results were rationalized by the thermal effects on both the loosening of the CO adlayer and the activation of surface oxide on increasing the temperature.     

In situ FTIR studies on the effect of temperature on the electro-oxidation of small organic molecules at the Ru(0001) electrode

The adsorption and electro-oxidation of formaldehyde, formic acid and methanol at the Ru(0001) electrode in perchloric acid solution have been studied as a function of temperature, potential and time using in situ FTIR spectroscopy, and the results interpreted in terms of the surface chemistry of the Ru(000 1) electrode and compared to those obtained during our previous studies on the adsorption of CO under the same conditions. It was found that no dissociative adsorption or electro-oxidation of methanol takes place at Ru(0001) at potentials < 900 mV vs. Ag/AgCl, and at all three temperatures employed, 10, 25 and 50 degrees C. However, both formaldehyde and formic acid did undergo dissociative adsorption, even at -200 mV, to form linear (CO(L)) and 3-fold-hollow (COH) binding CO adsorbates. In contrast to the adsorption of CO, it was found that increasing the temperature to 50 degrees C markedly increased the amount of CO adsorbates formed on the Ru(0001) surface from the adsorption of both formaldehyde and formic acid. On increasing the potential, the electro-oxidation of the CO adsorbates to CO2 took place via reaction with the active (1 x 1)-O oxide. Formic acid was detected as a partial oxidation product during formaldehyde electro-oxidation. At all three temperatures employed, it was found that adsorbed CO species were formed from the adsorption of both formic acid and formaldehyde, and were oxidised to CO2 faster than was observed in the experiments involving CO adsorbed from CO(g), suggesting a higher mobility of the CO adsorbates formed from the adsorption of the HCOOH and HCHO. At potentials > 1000 mV, both the oxidation of formic acid to CO2 and the oxidation of formaldehyde to both CO2 and formic acid were significantly increased, and the oxidation of methanol to CO2 and methyl formate was observed, all of which were attributed to the formation of an active RuO2 phase on the Ru(0001) surface.     

Thermodynamic investigation of the adsorption of amides on graphite from their liquids and binary mixtures

We report a thermodynamic investigation of the adsorption of saturated and unsaturated (cis- and trans-) alkyl amides onto the surface of graphite from their pure liquids and from binary mixtures. We identify the formation of solid monolayers of the amides at temperatures when the bulk materials are liquid. The extent of this presolidification is much more extensive than other related materials, indicating that these amide layers are significantly more stable. The monolayer stability is found to be greatest for saturated amides. In addition, the stability of unsaturated amides is extremely sensitive to the location of the double bonds in the alkyl chain of the molecules, and trans isomers are found to be more stable than cis. We also address the preferential adsorption and mixing behavior of amide mixtures and amides mixed with other species coadsorbed onto graphite from binary solution. The results indicate that the amide molecules appear to be adsorbed with their principal axis parallel to the graphite surface and that amides are found to be strongly preferentially adsorbed with respect to alkanes. Interestingly the amides appear to mix rather better than might have been expected. There is also evidence of a number of other transitions in the adsorbates.     

Special features of methanol interaction with adsorbed oxygen at platinized platinum electrode: Transients of the open-circuit potential

Open-circuit potential transients are measured under the conditions of methanol interaction with the pre-adsorbed oxygen at platinized platinum electrode. The time necessary for complete removal of the adsorbed oxygen monolayer appeared being shorter by a factor of ～1.5 as compared with smooth polycrystalline platinum. The dependence of platinum surface coverage with adsorbed oxygen on the potential during its decay is found. It was shown that the reaction of methanol with the adsorbed oxygen is most slow at a high coverage (1–0.8). It is suggested that at these coverages, like the case of polycrystalline platinum, the adsorbed oxygen directly interacts with the methanol molecules from the solution. At moderate coverages (0.8–0.2), the reaction of the adsorbed oxygen with methanol at the platinized platinum is better described by the “conjugated reactions” mechanism. The specific rates of the methanol dissociative adsorption at the platinized platinum turned out to be close to those observed earlier for the polycrystalline platinum.     

The nature of the interactions between Pt4 cluster and the adsorbates *H, *OH, and H2O

The nature of the interactions between the platinum cluster Pt4 and the adsorbates (*)H, (*)OH, and H2O, as well as the influence of these adsorbates on the electronic structure of the Pt4 cluster, was investigated by density functional theory (B3LYP, B3PW91, and BP86) together with the effective core potential MWB for the platinum atoms, and 6-311++G(d,p) and aug-cc-pVTZ basis set for the H and O atoms. Identification of the optimal spin multiplicity state and the preferential adsorption sites were also evaluated. Adsorption changes the cluster geometry significantly, but the relaxation effects on the adsorption energy are negligible. The adsorbates bind preferentially atop of the cluster, where high bonding energies were observed for the radical species. Adsorption is followed by a charge transfer from the Pt4 cluster toward radical adsorbates, but this charge transfer occurs in a reversed way when the adsorbate is H2O. In contrast with water, adsorption of the radicals (*)H and (*)OH on platinum causes a remarkable re-distribution of the spin density, characterized by a spin density sharing between the (*)H and (*)OH radicals and the cluster. The covalent character of the cluster-adsorbate interactions, determined by electron density topological analysis, reveals that the Pt4-H interaction is completely covalent, Pt4-OH is partially covalent, and Pt4-H2O is almost noncovalent.     

