Tribo-films are nanometer-to micrometer-scale reaction layers formed by tribological processes (friction, wear, lubrication) under boundary lubrication. They play a key role in anti-wear performance, with functionality strongly linked to the presence and distribution of specific chemical groups. Characterizing these features in real components requires advanced spectroscopic methods with high chemical specificity and depth resolution. We present a depth-profiling technique combining infrared reflection-absorption spectroscopy (IRAS) with controlled Ar+ ion sputtering under high or ultra-high vacuum conditions. The method was applied to washers from two axial cylindrical roller bearings that showed distinct wear behaviors in performance tests. It is fully compatible with industrial components and enables direct comparative analysis. Maintaining optical alignment during sputtering yields high signal-to-noise ratios, allowing detection of trace IR-active species down to a few percent of a monolayer. The approach also permits evaluation of film thickness and homogeneity. Most importantly, the combination of depth sensitivity and chemical specificity enables vertical mapping of functional groups and reconstruction of the tribo-film's composition. This IRAS-based method thus provides a powerful tool for studying tribological films and advancing understanding of anti-wear mechanisms under real-world conditions.

The redox interactions between transition metal oxides and sulfur-containing compounds play a key role in catalytic processes and gas sensing technologies. In this study, we investigated the redox dynamics of Co3O4(111)/Ir(100) model catalysts in response to the adsorption and decomposition of hydrogen sulfide (H2S) using synchrotron radiation photoelectron spectroscopy. Upon adsorption at 300 K, H2S partially dissociates to form a mixture of SO32-, S2-, OH-, SH-, and chemisorbed H2S. Subsequent annealing in ultrahigh vacuum induces H-2 desorption below 400 K followed by desorption of H2S and H2O above 400 K. At temperatures exceeding 500 K, S2- is progressively oxidized to SO32- and subsequently to SO42-. These transformations are accompanied by temperature-dependent redox processes involving the Co3O4(111) surface: initial reduction upon formation of SO32- species at 300 K, partial re-oxidation upon H-2 desorption, and further reduction with H2O release. Above 550 K, annealing induces charge redistribution and lattice oxygen migration, leading to a more homogeneous stoichiometry of the Co3O4(111) film. This phenomenon reduces the redox response to chemical transformations at the surface. The obtained insights into H2S-Co3O4 redox interactions provide a foundation for the rational design of cobalt oxide-based catalytic gas sensors.

The reverse water-gas shift (RWGS) reaction is critical for efficient CO2 utilization in thermochemical conversion processes. Here, we investigate how lanthanum (La) doping modulates the redox properties of Ni/CeO2 catalysts and influences their RWGS performance. Using a combination of catalytic testing, operando diffuse reflectance infrared Fourier transform spectroscopy, and density functional theory calculations, we identify key surface intermediates and establish composition-activity relationships. CO2 initially adsorbs as bicarbonate species preferentially stabilized at oxygen vacancies, which subsequently convert to formates, the dominant intermediates under RWGS conditions. Methoxy and dioxymethylene species serve as spectroscopic markers for Ce4+ and Ce3+/oxygen vacancy sites, respectively. Notably, catalysts with intermediate La loading exhibit the highest CO selectivity due to an optimal balance between oxygen vacancy formation and redox flexibility. These results reveal a direct link between catalyst redox state and RWGS activity, underscoring the value of rational dopant design. La incorporation thus offers a viable strategy to enhance the performance of Ni/CeO2-based catalysts for CO2 conversion.

