中村 将志

The structural and electrochemical properties of Ag cubic-particles supported on highly oriented pyrolytic graphite (HOPG) have been studied using atomic force microscopy (AFM)) and voltammetry. Ag cubic-particles aggregate in an array on HOPG in solution. The AFM image of the Ag particles is similar to that obtained using transmission electron microscopy. Voltammogram of the Ag particles on HOPG electrode gives a pair of peaks at around -0.7 V (Ag/AgCl) in NaBr solution, which corresponds to the order-disorder structural transition of Br layer adsorbed on Ag(100) electrode. The surface structure and electrochemical properties of Ag cubic-particles are similar to those of Ag(100).

Surface structure of Pt(310) = 3(100)-(110), which contains kink atoms in the step, has been determined with the use of in situ surface X-ray scattering (SXS) in the double layer region (0.50 V(RHE)) in 0.1 M HClO4. Clean Pt(310) surface has pseudo (1 x 1) structure on which lateral displacements of 2-9% and 0.3-1% are found along a and b directions, respectively, whereas the surfaces of Pt(110) = 2(111)-(111) and Pt(311) = 2(100)-(111) are reconstructed to (1 x 2) according to previous reports. Interlayer spacing between the first and the second layers d(12) is contracted about 5% compared with the bulk spacing, whereas those between underlying layers are expanded down to fourth layer. Fully adsorbed CO has no effect on the surface structure of Pt(310). This result differs from that on Pt(111), where d(12) is expanded after CO adsorption. (C) 2008 Elsevier Ltd. All rights reserved.

Spectroscopic characterization of adsorbed water has been carried out on (111) surfaces of Pt, Pd, Rh, Au, and Cu in sulfuric acid solution using infrared reflection-absorption spectroscopy (IRAS). The absorption band of the HOH bending mode (delta(HOH)) is measured below the onset potential of (bi)sulfate adsorption. The band frequency of delta(HOH) of adsorbed water is lower than that of bulk water. The delta(HOH) band shifts to higher frequencies with the increase of the positive potentials on Pt, Pd, and Rh, whereas the band intensity is unchanged between the potentials of hydrogen evolution and (bi)sulfate adsorption. This suggests that water is adsorbed through an oxygen lone pair, with its molecular plane slightly tilted from the surface. On Au(111), the delta(HOH) band intensity decreases with the increase of the electrode potential. This result indicates that the orientation of water depends on the applied potential. No absorption band of water is found on Cu(111), which indicates different behavior of adsorbed water compared with the other metal electrode surfaces.

We have developed a nondestructive analysis method, which is named X-ray reciprocallattice space imaging, based on synchrotron diffraction for quickly characterizing a crystalline nanometer-scale structure in a non-vacuum environment. The basic idea behind the method is that the reciprocal lattice of 1 D or 2D structures are an array of sheets or rods, respectively. Thus the reciprocal-lattice space can be recorded for a fixed sample with a 2D X-ray detector fixed. We successfully demonstrated that the method was applicable to structural evaluation of ultrathin NiO wires on a sapphire surface in air, Bi nanolines buried in Si, an interfacial structure of a Au electrode in solution, and a thinfilm of Bi₄Ti₃O₁₂.

Surface structure of a stepped surface of Pt, Pt(31 1) (=2(100) - (111)), has been determined under potential control in 0.1 M HClO4 with the use of in situ surface X-ray scattering (SXS). The crystal truncation rods (CTRs) are reproduced well with the (1 x 2) missing-row model. Relaxation of surface layers, which is observed on the low-index planes of Pt, is not found on Pt(31 1) in the "adsorbed hydrogen region". CTRs at 0.10 (RHE) have the same feature as those at 0.50 V, showing that the surface layers of Pt(311) have no potential dependence. Scanning tunneling microscopy (STM) also supports the (1 x 2) structure of Pt(311) in 0.1 M HClO4.

Chlorobenzene was electrolyzed on poly cry stalline platinum electrode in acetonitrile with various water concentrations at -3.02 V(vs. Fc/Fc(+)). Formation rate of the reduction products depend on water concentration remarkably. Benzene is a main product at [H2O] <= 0.3 mol dm(-3). At [H2O] >= 0.35 mol dm(-3), toluene is obtained as well as benzene. Partial current density of toluene gives maximum at [H2O] = 0.44 mol dm(-3). Formation of toluene closely relates with production of methane resulting from the decomposition of acetonitrile.

