## 1 Introduction  
With the development of human society, there is an increasing demand for energy. Fossil fuels, particularly coal, oil, and natural gas, remain the mainstay of the energy mix today [1]. However, the substantial quantity of carbon dioxide released by the heavy use of fossil fuels has caused significant harm to the environment, highlighting the urgent need to prioritize the advancement of power generation technologies that are both clean and efficient. Solid oxide fuel cells (SOFCs) are a very promising clean energy technology that effectively converts the chemical energy stored in fuel and oxidant gases into electricity [2; 3; 4; 5], as shown in Figure 1. They exhibit many notable merits, such as high efficiency, ecological compatibility, a broad spectrum of fuel options, and the absence of the need for precious metal catalysts [6; 7; 8; 9; 10]. Given the current increasing energy demands, the importance of developing and implementing SOFCs is of utmost significance. SOFCs are widely recognized as the optimal option for future environmentally friendly power generation. Nonetheless, as SOFCs progress towards becoming commercially viable, they face obstacles related to maintaining stability over extended periods and managing the expenses associated with manufacturing. These issues arise from the necessity of running SOFC systems at high temperatures [11; 12]. In order to address this difficulty, researchers have initiated the development of SOFCs that function at intermediate temperatures ranging from 500 to 800 \({}^{\circ}\)C [9; 13; 14; 15]. The successful operation of SOFCs at intermediate temperatures depends not only on the advancement of electrolyte materials that exhibit excellent conductivity within this temperature range [16; 17; 18; 19] but also on the utilization of thin-film electrolytes and nanostructured electrodes [20; 21; 22; 23]. To achieve densification in SOFCs, electrode supports and high-temperaturesintering exceeding 1400 \({}^{\circ}\)C are necessary for obtaining thin-film electrolytes. Nevertheless, this elevated temperature not only limits the melting point of other co-sintered materials, such as the metal supports used in SOFCs, but also hinders the achievement of electrode nanostructures. Hence, lowering the sintering temperature is advantageous for achieving thin-film electrolytes and nanostructured electrodes in SOFCs [24; 25]. In order to reduce the sintering temperature of the electrolyte, researchers have investigated field-assisted sintering and current-assisted sintering techniques, resulting in the creation of various low-temperature sintering methods [26; 27; 28]. These sintering techniques not only reduce sintering temperatures but also significantly shorten the sintering durations. Some examples of sintering techniques include microwave sintering (MWS), spark plasma sintering (SPS), flash sintering (FS), and, more recently, ultrafast high-temperature sintering (UHS) [29; 30; 31; 32; 33; 34; 35]. Figure 2 displays the process sketches of several typical field-assisted and current-assisted sintering technologies. MWS uses the dielectric loss of ceramic materials in microwave electromagnetic fields to heat the materials to the sintering temperature, resulting in the sintering and densification of ceramics [36; 37]. The SPS process predominantly employs the Joule heating effect induced by a pulsed direct current (DC), along with mechanical pressure exerted on the die. This die is heated by the Joule effect and subsequently transfers the heat to the material through conduction, swiftly raising its temperature and achieving densification [29; 30; 31; 32]. Nevertheless, these two techniques encounter challenges when it comes to implementing a diverse array of industrial applications. This is due to their specific demands for sintering equipment and material types, as well as their limitations in terms of the size of the samples that can be sintered [38]. On the other hand, FS and UHS are innovative and more user-friendly techniques for ceramic densification.