| 1. |
- Benko, Gabor, et al.
(författare)
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Particle size and crystallinity dependent electron injection in Fluorescein 27-sensitized TiO2 films.
- 2003
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 107:6, s. 1370-1375
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Tidskriftsartikel (refereegranskat)abstract
- Influence of processing parameters, such as autoclaving and firing temperature, on the optical properties of nanocrystalline anatase TiO2 film and on the process of electron injection from the dye fluorescein 27 to the as-prepared films is studied. Transmission electron microscopy and steady-state and time-resolved femtosecond spectroscopy measurements indicate that the larger the TiO2 particle and the better its overall crystallinity, the faster the process of electron injection. Unraveling factors that control the properties of the sub-20-nm sized semiconductor particles, and by this the electron injection to them, is important for understanding the process of interfacial electron transfer from the dye to the semiconductor, as well as future optimization of the function of the photoelectrochemical cell based on dye-sensitized TiO2 films.
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| 2. |
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| 3. |
- Chamoun, Mylad, et al.
(författare)
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Bifunctional Performance of Flow Assisted Rechargeable Iron-Air Alkaline Batteries
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Low cost rechargeable iron-air alkaline batteries have all essential attributes to adapt for large scale energy storage applications. To actualize this implementation needs to overcome the challenges including poor efficiency and short cycle lifetime. Herein, suitable synthesized catalysts for the air electrode were investigated prior to iron-air cell testing. NiCo2O4 as sole catalyst proved exceptional bifunctional OER/ORR activity and stability over 440 h operation in air. This catalyst fitted into an electrolyte and oxygen flow assisted rechargeable iron-air prototype and performed stable over 588 h and had an energy density of 377 Wh kg-1 Fe. Inadequate coulombic efficiencies of 75 – 85% and energy efficiencies around 50% hurt the performance of the cell though and needed further development. Nevertheless, the findings in this work reports the opportunities and obstacles of the rechargeable iron-air battery.
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| 4. |
- Chamoun, Mylad, et al.
(författare)
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Electrochemical Performance and in Operando Charge Efficiency Measurements of Cu/Sn-Doped Nano Iron Electrodes
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Fe-air or Ni-Fe cells can offer low-cost and large-scale sustainable energy storage. At present, they are limited by low coulombic efficiency, low active material use, and poor rate capability. To overcome these challenges, two types of nanostructured doped iron materials were investigated: (1) copper and tin doped iron (CuSn); and (2) tin doped iron (Sn). Single-wall carbon nanotube (SWCNT) was added to the electrode and LiOH to the electrolyte. In the 2 wt. % Cu + 2 wt. % Sn sample, the addition of SWCNT increased the discharge capacity from 430 to 475 mAh g−1, and charge efficiency increased from 83% to 93.5%. With the addition of both SWCNT and LiOH, the charge efficiency and discharge capacity improved to 91% and 603 mAh g−1, respectively. Meanwhile, the 4 wt. % Sn substituted sample performance is not on par with the 2 wt. % Cu + 2 wt. % Sn sample. The dopant elements (Cu and Sn) and additives (SWCNT and LiOH) have a major impact on the electrode performance. To understand the relation between hydrogen evolution and charge current density, we have used in operando charging measurements combined with mass spectrometry to quantify the evolved hydrogen. The electrodes that were subjected to prolonged overcharge upon hydrogen evolution failed rapidly. This insight could help in the development of better charging schemes for the iron electrodes.
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| 5. |
- Hinz, A, et al.