Model studies in electrocatalysis provide valuable insights into complex structure-property relationships and rely heavily on experimental techniques that enable the preparation of electrode surfaces with atomic-scale control over morphology. This work investigates the nanopatterning of single-crystalline metal electrodes through ion erosion. On Pt(111), ion erosion produces surfaces with distinct corrugation, characterized by the formation of erosion pits, an equal proportion of (110) and (100) steps, and a high density of kinks. The obtained structural motifs influence the electrochemical behavior of H/OH adsorption/desorption and surface electrooxidation in a unique manner, illustrating that ion-eroded metal surfaces represent a complex but atomically precise platform for exploring the synergistic action of various types of surface defects on the electrode properties. A general applicability of ion erosion is demonstrated by preparing and characterizing ion-eroded surfaces of Ru(0001) and Cu(111), showing that this method can control the density of surface defects in ways that are challenging to achieve through the traditional Clavilier method. Ion erosion enables the imprinting of a variety of surface configurations, ranging from atomically flat to stepped and disordered structures, on a single-crystal substrate, offering new avenues for designing electrodes with tailored reactivity.

This document is the unedited not peer-reviewed Author’s version of a Submitted Work to Chemistry of Materials. The controlled assembly of supraparticles using spray-drying enables the synthesis of nanoporous materials. Changing the size of the constituent nanoparticles or their agglomeration states provides access to a diverse range of pore frameworks. This turns supraparticles into ideal scaffolds in heterogeneous catalysis. The combination of supraparticles with atomic layer deposition (ALD) as a surface functionalization technique offers excellent control over the deposition of a functional material and its distribution over the scaffold on the nanoscale. This work reports the combination of SiO2 supraparticles as tunable scaffolds and their loading with a platinum-based ALD catalyst. The deliberate adjustment of the scaffold pore framework via spray-drying and its effects on the catalyst deposition are highlighted. Furthermore, varying numbers of Pt ALD cycles are applied to explore the capability of the combinational approach with respect to catalyst loading and Pt efficiency. High-resolution electron microscopy reveals ultra-small Pt clusters deposited on the supraparticles after the very first ALD cycle. Using the hydrogenation of 4-nitrophenol as a demonstration, the impact of the pore framework and the Pt deposition variation in ALD on the catalytic functionality is investigated.

The condensation of silane molecules onto oxidic surfaces, known as self-assembled monolayers (SAMs), is a key methodology to control surface properties in a simple and versatile fashion. SAM formation, however, can be sensitive to subtle changes in the reaction conditions, which can lead to varying macroscopic properties. Here, we use attenuated total internal reflection infrared (ATR-IR) spectroscopy and quartz crystal microbalance with dissipation (QCM-D) as in situ methods to investigate SAM formation pathways, which we complement with X-ray photoelectron spectroscopy, atomic force microscopy, and contact angle measurements as ex situ methods to assess the final composition, morphology, and functionality of the formed SAMs. We first spectroscopically resolve and quantify differences in the reaction pathway in dry and wet reaction conditions, corroborating the existing literature. Second, we investigate the formation of binary SAMs using n-butyltrimethoxysilane and 1-(3-triethoxysilylpropyl)-2-imidazoline silane as a model system. We show that imidazoline silane is preferentially incorporated into the SAM at low concentrations and that mixed SAMs exhibit much increased surface roughness compared to the pure silane surfaces. The in situ investigation reveals that the SAM deposition of imidazoline-based SAMs is not self-limiting and continuously adds deposited mass on the surface. ATR-IR spectroscopy suggests multiple interactions of the imidazoline moiety with the surface, which enable the polymerization of silane moieties into solution and thus rationalize the increased mass deposition and surface roughness. Our study demonstrates the potential of combining in situ and ex situ characterization methods to reveal differences in reaction pathways that can rationalize surprising macroscopic property changes observed in the formation of functional SAMs.

