XPS Surface Analysis Research Articles

Self-Healing Superhydrophobic CeO2 Coating Prepared By Anodic Deposition

Superhydrophobic surfaces, in which water contact angle is >150o and the contact angle hysteresis is less than 10°, have attracted much attention, because of their superior properties including self-cleaning, anti-biofouling, corrosion resistance, icephobicity, and oil/water separation. In order to obtain superhydrophobicity, highly rough surfaces have been coated with an organic layer with a low surface energy. In the last decades a lot of studies have been conducted on the fabrication and application of superhydrophobic surfaces, but the superhydrophobic surfaces have not been used practically, because of poor durability of superhydrophobicity. Thus, there is a strong demand for the preparation of durable superhydrophobic surfaces. Recently, it was reported that the surface of rare-earth oxides (REOs) prepared by a magnetron sputtering method exhibits hydrophobicity even without organic coating [1]. If an organic thin coating on the oxide surface is not necessary for superhydrophobicity, it can be expected that the robustness of superhydrophobic surface is enhanced and more durable superhydrophobicity is obtained. In the present study, we have prepared a CeO2 coating on Type 304 stainless steel by an anodic deposition method, which is more suitable for practical application rather than PVD techniques. Prior to the anodic deposition, Type 304 stainless steel plates was electropolished in a mixed solution of HClO4 and ethylene glycol at 20 V below 10°C or roughened by electrochemical etching in solution containing 1.2 wt% HNO3 and 3.6 wt% HCl at a constant current density of 10 kA m-2 or 100 A m-2 for 400 s or 60 s at 313 K, respectively. The electrochemical etching was also conducted on Type 304 stainless steel mesh. The anodic deposition was conducted at a constant current density of 10 A m-2 in solution containing 0.01 mol dm-3 Ce(NO3)3 and 0.05 mol dm-3 hexamethylenetetramine for 1 h at 333 K. After deposition, the surface wettability was evaluated by static contact angle measurement for water (4 μL). The measurements were performed after exposure to laboratory air for various periods of time. The surface and cross-sectional morphology were observed by FE-SEM and TEM, respectively. Surface composition were evaluated XRD, XPS and GDOES. SEM observation of the surface of the CeO2 coating on the flat stainless steel plate revealed that the coating consisted of densely packed CeO2 nanoparticles (10-15 nm in diameter). It was also found from TEM observation that the thickness of the CeO2 layer was approximately 60 nm. The coating consists of a crystalline CeO2 single phase and the species derived from substrate (Fe, Cr and Ni) were practically absent, as confirmed by XRD and GDOES, respectively. The water contact angle of the coating on the flat stainless steel plate was only 20° immediately after deposition. This is contrast to the hydrophobicity of magnetron-sputtered CeO2 surface. However, the water contact angle increased gradually with time of air exposure, and reached approximately 105o after three days. This means CeO2 surface changed from hydrophilic to hydrophobic. In contrast, water contact angle on anodized aluminum surface remained hydrophilic even after three days. XPS surface analysis revealed that this wetting behavior was due to adsorption of contaminant hydrocarbon species on the CeO2 surface from air. In order to enhance the water repellency, surface roughness was introduced on stainless steel by electrochemical etching. The etching in a mixed solution of HNO3 and HCl produced a number of etch pits; the sized of the pits extended to several tens micrometers at 10 kA m-2. The CeO2 coating on the etched stainless steel was also hydrophilic initially, but the water contact angle increased to ~130° after air exposure. The superhydrophobic surface, which showed the static contact angle >150° and contact angle hysteresis of less than 10°, was obtained when CeO2 was coated on the etched stainless steel mesh. The superhydrophobicity of the present CeO2 coating on the etched stainless steel mesh was associated with the formation of contaminant hydrocarbon layer. This means that even if the hydrocarbon layer is removed, the layer will be regenerated and the superhydrophilicity will be healed. In order to examine the self-healing property, the CeO2 coating on the etched stainless steel mesh was treated with O2 plasma and exposed in air. We found that the water contact angle reduced to ~0° after O2 plasma treatment, but recovered to ~160° after air exposure. This self-healing was repeated at least four times. Thus, the CeO2 coated stainless steel is promising as a self-healing superhydrophibic material. Reference [1] G. Azimi, R. Ghiman, H. Kwon, A. T. Paxson and K. K. Varanasi, Nat. Mater. 12, 315 (2013). Figure 1

