Ceria nanoparticles as promoters of CO2 electroreduction on Ni YSZ An efficient preparation strategy and insights into the catalytic promotion mechanism

Since many decades nickel yttria stabilized zirconia cermet Ni YSZ has been the most frequently used fuel electrode material for high temperature solid oxide cells SOCs . However, in recent years there has been considerable effort to improve the Ni YSZ performance through surface engineering. In this work, we report a simple strategy to apply nanosized un doped CeOx and Ni doped NiCeOy ceria particles into porous Ni YSZ cermet electrodes via infiltration from hexane solution. Detailed characterization of the particles in their solution revealed differences in the ease of agglomeration, with NiCeOy nanoparticles being better dispersed and thus forming smaller aggregates. This property is critical for the effectiveness of the solution in filling the pores of Ni YSZ cermet and the consequent ceria deposition. In particular, morphological and microstructural characterization reveals that NiCeOy nanoparticles decorate uniformly the pores of Ni YSZ backbone, deep up to the interface with the electrolyte. More importantly, this can be done with relatively high ceria loading per infiltration co firing step. Electrochemical tests demonstrate that infiltrated Ni YSZ fuel electrodes have improved I V performance in CO2 electrolysis as compared to pristine Ni YSZ. Synchrotron based operando NAP XPS experiments using both soft and tender X rays revealed the formation of an ultrathin Ni Ce3 layer on the electrode surface, which can rationalize the ameliorated CO2 electrolysis performanc

Étude de la composition de la surface des catalyseurs à base de cobalt pour le reformage des vapeurs d'éthanol

The aim of the thesis was determination the influence of the ethanol steam reforming (ESR) reaction conditions, catalyst’s dispersion and potassium promotion on a surface’s composition and understanding the influence of these changes on catalysts’ performance. Cobalt-based catalysts (unpromoted and promoted with potassium) with low- and high-dispersed ceria and zirconia supports were used. The changes of the surface state of catalysts during the ESR were studied by means of X-ray photoelectron spectroscopy, whereas the reaction products evolution was followed by mass spectrometer or gas chromatograph. Highly-dispersed ceria-supported catalyst was characterized under low pressure conditions (0.2–20 mbar) with the water/ethanol molar ratio equal to 3/1 (at 420ºC). The other tests were carried out over all catalysts under total pressure of 1 atm with 3/1, 9/1 and 12/1 molar ratios (at 420ºC). The water/ethanol ratio of 12/1 was chosen for studies of the surface state of all catalysts with time-on-stream. It was found that the ESR selectivity to gaseous products and carbon deposition is governed mainly by surface hydroxyl species concentration; in the promoted catalysts together with Kδ+–Osurfδ- surface sites.L’objectif de cette thèse de doctorat a consisté à déterminer l’influence des conditions réactionnelles du vaporeformage de l’éthanol (ESR), de la dispersion du catalyseur et de la promotion par le potassium sur l’état de la surface. Ce travail a aussi aidé à comprendre l’influence de ces facteurs sur les propriétés catalytiques. Nous avons utilisé les catalyseurs à base de cobalt (promus et non promus par le potassium) supportés à l’oxyde de cérium et à l’oxyde de zirconium à faible et à forte dispersion. Les changements de l’état de la surface des catalyseurs pendant la réaction d’ERS ont été étudiés à travers la spectrométrie photoélectronique X (XPS), alors que les changements des produits ont été analisés en utilisant la spectrométrie de masse et la chromatographie en phase gazeuse. Le catalyseur supporté sur oxyde de cérium à forte dispersion a été caractérisé sous une basse pression (0.2-20 mbar) avec le rapport molaire eau/éthanol de 3/1 (420ºC). Les autres tests ont été faits sur tous les catalyseurs sous une pression totale de 1 atm avec les rapports molaires de 3/1, 9/1, 12/1 (420ºC). Nous avons utilisé un mélange eau/éthanol dans un rapport molaire de 12/1 pour étudier les changements de l’état de la surface de tous les catalyseurs dans le temps. Il a été démontré que la sélectivité d’ESR des catalyseurs pour produire des gaz et pour déposer le carbone est réglée par la concentration des groupes hydroxyles sur la surface. Quant aux catalyseurs promus, elle dépend aussi de la concentration Kδ+–Osurfδ-

Effect of the surface state on the catalytic performance of a Co CeO2 ethanol steam reforming catalyst

This work examines the impact of the Co/CeO₂ catalysts’ surface oxidation state and composition on the ethanol steam reforming (ESR) reaction performance. To this purpose, in situ and ex situ X-ray photoelectron spectroscopy (XPS) combined with on-line mass spectrometry were applied in a wide pressure range (0.2–20 mbar). When the reaction was performed at 0.2 mbar, metallic cobalt and partly reduced cerium oxide were found regardless of the catalysts’ pretreatment conditions. This surface state favors CO and H₂ production, indicating that Csingle bondC bond cleavage is the most important pathway in this pressure regime. A higher reduction degree of ceria gave rise to a larger population of adsorbed hydroxyl groups, which, contrary to the expected behavior, suppressed the activity and the Csingle bondC bond cleavage yield. Under higher pressure (4–20 mbar), gradual oxidation of cobalt and ceria was noted. The presence of ionic cobalt species appears to enhance CO₂ and acetaldehyde yields. On the basis of the present results and the available literature a plausible pressure-dependent reaction mechanism is proposed

The role of tungsten species in the transition of anodic nanopores to nanotubes formed on iron alloyed with tungsten