Photoswitches, which reversibly switch between isomeric forms upon light exposure, offer promising applications in optical computing, photoresponsive materials, and molecular energy storage. Efficient and controllable back-isomerization is essential for practical applications and can be achieved electrochemically. In this study, we explore how electrochemical oxidation governs the back-conversion of the azobenzene-based photoswitch 4,4 '-(diazene-1,2-diyl)bis(N,N '-diethylaniline) (A-AZO). Combining in situ photoelectrochemical infrared reflection absorption spectroscopy with density functional theory calculations, we show that A-AZO undergoes reversible two-step oxidation, forming singly and doubly oxidized species (A-AZO1+ and A-AZO2+), with the positive charge primarily localized on the nitrogen atoms of the amino groups. Photochemically, (E)-A-AZO isomerizes to its (Z)-form. Upon electrochemical triggering, the oxidized (Z)-A-AZO x+ species act as catalytic intermediates that accelerate the back-conversion to the (E)-isomer. This autocatalytic reaction proceeds with high selectivity and requires minimal external energy input, making it particularly attractive for energy-efficient switching in molecular systems.

The stabilities of monometallic Rh and Pd nanoparticles and bimetallic Pd-Rh core-shell nanoparticles supported on Co3O4(111) thin films grown on Ir(100) were investigated with respect to the oxidation state and dissolution in alkaline electrolyte under the conditions relevant for electrochemical ethanol oxidation. Towards this aim, the well-defined model systems were characterized by means of synchrotron radiation photoelectron spectroscopy coupled with an ex situ emersion electrochemical cell (EC-SRPES) and scanning tunneling microscopy (STM). We found that the electronic metal-support interaction (EMSI) has a strong influence on the oxidation state of Rh, resulting in a strong oxidation and anchoring of the oxidized Rh3+ species on the surface of Co3O4(111). Consequently, the EMSI prevents the dissolution of Rh into the electrolyte regardless of the potential range. In contrast, it has no effect on the oxidation state and dissolution of Pd in the potential range of 0.3-1.1 VRHE. However, extending the potential range to 0.3-1.5 VRHE results in a stronger dissolution of Pd due to the reversible oxidation/reduction of Pd, which is enhanced in the presence of the EMSI. Most importantly, the magnitude of the EMSI and, thus, the extent of noble metal oxidation, can be effectively controlled by the nature of the metal/Co3O4(111) interface in the bimetallic Pd-Rh core-shell nanoparticles.

For most functional oxides, structure-selective synthesis is the key for the task-specific production of nanomaterials. Herein, the low-temperature synthesis in ionic liquids (ILs) is an attractive strategy to produce nanomaterials which are not accessible otherwise is described. In this study, a bench-scale synthesis route toward Co3O4 by applying O-3 on the molecular precursor Co-2(CO)(8) in IL medium is reported. The Co3O4 nanoparticles (NPs) are characterized by infrared (IR) spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). This protocol yields Co3O4 with good crystallinity and narrow size distribution. In addition to conventional materials characterization, a new experimental approach is described in which the material synthesis in situ by IR reflection absorption spectroscopy (IRAS) (in situ IRAS) is followed. The in situ approach provides additional information on the growth mechanisms and kinetics and confirms that O-3 treatment of Co-2(CO)(8) in IL exclusively yields pure Co3O4 without the formation of byproducts or intermediates.

Carbon is a common support material for noble metal nanoparticles in heterogeneous catalysis and electro-catalysis. Very few surface-science-based model studies have been performed, however, with noble metal nanoparticles on carbon supports. In this work, we present the first model study on carbon-supported noble metal nanoparticles using infrared reflection absorption spectroscopy (IRAS). The model catalyst is prepared on highly oriented pyrolytic graphite (HOPG) by physical vapor deposition (PVD) of Pd metal. We characterize the particle growth and morphology by scanning tunneling microscopy (STM) and atomic force microscopy (AFM) and probe the adsorption properties by IRAS of adsorbed CO. PVD of Pd on clean HOPG leads to the formation of very large, weakly interacting particles. In order to increase the nucleation density upon Pd deposition, the HOPG surface was modified by Ar+ and O+ bombardment. The defect structures formed were characterized by STM and by IRAS during the ion bombardment. On the pretreated HOPG, Pd nucleates homogeneously and stable Pd nanoparticles (NPs) are formed. We investigated the adsorption properties of the Pd NPs as a function of the particle size and their thermal stability upon annealing. It is shown that carbon species migrate from the HOPG modified by ion bombardment onto the Pd NPs leading to modification of the CO adsorption properties. The work shows that Pd/HOPG is a very well-suited model system for in-situ adsorption and reaction studies by IRAS, in spite of the non-metallicity of the support.