Impact of molecular structure of two natural phenolic isomers on the protective characteristics of electropolymerized nanolayers formed on copper

A comparative study of the electropolymerization of two natural phenolic isomers, carvacrol (Carv) and thymol (TOH) on copper was made. They are components of Origanum vulgare and Thymus vulgaris essential oils. Polymerized layers (polyCarv and polyTOH) were attained by cyclic voltammetry (CV). Electrochemical techniques complemented by ATR-FTIR, XPS, SEM and AFM surface analyses were used to evaluate the composition and protective characteristics of the films. Results revealed that the electrochemical response in chloride solutions was dissimilar. Copper ions release by polyCarv in chloride solutions was lower than 30% of that obtained with TOH treatments. PolyCarv is a highly protective, transparent film, remarkably different from the brownish, rough and non-protective film obtained with TOH. ATR-FTIR results showed that the oxidation of adsorbed Carv and TOH led to cetonic structures while after electropolymerization ether bonds were also found. However, polyCarv and polyTOH showed important differences in ν-OH band. Deconvolution of C1s signal of XPS spectra led to four contributions with different proportions for polyCarv and polyTOH. Accordingly, C(ph)-O is 50% of total C1s for polyCarv and 30% for polyTOH. C1s/O1s relationships were also different. AFM and SEM observations showed the presence of round flakes, smaller for polyCarv (5nm height) than for TOH (35nm height). A compact layer was found in case of polyCarv but cauliflower and sticks structures with cracks were found for polyTOH. In summary, results showed the important impact of the molecular structure on the composition, structure and protective characteristics of the polymeric layers. A mechanism is proposed to interpret these results.

Water in Ionic Liquid for Electrochemical Li Cycling

A solution of water in ionic liquid was tested as a practical electrolyte for Li–air batteries. Li metal deposition and stripping were repeatedly performed with an acceptable polarization voltage (<±250 mV) even under 1 vol % of water in the ionic liquid electrolyte. Such an advantageous performance was explained by XPS surface analysis on a Li metal after cycling and the thermodynamic state of water in ionic liquid as a bulk electrolyte. Remarkably, the chemical species (LiF and LiOH) forming at the Li/electrolyte interface did not evolve through the addition of water, suggesting that water did not exist as free water that intensively reacts with Li metal. Furthermore, free water was not thermally observed in the ionic liquid electrolyte, indicating that water may be bound to the electrolyte. The water in an ionic liquid will become a new avenue to design the water-tolerant electrolyte against Li metal.

Vacancy ordered γ-Fe2O3 nanoparticles functionalized with nanohydroxyapatite: XRD, FTIR, TEM, XPS and Mössbauer studies

Vacancy ordered maghemite (γ-Fe2O3) nanoparticles functionalized with nanohydroxyapatite (HAp – Ca10(PO4) 6(OH)2) have been successfully synthesized using an inexpensive co-precipitation chemical route. Evidence for the presence of vacancy order in maghemite was shown by the superstructure lines observed in X-ray diffraction. The adsorption of carboxyl groups of citric acid (C6H8O7) onto γ-Fe2O3 nanoparticles was investigated by FTIR, XPS and Mössbauer spectroscopy. From XPS surface analysis, two binding energies related to oxygen were attributed to bindings between C6H8O7/γ- Fe2O3 and C6H8O7/HAp from an interfacial reaction promoted by strongly adsorbed H2O molecules at the surface of these nanomaterials. Le Bail refinement of the XRD patterns showed the formation of well-crystallized pure tetragonal maghemite before and after functionalization with nanoHAp. The temperature dependence of hyperfine parameters of pure and functionalized γ-Fe2O3 nanoparticles was investigated via Mössbauer spectroscopy. TEM revealed the formation of quasi-spherical γ- Fe2O3 nanoparticles with an average diameter of ca. 12nm and 16nm before and after functionalization with nanoHAp in agreement with Le Bail refinement. Magnetometry measurements showed a saturation magnetization of 12emu/g and a blocking temperature of 340K for the functionalized γ- Fe2O3 nanoparticles.