Structural effects on intermediate species of methanol oxidation ore studied on low-index planes of platinum using in-situ infrared (IR) spectroscopy. A flow cell is designed for rapid migration of reactant and product species on the electrode surface. IR spectra show adsorption of formate and the formation of carbonate species on the Pt(111) surface at potentials higher than that of CO oxidation. The band assignments for carbonate and formate are confirmed by vibrational isotope shifts. On Pt(100), the absorption band of adsorbed formate is much smaller than that on Pt(117). On the other hand, there is no adsorbed formate on Pt(110) in the potential region examined. The band intensity of formote follows the order: Pt(117) > Pt(100) > Pt(110). This order is opposite to that of the current density in the regions of higher potential. Adsorbed formate on PtO 10 behaves like a catalyst-poisoning intermediate, like adsorbed CO.

Electrochemical oxidation of formic acid has been studied on the stepped and kinked-stepped surfaces of Pd in 0.1 M HClO4 containing 0.1 M formic acid with the use of voltarnmetry. The surfaces examined are Pd(S)-[n(100) x (110)], Pd(S)-[n(111) x (100)] and Pd(S)-[n(111) x (111)] series (n=2-9). The results are compared with those of Pd(S)-[n(100) x (111)] series reported previously. All the electrodes give maximum currents of formic acid oxidation j(p) between 0.5 and 0.8 V (RHE). The values of j(p) plotted against the density of step (kink) atoms d(s) depend on the surface structure remarkably. Pd(S)-[n(111) x (100)] surfaces provide maximum of j(p) at n=5, whereas Pd(S)-[n(100) x (110)] and Pd(S)-[n(111) x (111)] do not give maximum of j(p). The values of j(p) have the following order: Pd(S)[n(111)x(111)]< Pd(S)-[n(111)x(100)]< Pd(S)-[n(100)x(110)]< Pd(S)-[n(100)x(111)]. The anodic current at more negative potential 0.20 V (RHE) shows different activity series: Pd(111) and Pd(110) have the highest rate for formic acid oxidation at 0.20 V (RHE). (c) 2006 Elsevier B.V. All rights reserved.

Structural effects on the rates of formic acid oxidation have been studied on Pd(111), Pd(100), Pd(110), and Pd(S)-[n(100) x (111)] (n = 2-9) electrodes in 0.1 M HClO4 containing 0.1 M formic acid with use of voltammetry. On the low index planes of Pd, the maximum current density of formic acid oxidation (j(P)) increases in the positive scan as follows: Pd(110) < Pd(111) < Pd(100). This order differs from that on the low index planes of Pt: Pt(111) < Pt(100) < Pt(110). Pd(S)-[n(100) x (111)] electrodes with terrace atomic rows n >= 3 have almost the same j(P) as Pd(100), except Pd(911) n = 5. The value of j(P) on Pd(911) n = 5 is 20% higher than those of the other surfaces. Pd(311) n = 2, of which the first layer is composed of only step atoms, has the lowest j(P) in the Pd(S)-[n(100) x (111)] series. The adsorption geometry of the reaction intermediate (formate ion) is optimized by using density functional theory.

Structural effects on the rate of the dechlorination of chlorobenzene have been studied using the low index planes of platinum and silver in acetonitrile solution. Chlorobenzene is electrolyzed on platinum electrodes using naphthalene as a mediator at - 2.94 V vs. Ag/Ag+. The main product is benzene. A reaction via a mediator does not depend on electrodes in general, because it is a homogeneous catalytic reaction. Surface structure, however, affects the partial current density of benzene (j(C6H6)) on platinum electrodes: Pt(111)< Pt(110)similar to Pt(100). On silver electrodes, j(C6H6) shows no structural effect in the electrolysis using naphthalene. Electrolysis without naphthalene gives the same structural effect as that with naphthalene on platinum electrodes, whereas no silver electrode reduces chlorobenzene at - 2.94 V vs. Ag/Ag+ without naphthalene. Therefore, the anomalous structural effect on the electrolysis with naphthalene is attributed to the existence of a direct reduction of chlorobenzene on platinum electrodes. Silver electrodes reduce chlorobenzene to benzene at more negative potential - 3.17 V vs. Ag/Ag+ without naphthalene. The value of j(C6H6) depends on the surface structure: Ag(110)similar to Ag(111)< Ag(100). The flat (100) terrace has the highest activity for the dechlorination of chlorobenzene.