(författare)
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Platinum on alumina, titania, and magnesia supports for the combustion of methanol in a waste gas with trace amount of ammonia
- 2001
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Ingår i: Applied Catalysis B: Environmental. - 0926-3373. ; 34:2, s. 161-178
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Tidskriftsartikel (refereegranskat)abstract
- Pt (0.1 wt.%) on Al2O3, TiO2, and MgO supports were used for the low temperature combustion of methanol in both the absence and the presence of ammonia. Without NH3 in the gas the performance for the complete combustion decreases in the order Pt/MgO greater than or equal to Pt/TiO2 much greater than Pt/Al2O3 comparing a fixed amount of Pt surface area. In the presence of ammonia strong deactivation of Pt/Al2O3 and Pt/TiO2 is observed, whilst almost no deactivation of Pt/MgO occurs. The results are explained considering CO chemisorption and XPS measurements as well as the TPD profiles generated by adsorbed ammonia and methanol. A comparison of the TPD profiles of the N-2 which is formed from adsorbed ammonia on supported Pt and the support, respectively, reveals that Pt on Al2O3 and TiO2 interacts with the support surface, possibly through Pt-O-support bonding. The inference is supported by the XPS measurements showing that the Pt on Al2O3 and TiO2, as opposed to that on MgO, is slightly positively charged, making the interaction between ammonia and Pt stronger. Additional insight into the deactivation cause is obtained from TPD experiments with adsorbed methanol. These experiments reveal that on both Pt/Al2O3 and Pt/TiO2 there is competition between methanol and ammonia for adsorption sites, which is not the case on Pt/MgO. (C) 2001 Elsevier Science B.V. All rights reserved.
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| 6. |
- Kallioinen, J, et al.
(författare)
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Photoinduced ultrafast dynamics of Ru(dcbpy)(2)(NCS)(2)-sensitized nanocrystalline TiO2 films: The influence of sample preparation and experimental conditions
- 2004
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 108:20, s. 6365-6373
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Tidskriftsartikel (refereegranskat)abstract
- In most of the previous ultrafast electron injection studies of Ru(dcbpy)(2)(NCS)(2)-sensitized nanocrystalline TiO2 films, experimental conditions and sample preparation have been different from study to study and no studies of how the differences affect the observed dynamics have been reported. In the present paper, we have investigated the influence of such modifications. Pump photon density, environment of the sensitized film (solvent and air), and parameters of the film preparation (crystallinity and quality of the film) were varied in a systematic way and the obtained dynamics were compared to that of a well-defined reference sample: Ru(dcbpy)(2)(NCS)(2)-TiO2 in acetonitrile. In some cases, the induced changes in the dynamics were uncorrelated to the electron injection process. High pump photon density (not in the linear response region) and exposure of the sensitized film to air altered the picosecond-time- scale kinetics considerably, and the changes were attributed mostly to degradation of the dye. In other cases, changes in the measured kinetics were related to the electron injection processes: reducing the firing temperature of the nanocrystalline film or making the film via electron beam evaporation (EBE) resulted in a decrease of the overall crystallinity of the film, and the electron injection slowed. In the sensitized EBE films, in addition to an increased contribution of triplet excited-state electron injection, a new electron transfer (ET) process with a time constant of 200 fs was observed.
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| 7. |
- Lundberg, Mats, et al.
(författare)
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Crystallography and porosity effects of CO conversion on mesoporous CeO2
- 2004
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811. ; 69:3, s. 187-195
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Tidskriftsartikel (refereegranskat)abstract
- Catalytic properties and thermal stability were studied for samples of mesoporous ceria with different BET specific surface area. The catalytic conversion of carbon monoxide to carbon dioxide and how thermal treatments of the catalysts influence the catalytic properties have been investigated. The materials were studied by transmission electron microscopy and by conversion profile measurements of CO versus temperature using a plug flow micro reactor made in quartz glass only. In order to compare the catalytic properties associated with a specific structure or morphology directly, aliquots of surface area (0.6 m(2)) of the catalyst was used. Scanning electron microscopy and X-ray energy-dispersive spectrometry (XEDS) were used for surface morphology studies and elemental analysis. It was found that the proportion of {100} surfaces determine the catalytic properties of the material and these surfaces become important at calcination temperatures between 773 and 973 K. The internal mesoporous structure is destroyed at calcination temperatures around 873 K. (C) 2004 Elsevier Inc. All rights reserved.
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| 8. |
- Lundberg, Mats, et al.