Chlorine-rich plasma polymer coating for the prevention of attachment of pathogenic fungal cells onto materials surfaces

The attachment of pathogenic fungal cells onto materials surfaces, which is often followed by biofilm formation, causes adverse consequences in a wide range of areas. Here we have investigated the ability of thin film coatings from chlorinated molecules to deter fungal colonization of solid materials by contact killing of fungal cells reaching the surface of the coating. Coatings were deposited onto various substrate materials via plasma polymerization, which is a substrate-independent process widely used for industrial coating applications, using 1,1,2-trichloroethane as the process vapour. XPS surface analysis showed that the coatings were characterized by a highly chlorinated hydrocarbon polymer nature, with only a very small amount of oxygen incorporated. The activity of these coatings against human fungal pathogens was quantified using a recently developed, modified yeast assay and excellent antifungal activity was observed against Candida albicans and Candida glabrata. Plasma polymer surface coatings derived from chlorinated hydrocarbon molecules may therefore offer a promising solution to preventing yeast and mould biofilm formation on materials surfaces, for applications such as air conditioners, biomedical devices, food processing equipment, and others.

Na Vs. Li - Thermodynamic Surprises for Graphite and CuO As Anode Materials for Sodium-Ion Batteries

Research on sodium-ion batteries (NIBs) is well motivated by the large abundance of sodium and strategies for commercializing such systems are mainly based on principles known from lithium-ion technology. From a scientific perspective it is an intriguing questions of how lithium and sodium compare in their redox chemistry with identical electrodes. Graphite, for example, was long thought to be inactive as electrode in NIBs but has been shown to be active under the right conditions1 . In metal-batteries, Li2O2 forms in the case of lithium whereas NaO2 can form in the case of sodium2, 3. The differences in physic-chemical properties might also provide an opportunity for improved performance in next-generation electrodes that are so far not performing well enough for LIBs. For example, conversion reactions are being studied for many years with the hope to achieve higher capacity electrodes but many challenges remain. In this presentation, will focus on lithium and sodium ion storage in graphite and copper oxide (CuO). We will first discuss the peculiar properties of sodium-ion intercalation into graphite. Inactive when carbonates are used as electrolyte solvents, a highly reversible storage mechanisms (> 1000 cycles without significant capacity decay) with low irreversible capacity and fast kinetics is found when ether solvent molecules are used. This is because ether molecules can co-intercalate into the graphite structure without leading to exfoliation. This redox process is more reversible as compared to lithium. In the second example, we will discuss CuO as model system for conversion reactions. We prepared CuO thin films by sputtering and studied the surface film formation by XPS (surface analysis and depth profiling) and SEM. As important finding, the reaction mechanism changes when replacing lithium by sodium. In the latter case, CuO conversion is only partially reversible but oxygen becomes redox active as well and Na2O2 forms as additional intermediate. On the contrary, oxygen is inactive in Li-CuO cells. Further, significant differences occur in the surface film formation on CuO electrodes in Li and Na cells.4 The results clearly demonstrate that significant differences in the redox chemistry in LIBs and NIBs exist for identical electrode materials and these differences need to be understood and used accordingly to achieve high performance electrodes. 1. Jache, B.; Adelhelm, P., Use of Graphite as a Highly Reversible Electrode with Superior Cycle Life for Sodium-Ion Batteries by Making Use of Co-Intercalation Phenomena. Angewandte Chemie-International Edition 2014, 53, (38), 10169-10173. 2. Hartmann, P.; Bender, C. L.; Vracar, M.; Duerr, A. K.; Garsuch, A.; Janek, J.; Adelhelm, P., A rechargeable room-temperature sodium superoxide (NaO2) battery. Nature Materials 2013, 12, (3), 228-232. 3. Adelhelm, P.; Hartmann, P.; Bender, C. L.; Busche, M.; Eufinger, C.; Janek, J., From lithium to sodium: cell chemistry of room temperature sodium-air and sodium-sulfur batteries. Beilstein Journal of Nanotechnology 2015, 6, 1016-1055. 4. Klein, F.; Pinedo, R.; Hering, P.; Polity, A.; Janek, J.; Adelhelm, P., Reaction Mechanism and Surface Film Formation of Conversion Materials for Lithium- and Sodium-Ion Batteries: An XPS Case Study on Sputtered Copper Oxide (CuO) Thin Film Model Electrodes. The Journal of Physical Chemistry C 2016. - advance online - DOI: 10.1021/acs.jpcc.5b10642

