Advances in Nanoparticle Condensation from the Gas Phase: MG-Based and TiO2-Based Materials for Energy Applications

This Thesis aims to study nanoparticles (NPs) synthesised via condensation from the gas phase. The advances achieved with this technique, first of all the development of a controlled reactive atmosphere and in situ capabilities, are presented. With the set-up developed, it is possible to synthesise NPs of a variety of compounds: alloys, oxides, hydrides, and also complex morphologies like nanocomposites and core-shell structures. Mg-based NPs are studied for their interest in hydrogen storage applications. Firstly, the problem of severe crystal growth in metallic Mg NPs is addressed. The dynamics of the self-assembly process is studied and the synthesis of Mg metal-oxide core-shell NPs is proved as a way to stabilise small size (in the 20-30 nm range) NPs. Addition of Ti is known to improve the hydrogen storage properties of Mg. Mg-Ti NPs in the form of air-stable pellets or nanopowders, are synthesised via condensation from inert or hydrogen rich atmosphere. The resulting MgH2-TiH2 nanocomposites show excellent hydrogen sorption kinetic properties with fast hydrogen absorptions as well as desorptions observed at temperatures as low as 343 K. Slight to no thermodynamics changes compared to the bulk Mg-H system are retrieved over a wide, low temperature range. Finally, the addition of V is studied as a method to improve light absorption in the visible range and photocatalytic efficiency of TiO2 NPs. A deep characterisation of the overall V-TiO2 NPs structure, morphology and optical properties is carried out along with the characterisation of the local chemical environment of the V ions, proving that V is always substitutional of the cation in TiO2, irrespective of the TiO2 polymorph present.