# GDC-Based Infiltrated Electrodes for Solid Oxide Electrolyzer Cells (SOECs)
## 1 Introduction  
The electrochemical conversion of CO\({}_{2}\) for fuels and chemical production is one of the most promising methods for greenhouse gas recycling and reutilization [1]. Unfortunately, it is known that low-temperature electrochemical processes exhibit several major issues related to slow reaction kinetic, the strict control of operating conditions, and catalyst poisoning [2; 3; 4]. Low-temperature electrochemical processes for CO\({}_{2}\) reduction involving molecular catalysts or non-aqueous solvent systems have also been proposed, but they show some major drawbacks such as high costs and low current densities [5; 6; 7]. Otherwise, high-temperature solid oxide electrolyzer cells (SOECs) show several positive features: firstly, SOECs are whole-ceramic devices and do not make use of liquid electrolytes, avoiding the problem of leakage and corrosion [8; 9]. Then, the high operating temperature favors the kinetic at the electrodes and increases the overall efficiency of the cells [10]. Finally, SOECs can exploit all advantages of the development of solid oxide fuel cell (SOFC) materials [11; 12; 13] and technologies [14; 15]. Therefore, extensive studies of SOECs and CO\({}_{2}\) electrolysis are largely available in the recent literature [1; 16; 17], as durable, stable, and efficient working electrodes for SOEC are greatly required. Nickel/yttria stabilized zirconia (Ni-YSZ) has been widely investigated and proposed as the best cathode material for SOECs, mainly because of its very good ionic and electronic conductivity, high catalytic activity, low cost, and an expansion coefficient comparable to those of other cell components. Despite the high CO\({}_{2}\) conversion efficiency, however, Ni-based electrodes have shown some severe limitations due to the strict requirements of fuel compositions(to avoid Ni oxidation) and the carbon coke formation [18]. To replace Ni-based electrodes, perovskite materials such as variously doped lanthanum chromites or lanthanum ferrites and their mixtures have been recently investigated. They show good stability in carbon-rich environments and promising electro-catalytic activity for CO\({}_{2}\) conversion [19; 20]. For example, perovskite oxides such as (La\({}_{0.75}\)Sr\({}_{0.25}\))\({}_{0.95}\)Cr\({}_{0.5}\)Mn\({}_{0.5}\)O\({}_{3-\delta}\)[21], La\({}_{0.35}\)Sr\({}_{0.65}\)TiO\({}_{3-\delta}\)[22], La\({}_{0.6}\)Sr\({}_{0.4}\)VO\({}_{3-\delta}\)[23], and Sr\({}_{2}\)Fe\({}_{1.5}\)Mo\({}_{0.5}\)O\({}_{6-\delta}\)[24] can represent valid alternatives to Ni-YSZ cathodes. In particular, these perovskite oxides exhibit high mixed electronic and ionic conductivity, very good redox stability, and a very high resistance to both sulfur poisoning and coke formation. Unfortunately, such perovskite-based cathodes do not reach a CO\({}_{2}\) electrolysis performance comparable to Ni-YSZ cathodes, mainly because of their reduced electrocatalytic activity. However, recently, a novel composite cathode based on lanthanum strontium chromium manganite (LSCM)/gadolinium-doped ceria (GDC) seems to be a good alternative to Ni-YSZ cathodes [25]. It was already reported that the infiltration of GDC nanoparticles into the LSCM backbone is crucial because it increases the triple-phase boundaries (TPBs) and favors the CO\({}_{2}\) chemical adsorption [26; 27], enhancing the electrochemical CO\({}_{2}\) dissociation. Nevertheless, the agglomeration of doped-ceria nanoparticles occurring upon preparation and/or long-term runs can affect the stability of the cell. Moreover, the morphological properties of GDC-infiltrated powders may also depend on the starting solutions used for the infiltration into the LSCM backbone [28]. Generally speaking, oxide particles precipitated from aqueous solutions often show a tendency to agglomerate [29; 30] and, in the case of ceria-based systems, the use of non-aqueous solutions can give some advantages in terms of the morphology of the infiltrated powders [31].