Determination of the corrosion rate inside historical brass wind instruments – Proof of concept

An electrochemical sensor has been tested on brass reference samples and applied on a mouthpiece of a historical brass instrument. Using a phosphate buffer solution pH 7 with 10−2, 10−3 and 10−4 M NaCl, the electrochemical response (open circuit potential, polarisation resistance) of the sensor corresponds to the results obtained in a traditional electrochemical cell. XPS surface analysis has shown that the brass surface composition after 7 min contact with the sensor is not altered when using 10−3 or 10−4 M NaCl. The sensor is fit for purpose and has already been applied in brass wind instruments.

Electrochemical and XPS surface analytical study on the reactivity of Ni‐free stainless steel in artificial saliva

Nowadays, there is a strong demand to replace CrNi stainless steels used for biomedical applications such as brackets in orthodontics with a new generation of more biocompatible austenitic, nickel‐free alloys. The aim of this work is the investigation of the growth and stability of the surface films formed on DIN 1.4456 Ni‐free stainless steel (18% Cr, 18% Mn, 2% Mo) in artificial saliva (pH 7.9) at 37 °C by electrochemistry and XPS surface analyses and the assessment of the ions that leach from the steel. These results show that the open circuit potential asymptotically increases and the corrosion current density decreases from 1 to 24 h exposure time to the artificial saliva. XPS provides evidence that the surface film present on the surface after mechanical polishing transforms into a passive film that becomes progressively enriched in Cr (III) oxy‐hydroxides whereas iron and manga­nese oxides are depleted. It is found that the instantaneous corrosion rate decreases exponentially with the amount of Cr (III) in the passive film. The results are discussed regarding the biocompatibility, thus the release of ions into solution, of the new nickel‐free stainless steel. Based on the results presented in this paper and literature evidence, a comprehensive model is proposed that substantiates the biocompatibility of these alloys.

Reduction of copper ions release by a novel ecofriendly electropolymerized nanolayer obtained from a natural compound (carvacrol)

The release of copper ions by copper-containing devices, equipments and facilities represents a potential risk for biological systems. Different inhibitory treatments (CuIT) that use organic compounds have been proposed to reduce this environmental hazard but many of them are not in accordance with new regulations. The development of an ecofriendly CuIT based on the use of carvacrol, a natural phenolic compound present in essential oils, is reported here. The effects of carvacrol adsorption (adCarv) and its electropolymerization (polyCarv) were examined. Electropolymerization was attained after cycling the copper electrode in the 0.3–1.0V potential range. Electrochemical techniques complemented by ATR-FTIR, XPS, SEM and AFM surface analyses were used to evaluate the composition and characteristics of the layers. Results demonstrated that adCarv includes cetonic structures while polyCarv additionally contains ether bonds. AFM and SEM observations showed the presence of round nanoglobules, larger for adCarv (close to 50nm diameter). Cytotoxicity of adCarv and polyCarv layers on copper was also evaluated. The comparative analysis of both treatments revealed that polyCarv nanolayer is highly protective while the adCarv layer is weakly protective and reduction in cell viability was found. It was concluded that CuIT that leads to polyCarv nanolayer is very effective and ecofriendly.