The adsorption of water molecule on a Cu(1 1 1) surface at 25 K was studied by infrared reflection absorption spectroscopy (IRAS). The four characteristic absorption bands in a v(OD) stretching region were observed on Cu(1 1 1) surface and assigned to be OD stretchings from dimer and hexamer water cluster molecules. The appearances of the key OD stretching bands observed on M(1 1 1) (M = Cu, Ni, Pt) and Ru(0 0 1) surfaces indicate that water dimer and hexamer clusters are coadsorbed dominantly on those surfaces at 25 K. (c) 2005 Elsevier B.V. All rights reserved.

The adsorption of sulfate or OH species and subsequent Ni(OH)(2) film growth on Ni(1 1 1) single crystal electrodes has been investigated using in situ infrared reflection absorption spectroscopy (IRAs) as well as scanning tunneling microscopy (STM). In a pH 3 sulfuric acid solution, STM images show that a well-defined Ni(1 1 1) surface with a (I x 1) lattice is exposed at -300 mV, while hexagonal close-packed images with an atomic spacing of 0.32 nm are grown on this electrode at 300 mV. On the other hand, IRAs results in a sulfuric acid solution (pH 3) reveal that an absorption band at 1116 cm(-1), which can be ascribed to v(S-O) symmetric stretching of sulfate anion on Ni(1 1 1) surface, starts to appear at -400 mV and develops its intensity with an electrode potential increase, while an absorption band at 930 cm(-1) begins to develop at 0 mV on Ni(1 1 1), Ni(1 0 0) and Ni(1 1 0) electrodes, which can be assigned to an in-plane delta(Ni-OH) bending vibration in Ni(OH)(2) passive film. (C) 2003 Elsevier B.V. All rights reserved.

Carbon monoxide (CO) and sulfuric acid anion contacted with underpotential deposition (upd) copper on Pd(111) and Pt(111) electrode surfaces in 0.5 M H2SO4 solution were studied by cyclic voltammetry (CV) and in situ infrared reflection absorption spectroscopy (IRAS). CO was stabilized on copper covered Pd(111) and Pt(111) electrode surfaces. Both CO and (bi)sulfate molecules that were stabilized with copper, showed no potential dependent frequency shift in band center position over a certain potential range. Copper (bi)sulfate or copper carbonyl surface metal complexes are formed on Pd(111) and Pt(111) electrode surfaces in the potential range. The copper atoms in the upd potential range on Pd(111) or Pt(111) electrode do not form an ordinal metal ds band structure, but exhibit insulator like characteristics, due to excess positive charge of copper and ionic pseudo-copper metal complex formation on the surface. (C) 2003 Elsevier B.V. All rights reserved.

Monomer and cluster molecules of water (D2O) adsorbed on Ni(111) surface were studied at 20 K by infrared reflection absorption spectroscopy. At a low coverage of water (less than theta = 0.03), a singleton-like monomer water molecule dominated on top of a Ni atom on Ni(111) surface. When the coverage of water was increased (0.03 < theta < 0.33), ring hexamer like water cluster molecules grew on the surface at wide coverage ranges at 20 K. The spectroscopic features of the infrared spectra of the ring hexamer like cluster molecule adsorbed on Ni(111) surface were quite similar to those on Pt(111) and Ru(001) surfaces. (C) 2003 Elsevier B.V. All rights reserved.

The electric double layer at electrolyte-electrode interface has been investigated by an experimental simulation under ultra high vacuum (UHV). In order to reproduce an electric double layer on an electrode surface, water is adsorbed on the surface treated with electrolyte components (HCl, Na and sulfuric acid) and CO. The coadsorption of water molecules with the electronegative and electropositive additives indicates the existence of various hydration structures or orientation of water molecules on the surfaces. By comparing the results under UHV conditions with those from in-situ electrode surfaces in solution, there appears to be a correlation between orientation of water molecules and electrode potential. Over-layer water molecules as well as adsorbed ones on the surface provides ordered or disordered structures that determine the electrode potential values.