In this work, we investigated the interaction of phenylphosphonic acid (PPA, C6H5PO3H2) with atomically-defined Co3O4(111) thin films, grown on Ir(100), under ultrahigh vacuum (UHV) conditions and in the electrochemical environment. In the first step, we employed infrared reflection absorption spectroscopy (IRAS) and followed the formation of a saturated monolayer (380 K) in UHV. We observed that the binding motif changes from a chelating tridentate in the sub-monolayer regime to a chelating bidentate at full monolayer coverages. In the electrochemical environment, we analyzed the interaction of PPA with the same Co3O4(111) surface by electrochemical infrared reflection absorption spectroscopy (EC-IRRAS) (0.3 VRHE-1.3 VRHE). When adsorbed at pH 10 from an ammonia buffered aqueous solution, PPA binds to the surface in form of a fully deprotonated chelating bidentate. With increasing electrode potential, we observed two fully reversible processes. At low buffer concentration, protons are released upon oxidation of surface Co2+ ions and lead to protonation of the anchored phosphonates. At high buffer concentration, most of the protons released are accepted by NH3. Simultaneously, the surface phosphonate changes its adsorption motif from bidentate to tridentate while adopting a more upright geometry.

Supported catalytically active liquid metal solutions (SCALMS) represent a class of catalytic materials that have only recently been developed, but have already proven to be highly active, e.g., for dehydrogenation reactions. Previous studies attributed the catalytic activity to isolated noble metal atoms at the surface of a liquid and inert Ga matrix. In this study, we apply diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) with CO as a probe molecule to Ga/Al2O3, Pt/Al2O3, and Ga37Pt/Al2O3 catalysts, to investigate in detail the nature of the active Pt species. Comparison of CO adsorption on Pt/Al2O3 and Ga37Pt/Al2O3 shows that isolated Pt atoms are, indeed, present at the surface of the liquid SCALMS. Combining DRIFTS with online gas chromatography (GC), we investigated the Ga/Al2O3, Pt/Al2O3, and Ga37Pt/Al2O3 systems under operando conditions during propane dehydrogenation in CO/propane and in Ar/propane. We find that the Pt/Al2O3 sample is rapidly poisoned by CO adsorption and coke, whereas propane dehydrogenation over Ga37Pt/Al2O3 SCALMS leads to higher conversion with no indication of poisoning effects. We show under operando conditions that isolated Pt atoms are present at the surface of SCALMS during the dehydrogenation reaction. IR spectra and density-functional theory (DFT) suggest that both the Ga matrix and the presence of coadsorbates alter the electronic properties of the surface Pt species.

Photochemical in situ studies in a well-controlled surface science environment can help to understand photochemical reactions in organic thin films in more detail. To perform such studies without external focusing or light guiding systems, we designed a high-intensity UV-photon source, which is compatible with an ultra-high vacuum (UHV) environment. The UV source is based on a high power light-emitting diode (LED), soldered onto a copper heat reservoir to avoid overheating. The LED can be placed in close vicinity in front of a single crystal, providing flux densities of 2 × 1018 photons s-1 cm-2 at a wavelength of 365 nm. Thus, the device provides light intensities one order of magnitude higher as compared to conventional continuous wave arc lamps, at only a small variation of the flux of less than ±20% over a sample surface of 10 × 8 mm2. The UV source is mounted in a UHV infrared reflection absorption spectroscopy system and triggered by using the IR spectrometer. This allows fully automatized in situ IR studies of photochemical reactions at interfaces and thin films. We prove the functionality of the device by studying the photochemical conversion of norbornadiene (NBD) to quadricyclane (QC) mediated by the photosensitizer 4,4'-bis(dimethylamino)benzophenone (Michler's ketone, MK). NBD and MK were grown by physical vapor deposition in the form of thin films on Pt(111) at 120 K. Even at prolonged UV irradiation (>100 s), the temperature of the sample increased by less than 10 K. We report first successful conversion of NBD to QC under UHV conditions and follow the conversion behavior as a function of the photon dose and NBD/MK ratio. Initial quantum yields of up to 23% and selectivity for a QC of 70% are obtained at NBD/MK of 7.4:1, indicating good electronic coupling between NBD and MK even in a frozen multilayer. For both very small and very large NBD loadings, the conversion efficiency decreases, which is attributed to the effect of the metallic substrate and phase separation in thick multilayers, respectively.

