In-situ Infrared Reflection Absorption Spectroscopy Research Articles

Phosphorus coordinated Co/Se2 heterointerface nanowires: in-situ catalyst reconstruction toward efficient overall water splitting in alkaline and seawater media

Designing a highly efficient electrocatalyst to realize overall water splitting is vital, yet identifying the active site remains an ongoing challenge. Herein, the electrochemical in situ surface activation of P@Co/Se2-NW/CC was investigated to understand the enhanced OER activity of P@Co/Se2-NW/CC. The incorporation of phosphorus is thought to increase the vacancies surrounding the Co cations in the initial Co/Se2 and speed up the structural change into "active species" like cobalt oxide/oxyhydroxide. The as-synthesized P@Co/Se2-NW/CC required a low overpotential for OER (η100 = 230 and 280 mV) and HER (η100 = 111 and 132 mV), respectively, in alkaline water and alkaline seawater media. In-situ infrared reflection-absorption spectroscopy (IRRAS) and Post characterization unraveled the existence of surface-bounded Co oxide species on P@Co/Se2-NW/CC after OER catalysis, which is responsible for the enhanced electrocatalytic activity. This study offers a valuable strategy for developing noble-metal-free bifunctional catalysts for efficient hydrogen generation from alkaline seawater and alkaline water electrolysis.

Triggering the energy release in molecular solar thermal systems: Norbornadiene-functionalized trioxatriangulen on Au(111)

Molecular solar thermal systems (MOST) based on molecular photoswitches are a promising technology for the smart management of solar energy at small scale. In this work, we study the catalytically triggered energy release mechanism in the norbornadiene/quadricyclane (NBD/QC) couple. We scrutinize a tailor-made NBD-functionalized trioxatriangulen (TOTA-NBD) derivative, which is assembled in form of atomically defined films on an ultraclean Au(111) surface. By in-situ infrared reflection absorption spectroscopy (IRAS) we show that TOTA-QC in direct contact with Au is rapidly back-converted to TOTA-NBD, while there is no back-conversion of TOTA-QC molecules in the second layer or in the multilayer. Our results suggest that Au catalyzes the energy release from QC with very high efficiency through direct electronic coupling to the metal states. This mechanism provides a pathway for the energy release from NBD/QC photoswitches without activation of CH bonds and may enable the design of catalytically triggered MOST devices with very high cyclability

Pt-modified TaC as an efficient electrocatalyst for ethanol oxidation in acid and alkaline electrolytes

Ethanol is an ideal fuel in low-temperature fuel cells. The ethanol oxidation reaction (EOR) on platinum-modified tantalum carbide (TaC) has been investigated using both model thin films and powder catalysts. The results demonstrate that the 1.5 wt% Pt-modified TaC catalyst shows enhanced EOR activity compared to Pt. In-situ infrared reflection absorption spectroscopy (IRRAS) study reveals that the Pt surface is less poisoned by EOR intermediates and a higher CO2 selectivity (7∼9%) is achieved on the 1.5 wt% Pt/TaC catalyst, compared to the 40 wt% Pt/C. Density functional theory (DFT) calculations reveal that the binding energies of EOR intermediates on the Pt/TaC(111) surface are weaker than on Pt(111), suggesting an enhanced poison-tolerance from the adsorption of these intermediates. The combined experimental and theoretical investigations indicate that Pt/TaC is a promising electrocatalyst for EOR.

Palladium-Modified Tungsten Carbide for Ethanol Electrooxidation: From Surface Science Studies to Electrochemical Evaluation

In this study we report a combined surface science and electrochemical investigation of using palladium-modified tungsten carbide (Pd/WC) as an efficient catalyst for the ethanol oxidation reaction (EOR). Compared to the Pd(111) surface, DFT calculations suggested that the Pd/WC(0001) surface should be less poisoned by the ethanol decomposition intermediates, consistent with surface science results that desorption temperatures of the detected intermediates were lower on the Pd/WC surface. Electrochemical evaluation coupled with in-situ infrared reflection absorption spectroscopy (IRRAS) measurements of 5 wt% Pd/WC/C powder catalysts were then conducted. The EOR activity of the 5 wt% Pd/WC/C catalyst was noticeably enhanced, compared to the benchmark 40 wt% Pd/C. The IRRAS results showed that the EOR products were detected at a lower onset potential on 5 wt% Pd-WC/C than on 40 wt% Pd/C.