(författare)
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Mesoporous thin films of high-surface-area crystalline cerium dioxide
- 2002
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Ingår i: Microporous and Mesoporous Materials. - 1387-1811. ; 54:1-2, s. 97-103
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Tidskriftsartikel (refereegranskat)abstract
- Mesoporous thin films of cerium dioxide were prepared by using a copolymer surfactant (Pluronics 123) at ambient conditions in alcohol as a solvent. The material was produced via a direct calcination step, without the necessity of a gelling stage. The synthesised CeO2 matrix was crystalline with a high surface area. The solution height over the synthesis vessel before the calcination step was found to play an important role in the direct calcination synthesis of mesoporous ceria. The material was characterised by scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, and determination of the specific surface area after the BET method. Small angle X-ray scattering was used to study differences in how the surfactant with ethanol as a solvent was ordered before and after addition of cerium chloride, prior to the calcination step.
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| 9. |
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| 10. |
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| 11. |
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| 12. |
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| 13. |
- Paulraj, Alagar Raj, et al.
(författare)
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Electrochemical Performance and in Operando Charge Efficiency Measurements of Cu/Sn-Doped Nano Iron Electrodes
- 2019
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Ingår i: Batteries. - : MDPI. - 2313-0105. ; :1
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Fe-air or Ni-Fe cells can offer low-cost and large-scale sustainable energy storage. At present, they are limited by low coulombic efficiency, low active material use, and poor rate capability. To overcome these challenges, two types of nanostructured doped iron materials were investigated: (1) copper and tin doped iron (CuSn); and (2) tin doped iron (Sn). Single-wall carbon nanotube (SWCNT) was added to the electrode and LiOH to the electrolyte. In the 2 wt. % Cu + 2 wt. % Sn sample, the addition of SWCNT increased the discharge capacity from 430 to 475 mAh g−1, and charge efficiency increased from 83% to 93.5%. With the addition of both SWCNT and LiOH, the charge efficiency and discharge capacity improved to 91% and 603 mAh g−1, respectively. Meanwhile, the 4 wt. % Sn substituted sample performance is not on par with the 2 wt. % Cu + 2 wt. % Sn sample. The dopant elements (Cu and Sn) and additives (SWCNT and LiOH) have a major impact on the electrode performance. To understand the relation between hydrogen evolution and charge current density, we have used in operando charging measurements combined with mass spectrometry to quantify the evolved hydrogen. The electrodes that were subjected to prolonged overcharge upon hydrogen evolution failed rapidly. This insight could help in the development of better charging schemes for the iron electrodes.
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| 14. |
- Shtender, Vitalii, et al.
(författare)
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Influence of nano-VC on the structural and magnetic properties of MnAlC-alloy
- 2021
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Alloys of Mn55Al45C2 with additions of VC nano-particles have been synthesized and their properties evaluated. The Mn55Al45C2(VC)(x) (x=0.25, 0.5 and 1) alloys have been prepared by induction melting resulting in a high content of the ferromagnetic tau -phase (>94 wt.%). Powder X-ray diffraction indicates that nano-VC can be dissolved in the alloy matrix up to 1 at.%. On the other side, metallography investigations by scanning electron microscopy and scanning transmission electron microscope show inclusions of the nanosized additives in the microstructure. The effect of nano-VC on the grain and twin boundaries has been studied by electron backscattering diffraction. The magnetization has been measured by magnetometry up to 9 T while the domain structure has been studied using both magnetic force microscopy as well as Kerr-microscopy. For nano-VC contents above 0.25 at.%, a clear increase of the coercive force is observed, from 57 to 71 kA/m. The optimum appears to be for 0.5 at.% nano-VC which shows a 25% increase in coercive force without losing any saturation magnetization. This independent increase in coercivity is believed to originate from the nano-VC reducing the overall magnetic domain size. Overall, we observe that addition of nano-VC could be an interesting route to increase the coercive force of MnAl, without sacrificing saturation magnetization.
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| 15. |
- Skårman, Björn, et al.