The interaction of water with metal oxides controls their activity and stability in heterogeneous catalysis and electrocatalysis. In this work, we combine density functional theory calculations and infrared reflection absorption spectroscopy (IRAS) to identify the structural motifs formed upon interaction of water with an atomically defined Co3O4(111) surface. Three principal structures are observed: (i) strongly bound isolated OD, (ii) extended hydrogen-bonded OD/D2O structures, and (iii) a third structure which has not been reported to our knowledge. In this structure, surface Co2+ ions bind to three D2O molecules to form an octahedrally coordinated Co2+ with a "half hydration shell". We propose that this hydration structure represents an important intermediate in reorganization and dissolution on oxide surfaces which expose highly unsaturated surface cations.

We have prepared model systems for Pd-Ga supported catalytically active liquid metal solutions (SCALMS) by physical vapor deposition of Pd and Ga in ultrahigh vacuum onto highly oriented pyrolytic graphite (HOPG) pre-modified by Ai(+) bombardment. Combining AFM and IRAS with CO as a probe molecule, we investigate the growth behavior, the morphology, the surface chemistry, and the stability of Pd-Ga alloys on HOPG. Our results prove the single atom character of the active sites in Ga-rich Pd-Ga alloys. We show that upon interaction with CO, Ga is displaced from the surface and CO adsorbs in on-top position on surface Pd atoms. Experimental data on the vibrational frequencies and binding energies of CO are compared to the results of DFT calculations for CO adsorption on four different Pd-Ga models, i.e. PdGa(1 00), PdGa (1 1 1), Pd-doped alpha-Ga(0 0 1), and Pd-doped fcc-Ga(1 0 0). The comparison suggests that widely separated Pd sites are formed in the Ga matrix. (C) 2018 Elsevier Inc. All rights reserved.

We have studied the anchoring mechanism of a phosphonic acid on an atomically defined oxide surface. Using time-resolved infrared reflection absorption spectroscopy, we investigated the reaction of deuterated phenylphosphonic acid (DPPA, C6H5PO3D2) with an atomically defined Co3O4(111) surface in situ during film growth by physical vapor deposition. We show that the binding motif of the phosphonate anchor group changes as a function of coverage. At low coverage, DPPA binds in the form of a chelating tridentate phosphonate, while a transition to a chelating bidentate occurs close to monolayer saturation coverage. However, the coverage-dependent change in the binding motif is not associated with a major change of the molecular orientation, suggesting that the rigid phosphonate linker always maintains the DPPA in a strongly tilted orientation irrespective of the surface coverage.

Hybrid materials consisting of functional organic molecules on metal oxide nanomaterials are key components in emerging technologies, for example in energy conversion and molecular electronics. In this work, we present the results of a comparative study of carboxyl-functionalized porphyrins on different oxide nanomaterials. Specifically, we investigated the interaction of 5(3-carboxyphenyl)-10,15,20-triphenyl-21,23H-porphyrin (2H-3-MCTPP) and 5(4-carboxyphenyl)-10,15,20-triphenyl-21,23H-porphyrin (2H-4-MCTPP), on MgO, TiO2, and Co3O4 nanoparticles (NPs) using isothermal and temperature-programmed diffuse reflection infrared Fourier transform spectroscopy (DRIFTS). We show that both porphyrins bind to the NPs, yielding stable monolayer films consisting of tilted surface carboxylates. In all cases, anchoring through the carboxylic acid group suppresses self-metalation of the porphyrin unit. Upon annealing, all anchored porphyrin films undergo metalation. The position of the acid group has no major influence on the reactivity. The same is true for the nature of the metal oxide, suggesting that the observed behaviour is general for most anchored porphyrin films on oxide nanomaterials.

