Nathalie Guillou

Bio: Nathalie Guillou is an academic researcher from University of Rennes. The author has contributed to research in topics: Thermal decomposition & Powder diffraction. The author has an hindex of 1, co-authored 1 publications receiving 12 citations.

Morphology and formation mechanism of ceria nanoparticles by spray pyrolysis

Abstract: Ceria-based materials are used in industrial applications such as catalyst supports, carbon monoxide reduction catalysts, and solid oxide fuel cell electrolytes. Various applications require different morphological particles. The ceria particles with various morphologies from the precursors of cerium(III) acetate hydrate, cerium(IV) nitrate hydrate, and cerium(IV) ammonium nitrate were prepared by spray pyrolysis (SP) because SP has the potential for simple and continuous process. The precursor behaviors and the particle morphologies were characterized by thermogravimetric analysis and by transmission electron microscopy. Four main morphologies of solid spherical, hollow spherical with a single pore, hollow concave, and hollow spherical with multiple pores were observed. The experimental results suggest that the morphological formation mechanism is highly correlated with the factors of precursor solubilities, solvent evaporation rates (droplet diameters), and precursor melting temperatures. In addition, total concentrations of cerium(III) in the ceria particles from various precursors were examined using X-ray photoelectron spectroscopy.

Development of magnesium-based hybrid metal matrix composite through in situ micro, nano reinforcements

Abstract: Present work aims at developing Magnesium based metal matrix composite (MMC) through in-situ reaction. In-situ generation of micro and nano particles in the Mg-melt is supposed to have a better bon...

Surface Modification of Hematite Photoanodes with CeOx Cocatalyst for Improved Photoelectrochemical Water Oxidation Kinetics.

Abstract: Hematite is a promising photoanode for solar water splitting by photoelectrochemical (PEC) cells, but its performance is limited by the slow kinetics of water oxidation reaction or oxygen evolution reaction (OER). Surface modification of hematite photoanodes with a suitable water oxidation cocatalyst is a key strategy for improving the kinetics of water oxidation. In this study, a CeOx overlayer is deposited on the surface of the hematite photoanode by a water-based solution method with ceric ammonium nitrate (CAN) followed by heat treatment. The photocurrent of CeOx -modified hematite is 3 times higher than that of pristine hematite (at 1.23 V vs. RHE) under AM 1.5G, 1 sun conditions. Through hole-scavenger measurements, Tafel plot analysis, and electrochemical impedance spectroscopy, it is concluded that CeOx overlayer increases the hole injection efficiency, improves the surface catalytic activity, and enhances charge transfer across the photoanode/electrolyte interface. These observations are attributed to the synergistic effects of Ce3+ /Ce4+ redox species in CeOx and the oxygen vacancies. This work elucidates the role of CeOx as an efficient cocatalyst overlayer to improve the OER kinetics of photoanodes.

The role of in-situ ceramic reinforcements on microstructure evolution and mechanical properties on developed hybrid Mg-MMCs

Abstract: In-situ generation of ceramic reinforcements during the manufacturing of metal matrix composites (MMCs) have wide advantages ranging from better dispersion, generation of nanoceramics to increased compatibility with matrix. The present work aims to explore the effect of precursor concentration on the in-situ generation of CeO2 and MgO particles in Mg-based MMC. The contribution of different strengthening mechanisms is also explored. Optical microscopy, Scanning electron microscope (SEM), Energy dispersive spectroscopy (EDS) analysis, and X-ray diffraction (XRD) of the developed MMCs lead to categorization of particles and features into cauliflower structure, agglomerated nanoceramics, composite ceramic particles (CCP), nanoceramics, nanopores and intermetallic. Vickers hardness tests, compression tests, and scratch tests are carried out to evaluate the mechanical response of MMCs. The compression fractured surfaces are analyzed using SEM. Preliminary wear response is evaluated using a 3-D optical profilometer to evaluate the scratched surfaces. The effect of particle size and concentration on various strengthening mechanisms is evaluated. It is possible to manipulate the mechanical properties through controlling the in-situ reinforcement type and distribution, which is also further possible, as reported here.