(författare)
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Carbon monoxide oxidation on copper oxide thin films supported on corrugated cerium dioxide {111} and {001} surfaces
- 1999
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 1090-2694 .- 0021-9517. ; 181:1, s. 6-15
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of CeO2 with and without a thin layer of copper oxide were prepared by rf magnetron sputtering on surfaces of alpha-Al2O3 (sapphire) substrates. Careful characterisation of the surfaces was performed down to the atomic level using high-resolution electron-microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Surprisingly, the as-deposited, corrugated ceria surfaces, nominally (001), consist exclusively of {111}-type lattice planes, but, upon annealing at 800 degrees C, a well-defined portion of (001) surfaces are formed. Oxidation of carbon monoxide to carbon dioxide was studied, having the prepared films in a stirred batch reactor. A batch reactor was chosen so that the conversion over the small sample surface area (ca 10(-4) m(2)) could be monitored as a function of the reaction time. The activity of copper oxide on annealed ceria surfaces is markedly higher than on nonannealed surfaces, indicating a favourable synergetic effect between the ceria (001) surface and the copper oxide phase. (C) 1999 Academic Press.
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| 16. |
- Skårman, Björn, et al.
(författare)
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Carbon monoxide oxidation on nanostructured CuOx/CeO2 composite particles characterized by HREM, XPS, XAS, and high-energy diffraction
- 2002
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 1090-2694 .- 0021-9517. ; 211:1, s. 119-133
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Tidskriftsartikel (refereegranskat)abstract
- Nonstoichiometric CuOx/CeO2 nanocomposite particles have been synthesized by inert gas condensation (IGC) over the whole compositional range (2 to 98 at.% Cu). The composition influences greatly the formation of various nanostructures, such as core-shells. A wide range of techniques were used to characterize the catalysts: high-resolution TEM and X-ray photoelectron spectroscopy, as well as high-energy diffraction (HED) and X-ray absorption spectroscopy (XANES and EXAFS) using synchrotron radiation. Catalytic oxidation of carbon monoxide was performed on catalysts with equal specific surface area, using both a batch reactor and a fixed-bed flow reactor. X-ray absorption spectroscopy showed that copper was present as a mixture of Cu(I) and Cu(II) species ranging from ca. 36% Cu(I) in one of the fresh samples to less than 5% in the activated samples. The coordination of Cu(I) was found to be mostly linear 2-coordinate as in the model compound Cu2O or alternatively 3-coordinate planar, while Cu(II) was found to present a mixture of tetrahedral and highly distorted octahedral coordination. EXAFS showed that both copper species were part of a very dispersed and highly disordered structure. The main chemical factors that control the activity for the oxidation of carbon monoxide are (i) the nanostructured morphology, (ii) the X-ray crystallinity as determined by HED, and (iii) the dispersion of copper at the surface. These three factors can be tailored during the IGC synthesis, but they can also change during the thermal activation. Copper ions migrate toward the particle surface and create new and highly dispersed superficial copper species/clusters, accompanied by a slight reduction of the CeO2 sur ace. This favorable morphological evolution, or diminutive structural rearrangement, which was not adequately resolved by HREM, can be monitored as a shift of the light-off temperature. The wide variation in X-ray crystallinity between the catalysts can be used to quantify the processes occurring during the thermal activation. Easily reducible, high-energy surfaces Of CeO2 are better in stabilizing extremely dispersed copper species by a close synergistic interaction, which promotes a rapid change of valency and supply of oxygen. (C) 2002 Elsevier Science (USA).
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| 17. |
- Skårman, Björn, et al.
