Angewandte Chemie (International ed. in English), Jan 26, 2015
A photoelectrochemical (PEC) cell consisting of an n-type CdS single-crystal electrode and a Pt c... more A photoelectrochemical (PEC) cell consisting of an n-type CdS single-crystal electrode and a Pt counter electrode with the ruthenium-2,2'-bipyridine complex [Ru(bpy)3 ](2+/3+) as the redox shuttle in a non-aqueous electrolyte was studied to obtain a higher open-circuit voltage (VOC ) than the onset voltage for water splitting. A VOC of 1.48 V and a short-circuit current (ISC ) of 3.88 mA cm(-2) were obtained under irradiation by a 300 W Xe lamp with 420-800 nm visible light. This relatively high voltage was presumably due to the difference between the Fermi level of photo-irradiated n-type CdS and the redox potential of the Ru complex at the Pt electrode. The smooth redox reaction of the Ru complex with one-electron transfer was thought to have contributed to the high VOC and ISC . The obtained VOC was more than the onset voltage of water electrolysis for hydrogen and oxygen generation, suggesting prospects for application in water electrolysis.
The transient response of 10 molecular layers of D 2 O ice on CO/Pt(1 1 1) at 130 K was investiga... more The transient response of 10 molecular layers of D 2 O ice on CO/Pt(1 1 1) at 130 K was investigated under ultra-high vacuum following a near-infrared pump pulse of 35 ps by sum frequency generation (SFG) spectroscopy. The D 2 O molecules in the ice crystalline layer formed an amorphous or liquid-like structure in response to the pumping without desorption of D 2 O to the gas phase, and the crystals returned to the crystal structure on a sub-nanosecond time scale.
The catalytic deep oxidation of methanol by oxygen on the Pt(111) surface under ambient pressure ... more The catalytic deep oxidation of methanol by oxygen on the Pt(111) surface under ambient pressure conditions has been studied by in situ infrared reflection absorption spectroscopy (IRAS). It was found that the Pt(111) surface was covered with formate in a flow of 0.16 kPa of methanol and >1.3 kPa of oxygen mixture at 350 K while it was covered with CO at the oxygen pressure below 1.3 kPa. CO 2 was detected in the product gas and the reaction kinetics was examined. The relation between the production rate of CO 2 and the coverage of adsorbates as a function of oxygen pressure indicated that the CO 2 mainly originated from the formate which was produced from oxidation of methanol. Although CO produced by methanol decomposition seems to be one of precursors of CO 2 formation, this reaction was found to be a minor pathway. The detailed mechanism of oxidation of methanol on Pt(111) was discussed.
The reaction of methanol with oxygen on Pt(111) under ultrahigh vacuum condition has been investi... more The reaction of methanol with oxygen on Pt(111) under ultrahigh vacuum condition has been investigated by infrared reflection absorption spectroscopy (IRAS). Molecular and atomic states of adsorbed oxygen existed on the Pt(111) surface, and the adsorption of oxygen at 100 K gave molecularly adsorbed oxygen that dissociated to adatoms at ∼160 K. Formate species, which gave the symmetric C-O stretching band at 1327 cm -1 , was observed when methanol-adsorbed Pt(111) surface, which was precovered by molecular oxygen, was heated to 160 K. The IRAS band of formate was verified by comparison with the band of the formate derived from formic acid on the Pt(111) surface and by the isotope shift of the band observed by using deuterated methanol. The amount of produced formate was proportional to the amount of the molecularly adsorbed oxygen. The formate band disappeared at 270 K, at which temperature desorption of CO 2 and H 2 was observed on temperature-programmed desorption spectra. Molecular oxygen on the Pt(111) surface dissociated at 300 K and the produced adatoms did not oxidize methanol, but the methanol was decomposed to CO and H 2 . Molecularly adsorbed oxygen is thus considered to be responsible for the oxidation of methanol to formate.
