Mixed ionic and electronic conductors represent a technologically relevant materials system for electrochemical device applications in the field of energy storage and conversion. Here, we report about the design of mixed-conducting nanocomposites by facile surface modification using atomic layer deposition (ALD). ALD is the method of choice, as it allows coating of even complex surfaces. Thermally stable mesoporous thin films of 8 mol-% yttria-stabilized zirconia (YSZ) with different pore sizes of 17, 24, and 40 nm were prepared through an evaporation-induced self-assembly process. The free surface of the YSZ films was uniformly coated via ALD with a ceria layer of either 3 or 7 nm thickness. Electrochemical impedance spectroscopy was utilized to probe the influence of the coating on the charge-transport properties. Interestingly, the porosity is found to have no effect at all. In contrast, the thickness of the ceria surface layer plays an important role. While the nanocomposites with a 7 nm coating only show ionic conductivity, those with a 3 nm coating exhibit mixed conductivity. The results highlight the possibility of tailoring the electrical transport properties by varying the coating thickness, thereby providing innovative design principles for the next-generation electrochemical devices.

Thin, porous films of WO3 were fabricated by solution-based synthesis via spin-coating using polyethylene glycol (PEG), a block copolymer (PIB50-b-PEO45), or a combination of PEG and PIB50-b-PEO45 as structure-directing agents. The influence of the polymers on the composition and porosity of WO3 was investigated by microwave plasma atomic emission spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray diffraction, and gas sorption analysis. The electrochromic performance of the WO3 thin films was characterized with LiClO4 in propylene carbonate as electrolyte. To analyze the intercalation of the Li+ ions, time-of-flight secondary ion mass spectrometry, and X-ray photoelectron spectroscopy were performed on films in a pristine or reduced state. The use of PEG led to networks of micropores allowing fast reversible electrochromic switching with a high modulation of the optical transmittance and a high coloration efficiency. The use of PIB50-b-PEO45 provided isolated spherical mesopores leading to an electrochromic performance similar to compact WO3, only. Optimum characteristics were obtained in films which had been prepared in the presence of both, PEG and PIB50-b-PEO45, since WO3 films with mesopores were obtained that were interconnected by a microporous network and showed a clear progress in electrochromic switching beyond compact or microporous WO3.

Here, we present a study of the development of the micro- and mesoporosity of a CexZr1-x-y-zYyLazO2-δ oxygen storage material upon treatment at temperatures up to 1050 °C. The investigated powder, obtained from nitrate-based metal oxide precursors in a specially developed hydrothermal synthesis, is highly crystalline, features a high surface area and does not show phase segregation at high temperatures. By employing an advanced methodology, consisting of state-of-the-art argon physisorption, thermogravimetric analysis coupled with mass spectrometry (TG-MS) and X-ray powder diffraction (XRD) along with Raman spectroscopy, we correlate the stability of the mesopore system to the presence of surface-bound nitrate groups introduced during synthesis, which prevent sintering up to a temperature of 600 °C. In addition, the connectivity of mesopores was further studied by hysteresis scanning within the argon physisorption measurements. These advanced physisorption experiments suggest a three-dimensionally interconnected pore system and, in turn, a 3D network of the material itself on the nanometer scale which appears to be beneficial to endow the mesopore space with enhanced stability against sintering and mesopore collapse once the removal of nitrate groups is completed.

Here, we demonstrate that oxide thin film devices could be affected by humidity in their in-plane stress and in substrate curvature. We prepared silica glass and ceria crystalline thin films on Si(100) wafers by the sol-gel method. Both films had “tensile” in-plane residual stress. We cycled the relative humidity between ca. 20% and 80% in the square wave and monitored the substrate curvature in situ, from which in-plane stress was calculated. The increase and decrease in humidity resulted in a decrease and an increase in tensile stress, respectively. In situ ellipsometric measurements during humidity cycles showed that both thickness and refractive index increase and decrease on the increase and decrease in humidity, respectively. This guarantees that the volume expansion and shrinkage caused by water molecule adsorption/absorption and desorption, respectively, are the origins of the response of the stress to humidity. Responding to the change in humidity, thicker silica glass films with low porosities of 1%–3% showed more sluggish change in stress, suggesting absorption/desorption of water via diffusion in siloxane network in such dense films. Silica glass films with a larger porosity showed more quick response to humidity, indicating adsorption/desorption on the pore wall as the primary cause of the response. “Compressive” stress in a silica glass film with ca. 1% porosity exhibited very slight response in stress to humidity, which was attributed to the hard diffusion of water in compressed siloxane network.