Throughout the whole potential ranges where underpotential deposition (upd) proceeds, the stretching absorption bands of both sulfate and phosphate anions (Vs-O and Vp-O) do not change at all with regard to band-center position. Sulfate and phosphate anions are combined with copper or zinc ions to form surface metal complexes on a Au(1 1 1) electrode surface, respectively: transition metal-oxianion (sulfate and phosphate) pseudo-complexes are formed in the course of upd processes. The surface structure of the Au(1 1 1) electrode in the topmost layer is the same as the bulk structure (I x 1), and lifting of surface reconstruction takes place in the case of Cu-upd where Cu(I)(2)SO4 and Cu(I)(3)SO4 pseudo-complexes extend on the surface, while surface reconstruction of a Au(1 1 1) electrode continues to occur in the case of Zn-upd where the Zn(I)(2)PO4 or Zn(I)(3)PO4 pseudo-complex locates. (C) 2003 Elsevier B.V. All rights reserved.

The main components of a new beamline for surface and interface crystal structure determination at SPring-8 are briefly described. Stages for the beamline monochromator are modified for making an incident X-ray intensity more stable for surface X-ray experiments. Absolute photon flux densities were measured with an incident photon energy. A new ultrahigh vacuum system is introduced with preliminary X-ray measurements from an ordered oxygen on Pt (111) surface.

The structure of underpotential deposition (UPD) copper, a hydration water molecule, and a bisulfate anion on Au(111) surface in 0.5 M H2SO4 solution has been determined by in situ surface X-ray diffraction study. The bisulfate anion and the UPD copper form a root3 x root3R30degrees structure on an Au(111) electrode at a potential between 250 and 400 mV. At this potential range, UPD Cu, a bisulfate anion, and a hydration water molecule coadsorb on Au(111), while the coverages of copper and bisulfate anion are 0.6667 and 0.3333, respectively. The coadsorption structure is represented by Laue symmetry of P31m. On top of each copper atom, a hydration water molecule is accommodated to form a stable and closest-packed water adlayer with a large density. At a more positive potential than 940 mV, the bisulfate anion forms a root3 x root7 structure on a bare Au(111) surface. (C) 2002 Elsevier Science B.V. All rights reserved.

Four different hydration water molecules. a flat monomer, a tilted monomer, a tetramer cluster and an upright monomer, were observed on Ru(0 0 1). In Situ scanning tunneling microscopy (STM) images of M(1 1 1)-root3 x root7(HSO4- + H5O(2)(+)) (M - Pt, Ir, Au Ru(0 0 1)) in H2SO4 solution produced a zig-zag chain of hydration water molecules, revealing a large stabilization energy due to the formation of a hydrogen bonding network. Also 2 x 2-2CO + H2O structure was observed on both Ru(0 0 1) electrode and Ru(0 0 1) ultra-high vacuum surfaces by STM and low energy electron diffraction. These model double layers including over-layer water Molecules form it preferentially ordered structure in terms of hydrogen bonding at a negative electrode potential while also forming a disordered structure with a relatively random orientation in the over layer at a positive electrode potential. The preferential orientation of the large water dipole yields a strong electric field on the surface and lowers the frequencies of the adsorbed bisulfate S-O stretching or the CO stretching absorption band. (C) 2002 Elsevier Science B.V. All rights reserved.

The coadsorption of I water Molecule with Na atoms on the Ru(001) Surface has been studied by infrared reflection absorption spectroscopy. Five different kinds of hydration water monomers were observed oil Ru(001) over a wide coverage range of Na. At a low Na coverage. one of the hydrogen atoms was found to point toward and the other away from the surface. When the Na coverage increased to above 0.06 NIL, both hydrogen atoms rotated to face the surface (oxygen-up orientation). The monomer water molecules coadsorbed with Na were found to remain stable without decomposition on a Ru(001) surface over a wide temperature range at 20-220 K. (C) 2002 Elsevier Science B.V. All rights reserved.

Water adsorption on Pt(111) and Ru(001) treated with oxygen, hydrogen chloride and sodium atom at 20 K has been studied by Fourier transform infrared spectroscopy, scanning tunneling microscopy and surface X-ray diffraction. Water molecules chemisorb predominantly on the sites of the electronegative additives, forming hydrogen bonds. Three types of hydration water molecules coordinate to an adsorbed Na atom through an oxygen lone pair. In contrast, water molecules adsorb on electrode surfaces in a simple way in solution. In 1 mM CuSO4 + 0.5 M H2SO4 solution on an Au(111) electrode surface, water molecules coadsorb not only with sulfuric acid anions through hydrogen bonding but also with copper, over wide potential ranges. In the first stage of underpotential deposition (UPD), each anion is accommodated by six copper hexagon ( honeycomb) atoms on which water molecules dominate. At any UPD stage water molecules interact with both the copper atom and sulfuric acid anions on the Au(111) surface. Water molecules also coadsorb with CO molecules on the surface of 2 x 2-2CO Ru(001). All of the hydration water molecules chemisorb weakly on the surfaces. There appears to be a correlation between the orientation of hydrogen bonding water molecules and the electrode potential.