Anomalous coverage dependence was observed on the sum-frequency generation signal of bridge CO on... more Anomalous coverage dependence was observed on the sum-frequency generation signal of bridge CO on the Ni(111) surface when co-adsorbed by on-top CO. The bridge CO peak was distinct and normal from 0.04 to ∼0.40 monolayer (ML) but weakened after the appearance of the on-top CO peak at 0.47 ML and disappeared at 0.60 ML, although both peaks were observed in
... Accelerator in Continuous Casting Mold Noriko KUBO,1) Jun KUBOTA,2) Makoto SUZUKI3) and Toshi... more ... Accelerator in Continuous Casting Mold Noriko KUBO,1) Jun KUBOTA,2) Makoto SUZUKI3) and Toshio ISHII1) ... 11) J. Kubota, S. Kuriyama and T. Teshima: CAMP-ISIJ, 2 (1989), 301. 12) MB Assar, PH Dauby and GD Lawson: Steelmaking Conf. ...
The behavior of D2O ice on CO/Pt(111) and Pt(111) under the irradiation of near-IR pulses (NIR) w... more The behavior of D2O ice on CO/Pt(111) and Pt(111) under the irradiation of near-IR pulses (NIR) was studied by sum-frequency generation (SFG) spectroscopy. The peaks assigned to the O–D stretching modes of ice were obtained for the first 30 molecular layers on Pt(111). When the D2O/CO/Pt(111) was irradiated, the signal of D2O was weakened after 500 ps, but that of
Adsorption of CO and NO on NiO(111) thin films epitaxially grown on Ni(111) substrate has been st... more Adsorption of CO and NO on NiO(111) thin films epitaxially grown on Ni(111) substrate has been studied by infrared-visible sum frequency generation (SFG) and the results were compared with those of infrared reflection absorption spectroscopy. From SFG measurements, the CO stretching band of adsorbed CO was observed at 2144 cm−1 for both p- and s-polarized visible (532 nm) light whereas
Thin films of the lanthanum titanium oxynitride perovskite (LaTiO x N y ) synthesized by reactive... more Thin films of the lanthanum titanium oxynitride perovskite (LaTiO x N y ) synthesized by reactive radio-frequency sputtering on conductive Nb-doped strontium titanate (Nb:SrTiO 3 ) substrates are evaluated as photoelectrodes for water splitting reaction under visible light. The films are characterized by X-ray diffraction analysis, energy-dispersive spectroscopy, scanning electron and atomic force microscopy, and ultraviolet-visible spectroscopy. Thin films with polycrystalline, oriented, or epitaxial structures are obtained depending on the substrate temperature and plasma composition. The band-gap energies of the films thus prepared are in the range 2.05-2.35 eV. Photoelectrochemical measurements reveal that the photoactivity of these films increases with the quality of film crystallization. The flat-band position of LaTiO x N y is found to change with pH of the reactant solution. Surface modification with colloidal IrO 2 is also demonstrated to result in a marked increase in photoactivity, with the modified epitaxial LaTiO x N y film exhibiting a photocurrent density of ca. 70 µA cm -2 at +1.0 V vs. Ag/AgCl at pH 4.5 in aqueous Na 2 SO 4 solution under irradiation at visible wavelengths (λ > 420 nm).
The mechanism of hydrogen evolution by a core/shell noble-metal/Cr 2 O 3 particulate as a highly ... more The mechanism of hydrogen evolution by a core/shell noble-metal/Cr 2 O 3 particulate as a highly efficient cocatalyst for overall water splitting under visible light using the photocatalyst (Ga 1-x Zn x )(N 1-x O x ) is investigated by electrochemical and in situ spectroscopic measurements of model electrodes. The electrodes are prepared by electrochemical deposition of 1.8-3.5 nm thick Cr 2 O 3 films on Rh and Pt plates and are evaluated as model systems of Rh/Cr 2 O 3 and Pt/Cr 2 O 3 core/shell particulates, which have previously been applied effectively as cocatalysts for hydrogen evolution in this system. Proton adsorption/desorption and H 2 evolution currents are observed for both the Cr 2 O 3 -coated and the bare electrodes, and the infrared absorption band due to Pt-H stretching (2039 cm -1 ) is apparent for both the coated and the bare electrodes. These observations indicate that the Cr 2 O 3 layer does not interfere with proton reduction or hydrogen evolution and that proton reduction takes place at the Cr 2 O 3 /Pt interface. However, the reduction of oxygen to water is suppressed only in the Cr 2 O 3 -coated samples. The Cr 2 O 3 layer is thus permeable to protons and the evolved hydrogen molecules, but not to oxygen. Cocatalyst modification by thin films with this type of functionality thus appears to be a useful strategy for improving the efficiency of photocatalytic overall water splitting.