Friction reduction efficiency of organic Mo-containing FM additives associated to ZDDP for steel and carbon-based contacts

The lubricating properties of two different organomolybdenum additives combined with ZDDP were evaluated for different tribopairs involving carbon-based coatings, hydrogenated DLC and nanocrystalline diamond NCD. Their performances were investigated using reciprocating linear tribometer and compared with the traditional additivation MoDTC/ZDDP. The highly sulfurised moly-trimer additive and organic molybdate ester additive displayed good friction reducing properties in comparison with traditional additivation MoDTC for all tribopairs tested, especially organic molybdate ester. XPS and ToF-SIMS surface analyses performed on the tribofilms formed with these different organomolybdenum additives showed the formation of MoS2/MoS2−xOx species exhibiting a solid lubricant character, but preferentially on steel surfaces. HRTEM/EDS analyses confirmed the presence of MoS2/MoS2−xOx sheets embedded inside an oxygen-rich amorphous matrix. This is different from the traditional additivation that leads to the polyphosphate/phosphate glass matrix. Organic molybdate ester is a sulfur- and phosphorus-free additive that appears particularly interesting for achieving low friction while minimizing the S content of the lubricant.

The Adsorption of Cu Species onto Pyrite Surface and Its Effect on Pyrite Flotation

The adsorption of Cu species onto pyrite surface and its effect on flotation were investigated by using microflotation tests, first-principle calculations, and XPS surface analysis. The results indicated that the flotation of pyrite appears to be activated with CuSO4only at alkaline pH, while being depressed at acidic and neutral pH. The adsorption of copper ions on pyrite surface was pH-dependent, and the adsorption magnitude of copper ions at alkaline pH is higher than that at acidic and neutral pH due to a strong interaction between O atom in Cu(OH)2and surface Fe atom except for the interaction between Cu atom and surface S atom. At acidic and neutral pH, there is only an interaction between Cu atom and surface S atom. The adsorption was relatively weak, and more copper ions in solution precipitated the collector and depressed the flotation of pyrite. XPS analysis confirmed that more copper ionic species (Cu(I) and Cu(II)) are adsorbed on the pyrite surface at alkaline pH than that at acidic and neutral pH.

Preferential CO oxidation in a hydrogen-rich stream over gold supported on Ni–Fe mixed metal oxides for fuel cell applications

This paper reports the catalytic performance of gold nanoparticles supported on high surface area mixed metal oxides derived from Ni and Fe hydrotalcite-like precursors. The gold catalysts were prepared by deposition-precipitation and characterised by XRD, TGA, BET, H2-TPR, XPS, ICP and HR-TEM. From HR-TEM analysis, gold particles ranging from 4 to 10 nm were observed. XPS surface analysis revealed that gold existed in the metallic state, whereas surface oxides were NiO and Fe2O3. For the preferential CO oxidation reaction, the 1.5 wt.% Au catalyst gave almost complete conversion (≈40% selectivity) at 60 °C using 2 vol.% O2 with the GHSV fixed at 12 000 h−1. The addition of CO2 to the feed stream resulted in a 10–15% decrease in conversion, whereas the addition of H2O improved CO conversion. The addition of H2O to the feed containing CO2 showed signs that H2O mitigated the negative effect of CO2.

