Solid Oxide Cells (SOCs) are reversible and efficient energy-conversion systems for the production of electricity and green hydrogen. Nowadays, they are considered as one of the key technological solutions for the transition to a renewable energy market. A SOC consists of a dense electrolyte sandwiched between two porous electrodes. To date, the large-scale commercialization of SOCs still requires the improvement of both their performances and lifetime. In this context, the main limitations in terms of efficiency and degradation of SOCs have been attributed to the conventional oxygen electrode in La0.6Sr0.4Co0.2Fe0.8O3. To overcome this issue, it has recently been proposed to replace this material with an alternative electrode based on PrOx. Indeed, this material has a high electro-catalytic activity for the oxygen reduction and good transport properties. The performance of cells incorporating this new electrode is promising and might enable to reach the targets required for large-scale industrialization (i.e. -1.5A/cm2 at 1.3V at 750°C and a degradation rate of 0.5%/kh). However, it has been shown that PrOx undergoes phase transitions depending on the cell operating conditions. The impact of these phase transitions on the electrode properties and on its performance and durability are still unknown. Thus, the purpose of the PhD is to gain an in-depth understanding of the physical properties for the different PrOx phases in order to investigate their role in the electrode reaction mechanisms. The study will contribute to validate whether PrOx based electrodes are good candidates for a new generation of SOCs and help to identify an optimized electrode using a methodology combining ab-initio calculation with electrochemical modelling.