Investigation of Interfacial and Transport properties of LIBs/NIBs anodes and commercial SOFCs

In this thesis work, two types of electrochemical energy systems (EESs) have been studied, i.e.: electrochemical energy storage by Li-/Na-ion batteries, and electrochemical energy conversion by Solid Oxide Fuel Cells. Energy production worldwide is moving toward renewable energy sources to decrease the greenhouse gases emissions. In this context, electrochemical energy systems will be in the very next future the key enablers for the production and storage of green energy. Furthermore, Li-ion batteries will play the main role for the transport electrification. To achieve this goal, several aspects of EESs needs to be studied and optimized, considering both performances and sustainability. Speaking of Li-ion batteries, graphite is the state-of-the-art anode material. However, it must be partially or totally replaced because of its low specific capacity (372 mAh g-1 ) as well as its introduction into the critical raw materials list of the European Union. SnO2 is a potential candidate because of its high theoretical capacity (1484 mAh g-1 ), environmentally friendliness, and at the moment is not considered a critical raw material by the European Union. However, it suffers of cycling instability due to the structural rearrangements upon cycling, and large voltage hysteresis. In this regard, three different nanocomposite anodes based on SnO2 have been synthesized and characterized in terms of both performance and interfacial and transport properties. The effect of an active/inactive matrix, as well as the morphology of SnO2 has been deeply studied. As a result, the studied SnO2-based anodes can offer promising and tailored performances in terms of energy density, energy efficiency, and rate capability according to the end user application. Speaking of Na- ion batteries, a Fe3O4-based anode was studied as a sustainable high-power anode material. In this regard, the material was structurally, morphologically, and electrochemically characterized. A deep electrochemical characterization in terms of interfacial and transport properties has been carried out by means of cyclic voltammetry at different scan rates, potentiostatic electrochemical impedance spectroscopy, and ex-situ Raman spectroscopy. The last section is focused on electrochemical energy conversion by Solid Oxide Fuel Cells. In this regard, a new technique, based on electrochemical impedance spectroscopy and the study of the distribution of relaxation times, has been proposed for assessing the state-of-health of the SOFC under real operating conditions. Firstly, an extended experimental campaign has been pursued to build a meaningful equivalent circuit model. Subsequently, an a priori known stress agent was applied to validate the obtained electrochemical model.