Kinetics of dissociative adsorption of formic acid on electrodes of tetrahexahedral platinum nanocrystals

In the present paper we study the kinetics of dissociative adsorption of formic acid on the electrode of tetrahexahedral platinum nanocrystals (THH Pt NCs). In situ FTIR spectroscopic results demonstrate that HCOOH can be oxidized to CO2 at a low potential (-0.2 V(SCE)) on the THH Pt NCs electrode, and the chemical bonds inside formic acid molecule are broken to form adsorbed COL species. The kinetics of the dissociative adsorption of HCOOH was quantitatively investigated by employing programmed potential s...     

UPD铅对甲酸在铂上电氧化的助催化功用的研究

应用电位扫描和电位-时间程序技术研究了在UPD铅不存在和存在的情况下,各种因素对甲酸在铂上和酸介质中电催化氧化的影响。结果表明,在甲酸的CV图上,阳极方向的第一氧化峰和阴极方向的氧化峰是由于同一的弱吸附中间物的氧化,而阳极方向的第二和第三氧化峰是由于两种不同的强吸附中间物的氧化。cps值的测定和电极表面宏观结构的影响等实验表明,这些吸附中间物在电极表面上都呈线性吸附,它们分别可能是单键吸附的HCOO_ad双键吸附的CO_ad和叁键吸附的COH_ad。据此可以推论,UPD铅的主要功用是一种电子效应。     

Scanning electrochemical microscopy of hydrogen electro-oxidation. Rate constant measurements and carbon monoxide poisoning on platinum

We describe an application of the scanning electrochemical microscope that uses tip–sample feedback to characterize the electro-oxidation of hydrogen on a polycrystalline platinum electrode in sulfuric acid solutions in the presence and absence of adsorbed carbon monoxide. The hydrogen oxidation reaction is probed by reducing protons at a diffusion-limited rate at the microscope's tip electrode while it is positioned near a platinum substrate. A series of approach curves measured as a function of the substrate potential provides hydrogen oxidation rate constant values over a wide range of substrate conditions. In the absence of CO, the rate of hydrogen oxidation exceeds 1 cm s⁻¹ at potentials within the hydrogen adsorption and double layer charging regions. A Tafel slope of 30 mV per decade is determined near the reversible potential. At increasingly positive substrate potentials, the hydrogen oxidation rate decreases exponentially with increasing potential as the surface is covered with an oxide layer. The adsorption of solution-phase carbon monoxide completely deactivates the platinum substrate towards steady-state hydrogen oxidation over a large range of substrate potentials. Approach curves indicate a near-zero rate constant for hydrogen oxidation on CO-covered platinum at potentials below oxide formation. An increase in the hydrogen oxidation rate is seen at potentials sufficiently positive that CO fails to adsorb and the platinum oxide forms. In comparison, dynamic tip–substrate voltammetry depicts a complex substrate response whereby the adsorbed carbon monoxide layer transforms from a weakly adsorbed state at low potentials to a strongly adsorbed state at high potentials. Although steady-state approach curve measurements depict the complete deactivation of catalytic activity at these potentials, a significant hydrogen oxidation current is observed during the potential-induced transformation between these weakly and strongly adsorbed CO states. The rate of hydrogen oxidation approaches that of a pristine platinum surface during this surface transformation before returning to the poisoned state.     

Cation effects on the vibrational frequencies of adsorbed thiocyanate on platinum

Infrared spectra of thiocyanate adsorbed on a platinum electrode surface were obtained in the presence of perchlorate electrolytes of various alkali metal cations. It was discovered that the vibrational frequency of the C-N stretching mode is dependent upon the nature of the supporting electrolyte cation. Two bands were observed in the 2050 to 2150 cm⁻¹ range; one band was attributed to nitrogen-bound thiocyanate, and the other to species adsorbed via the sulfur atom. Each of these bands demonstrated independent frequency dependencies on cation nature and on the applied electric field within the interfacial region. Differences were also observed in the intensity dependence of the bands on the applied potential. The results were explained in terms of changes in the distance between the outer Helmholtz plane (OHP) and the surface of the electrode, and also in terms of the possible influence of coadsorbed alkali metal cations on the vibrational frequency of thiocyanate species adsorbed through the nitrogen atom. The effects that variations in the OHP-electrode distance impart on the magnitude of the potential drop across the interface, and the influence of small changes in this potential field on the C-N stretching frequency of N- and S-adsorbed thiocyanate species, are discussed.     