Preparation and Characterization of New Pt/Rh/SnO2 Nanoparticle Catalysts for Ethanol Oxidation Reaction to CO2

Rh was deposited on Pt/SnO2(3:1) nanoparticle-loaded carbon black (Pt/SnO2/C) by two methods, normal and controlled Rh deposition (Ter-1, Ter-2). The particle size of Pt in the Pt/SnO2/C, Ter-1 and Ter-2 was estimated as 2.5, 2.8 and 2.8 nm by X-ray diffraction spectroscopy (XRD), respectively. Energy-dispersive X-ray spectroscopy (EDX) revealed the content of Rh in Ter-1 and Ter-2 was approximately 5%. The current for ethanol oxidation reaction (EOR) at 0.6 V vs. RHE for Ter-2 was ca. 1.5 and 2 times higher than that for Pt/SnO2/C and Ter-1, respectively. The onset potential of the EOR current for Ter-1 is the highest among 3 catalysts. The in-situ infrared reflection absorption spectroscopy (IRAS) exhibited the great facilitation of CO2 formation for Ter-2 in comparison with the facilitation of acetic acid formation for Pt/SnO2/C, whereas Ter-1 showed the lowest performance towards EOR.

ZnO Nanoparticle Formation from the Molecular Precursor [MeZnOtBu]4 by Ozone Treatment in Ionic Liquids: in‐situ Vibrational Spectroscopy in an Ultrahigh Vacuum Environment

As reported previously, novel ZnO nanostructures can be grown by oxidation of [MeZnOtBu]4 “building blocks” with O3 in ionic liquids (ILs). In this study, we have explored the role of the IL during ZnO formation by in‐situ infrared reflection absorption spectroscopy (IRAS) in ultrahigh vacuum (UHV). [MeZnOtBu]4 and [C2C1Im][OTf] were (co‐)deposited as thin films by physical vapor deposition (PVD) onto Au(111), separately or simultaneously. The IR spectrum of [MeZnOtBu]4 was analyzed between 300 and 4000 cm–1 based on calculated spectra from density‐functional theory (DFT). Spectral changes in the IL‐related bands during the thermal treatment of [MeZnOtBu]4 in [C2C1Im][OTf] indicate the loss of the precursor ligands and the interaction of the IL with the growing ZnO aggregates. The films were treated with ozone (10–6 mbar) in UHV and the spectral changes were monitored in‐situ by IRAS. Slow ozonolysis of [C2C1Im][OTf] is observed. Spectroscopically we identify the primary ozonide formed by addition of O3 to [C2C1Im]+ and suggest a reaction mechanism, which leads to a biuret derivative. Upon ozone treatment of mixed [MeZnOtBu]4/[C2C1Im][OTf] films, ZnO aggregates are formed at the IL/vacuum interface. Ozonolysis of [C2C1Im][OTf] is suppressed. Upon annealing to 320 K, further ZnO aggregates are formed, leading to enclosure of [C2C1Im][OTf] in the ZnO film. At 380 K the IL is released from the mixed film. The pure [C2C1Im][OTf] desorbs at 420 K, leaving behind the ZnO phase.

Structure-Controlled Rh/Sn/Pt Ternary Catalysts for Complete Oxidation Reaction of Ethanol to Carbon Dioxide

Sn was deposited on a Pt electrode (Sn/Pt) with the coverage of 0.23, following by the Rh deposition by different methods: random arrangement (Rh/Sn/Pt(1)) and controlled arrangement (Rh/Sn/Pt(2)). Inductive coupled plasma mass spectroscopy (ICP-MS) was used to evaluate the Sn/Rh molar ratio, which was 3 for Rh/Sn/Pt(1) and 6 for Rh/Sn/Pt(2). The ethanol oxidation reaction (EOR) activity of Rh/Sn/Pt(2) was similar to that of Sn/Pt, which was ca. 3 times as high as that of Pt. However, the EOR activity of Rh/Sn/Pt(1) was ca. 1.5 times as high as that of Sn/Pt. The onset potential of EOR for the Sn/Pt and Rh/Sn/Pt electrodes was 0.1 V and 0.2 V lower than that for the Pt electrode, respectively. The in-situ infrared reflection absorption spectroscopy (IRRAS) exhibited that, for Rh/Sn/Pt(1), the formation of acetic acid was predominant over CO2, whereas Rh/Sn/Pt(2) with lower EOR activity was superior in CO2 selectivity to Rh/Sn/Pt(1).