CO oxidation on CuO/CeO2 catalyst prepared by solvothermal synthesis: influence of catalyst activation temperature

A series of CuO/CeO2 catalysts were prepared using a solvothermal method and a subsequent activation process. The influences of activation temperature (300–600 °C) on physicochemical properties and catalytic behavior of the prepared CuO/CeO2 catalysts have been investigated by XRD, SEM, Raman spectroscopy, S BET measurement, XPS surface analysis, H2-TPR, CO-TPD techniques, and CO oxidation testing. The catalyst activated at 450 °C was found to have the highest catalytic activity, which can be ascribed to its higher dispersion of Cu species, higher concentration of oxygen vacancies, and larger amount of more active lattice oxygen. The lower activity of the CuO/CeO2 catalysts activated at lower ( 450 °C) temperatures are attributed to the weaker interaction between CuO and CeO2, and to the sintering of CuO nanoparticles, respectively.

Investigating the Fate of an Electrolyte Additive: A Combined Theoretical and Experimental Study of Prop-1-Ene-1,3-Sultone (PES) in Li-Ion Cells

INTRODUCTION One way to improve the cycling performance and stability of Li-ion cells is the use of electrolyte additives. In recent years, prop-1-ene-1,3-sultone (PES) has shown great promise for improving cell lifetime and decreasing gas formation.1–5Voltage cycling experiments and surface analysis studies have provided important clues for understanding the fate of PES in cells. However, the details of this additive’s mechanism of action remains unknown. This presentation will discuss computational chemistry methods, including the accurate representation of solvation for ethylene carbonate (EC)/ethylmethyl carbonate (EMC) mixtures, and the application of these methods to gain insight into the role and ultimate fate of PES in Li-ion cells. EXPERIMENTAL Calculations were performed with the Gaussian 09 (G09.D01) software package using the B3LYP/6-311++G(d,p) method. The IEFPCM-UFF solvation model and its parameterization will be discussed. A cylindrical, stainless steel capacitance cell, based on the design of Greer and Jacobs, was used for dielectric constant measurements.6 Machine-made 220 mAh graphite/Li[Ni1/3Mn1/3Co1/3]O2 (NMC) pouch cells were filled with 3:7 EC/EMC, 1 M LiPF6, and 0 – 2 % PES, and galvanostatically cycled.4 Select cells were disassembled in an argon-filled glove box for XPS surface analysis as described by Madec et al.7 Volumetric and GC-MS analysis of gas formation was performed as described by Self et al.5 RESULTS AND DISCUSSION Computational chemistry can be used to determine standard electrode potentials, free energies of reactions and transition state energies. It is, however, imperative that solvation is properly modeled to obtain meaningful results. The polarizable continuum model (PCM) is a simple yet robust approach that requires only the dielectric constant (static permittivity) of the reaction medium. Therefore, dielectric constants of EC/EMC solvent blends were measured at various compositions and temperatures. It was found that measured values do not exactly match those predicted by a simple linear combination of EC and EMC. The reactions of PES at the electrodes were then investigated. PES reduction has a calculated reduction potential of 1.0 V vs. Li/Li+, which closely matches experimental dQ/dV plots.4 The subsequent reduction is predicted to occur very rapidly and results in the reactive Li2PES compound shown in Figure 1. The decomposition of this compound and its various reactions with the solvent (EC and EMC) and with other PES molecules will be discussed. These reactions are spontaneous and result in the formation of Li2SO3 and organic sulfate species (RSO3Li) at the anode. This is a good match to the S 2p peaks observed in the XPS spectrum of the anode after formation. The predicted gas-phase products, including several hydrocarbons at the anode and the formation of O=C=S at the cathode, are also consistent with those observed by GC-MS. In summary, carefully developed theoretical methods coupled with experimental data reveal several spontaneous pathways for the reductive decomposition of PES. It is hoped that these results will also prove useful for developing new and improved electrolyte additives. REFERENCES 1. B. Li et al., J. Mater. Chem. A, 1, 12954–12961 (2013). 2. B. Li et al., Electrochimica Acta, 105, 1–6 (2013). 3. B. Li, M. Xu, T. Li, W. Li, and S. Hu, Electrochem. Commun., 17, 92–95 (2012). 4. J. Xia et al., J. Electrochem. Soc., 161, A1634–A1641 (2014). 5. J. Self, C. P. Aiken, R. Petibon, and J. R. Dahn, J. Electrochem. Soc., 162, A796–A802 (2015). 6. D. T. Jacobs and S. C. Greer, Rev. Sci. Instrum., 51, 994–995 (1980). 7. L. Madec et al., J. Phys. Chem. C, 118, 29608–29622 (2014). 8. K. Xu, Chem. Rev., 114, 11503–11618 (2014). Figure 1 – The reduced Li2PES compound predicted to form at the anode during cell formation. Figure 1