In this work, we investigate the interaction of deuterated phenylphosphonic acid (DPPA, C6H5PO3D2) with two different well ordered cobalt-oxide thin films, CoO(111) and CoO(100), grown on Ir(100). We applied coverage-dependent infrared reflection absorption spectroscopy (IRAS) and temperature-programmed (TP)-IRAS under ultrahigh vacuum conditions to study surface reactions, film growth, and thermal stability, both in monolayer and multilayer regimes. The results are compared to our previous studies on Co3O4(111). In the multilayer regime, amorphous multilayer films of DPPA are formed at a low temperature (180 K), which are very similar on all surfaces. At 250 K, the multilayer films crystallize, leading to changes in the molecular orientation relative to the surface. Above 340 K, the multilayer desorbs while only the chemically anchored monolayer remains on the surface. The monolayer films on all three surfaces are stable up to at least 400 K. Coverage and binding geometry, however, depend sensitively on the structure of the oxide surface. On CoO(100), DPPA undergoes complete deprotonation and anchors to the surface forming a fully deprotonated tridentate phosphonate, which dominates over the full range of coverages. On the oxygen terminated CoO(111), we find, in contrast, the formation of a bidentate species in the limit of zero coverage. At a higher coverage, we observe full deprotonation and the formation of tridentate species, which we attribute to the restructuring of the surface. The behavior differs from Co3O4(111), where DPPA forms a fully deprotonated tridentate phosphonate at a low coverage and a partially protonated bidentate phosphonate at higher coverage.(1) The different binding motifs are discussed in view of the arrangement of surface Co ions on the three oxide surfaces.

A novel gas purification material using a supported ionic liquid phase (SILP) has been investigated for removal of NH3 from ambient gas streams (1500 ppm NH3 in Ar). The SILP material is made of a thin film of an imidazolium based ionic liquid and a dissolved copper metal complex ([C(2)C(1)Im]Cl/CuC1(2)), which were dispersed in the pores of a silica 100 support. Diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) was used to investigate the irreversible absorption from a 1500 ppm NH3 gas stream and to identify species formed upon physisorption and chemisorption of ammonia. Additionally, temperature-programmed DRIFTS combined with in situ mass spectrometry were used to evaluate the reversibility and regenerability of the system. (C) 2016 Elsevier B.V. All rights reserved.

We have investigated the surface chemistry of the polycyclic valence-isomer pair norbornadiene (NBD) and quadricyclane (QC) on Pt(111). The NBD/QC system is considered to be a prototype for energy storage in strained organic compounds. By using a multimethod approach, including UV photoelectron, high-resolution X-ray photoelectron, and IR reflection-absorption spectroscopic analysis and DFT calculations, we could unambiguously identify and differentiate between the two molecules in the multilayer phase, which implies that the energy-loaded QC molecule is stable in this state. Upon adsorption in the (sub)monolayer regime, the different spectroscopies yielded identical spectra for NBD and QC at 125 and 160 K, when multilayer desorption takes place. This behavior is explained by a rapid cycloreversion of QC to NBD upon contact with the Pt surface. The NBD adsorbs in a η2 :η1 geometry with an agostic Pt-H interaction of the bridgehead CH2 subunit and the surface. Strong spectral changes are observed between 190 and 220 K because the hydrogen atom that forms the agostic bond is broke. This reaction yields a norbornadienyl intermediate species that is stable up to approximately 380 K. At higher temperatures, the molecule dehydrogenates and decomposes into smaller carbonaceous fragments.