Optimizing the oxide support composition in Pr-doped CeO_(2) towards highly active and selective Ni-based CO_(2) methanation catalysts

In this study,Ni catalysts supported on Pr-doped Ce O_(2) are studied for the CO_(2) methanation reaction and the effect of Pr doping on the physicochemical properties and the catalytic performance is thoroughly evaluated.It is shown,that Pr^(3+)ions can substitute Ce^(4+)ones in the support lattice,thereby introducing a high population of oxygen vacancies,which act as active sites for CO_(2) chemisorption.Pr doping can also act to reduce the crystallite size of metallic Ni,thus promoting the active metal dispersion.Catalytic performance evaluation evidences the promoting effect of low Pr loadings(5 at%and 10 at%)towards a higher catalytic activity and lower CO_(2) activation energy.On the other hand,higher Pr contents negate the positive effects on the catalytic activity by decreasing the oxygen vacancy population,thereby creating a volcano-type trend towards an optimum amount of aliovalent substitution.

Surface Characterisation of Silicon Based MEMS

Polysilicon Microelectromechanical systems(MEMS) are the subject of intensive researches. Surface chemistry and topography of a MEMS test structure fabricated at Sandia National Laboratory, USA, were studied by means of scanning electron microscopy(SEM), X-ray photoelectron spectroscopy(XPS) and atomic force microscopy(AFM). XPS C_ 1sand Si_ 2pspectra from the polysilicon components, silicon nitride substrate and a reference silicon wafer were compared. The results confirm the presence of a self-assembled monolayer(SAM) on the MEMS surface. An island-like morphology was found on both polysilicon and silicon nitride surfaces of the MEMS. The islands take the form of caps, being up to 0.5 μm in diameter and 20 nm in height. It is concluded that the co-existence of columnar growth and equiaxed growth during the low pressure chemical vapor deposition(LPCVD) of these layers leads to the observed morphology and the islands are caps to the columnar structures.

Development of a Novel Hybrid Aluminum-Based Sol-Gel Materials: Application to the Protection of AA2024-T3 Alloys in Alkaline Environment

Extensive research on environmentally complaint sol-gel coatings is currently underway for a wide range of applications. Sol-gel technology combines the synergistic properties of inorganic and organic components to design nanostructured coating materials with advanced physical properties. Through a judicious choice of precursors and additives improved performances, such as chemical resistance or pH stability, it can be achieved. This is of particular interest for copper rich AA 2024-T3 aluminium alloys used on aircraft, where increase in local pH occurs at corrosion sites. This work focuses on improving the alkaline stability and anticorrosion properties of such a sol-gel coatings on AA2024-T3 by incorporating aluminium functionality into hybrid materials prepared from hydrolysis and condensation of 3-methacryloxypropyltrimethoxysilane, zirconium n-propoxide and zirconium/alkoxide precursors. Dynamic light scattering technique was used to study the particle size nature of the sol-gel materials in colloidal form. X-ray photoelectron spectroscopy was used to study the oxidation state of the aluminium and zirconium at the sol-gel coating surface. Field emission scanning electrochemical microscopy coupled with energy dispersive spectroscopy was used to assess the microstructural features. Electrochemical characterisations employing potentiodynamic scanning and electrochemical impedance spectroscopy were performed to investigate the anticorrosion performance of the hybrid sol-gel coatings. The best anti-corrosive protection of AA2024-T3 in an alkaline saline solution (pH = 10) was achieved with materials containing 10 mol% and 15 mol% aluminium doped sol-gel coatings. This study shows that presence of aluminium has a positive effect on alkaline stability of the coatings and is a potential green candidate for the protective coatings on aerospace alloys.

Influence of Halide Choice on Formation of Low-Dimensional Perovskite Interlayer in Efficient Perovskite Solar Cells

Recent advances in heterojunction and interfacial engineering of perovskite solar cells(PSCs)have enabled great progress in developing highly efficient and stable devices.Nevertheless,the effect of halide choice on the formation mechanism,crystallography,and photoelectric properties of the lowdimensional phase still requires further detailed study.In this work,we present key insights into the significance of halide choice when designing passivation strategies comprising large organic spacer salts,clarifying the effect of anions on the formation of quasi-2D/3D heterojunctions.To demonstrate the importance of halide influences,we employ novel neo-pentylammonium halide salts with different halide anions(neoPAX,X=I,Br,or Cl).We find that regardless of halide selection,iodide-based(neoPA)_(2)(FA)_((n-1))PbnI_((3n+1))phases are formed above the perovskite substrate,while the added halide anions diffuse and passivate the perovskite bulk.In addition,we also find the halide choice has an influence on the degree of dimensionality(n).Comparing the three halides,we find that chloride-based salts exhibit superior crystallographic,enhanced carrier transport,and extraction compared to the iodide and bromide analogs.As a result,we report high power conversion efficiency in quasi-2D/3D PSCs,which are optimal when using chloride salts,reaching up to 23.35%,and improving long-term stability.