In vitro apatite formation on nano-crystalline titania layer aligned parallel to Ti6Al4V alloy substrates with sub-millimeter gap.

Pure titanium substrates were chemically oxidized with H2O2 and subsequent thermally oxidized at 400°C in air to form anatase-type titania layer on their surface. The chemically and thermally oxidized titanium substrate (CHT) was aligned parallel to the counter specimen such as commercially pure titanium (cpTi), titanium alloy (Ti6Al4V) popularly used as implant materials or Al substrate with 0.3-mm gap. Then, they were soaked in Kokubo's simulated body fluid (SBF, pH 7.4, 36.5°C) for 7days. XRD and SEM analysis showed that the in vitro apatite-forming ability of the contact surface of the CHT specimen decreased in the order: cpTi>Ti6Al4V>Al. EDX and XPS surface analysis showed that aluminum species were present on the contact surface of the CHT specimen aligned parallel to the counter specimen such as Ti6Al4V and Al. This result indicated that Ti6Al4V or Al specimens released the aluminum species into the SBF under the spatial gap. The released aluminum species might be positively or negatively charged in the SBF and thus can interact with calcium or phosphate species as well as titania layer, causing the suppression of the primary heterogeneous nucleation and growth of apatite on the contact surface of the CHT specimen under the spatial gap. The diffusion and adsorption of aluminum species derived from the half-sized counter specimen under the spatial gap resulted in two dimensionally area-selective deposition of apatite particles on the contact surfaces of the CHT specimen.

Deoxygenation of m-Cresol: Deactivation and Regeneration of Pt/γ-Al2O3 Catalysts

Pt/Al2O3 catalysts were used to deoxygenate m-cresol, which was used as a bio-oil model compound. The catalysts were characterized by XRD, TEM, XPS, hydrogen chemisorption, and BET surface analyses. The coke deposits on spent catalysts were analyzed by TPO. In this work, the catalysts deactivation and regeneration were addressed. Deactivation was caused by carbonaceous deposits formed mainly by cresol condensation products, in a parallel-type coke formation mechanism. The amount of carbon formed on the catalyst strongly depends on the metal/acid functions ratio. The gas phase reaction was carried out in a fixed bed reactor in the presence of H2 at 300 °C and atmospheric pressure. The regeneration by coke removal using hydrogen or air was addressed. It was found that treatments in air at mild temperature led to the recovery of the catalytic activity, while the effectiveness of the treatment with H2 strongly depends on the temperature, not being possible to recover the activity at 400 and 500 °C, while at 4...

Anion-controlled passivation effect of the atomic layer deposited ZnO films by F substitution to O-related defects on the electronic band structure for transparent contact layer of solar cell applications

Anion-controlled chemistry in ZnO films is essential to obtain stable charge–carrier transport and to prevent degradation in the performance of the transparent contact layer in solar cells through passivation of O-related defects by F substitution. Therefore, in this work, the passivation effect of F doping in ZnO was confirmed by analysis for the chemical state of O in ZnO films using XPS surface analysis in the O 1s region. Furthermore, we investigated the effect of F doping in a ZnO matrix on the electronic structure of the resulting films as a function of electron concentration by optical band gap shift (Burstein–Moss theory) and near-band-edge transition (photoluminescence with Stokes shift theory) measurements in ZnO films with different F doping concentrations. The band gap narrowing effect was not significant in the F-doped ZnO films due to valence band perturbation from anion doping rather than conduction band perturbation. Finally, the band structure could be approximated by the relationship between experimental analysis and the formation of valence and conduction bands in ZnO orbitals.