Hydrogenation of ethylene on a Pt(111) surface in the presence of gaseous ethylene and hydrogen i... more Hydrogenation of ethylene on a Pt(111) surface in the presence of gaseous ethylene and hydrogen in the 10 3 Pa range was investigated by infrared reflection absorption spectroscopy (IRAS). The IRA peaks assigned to di-σ-bonded ethylene and ethylidyne were observed on Pt(111) under the flow of 1.3 × 10 2 Pa of ethylene and 6.5 × 10 3 Pa of hydrogen at 200-300 K, and the apparent activation energy of ethylene hydrogenation was estimated to be 37 ( 5 kJ mol -1 from the rate of temperature-dependent ethane production. The ethylene hydrogenation on ethylidyne-covered Pt(111) was also examined under the same condition. The peak due to the di-σ-bonded ethylene was not observed on ethylidyne-covered Pt(111), although the similar rate of hydrogenation and the similar activation energy (39 ( 5 kJ mol -1 ) were obtained as those on clean Pt(111). The π-bonded ethylene, which has been previously proposed as an intermediate by the sum-frequency generation (SFG) experiment under the catalytic hydrogenation condition and by IRAS under the low-temperature condition, was not detected in the present study. The similarity of the rate and activation energy for clean and ethylidyne-covered Pt(111) surfaces suggests that the rate of hydrogenation does not depend on either coverage of di-σ-bonded ethylene or ethylidyne. The role of the observed species in the hydrogenation of ethylene is discussed. * Corresponding
Vibrational assignments for the chiral molecule cinchonidine using a combination of experimental ... more Vibrational assignments for the chiral molecule cinchonidine using a combination of experimental vibrational spectroscopic measurements and ab initio computational methods are reported. Several bands in both the IR and Raman spectra are identified as useful in providing information regarding the mode of adsorption of cinchonidine on metal surfaces, a system of great relevance to enantioselective catalysis. In particular, vibrational modes associated with the quinoline group can be used to diagnose the degree of tilt of the molecule with respect to the plane of the substrate. The use of this information for the study of cinchonidine adsorption on polycrystalline platinum with both reflection-absorption infrared spectroscopy (RAIRS) and surface-enhanced Raman spectroscopy (SERS) is discussed. Adsorption geometries for cinchonidine on platinum at low and high concentrations are reported. Figure 1. Structure of cinchonidine.
Unstable intermediates are indispensable ingredients of chemical reactions, but their identificat... more Unstable intermediates are indispensable ingredients of chemical reactions, but their identification at solid surfaces has been hampered by the lack of techniques to detect short-lived and fractionally generated species. We succeeded in identifying the intermediate in a thermal decomposition reaction by utilizing the picosecond temperature jump induced by the irradiation of laser pulses and the observation by sum-frequency generation spectroscopy. We verified that the decomposition of formate on the NiO(111) surface is preceded by the transformation of stable bidentate formate to unstable monodentate formate, which is the reactive intermediate, and two species are found to be in equilibrium before decomposition. S1089-5647(98)01636-8 CCC: $15.00
... On the other hand, it is possible to bond in a bridging configuration if the surface is nicke... more ... On the other hand, it is possible to bond in a bridging configuration if the surface is nickel-terminated in which separation between the nearest cations of the surface is comparable with the distance between the two oxygens of formate as ... J.; Wada, A.; Domen, K.; Hirose, C. Surf. ...
The adsorption of cyclohexane on Ni(111) was studied by infrared-visible sum-frequency generation... more The adsorption of cyclohexane on Ni(111) was studied by infrared-visible sum-frequency generation (SFG) spectroscopy with and without near-infrared (NIR) pump pulse irradiation. Two adsorption states of cyclohexane were found in the monolayer region, a low-coverage state showing SFG peaks at 2740, 2815, and 2865 cm(-1), and a high-coverage state showing peaks at 2740, 2815, and 2905 cm(-1). Both states coexisted on the saturated Ni(111) surface. The broad peak at 2740 cm(-1) was due to the softened CH stretching mode of the axial CH groups of cyclohexane that point toward the Ni(111) surface. The peaks at 2815 and 2865 (or 2905) cm(-1) were due to the symmetric and asymmetric stretching modes of CH(2) groups, respectively, that were free from the surface. Irradiation with NIR pulses caused a temporary jump in temperature at the Ni(111) surface and enhanced the intensity of the 2905 cm(-1) peak, but weakened the other peaks. This indicates that the temperature jump excited the cyclohexane molecules from the low-coverage state to the high-coverage state. The dynamics of the structural change observed in the adsorbed cyclohexane on NIR irradiation is discussed.
