Due to their flexibility, high-temperature electrochemical converters based on solid oxide cells (SOCs) can co-electrolyse water vapour and CO2 to produce a synthetic gas, an essential precursor for the production of synthetic fuels (e-fuels). However, to reach industrial production levels, the performance and durability of SOCs must be improved. Indeed, during co-electrolysis, the standard Ni/YSZ electrode undergoes microstructural changes and suffers from carbon deposition. To limit these degradations, it has recently been proposed to infiltrate the electrode with a ceria-based catalyst (GDC). However, the exact role of the GDC remains unclear to date. This thesis therefore aims to improve our understanding of how the electrode functions and degrades by using an ab initio modelling approach coupled with electrochemical kinetics simulations. Firstly, the atomic-scale mechanisms will be studied using the electronic density functional theory (DFT). These reaction mechanisms will then be used as input data for an electrochemical model capable of simulating performance and degradation in relation to a given microstructure. Moreover, the CEA/Liten has developed a numerical tool that can generate synthetic microstructures representative of infiltrated electrodes. This tool, when applied to the GDC-Ni/YSZ electrode, will be coupled with electrochemical models to optimise the microstructure. The results obtained during this PhD will allow recommendations to be made for the manufacturing of optimised electrodes for co-electrolysis at the CEA.