Self-Assembled Monolayers as Inhibitors for the Atmospheric Corrosion of Copper Induced by Formic Acid: A Comparison between Hexanethiol and Hexaneselenol

The corrosion protection by self-assembled monolayers (SAMs) of hexanethiol and hexaneselenol has been explored on copper exposed to humid air containing formic acid, a corrosive environment relevant for indoor atmospheric corrosion. The kinetics of the formation of corrosion products on SAM covered copper was followed using in-situ infrared reflection/absorption spectroscopy (IRAS) and compared with that of bare copper. Both SAMs initially showed a corrosion protection ability. The prolonged exposure of hexanethiol copper resulted in a reduced formation rate of copper formate and copper hydroxide compared to bare copper, while on bare and hexaneselenol covered samples copper (I) oxide, copper formate, and copper hydroxide were observed. To assess the quality of the SAMs during the sample exposure, vibrational sum frequency spectroscopy (VSFS) was used. It was found that hexaneselenol molecules are locally removed from the surface during corrosion in contrast to their thiol counterparts. This created localized galvanic effects which resulted in an accelerated corrosion of selenol covered copper. X-ray photoelectron spectroscopy at elevated pressure demonstrated that the hexanethiol removed thin oxide layers upon adsorption. A contributing parameter to the enhanced corrosion inhibiting ability of hexanethiol could be its greater ability than hexaneselenol to bind to the copper surface during its deposition and sample exposure.

Controlling the Adsorption Kinetics via Nanostructuring: Pd Nanoparticles on TiO2Nanotubes

Activity and selectivity of supported catalysts critically depend on transport and adsorption properties. Combining self-organized porous oxide films with different metal deposition techniques, we have prepared novel Pd/TiO(2) catalysts with a new level of structural control. It is shown that these systems make it possible to tune adsorption kinetics via their nanostructure. Self-organized TiO(2) nanotubular arrays (TiNTs) prepared by electrochemical methods are used as a support, on which Pd particles are deposited. Whereas physical vapor deposition (PVD) in ultrahigh vacuum (UHV) allows us to selectively grow Pd particles at the tube orifice, Pd/TiNT systems with homogeneously distributed Pd aggregates inside the tubes are available by particle precipitation (PP) from solution. Both methods also provide control over particle size and loading. Using in-situ infrared reflection absorption spectroscopy (IRAS) and molecular beam (MB) methods, we illustrate the relation between the nanostructure of the Pd/TiNT systems and their adsorption kinetics. Control over the metal nanoparticle distribution in the nanotubes leads to drastic differences in adsorption probability and saturation behavior. These differences are rationalized based on differences in surface and gas phase transport resulting from their nanostructure. The results suggest that using carefully designed metal/TiNT systems it may be possible to tailor transport processes in catalytically active materials.

Reaction kinetics of organo-clay hybrid films: In-situ IRRAS, FIM and AFM studies

In this paper we report the reaction kinetics of nanodimensional clay saponite and hectorite with an amphiphilic cation octadecyl rhodamine B (RhB) in hybrid Langmuir monolayer at the air–aqueous clay dispersion interface. The surface pressure–molecular area ( π– A) isotherms were strongly influenced by the presence of clay and the lift-off area of the cationic amphiphile shifted to progressively larger area. In-situ fluorescence imaging microscopic (FIM) studies showed the formation of micro-order domains in the organo-clay hybrid monolayer films at the air–clay dispersion interface. In-situ infrared reflection–absorption spectroscopy (IRRAS) was used to demonstrate the reaction kinetics. The time taken to complete the reaction kinetics for RhB–hectorite hybrid films is larger than for RhB–saponite hybrid films. Atomic force microscopic images of hybrid Langmuir–Blodgett films gave compelling visual evidence of the incorporation of clay platelets into the hybrid films, whose density increased with the progress of reaction kinetics.

Structure-Dependent Kinetics for Synthesis and Decomposition of Formate Species over Cu(111) and Cu(110) Model Catalysts