Conversion/alloy active materials, such as ZnO, are one of the most promising candidates to replace graphite anodes in lithium-ion batteries. Besides a high specific capacity (qZnO = 987 mAh g-1), ZnO offers a high lithium-ion diffusion and fast reaction kinetics, leading to a high-rate capability, which is required for the intended fast charging of battery electric vehicles. However, lithium-ion storage in ZnO is accompanied by the formation of lithium-rich solid electrolyte interphase (SEI) layers, immense volume expansion, and a large voltage hysteresis. Nonetheless, ZnO is appealing as an anode material for lithium-ion batteries and is investigated intensively. Surprisingly, the conclusions reported on the reaction mechanism are contradictory and the formation and composition of the SEI are addressed in only a few works. In this work, we investigate lithiation, delithiation, and SEI formation with ZnO in ether-based electrolytes for the first time reported in the literature. The combination of operando and ex situ experiments (cyclic voltammetry, X-ray photoelectron spectroscopy, X-ray diffraction, coupled gas chromatography and mass spectrometry, differential electrochemical mass spectrometry, and scanning electron microscopy) clarifies the misunderstanding of the reaction mechanism. We evidence that the conversion and alloy reaction take place simultaneously inside the bulk of the electrode. Furthermore, we show that a two-layered SEI is formed on the surface. The SEI is decomposed reversibly upon cycling. In the end, we address the issue of the volume expansion and associated capacity fading by incorporating ZnO into a mesoporous carbon network. This approach reduces the capacity fading and yields cells with a specific capacity of above 500 mAh g-1 after 150 cycles.

Stoichiometric cerium oxide nanoparticles with different sizes, ranging between 2 and 12 nm, were prepared by a rational design of the synthetic concept, based on a special hydrothermal procedure. This tuning in particle size was achieved by the decoupling of nucleation and growth, as well as the suitable variation of synthesis temperature and time. In contrast to previous studies utilizing a trivalent cerium compound, we used a tetravalent cerium precursor which results in a cerium oxide powder consisting of single particles with low microstrain and low concentration of bulk defects and, hence, an almost ideal stoichiometry (CeO2.0) in the particles' interior. Owing to these features, the obtained nanoparticles were used as an ideal material for the investigation of the relationship between the particle size and the oxygen storage capacity (OSC). The OSC increased with decreasing particle size, which is expected, as this parameter corresponds to the exchange of oxygen at the surface. By contrast, as a key result, we found that the so-called complete OSC (OSCc) increases with the particle size, which is counterintuitive, as this parameter should not be dependent on the particles' dimension. Furthermore, these particles allowed for a quantitative description of the Raman redshift of the F2g mode of CeO2 in terms of solely the particle size, using theoretical calculations based on the phonon confinement model.

Complex perovskites have attracted extensive attention due to their fascinating physical properties and novel features owing to the coexistence of the ferro-/ferri-magnetic ground state and semiconducting behavior in the single material. Herein, the triple perovskite Sr3Co2WO9 (SCWO) has been successfully synthesized for the first time in the nanocrystalline form with an average crystallite size of 23 nm using a high yield (81%) aqueous citrate sol-gel method. At room temperature, the crystal structure of Sr3Co2WO9 is cubic, space group Fm (3) over barm, with lattice parameter a = 7.9073(6) angstrom. The formation of SCWO triple perovskite was studied in situ by X-ray diffraction and subsequently analyzed by the Rietveld analysis. The detected hysteresis loops with nonzero remanent magnetization and rather large coercive field reveal ferrimagnetic ordering with a Curie temperature of 144 K. The measured effective magnetic moment of mu(B) is close to the expected value for the rarely observed intermediate spin S = 1. It is found that the compound exhibits semiconducting properties with the optical band gaps equal to 3.52 eV (indirect) and 3.76 eV (direct), respectively, further confirmed by the determination of the AC conductivity, which in the measured temperature range (25-500 degrees C at 1 kHz) lies within the interval from 10(-5)-10(-4) Omega(-1) cm(-1). The Maxwell-Wagner model is employed to describe the frequency dependent dielectric constant. The frequency-dependent AC conductivity follows the universal Jonscher power law. Since it possesses both magnetic and semiconductor properties, this material could be a promising candidate to use in devices where its semiconducting properties would be spin-controlled.