Adsorption of ethene on clean and ethylidyne-covered Pt(111) surfaces was investigated by infrare... more Adsorption of ethene on clean and ethylidyne-covered Pt(111) surfaces was investigated by infrared reflection absorption spectroscopy (IRAS). Under gaseous ethene of ~ 10 -3 Pa, 7r-bonded ethene was reversibly formed on a Pt(lll) surface saturated with di-o--bonded ethene at 112 K. The 7r-bonded ethene gave infrared absorption peaks at 954 and 3090 cm-1 which were assigned to =CH 2 wagging (out-of-plane) and CH 2 asymmetric stretching modes, respectively. These two peaks indicated that the ~--bonded ethene was adsorbed on Pt(111) in such a way that the molecular plane is tilted with respect to the surface while the C=C bond is being kept parallel to the surface. The intensity of the C-H stretching band at 2908 cm-i of di<r-bonded ethene decreased with the increase of 7r-bonded ethene. The heat of adsorption of ~--bonded ethene was estimated to be 40 + 10 kJ/mol. The presence of ethylidyne with saturation coverage was found to inhibit the ~r-bonded ethene adsorption.
Surface modifications using platinum (Pt) particles and iron oxides (FeOx) were found to lead to ... more Surface modifications using platinum (Pt) particles and iron oxides (FeOx) were found to lead to a significant improvement in the current--potential (J--E) properties for hydrogen evolution from water in p-type silicon (p-Si) electrodes. The onset potential and cathodic photocurrent for hydrogen evolution from the Pt/p-Si(100) electrode were, respectively, 0.50 V\text{RHE and 0.28 mA/cm2 at 0 V\text{RHE (RHE: reversible hydrogen electrode).
Angewandte Chemie (International ed. in English), Jan 26, 2015
A photoelectrochemical (PEC) cell consisting of an n-type CdS single-crystal electrode and a Pt c... more A photoelectrochemical (PEC) cell consisting of an n-type CdS single-crystal electrode and a Pt counter electrode with the ruthenium-2,2'-bipyridine complex [Ru(bpy)3 ](2+/3+) as the redox shuttle in a non-aqueous electrolyte was studied to obtain a higher open-circuit voltage (VOC ) than the onset voltage for water splitting. A VOC of 1.48 V and a short-circuit current (ISC ) of 3.88 mA cm(-2) were obtained under irradiation by a 300 W Xe lamp with 420-800 nm visible light. This relatively high voltage was presumably due to the difference between the Fermi level of photo-irradiated n-type CdS and the redox potential of the Ru complex at the Pt electrode. The smooth redox reaction of the Ru complex with one-electron transfer was thought to have contributed to the high VOC and ISC . The obtained VOC was more than the onset voltage of water electrolysis for hydrogen and oxygen generation, suggesting prospects for application in water electrolysis.
The transient response of 10 molecular layers of D 2 O ice on CO/Pt(1 1 1) at 130 K was investiga... more The transient response of 10 molecular layers of D 2 O ice on CO/Pt(1 1 1) at 130 K was investigated under ultra-high vacuum following a near-infrared pump pulse of 35 ps by sum frequency generation (SFG) spectroscopy. The D 2 O molecules in the ice crystalline layer formed an amorphous or liquid-like structure in response to the pumping without desorption of D 2 O to the gas phase, and the crystals returned to the crystal structure on a sub-nanosecond time scale.
The catalytic deep oxidation of methanol by oxygen on the Pt(111) surface under ambient pressure ... more The catalytic deep oxidation of methanol by oxygen on the Pt(111) surface under ambient pressure conditions has been studied by in situ infrared reflection absorption spectroscopy (IRAS). It was found that the Pt(111) surface was covered with formate in a flow of 0.16 kPa of methanol and >1.3 kPa of oxygen mixture at 350 K while it was covered with CO at the oxygen pressure below 1.3 kPa. CO 2 was detected in the product gas and the reaction kinetics was examined. The relation between the production rate of CO 2 and the coverage of adsorbates as a function of oxygen pressure indicated that the CO 2 mainly originated from the formate which was produced from oxidation of methanol. Although CO produced by methanol decomposition seems to be one of precursors of CO 2 formation, this reaction was found to be a minor pathway. The detailed mechanism of oxidation of methanol on Pt(111) was discussed.