The coadsorption of carbon monoxide (CO) and water molecules on a Ru(0 0 1) surface has been studied by infrared spectroscopy, LEED and STM. At high CO coverage phases, a 2 x 2-(2CO + D2O) structure was observed on both UHV and electrode surfaces. Electrode potential dependent structures from CO and water adlayers on an electrode surface were reproduced on a UHV surface by controlling molecular orientations of the first layer and second overlayer water molecules. At lower CO coverages, a CO band center showed coverage dependent shift down to 1444 cm(-1) due to an electron transfer from a lone pair of a water molecule to CO 2 pi (*). (C) 2001 Elsevier Science B.V. All rights reserved.

Four hydration water molecules were observed on a Ru(001) surface by infrared reflection absorption spectroscopy (IRAS). An abnormally low frequency shift from 2145 to 1356 cm(-1) of a CO molecule adsorbed onto a Ru(001) surface was observed after coadsorption of water molecules with CO. A flat and a tilted monomer were found to exist as a singleton species at a low and a high coverages, respectively. The degree of charge transfer from an oxygen lone pair of the monomers to a Ru(001) surface is comparable with that from an alkaline atom on the same surface. (C) 2001 Elsevier Science B.V. All rights reserved.

Water-cluster molecules adsorbed on a Ru(0001) surface were studied by infrared reflection absorption spectroscopy (IRAS). Monomer and tetramer water clusters are stabilized on Ru(0001) at relatively wide coverage and temperature ranges. Annealing at higher temperatures than 170 K causes decomposition of the clusters into OH and H on the surface. Surface diffusion of those cluster molecules on Ru(0001) is deeply suppressed at low temperatures. Stretching frequencies observed at the bonded OD bands of root 3 x root 3 bilayer structures formed on Au(111), Pt(111) and Ru(0001) surfaces indicate that hydrogen-bonding interactions increase on those surfaces in this order due to the mismatch between metal and an ideal bilayer structure. (C) 2000 Elsevier Science B.V. All rights reserved.

Water adsorption on Pt(111) surfaces treated with oxygen or hydrogen chloride at 20 K has been studied by Fourier transform infrared spectroscopy and scanning tunneling microscopy. Water molecules chemisorb predominantly on the sites of the electronegative additives (O or Cl-), forming hydrogen bonds of O-H ... O or O-H ... Cl- On a Pt(111)-2 X 2-O surface, water adsorption produces species (O(D2O)), monomeric water (D2O), (O(D2O)(2)) and ring tetramer-like cluster (O(D2O)(3)) on a Pt(111) surface. On a Pt(111)-3 x 3-Cl- (theta = 0.44) surface, water adsorption gives rise to a Pt(111)-(4 X 2)(H3O+ + Cl-) co-adsorption structure to form a hydrogen-bonding network between Cl- and H3O+ ions. (C) 2000 Elsevier Science B.V. All rights reserved.

The adsorption of D2O on Pt(111) at 20 K has been investigated by infrared reflection absorption spectroscopy (IRAS). Water was found to form as a dimer at low coverages and it grew a tetramer molecule at high coverages. The structures of the cluster water molecules on the surface were derived from the intensities and the frequencies of symmetric and asymmetric v OD stretching absorptions. The annealing at higher temperatures than 130 K was needed to form an ice bilayer island structure. (C) 1999 Elsevier Science B.V. All rights reserved.

The adsorption of urea on Au(100) and Au(111) electrode surfaces was studied through a combination of cyclic voltammetry and Fourier-transform infra-red spectroscopy. The infra-red spectra indicate that urea molecule is adsorbed on Au(100) with a molecular plane normal to the electrode surface. On Au(111), urea showed a different coordination. Lifting from 5x20 to 1x1 on the Au(100) surface was accelerated by the adsorption of urea. The kinetics of the 5 x 20 to 1 x 1 transition was monitored by a time-resolved IRAS measurement. The lifting of a reconstructed 5 x 20 surface to 1 x 1 proceeded within 20 s. However, the reconstruction from the 1 x 1 to 5 x 20 surface, required a longer period of time, more than 70 s. (C) 1999 Published by Elsevier Science B.V. All rights reserved.