The effect of alloying of sputter-deposited Fe with 9 at.% tungsten on the growth of nanoporous anodic oxide was studied in ethylene glycol electrolyte containing 0.1 mol dm(-3) ammonium fluoride and 1.5 mol dm(-)(3) water. The classic nanoporous anodic film (Al2O3-like) was developed on pure Fe while the transition of nanopores to nanotubes (TiO2-like) was observed for anodizing of Fe-W alloy. The pores/ nanotubes having average diameter 50-110 nm and 30-60 nm on pure Fe and Fe-W alloy anodized at voltage 40-60 V, respectively. Both nanoporous/nanotubular anodic films grow in line with the field assisted flow model with a few fundamental details: i) transition of nanopores to nanotubes is observed upon anodizing of Fe-W alloy, ii) significant reduction of the cell size (nanotube diameter) is obtained on Fe-W alloy, iii) relatively thick layer is produced at Fe-W alloy/oxide interface. The primary reason of this transition to nanotubes as well as chemical changes is discussed in view of effective modification of the cell boundary region with tungsten species, probably WF6 compound, upon growth of anodic film under influence of high electric field strength. The possible reason of developing the space in between nanotubes is faster kinetics of WF6 reaction with water over the presence of low solubility FeFx species. Alloying of iron is one of the effective ways to modify the nanostructure of the anodic film on iron. (C) 2019 Elsevier Ltd. All rights reserved

WO₃ Nanopores Array Modified by Au Trisoctahedral NPs: Formation, Characterization and SERS Application

The WO3 nanopores array was obtained by an anodization method in aqueous solution with addition of F- ions. Several factors affecting the final morphology of the samples were tested such as potential, time, and F- concentrations. The morphology of the formed nanopores arrays was examined by SEM microscopy. It was found that the optimal time of anodization process is in the range of 0.5–1 h. The nanopores size increased with the increasing potential. The XPS measurements do not show any contamination by F- on the surface, which is common for WOx samples formed by an anodization method. Such a layer was successfully modified by anisotropic gold trisoctahedral NPs of various sizes. The Au NPs were obtained by seed-mediated growth method. The shape and size of Au NPs was analysed by TEM microscopy and optical properties by UV-VIS spectroscopy. It was found that the WO3-Au platform has excellent SERS activity. The R6G molecules could be detected even in the range of 10−9 M

Adopting a collaborative approach in developing a prehabilitation program for patients with prostate cancer utilising experience-based co-design methodology

Purpose: Engaging patients in a prehabilitation program prior to commencement of cancer treatment is a known challenge. Utilising experience-based co-design (EBCD) methodology, this study aimed to explore the prostate cancer treatment journey from the perspectives of the patient and health professionals and collaboratively develop a prehabilitation program for patients with prostate cancer. Methods: EBCD was utilised for this study. Patients, support persons and health professionals were selectively identified and recruited from two metropolitan health services in Melbourne. Selection criteria included (i) recent clinical/patient experience with prostate cancer treatment and (ii) willingness to share positive experiences and challenges in two 2-hour face-to-face workshops. Findings from these workshops were thematically analysed to identify key themes addressing aims of the study. Results: Twenty participants including eight patients, one support person and 11 health professionals were recruited. Four key touchpoints were identified. All participants acknowledged positive interactions between patients and health professionals. Patients often described the journey as lonely, stressful and frustrating especially prior to commencement of treatment. A lack of a consistent approach in identifying and preparing patients with prostate cancer for treatment was identified. A structured prehabilitation program was proposed as a solution. Practical ideas to be implemented including timing of commencement, educational content and strategies to boost engagement were formulated

Surface oxidation of Ni-cermet electrodes by CO2 and H2O and how to moderate it

International audienceThe oxidation of porous Ni-yttria-stabilized zirconia (YSZ) and Ni-gadolinia-doped ceria (GDC) ceramic-metal (cermet) electrodes in H2O and CO2 atmospheres was studied by near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). We show that the oxidation of nickel by the two gases is not similar, as is commonly believed, but it depends on the ceramic type. Nickel is vulnerable to oxidation in H2O but it resists to CO2 in Ni-GDC, as compared to the Ni-YSZ electrode. Inspired by this observation we conceptualize and fabricate Ni-YSZ electrodes modified by ceria nanoparticles, which show significantly higher resistance to CO2 oxidation as compared with conventional Ni-YSZ electrodes. The preparation of tailor-made cermet electrodes with identical bulk/mechanical characteristics but very different surface properties offers a promising fabrication strategy for high-performance and durability solid oxide electrolysis cells for CO2 conversion

Effect of potassium promoter on the performance of nickel-based catalysts supported on MnOxMnO_x in steam reforming of ethanol

The effect of a potassium promoter on the stability of and resistance to a carbon deposit formation on the Ni/MnOx catalyst under SRE conditions was studied at 420 °C for different H2O/EtOH molar ratios in the range from 4/1 to 12/1. The catalysts were prepared by the impregnation method and characterized using several techniques to study their textural, structural, and redox properties before being tested in a SRE reaction. The catalytic tests indicated that the addition of a low amount of potassium (1.6 wt.%) allows a catalyst with high stability to be obtained, which was ascribed to high resistance to carbon formation. The restriction of the amount of carbon deposits originates from the potassium presence on the Ni surface, which leads to (i) a decrease in the number of active sites available for methane decomposition and (ii) an increase in the rate of the steam gasification of carbon formed during SRE reactions