Gas-Phase Condensation of Nanoparticles and Nanocomposites for Energy Applications

Nanomaterials are not simply miniaturized materials. In this world halfway between the atomic and the bulk scale, high density of interfaces and surfaces, elemental composition, unique geometries and interactions constitute a virtually infinite set of parameters that allows to tailor material properties at the nanoscale. The aim of this Thesis is to contribute to the development of strategies for the growth of nanomaterials featuring complex morphologies and tailorable structures by careful design of Gas Phases Condensation (GPC) experiment. The proposed strategies are demonstrated for the growth of nanomaterials with applications in the energy storage field. The co-evaporation of Mg and Ti in a H enriched atmosphere is the key to grow small Mg-Ti-H nanoparticles (NPs), in which TiH2 and Mg/MgH2 coexist at the single NP level, despite the bulk immiscibility of Mg and Ti. The high density of MgH2/TiH2 interfaces gives rise to outstanding H-absorption and desorption kinetics in the 373-423 K temperature range. Moreover, a theoretical model is proposed to explain the altered thermodynamics induced by interface energetics. Thermal GPC and Pulsed Laser GPC were employed to grow Fe-Co alloy nanoparticles. The influence of the two techniques over the morphology of the nanoparticles is discussed and an application in the catalysis of CO2 reduction is presented. Finally, a novel strategy for the one-step synthesis of Fe-Co alloy nanoparticles supported on Ti oxide nanoparticles via Thermal GPC is presented. This new approach relies on the independent evaporation of two metallic precursors with strongly different oxidation enthalpies in an O2 enriched atmosphere. TEM and XRD morphological and structural characterizations clearly show that less negative enthalpy gives birth to metallic NPs, while the other to oxide NPs.