The formation of CeO2 colloidal particles upon heating an aqueous solution of (NH4)(2) Ce(NO3)(6) to 100 degrees C was investigated by time-resolved in situ SAXS analysis using synchrotron radiation, providing absolute intensity data. In particular, the experiments were performed by applying different temperatures between room temperature and 100 degrees C as well as under variation of the ionic strength and concentration. Using validated SAXS evaluation tools (SASfit and McSAS software), the analyses revealed the presence of two types of particle populations possessing average dimensions of ca. 2 nm and 5-15 nm, with the latter being agglomerates of the 2 nm particles rather than single crystallites. The analysis revealed not only the changes in the size, but also the relative volume fractions of these two CeO2 particle populations as a function of the aforementioned parameters. Increasing the temperature increases the number of the 5-15 nm agglomerates on one hand by the enhanced nucleation rate of the primary particles. On the other hand, especially at high temperatures (90 and 100 degrees C) the larger agglomerate particles precipitate, resulting in interesting trends in the fractions of the two populations as a function of time, temperature, ionic strength, and precursor concentration. The experimental studies are complemented by calculating colloidal interaction energies based on classical DLVO theory. Thereby, this study provides detailed insight into the nucleation, growth, and agglomeration of CeO2 nanoparticles. The primary objective of this study is to provide a better understanding of the nucleation and growth of particles by the hydrolysis of the tetravalent cerium ion in aqueous solutions.

Yttria-stabilized zirconia (YSZ) is a well-known solid electrolyte material in high-temperature applications that involve the conduction of oxygen ions. One possible way of enhancing the performance of devices like solid oxide fuel cells at lower operation temperatures is the design of the electrolyte's surface by increasing the surface area and modifying the surface properties by ceria coating to improve the oxygen incorporation reaction. However, the preparation of a conformal coating while maintaining a complex surface morphology on the nanoscale is challenging employing conventional evaporation methods. In this work we present thin ceria coatings (9-20 nm) that were deposited on porous 8 mol % YSZ thin films using atomic layer deposition (ALD). The YSZ films (with thicknesses between 90 and 130 nm) were prepared using pulsed laser deposition at various substrate temperatures, thus leading to different surface morphologies. The investigation of the sample cross section by high angle annular dark field transmission electron microscopy exhibits columnar growth of epitaxial grown ceria thin films with excellent coating conformity. This demonstrates the great potential of the ALD process for surface modification of porous materials, where controlled and conformal coating of high surface areas is desired.

The physicochemical properties of thin metal oxide layers strongly depend on the layer thickness and thus differ significantly from their bulk counterpart. In this work, we present the growth of defined thin layers of CeO2 within mesostructured ZrO2 thin films using atomic layer deposition (ALD). The prepared films consist of a cubic ordered arrangement of 15 nm spherical mesopores induced by the used diblock copolymer poly(isobutylene)-block-poly(ethylene oxide) (PIB50-b-PEO45), which allows studying the growth process and the successful coating of the interior pore surfaces via the combination of scanning electron microscopy (SEM), time-of-flight mass spectrometry (ToF-SIMS), and laser ellipsometry. These methods prove the CeO2 layer growth and impregnation of the pores up to 100 ALD cycles, at which the interconnecting channels between the mesopore layers are filled completely impeding further transport of the gaseous CeO2 precursors. X-ray photoelectron spectroscopy (XPS) and diffractometry (XRD) measurements point out the increased amount of Ce3+ after a low number of ALD cycles and show the presence of cubic CeO2 with increasing amount of ALD cycles, respectively. Impedance spectroscopic investigation further proves the formation of a continuous CeO2 path through the entire porous network of the insulating ZrO2 film and shows a strong influence of the layer thickness on the conductivity. All in all, our work presents the preparation of novel hybrid CeO2/ZrO2 model systems, which enable us to tailor their physicochemical properties by changing the thickness of the active oxide layer, and promises improvements for their use as catalysts in oxidation reactions such as the HCl oxidation reaction or as a three-way catalytic converter in automotives.

Porous carrier materials functionalized with organocatalysts offer substantial advantages compared to homogeneous catalysts, e.g., easy separation of the catalyst, scalability, and an improved implementation in continuous operations. Here, we report the immobilization of (3-aminopropyl)trimethoxysilane (APTMS) onto self-prepared silica monoliths and its application as a heterogeneous catalyst in the Knoevenagel condensation between cyano ethylacetate and various aromatic aldehydes under continuous-flow conditions. The meso-macroporous silica monoliths (6–7 cm in length) were optimized to be used in flow taking advantage of their hierarchical meso- and macroporosity. The monoliths were cladded with a poly(ether ether ketone) (PEEK) tube by a refined procedure to guarantee tight connection between the carrier material and PEEK. Functionalization of the bare silica monoliths consisting of APTMS can be efficiently performed in flow in ethanol and toluene. While a large grafting gradient is obtained for toluene, the grafting in ethanol proceeds homogenously throughout the monolith, as evidenced by elemental analysis and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The silica monoliths exhibit high conversion up to 95% with concurrent low back pressures, which is of importance in flow catalysis. By connecting two monoliths, high conversions can be maintained for several flow rates. Two types of monoliths were synthesized, possessing different mesopore sizes. The monolith bearing the larger mesopore size showed an enhanced turnover frequency (TOF), while the monolith with the smaller mesopores allowed for larger quantities of the product to be synthesized, due to the higher surface area. A long-term stability test showed that the functionalized monoliths were still active after 66 h of continuous usage, while the overall yield decreased over time.

