## 1 Introduction  
Solid oxide fuel cells (SOFCs) are the most promising electrochemical devices for the generation of clean energy in the near future [1]. However, they actually operate at high temperatures, i.e., between 700 and 1000 \({}^{\circ}\)C [2]. These high operating temperatures can cause very serious thermal and chemical instability issues at the electrolyte-electrode and sealant-interconnect interfaces, thus limiting their application [3; 4; 5]. Therefore, numerous researchers have focused their studies on reducing the operating temperature below 600 \({}^{\circ}\)C [6; 7; 8]. Low operating temperature SOFCs could minimize the durability and reliability issues, consequently increasing their life expectancy and range of application [9]. However, at reduced operating temperatures, the kinetics of thermally activated oxygen reduction reaction (ORR) at the cathode side were found to slow down the electrochemical reactions between the cells, and thereby contribute to high interfacial polarization resistance [10]. The functional requirements of a good cathode material must include high catalytic activity towards ORR, high electronic and ionic conductivity, adequate porosity (\(\approx\)30%), and excellent thermal stability with the other cell components. Therefore, it is necessary to develop new cathode materials compatible with the other cell components and with high electrocatalytic activity towards ORR at low operating temperatures [11]. Perovskite oxide La\({}_{0.6}\)Sr\({}_{0.4}\)Co\({}_{0.2}\)Fe\({}_{0.8}\)O\({}_{3-8}\) (LSCF) is one of the most promising cathode materials due to its high conductivity and excellent electro-catalytic activity for ORR at intermediate temperatures (600-800 \({}^{\circ}\)C) [12]. Furthermore, LSCF also exhibits excellent chemical and thermal compatibility with doped ceria electrolytes such as samarium-doped ceria (SDC) and gadolinium-doped ceria (GDC) materials, which are both promising electrolyte materials at reduced operating temperatures [13; 14; 15; 16]. However, LSCF cathode possesses severe microstructural and structural degradation at temperatures above 600 \({}^{\circ}\)C under fuel cell operating conditions [17]. To prevent or control the LSCF cathode degradation, researchers have adopted different strategies, such as surface enhancement treatment and nanostructured architecture [18; 19]. Constructing the composite cathode by mixing LSCF with pure ionic conducting electrolyte material is an effective strategy for suppressing the compositional changes within the LSCF structure. However, the presence of pure ionic conducting materials, such as SDC electrolyte, could affect the electronic network at the surface of the LSCF cathode, thus causing significant decreases in the electronic conductivity of the LSCF cathode material itself [20]. This eventually increases the charge transfer resistance at the LSCF cathode during the fuel cell operation, consequently affecting the overall performance of the cell. This is because the electrochemical reactions at the LSCF cathode consists of two physicochemical processes: (1) charge transfer process associated with incorporation of O\({}^{2-}\) ion at the cathode/electrolyte interface and electronic transfer at the interconnect/cathode interface, and (2) oxygen dissociation/adsorption on the cathode surface [21]. This electrochemical process at the cathode can be enhanced by introducing oxide ion conducting or superionic conducting materials to their microstructure. Many studies proved that the presence of eutectic carbonate salts ((Li/Na/K)\({}_{2}\)CO\({}_{3}\)) in the SOFC component backbone improved the overall performance of the fuel cell below 600 \({}^{\circ}\)C [22; 23; 24; 25; 26]. These carbonate based SOFC exhibited the highest cell performance, ranging from 300 mW/cm\({}^{2}\) to 1100 mW/cm\({}^{2}\) at 400 \({}^{\circ}\)C to 600 \({}^{\circ}\)C [27]. Therefore, the addition of carbonates to LSCF cathode material could improve its structural stability due to its melting characteristics at low temperatures.