The reaction of methanol with oxygen on Pt(111) under ultrahigh vacuum condition has been investi... more The reaction of methanol with oxygen on Pt(111) under ultrahigh vacuum condition has been investigated by infrared reflection absorption spectroscopy (IRAS). Molecular and atomic states of adsorbed oxygen existed on the Pt(111) surface, and the adsorption of oxygen at 100 K gave molecularly adsorbed oxygen that dissociated to adatoms at ∼160 K. Formate species, which gave the symmetric C-O stretching band at 1327 cm -1 , was observed when methanol-adsorbed Pt(111) surface, which was precovered by molecular oxygen, was heated to 160 K. The IRAS band of formate was verified by comparison with the band of the formate derived from formic acid on the Pt(111) surface and by the isotope shift of the band observed by using deuterated methanol. The amount of produced formate was proportional to the amount of the molecularly adsorbed oxygen. The formate band disappeared at 270 K, at which temperature desorption of CO 2 and H 2 was observed on temperature-programmed desorption spectra. Molecular oxygen on the Pt(111) surface dissociated at 300 K and the produced adatoms did not oxidize methanol, but the methanol was decomposed to CO and H 2 . Molecularly adsorbed oxygen is thus considered to be responsible for the oxidation of methanol to formate.
Anomalous coverage dependence was observed on the sum-frequency generation signal of bridge CO on... more Anomalous coverage dependence was observed on the sum-frequency generation signal of bridge CO on the Ni(111) surface when co-adsorbed by on-top CO. The bridge CO peak was distinct and normal from 0.04 to ∼0.40 monolayer (ML) but weakened after the appearance of the on-top CO peak at 0.47 ML and disappeared at 0.60 ML, although both peaks were observed in
... Accelerator in Continuous Casting Mold Noriko KUBO,1) Jun KUBOTA,2) Makoto SUZUKI3) and Toshi... more ... Accelerator in Continuous Casting Mold Noriko KUBO,1) Jun KUBOTA,2) Makoto SUZUKI3) and Toshio ISHII1) ... 11) J. Kubota, S. Kuriyama and T. Teshima: CAMP-ISIJ, 2 (1989), 301. 12) MB Assar, PH Dauby and GD Lawson: Steelmaking Conf. ...
The behavior of D2O ice on CO/Pt(111) and Pt(111) under the irradiation of near-IR pulses (NIR) w... more The behavior of D2O ice on CO/Pt(111) and Pt(111) under the irradiation of near-IR pulses (NIR) was studied by sum-frequency generation (SFG) spectroscopy. The peaks assigned to the O–D stretching modes of ice were obtained for the first 30 molecular layers on Pt(111). When the D2O/CO/Pt(111) was irradiated, the signal of D2O was weakened after 500 ps, but that of
Adsorption of CO and NO on NiO(111) thin films epitaxially grown on Ni(111) substrate has been st... more Adsorption of CO and NO on NiO(111) thin films epitaxially grown on Ni(111) substrate has been studied by infrared-visible sum frequency generation (SFG) and the results were compared with those of infrared reflection absorption spectroscopy. From SFG measurements, the CO stretching band of adsorbed CO was observed at 2144 cm−1 for both p- and s-polarized visible (532 nm) light whereas
Thin films of the lanthanum titanium oxynitride perovskite (LaTiO x N y ) synthesized by reactive... more Thin films of the lanthanum titanium oxynitride perovskite (LaTiO x N y ) synthesized by reactive radio-frequency sputtering on conductive Nb-doped strontium titanate (Nb:SrTiO 3 ) substrates are evaluated as photoelectrodes for water splitting reaction under visible light. The films are characterized by X-ray diffraction analysis, energy-dispersive spectroscopy, scanning electron and atomic force microscopy, and ultraviolet-visible spectroscopy. Thin films with polycrystalline, oriented, or epitaxial structures are obtained depending on the substrate temperature and plasma composition. The band-gap energies of the films thus prepared are in the range 2.05-2.35 eV. Photoelectrochemical measurements reveal that the photoactivity of these films increases with the quality of film crystallization. The flat-band position of LaTiO x N y is found to change with pH of the reactant solution. Surface modification with colloidal IrO 2 is also demonstrated to result in a marked increase in photoactivity, with the modified epitaxial LaTiO x N y film exhibiting a photocurrent density of ca. 70 µA cm -2 at +1.0 V vs. Ag/AgCl at pH 4.5 in aqueous Na 2 SO 4 solution under irradiation at visible wavelengths (λ > 420 nm).