Photoelectrochemical water splitting in a tungsten oxide - nickel oxide thin film material library

A combinatorial thin film library containing WO3 and NiO was produced using thermal co-evaporation of WO3 and Ni followed by high temperature reoxidation. Microstructure and crystallographic particularities of the WO3-NiO library investigated by SEM and XRD revealed three distinct compositional zones: A low Ni concentration zone containing crystalline WO3 and amorphous NiO, a high Ni concentration zone containing crystalline NiO and amorphous WO3 and a middle range amorphous zone connecting the extremes. Photo Electrochemical Scanning Droplet Cell Microscopy PE-SDCM was used for locally investigating the photoelectric response of the library as a function of Ni concentration. A substantial photocurrent peak was identified at 6.2 at.% Ni with values in excess of 2.5 mA cm−2 while Ni amounts above 9 at.% resulted in a completely photoinactive thin film. XPS surface analysis indicated a surface composition different than the bulk with WO3 being present up to 45 at.% Ni in the bulk. For bulk Ni amounts above this composition, the surface contained no WO3 anymore, only an amorphous Ni sub-oxide being suggested.

The Effect of Surface Roughness on the Corrosion Properties of Type AISI 304 Stainless Steel in Diluted NaCl and Urban Rain Solution

Due to their good corrosion resistance, favorable mechanical properties, and reasonable price regarding their excellent properties, austenitic stainless steels have, over recent decades, become one of the alloys that are increasingly used in civil engineering and building, as well as for specific architectural purposes. Architects often design stainless steel exterior elements with higher surface roughnesses, which are not resistant to corrosion processes. The aim of this work was to investigate the influence of different types of surface finishes to stainless steel of quality AISI 304 on the corrosion properties of this steel. In order to achieve this goal, electrochemical tests were performed on different surface finishes in two different environments: in an NaCl aqueous solution, and in simulated urban rain which contained no chlorides. In addition to the electrochemical methods used, surface roughness was also measured, and XPS surface analyses were performed. The results of the investigation showed that surface roughness affects the growth of the passive layer in urban rain significantly; however, the growth of such a film is retarded in the case of the NaCl aqueous solution. Based on the results of the performed analyses, it was found that, in the NaCl solution, the pitting potential depended strongly upon the surface roughness and the surface finish, but this was not true for the samples tested in urban rain.

Feasibility of an oxygen-getter with nickel electrodes in alkaline electrolysers

Alkaline electrolysis is the long-established technology for water splitting to produce hydrogen and has been industrially used since the nineteenth century. The most common materials used for the electrodes are nickel and derivatives of nickel (e.g. Raney nickel). Nickel represents a cost-effective electrode material due to its low cost (compared to platinum group metals), good electrical conductivity and exhibits good resistance to corrosive solutions. The steady degradation of the nickel electrodes over time is known as a result of oxide layer formation on the electrode surface. Reducing oxide layer growth on the electrode surface will increase the efficiency and lifetime of the electrolyser. Titanium has a higher affinity to oxygen than nickel so has been introduced to the electrolyser as a sacrificial metal to reduce oxide layer formation on the nickel. Two identical electrolysers were tested with one difference: Cell B had titanium chips present in the electrolyte solution, whilst Cell A did not have titanium present. SEM results show a reduction of 16 % in the thickness of the Cell B oxide layer on nickel compared to the Cell A nickel, which is supported by the large increase in oxide layer build-up on the titanium in Cell B. EDX on the same samples showed on average a 59 % decrease in oxygen on the Cell B nickel compared to Cell A. XPS surface analysis of the same samples showed a 17 % decrease in the oxygen on Cell B nickel. These results support the hypothesis that adding titanium to an alkaline electrolyser system with nickel electrodes can reduce the oxide layer formation on the nickel.