The kinetics and mechanism of formate synthesis by hydrogenation of CO2 (CO2 + 1/2H2 → HCOOa) and the formate decomposition into CO2 and H2 (HCOOa → CO2 + 1/2H2) over Cu(111) and Cu(110) surfaces were studied by in-situ infrared reflection−absorption spectroscopy (IRAS) using a high-pressure reactor (∼1 atm). The reaction rates and the apparent activation energy of the formate synthesis were measured for Cu(111) and Cu(110), indicating that the formate synthesis on Cu was found to be structure-insensitive. The pressure dependence of CO2 and H2 on the initial formation rate of formate suggested an Eley−Rideal type mechanism, in which a gaseous CO2 molecule directly reacts with an adsorbed hydrogen atom on Cu. This is analogous to the well-known mechanism of formate synthesis by organometallic catalysts, in which CO2 is inserted into a Cu−hydride bond. The reaction rates and the activation energy of the decomposition were measured for Cu(111) and Cu(110). It was found that the formate decomposition on Cu was structure-sensitive in contrast to the formate synthesis. The promotional effect of coexisting H2 upon the rate of formate decomposition by 17 times at maximum was incidentally found only on Cu(111). Interestingly, the increase in the decomposition rate was due to an increase in the preexponential factor of the rate constant for the formate decomposition with the activation energy being constant. Furthermore, the decomposition kinetics of the formate prepared by adsorption of formic acid on O/Cu(111) was identical with the H2-promoted decomposition kinetics of the synthesized formate. The difference in the decomposition kinetics was ascribed to the ordered structure of formate based on the previous STM results, in which a chainlike structure of formate was observed for the synthesized formate, whereas no formate chain was observed for the formate prepared by adsorption of formic acid on O/Cu(111). The unique character of both the decomposition kinetics and the structure of formate observed only for Cu(111) was discussed from the viewpoint of the mass transport of copper atoms creating added formate chains.

Complex model catalysts under UHV and high pressure conditions: CO adsorption and oxidation on alumina-supported Pd particles

The growth of metal particles on ordered oxide surfaces provides a strategy to prepare well-defined model systems for supported catalysts, which can by easily studied by most surface-science techniques. Here, we focus on Palladium particles grown on an ordered Al 2O 3 film on NiAl(110), a system which has previously been characterized in detail with respect to its structural, electronic and adsorption properties. In this contribution, we will provide several examples, showing how adsorption and reactivity phenomena on these systems can be addressed over a pressure range from ultrahigh vacuum (UHV) to near atmospheric pressure. In the low pressure region, we apply a combination of molecular beam methods and in-situ infrared reflection absorption spectroscopy (IRAS). For CO adsorption, angular resolved scattering and sticking coefficient measurements and structural information allow us to quantify different adsorption channels including reverse spillover effects. The coverage dependent kinetics of CO oxidation is derived and discussed in comparison with the single crystal kinetics. The adsorption of CO on alumina supported Pd aggregates at low and high pressure, i.e. from 10 −7–200 mbar, is examined by IR–VIS sum frequency generation (SFG) vibrational spectroscopy. At low pressure, the CO adsorption site distribution (bridged vs. on-top) depends on the particle surface structure and temperature, but under reaction conditions, the site occupancy is mainly governed by the CO pressure. The impact of these results on the extrapolation of UHV data to high pressure catalysis is discussed.

IRAS Analysis of the Early Stage of Thermal Oxidation on a SiC Surface

ABSTRACTThe structure of thermal oxide film thinner than 2nm on a SiC surface was investigated using in-situ infrared reflection absorption spectroscopy (IRAS). In the case of oxide films on 6H-SiC(0001), the peak frequencies of the TO mode (≈1050 cm−1) of the Si-O-Si stretch vibration shifts toward lower wave number with decreasing oxide thickness in the range of 0.2nm to 2nm and shift toward a higher frequency as the growth temperature rises. The LO mode (≈1250 cm−1) of the Si-O-Si stretch vibration remains almost constant with the increase in oxide thickness from 0.2 nm to 2 nm. These results indicate that there is a considerable difference in the structure near the interface between a thermally grown oxide layer formed on SiC and one formed on Si.

Sulfate adsorption on Cu(111) studied by in-situ IRRAS and STM: revealing the adsorption site and desorption behavior

Sulfate adlayers on a copper(111) electrode were investigated by in-situ infrared reflection absorption spectroscopy (IRRAS) combined with in-situ scanning tunneling microscopy (STM). The latter data show clear evidence for a bridging bidendate coordination of sulfate to the copper surface. The IR spectra exhibit one single absorption band in the frequency range of 1205–1225 cm −1. Further analysis of the band frequency and intensity with respect to the electrode potential leads to sulfate desorption with sulfate remaining in islands at the surface during the desorption process. This model is supported by additional STM measurements of the desorption behavior.