CeO2 is a promising material in the catalytic recovery of Cl-2 from HCl by oxidation with O-2 due to its beneficial redox properties (Ce3+/Ce4+) and accompanied oxygen storage capacity (OSC). Two options to tailor the OSC are the usage of dopants and nanostructuring. In this work, we report the synthesis of mesoporous doped Ce0.9M0.1O2 (M = Zr, Gd, Pr, and Tb) powders with identical mesopore size, shape, and specific surface area (approximate to 90 m(2) g(-1)) to investigate the impact of aliovalent (Gd), isovalent (Zr), and aliovalent/isovalent (Pr and Tb) dopants on the OSC as well as on the catalytic activity/stability. The cubic arrangement of spherical 12 nm mesopores surrounded by a crystalline framework is obtained by using a diblock copolymer as structure directing agent in the sol-gel-based preparation approach, indicated by small angle X-ray scattering (SAXS) and scanning electron microscopy (SEM). Pr-doped CeO2 revealed the highest oxygen storage capacity but the lowest catalytic activity/stability in the HCl oxidation together with the Tb- and Gd-doped samples. By contrast, the Zr-doped mesoporous CeO2 powders showed the highest catalytic performance and stability in the CO and HCl oxidation of all samples but a lower OSC. These findings suggest that the OSC should therefore be treated with caution when relating to the catalytic performance in oxidation reactions. The differences in the stability are in agreement with recent studies of the HCl oxidation on model cerium oxide films with defined stoichiometry: the low stability of the aliovalent doped CeO2 materials in the HCl oxidation reaction can be attributed to a large number of oxygen vacancies.

Earth-abundant visible light-absorbing photoelectrodes of the spinel ferrites ZnFe2O4 and MgFe2O4 have been prepared as dense and crack free thin films using pulsed laser deposition, to investigate the basic electronic properties of these two emerging absorber materials. X-ray diffraction and Raman spectroscopy confirm the phase purity of the prepared thin films, whereas magnetotransport and Hall measurements in combination with Mott-Schottky and photoelectrochemical measurements were performed to reveal the performance-limiting factors of those absorbers for photoelectrochemical water oxidation. Our results provide new insights to improve the performance of ferrite-based photoelectrodes in the future.

A strategy is presented to deposit defined layers of TiO2 onto the pore surface within ordered mesoporous, crystalline CeO2-ZrO2 thin films using atomic layer deposition (ALD). As structure-directing agent, a special diblock copolymer, poly(isobutylene)-block-poly-(ethylene oxide), was used, resulting in a three-dimensional arrangement of spherical pores with diameter around 13 nm. High resolution transmission electron microscopy investigations evidence the presence of anatase TiO2 coatings within the mesopores, while ellipsometric porosimetry studies together with time-of-flight secondary-ion mass spectrometry depth profiles indicate the deposition inside the mesopores up to 50 ALD cycles. Afterward, the interconnecting channels between the mesopores are filled completely prohibiting further transport of the gaseous TiO2 precursor into the ordered structure of mesopores and hence, limit the layer growth on the surfaces of the pores. Therefore, the size of the mesopores and their connections are decisive when growing transition-metal oxide layers on the surface of porous substrates and need to be considered for future depositions using ALD. The hybrid TiO2/CeO2-ZrO2 materials are studied by several complementary analytical techniques, to validate the deposition process and also the applicability of these techniques for such materials in general.

Dry impregnation of CeO2 on ZrO2 particles (CeO2@ZrO2) and calcination at 600 degrees C for 5 h result in a highly dispersed layer of the catalytically active CeO2 phase with an enriched concentration of Ce3+. The distinct morphology of CeO2@ZrO2 is responsible for the high (specific) activity in the gas-phase oxidation of HCl (Deacon reaction). Surprisingly, the CeO2@ZrO2 catalyst calcined at 600 degrees C is chemically even more stable toward chlorination under harsh Deacon condition than that calcined at 900 degrees C, where a solid solution of ZrO2 and CeO2 is formed at the solid interface. The improved stability of the CeO2 layer calcined at 600 degrees C is traced to its sharp interface formed with the ZrO2 support. We expect that this kind of active and stable layer morphology of CeO2 supported on ZrO2 is beneficial for other catalytic oxidation reactions as well, either as an active component or as a supporting material for another active metal component.

Characterization of nanocrystalline triple perovskites synthesized by a novel modified sol–gel route instead of bulk materials synthesized by a solid-state route.

CexZr1−xO2solid solutions were prepared to explore the relationship between oxygen storage capacity and activity of oxidation reactions.