The mechanism of hydrogen evolution by a core/shell noble-metal/Cr 2 O 3 particulate as a highly ... more The mechanism of hydrogen evolution by a core/shell noble-metal/Cr 2 O 3 particulate as a highly efficient cocatalyst for overall water splitting under visible light using the photocatalyst (Ga 1-x Zn x )(N 1-x O x ) is investigated by electrochemical and in situ spectroscopic measurements of model electrodes. The electrodes are prepared by electrochemical deposition of 1.8-3.5 nm thick Cr 2 O 3 films on Rh and Pt plates and are evaluated as model systems of Rh/Cr 2 O 3 and Pt/Cr 2 O 3 core/shell particulates, which have previously been applied effectively as cocatalysts for hydrogen evolution in this system. Proton adsorption/desorption and H 2 evolution currents are observed for both the Cr 2 O 3 -coated and the bare electrodes, and the infrared absorption band due to Pt-H stretching (2039 cm -1 ) is apparent for both the coated and the bare electrodes. These observations indicate that the Cr 2 O 3 layer does not interfere with proton reduction or hydrogen evolution and that proton reduction takes place at the Cr 2 O 3 /Pt interface. However, the reduction of oxygen to water is suppressed only in the Cr 2 O 3 -coated samples. The Cr 2 O 3 layer is thus permeable to protons and the evolved hydrogen molecules, but not to oxygen. Cocatalyst modification by thin films with this type of functionality thus appears to be a useful strategy for improving the efficiency of photocatalytic overall water splitting.
Hydrogenation of ethylene on a Pt(111) surface in the presence of gaseous ethylene and hydrogen i... more Hydrogenation of ethylene on a Pt(111) surface in the presence of gaseous ethylene and hydrogen in the 10 3 Pa range was investigated by infrared reflection absorption spectroscopy (IRAS). The IRA peaks assigned to di-σ-bonded ethylene and ethylidyne were observed on Pt(111) under the flow of 1.3 × 10 2 Pa of ethylene and 6.5 × 10 3 Pa of hydrogen at 200-300 K, and the apparent activation energy of ethylene hydrogenation was estimated to be 37 ( 5 kJ mol -1 from the rate of temperature-dependent ethane production. The ethylene hydrogenation on ethylidyne-covered Pt(111) was also examined under the same condition. The peak due to the di-σ-bonded ethylene was not observed on ethylidyne-covered Pt(111), although the similar rate of hydrogenation and the similar activation energy (39 ( 5 kJ mol -1 ) were obtained as those on clean Pt(111). The π-bonded ethylene, which has been previously proposed as an intermediate by the sum-frequency generation (SFG) experiment under the catalytic hydrogenation condition and by IRAS under the low-temperature condition, was not detected in the present study. The similarity of the rate and activation energy for clean and ethylidyne-covered Pt(111) surfaces suggests that the rate of hydrogenation does not depend on either coverage of di-σ-bonded ethylene or ethylidyne. The role of the observed species in the hydrogenation of ethylene is discussed. * Corresponding
Vibrational assignments for the chiral molecule cinchonidine using a combination of experimental ... more Vibrational assignments for the chiral molecule cinchonidine using a combination of experimental vibrational spectroscopic measurements and ab initio computational methods are reported. Several bands in both the IR and Raman spectra are identified as useful in providing information regarding the mode of adsorption of cinchonidine on metal surfaces, a system of great relevance to enantioselective catalysis. In particular, vibrational modes associated with the quinoline group can be used to diagnose the degree of tilt of the molecule with respect to the plane of the substrate. The use of this information for the study of cinchonidine adsorption on polycrystalline platinum with both reflection-absorption infrared spectroscopy (RAIRS) and surface-enhanced Raman spectroscopy (SERS) is discussed. Adsorption geometries for cinchonidine on platinum at low and high concentrations are reported. Figure 1. Structure of cinchonidine.