(författare)
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Morphology and structure of CuOx/CeO2 nanocomposite catalysts produced by inert gas condensation: An HREM, EFTEM, XPS, and high-energy diffraction study
- 2002
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 14:9, s. 3686-3699
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Tidskriftsartikel (refereegranskat)abstract
- Inert gas condensation (IGC) has been employed to produce nanoparticles of the low-temperature combustion catalyst CuOx/CeO2. For the first time we have used a multiple heating crucible setup to tailor various morphologies over the whole compositional range (2-98% Cu). The factors that control the growth, structure, and morphology of the nanocomposite have been studied. A powerful combination of complementary characterization methods has been used to elucidate the catalytic synergistics of this material. Investigations by high-resolution transmission electron microscopy (HRTEM) and energy-filtered TEM (EFTEM) are supported by X-ray photoelectron spectroscopy (XPS) and high-energy diffraction (HED) measurements. The nonstoichiometric CuOx/CeO2 composite displays an amorphous character consisting of aggregated CeO2 (ceria) nanocrystallites over which amorphous copper clusters (or a thin film of a solid solution) are finely dispersed. In the range 6similar to20% Cu, copper is predominantly located at the surface, which can give the material optimum catalytic properties. Development of crust structures, for example, core-shells, are formed in the 30similar to70% Cu concentration range and is attributable to a sequential oxidation of Ce followed by Cu and an ideal proportion of lattice expansion for the oxides. We suggest a model that illustrates the formation of the crust structure and may explain the observed extreme dispersion of copper on ceria. The helium gas pressure during the thermalization controls the crystal size and the degree of crystallite aggregation. Rounded particle shapes consisting of epitaxially interfaced nanocrystallites exhibit an X-ray amorphous character, while block-shaped crystals displaying sharp edges and distinct flat surfaces give rise to a higher X-ray crystallinity. Bulk CuO crystals were detected by high-energy diffraction above a 30% Cu content. However, the extreme copper dispersion is preserved even for higher copper contents, showing no limit of surface saturation.
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| 18. |
- Skårman, Björn
(författare)
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Structure, Morphology, and Catalytic Properties of CuOx/CeO2 Model Catalysts
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cerium dioxide, or ceria, is a chemically stable oxygen ion conducting material with a capacity to store and release oxygen, and is therefore extensively used in combustion catalysts. The Cu-Ce-O system has been identified as one of the most active catalysts for the combustion of carbon monoxide. To study the catalytic oxidation of CO, we have synthesised model CuOx/CeO2 catalysts by gas phase techniques. PVD rf-magnetron sputtering was used to produce thin film catalysts. Inert gas condensation (IGC) with multiple thermal heating sources was employed to produce nanocomposite particles. This allowed us also to study the growth of thin films and particles, respectively. The catalysts were characterised by a powerful complementary combination of methods, combining small-area and whole-sample characterisation of local structure and long-range order; High resolution electron microscopy, atomic force microscopy, nitrogen adsorption, and analytical X-ray techniques, such as energy-dispersive spectroscopy, and photoelectron spectroscopy. High-energy diffraction, and X-ray absorption fine structure spectroscopy using synchrotron radiation were employed to collect information on crystallinity and the local environment of Cu. The thin CeO2 films grown on surfaces of á-Al2O3 formed extremely sharp ridges exposing exclusively {111}-type surfaces despite the nominally (001)-orientation. We found that a well-defined portion of (001) could be created by annealing. Thin layers of CuOx were deposited on top of both the as-prepared and annealed ceria thin films. The annealed films with copper on top exhibit a markedly higher activity than the others, indicating a favourable synergistic effect between the copper oxide and CeO2(100) surfaces (i.e. catalytic anisotropy). In addition, it was realised that the as-prepared films are excellent for quickly evaluating AFM tips (i.e. as tip characteriser), and for studying artefacts and tip-sample phenomena occurring during tapping mode AFM imaging. Nanocomposite CuOx/CeO2 particles were produced over the whole compositional range. A change of the copper content clearly altered the nanostructured morphology, forming e.g. crust structures between 30 and 70 at.% Cu. A growth mechanism for the formation of crust structures is suggested. The dispersion of copper that controls the number of active sites and, hence, the catalytic activity was shown to be dependent on the: i) total copper content, ii) the nanostructured morphology, and iii) the crystallinity of ceria. A copper content between 5 and 30 at.% Cu was found to be beneficial for the combustion of carbon monoxide.
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| 19. |
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