Evidence for a special formate species adsorbed on the Cu–Zn active site for methanol synthesis

Formate species synthesized by the hydrogenation of CO 2 over clean Cu(111) and Zn-deposited Cu(111) surfaces at atmospheric pressure were studied by in-situ infrared reflection absorption spectroscopy (IRAS). The symmetric OCO stretching ( ν s(OCO)) peak of a bidentate formate species on clean copper was observed at ∼1330 cm −1 on both surfaces during the reaction. The initial formation rate of formate species on the clean Cu(111) surface at 353 K and 760 Torr was estimated to be 8.2×10 −4 (molecules site −1 s −1), which agreed with results previously obtained by XPS. In contrast, peaks at 1350 and 1585 cm −1 were observed during the hydrogenation of CO 2 only on the Zn-deposited Cu(111) surface. The peak at 1585 cm −1 agreed with the frequency of the asymmetric OCO stretching ( ν a(OCO)) of bridging bidentate formate species, thus indicating that an inclined formate species was adsorbed on two different atoms of the Cu–Zn site previously proposed as the active site of methanol synthesis.

Electrochemical Infrared Studies of Monocrystalline Iridium Surfaces. Part 2: Carbon Monoxide and Nitric Oxide Adsorption on Ir(110)

The adsorption of carbon monoxide and nitric oxide on an ordered Ir(110) electrode surface in aqueous 0.1 M HClO4 has been probed by voltammetry together with in-situ infrared reflection−absorption spectroscopy (IRAS). Exclusively atop coordination of both CO and NO is suggested from the relatively high C−O and N−O stretching (νCO, νNO) frequencies observed, 1980−2060 and 1820−1840 cm-1, respectively, that upshift with increasing coverage. Adsorption of NO as well as CO is essentially molecular, with near-unity saturation coverages, as deduced from voltammetry as well as infrared spectrophotometry. The potential-dependent νCO frequencies for the saturated CO adlayer are closely compatible with that for the corresponding Ir(110)/CO interface in ultrahigh vacuum (UHV) once the differences in surface potential are taken into account. In contrast to the case of the latter system, however, the electrochemical Ir(110)/CO interface exhibits a pair of νCO bands at intermediate CO coverages (θCO), suggestive of a difference in substrate-induced adlayer domains in the two environments. Closely similar θCO-dependent νCO spectra and voltammetric oxidation profiles were obtained for adlayers formed by either partial electroxidative stripping from a saturated adlayer or by direct dosing from a dilute CO solution. This unusual behavior indicates that extensive CO “islands” are not formed by partial adlayer electrooxidation, in contrast to the behavior of most ordered low-index Pt-group electrodes, suggesting that the substrate morphology features nanoscale domains rather than large terraces. The νCO and νNO frequencies for saturated adlayers on Ir(110) and (111) are similarly red-shifted from the gas-phase νCO and νNO values. However, the νCO−E and especially the νNO−E dependences (“Stark-tuning” slopes) are markedly larger than the predicted gas-phase values. The larger dνNO/dE values are ascribed to more extensive potential-dependent dπ−2π* back-donation for adsorbed atop NO compared with CO.

Nucleation and Growth of Plasma‐Polymerised Hexamethyldisilazane on Iron‐Substrates

AbstractPlasma polymer films of hexamethyldisilazane (HMDSN) were deposited on iron substrates by an audio frequency discharge. The investigations focus on the activation of the iron surface by an oxygen plasma, the adsorption of the monomer and the initial states of polymer formation. Surface compositions were examined by means of in‐situ Infrared‐Reflection‐Absorption‐Spectroscopy (IRRAS) and Quartz‐Crystal‐Nanoweighting (QCN). It turned out that during the oxygen plasma treatment an additional layer of iron oxihydroxide is formed. The resulting high density of surface hydroxyls leads to the hydrolysis of the adsorbed silazane. Plasma‐polymerised HMDSN is characterised by a reduced carbon and nitrogen content and the incorporation of siloxane units. In the range of about 4 nanometer the polymer structure changes significantly with the film thickness. With increasing film thickness the concentrations of siloxane and N‐H units decrease. The interface between the oxide and the polymer is characterised by strong polar interactions between surface hydroxyls and the siloxane group and additionally by directed bonds via silanolate units.

In situ characterization of the growing a-Si:H surface by IR spectroscopy

The surface hydrogen on the growing a-Si:H film in a glow discharge reactor is investigated by using real time in-situ infrared reflection absorption spectroscopy (IRRAS). The temperature dependence of the dominant bonding configuration for the surface hydrides is determined in the vibrational spectra of stretching modes. The integrated absorption intensities at temperatures below 380° C remain almost constant and correspond to the monolayer coverage of the growing surface by hydrogen.