Unstable intermediates are indispensable ingredients of chemical reactions, but their identificat... more Unstable intermediates are indispensable ingredients of chemical reactions, but their identification at solid surfaces has been hampered by the lack of techniques to detect short-lived and fractionally generated species. We succeeded in identifying the intermediate in a thermal decomposition reaction by utilizing the picosecond temperature jump induced by the irradiation of laser pulses and the observation by sum-frequency generation spectroscopy. We verified that the decomposition of formate on the NiO(111) surface is preceded by the transformation of stable bidentate formate to unstable monodentate formate, which is the reactive intermediate, and two species are found to be in equilibrium before decomposition. S1089-5647(98)01636-8 CCC: $15.00
... On the other hand, it is possible to bond in a bridging configuration if the surface is nicke... more ... On the other hand, it is possible to bond in a bridging configuration if the surface is nickel-terminated in which separation between the nearest cations of the surface is comparable with the distance between the two oxygens of formate as ... J.; Wada, A.; Domen, K.; Hirose, C. Surf. ...
The adsorption of cyclohexane on Ni(111) was studied by infrared-visible sum-frequency generation... more The adsorption of cyclohexane on Ni(111) was studied by infrared-visible sum-frequency generation (SFG) spectroscopy with and without near-infrared (NIR) pump pulse irradiation. Two adsorption states of cyclohexane were found in the monolayer region, a low-coverage state showing SFG peaks at 2740, 2815, and 2865 cm(-1), and a high-coverage state showing peaks at 2740, 2815, and 2905 cm(-1). Both states coexisted on the saturated Ni(111) surface. The broad peak at 2740 cm(-1) was due to the softened CH stretching mode of the axial CH groups of cyclohexane that point toward the Ni(111) surface. The peaks at 2815 and 2865 (or 2905) cm(-1) were due to the symmetric and asymmetric stretching modes of CH(2) groups, respectively, that were free from the surface. Irradiation with NIR pulses caused a temporary jump in temperature at the Ni(111) surface and enhanced the intensity of the 2905 cm(-1) peak, but weakened the other peaks. This indicates that the temperature jump excited the cyclohexane molecules from the low-coverage state to the high-coverage state. The dynamics of the structural change observed in the adsorbed cyclohexane on NIR irradiation is discussed.
Adsorption of ethene on clean and ethylidyne-covered Pt(111) surfaces was investigated by infrare... more Adsorption of ethene on clean and ethylidyne-covered Pt(111) surfaces was investigated by infrared reflection absorption spectroscopy (IRAS). Under gaseous ethene of ~ 10 -3 Pa, 7r-bonded ethene was reversibly formed on a Pt(lll) surface saturated with di-o--bonded ethene at 112 K. The 7r-bonded ethene gave infrared absorption peaks at 954 and 3090 cm-1 which were assigned to =CH 2 wagging (out-of-plane) and CH 2 asymmetric stretching modes, respectively. These two peaks indicated that the ~--bonded ethene was adsorbed on Pt(111) in such a way that the molecular plane is tilted with respect to the surface while the C=C bond is being kept parallel to the surface. The intensity of the C-H stretching band at 2908 cm-i of di<r-bonded ethene decreased with the increase of 7r-bonded ethene. The heat of adsorption of ~--bonded ethene was estimated to be 40 + 10 kJ/mol. The presence of ethylidyne with saturation coverage was found to inhibit the ~r-bonded ethene adsorption.
Surface modifications using platinum (Pt) particles and iron oxides (FeOx) were found to lead to ... more Surface modifications using platinum (Pt) particles and iron oxides (FeOx) were found to lead to a significant improvement in the current--potential (J--E) properties for hydrogen evolution from water in p-type silicon (p-Si) electrodes. The onset potential and cathodic photocurrent for hydrogen evolution from the Pt/p-Si(100) electrode were, respectively, 0.50 V\text{RHE and 0.28 mA/cm2 at 0 V\text{RHE (RHE: reversible hydrogen electrode).
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