Comparative study of carbon monoxide adsorption and oxidation of the chemisorbed species at smooth and platinized platinum electrodes

The adsorption of carbon monoxide and the anodic oxidation of the chemisorbed species were investigated at room temperature under the same experimental conditions on foils of smooth and platinized platinum for which hydrogen adsorption is very similar. Both the weakly and strongly bonded species (type II and type I species) were formed to the same extent on the two electrodes in acidic electrolytes. While the freshly platinized platinum electrode behaved like the smooth electrode with predominance of the one-site adsorption of CO, the aging of the platinized electrode led to an increase of the two-site adsorption. The oxidation rate of strongly bonded species at constant potential decreased when the extent of two-site adsorption increased. The electrochemical results are discussed in the light of recent work in the gas phase.     

The adsorption of quinizarin on boron-doped diamond

The voltammetric response of the quinone species 'quinizarin' (QZ) and its electrocatalytic reduction of oxygen are studied at a boron doped diamond electrode (BDD). It is demonstrated that, contrary to the widespread belief that adsorption of organic molecules on BDD is minimal, not only does QZ readily adsorb to the electrodes surface but this adsorption is also influenced at low surface coverages by the pre-exposure of the electrode to organic solvents. Furthermore, the nature of this adsorbed QZ species is investigated and a potential dependent phase transition is observed. This is to the authors knowledge the first system to exhibit a phase transition of an adsorbed species on a boron doped diamond surface. At low scan rates the system is found to oscillate; these oscillations are ascribed to the presence of a 'negative differential resistance'.     

The influence of electrolyte concentration on the adsorption of octadecanol on Au(111)

The influence of electrolyte concentration on the potential dependent adsorption and desorption of octadecanol to/from a Au(111) electrode was investigated utilizing electrochemical and elastically scattered light techniques. The electrolyte concentration was found to influence the potential driven changes of the adsorbed layer (adsorption and desorption). The capacitive changes in the adsorbed layer were found to occur at more negative potentials with lower electrolyte concentration. The changes in the optical measurement, used to measure the characteristics of the desorbed species, or aggregates, were also found to be affected similarly. The magnitude of the overall change in the scattered light intensity was slightly dependent on electrolyte concentration. The re-adsorption of the aggregates was influenced by electrolyte concentration. The scattered light signal for an intermediate adsorbed state (adsorbed aggregate) was more prevalent for higher electrolyte concentration, suggesting that these intermediates were somewhat different compared to lower electrolyte concentrations. The lower electrolyte concentration displayed a larger potential region where this intermediate was stable, but the intensity of the scattered light was much lower. The electrolyte concentration most strongly influenced the potentials of adsorption and desorption, as well as the potential region of stability for the adsorbed intermediates. The sweep rate also has an influence on the scattering characteristics of the desorbed species, suggesting a possible method for measuring the kinetics of the adsorption–desorption process or for controlling the character of the desorbed species. These changes were explained in terms of a mechanism for the wetting or de-wetting of a surface. The influence of electrolyte concentration provides another opportunity for investigating the dynamics of this adsorption–desorption process.     

The electrochemical behavior of ad-atoms and their effect on hydrogen evolution: Part IV. Tin and lead ad-atoms on platinum

Hydrogen evolution on a platinum electrode decays against X_pt with the deposition of Sn ad-atoms and Pb ad-atoms in the same way as it decays with that of Ge ad-atoms, in which all of these ad-atoms occupy two platinum sites. In general the decay depends on the number of sites occupied by an atom of the ad-atom species.The potential ranges for oxygen adsorption by Sn ad-atoms and Pb ad-atoms are 0.45 to 1.24 V and 0.48 to 0.77 V, respectively, but the oxygen adsorbed by the latter ad-atoms is very small in amount.     

酸性和碱性介质中甘氨酸解离吸附和氧化的EQCM研究

用电化学石英晶体微天平(EQCM)研究酸性和碱性介质中甘氨酸在Pt电极上的吸附和氧化过程.结果表明,甘氨酸的解离吸附和氧化行为与溶液的酸碱性密切相关.酸性溶液中甘氨酸吸附较弱,碱性溶液中则产生强吸附物,且当电位低于0V(vs.SCE)时可吸附于Pt电极表面.此外,碱性溶液中甘氨酸还表现出较高的电氧化活性.通过EQCM定量检测上述过程中Pt电极表面的质量变化,测定了不同电位区间(氢区、双电层区和氧区)每传递一个电子所对应的电极表面吸附物种的平均摩尔质量.