**2. Experimental procedure**

In the ultrasonic spray pyrolysis process, a precursor solution with a dissolved salt of a desired composition is generated into fine droplets using an ultrasonic generator, and the generated droplets are dried using a carrier gas in an oxidizing, inert, or reducing atmosphere through a high-temperature heating furnace. It undergoes a pyrolysis process and synthesizes particles of the desired composition through process controls, such as the type of salt used in this process, concentration of the solution, presence or absence of additives, type and speed of the carrier gas, temperature, length, and tube width of the heating furnace. Ag composite powder has the characteristic of being synthesized as a metal powder even if it passes through a high temperature of 900°C or higher using air, and transition-metal-based materials

such as Cu can be synthesized at a temperature of 900°C or higher under a reducing atmosphere. All particles of the core-shell structure used in this chapter were synthesized in one-step through the same process of synthesizing electrode powder of a single composition by including all desired compositions in the solution. The particles maintained spherical shape, because the synthesis was performed without a separate post-processing for composite powder synthesis. The particle morphology was observed through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and crystal structure analysis was performed with X-ray diffraction (XRD). In addition, by analyzing energy-dispersive spectroscopy (EDS) mapping through scanning transmission electron (STEM), the composition of the surface and the inside was observed. The powder thus synthesized was prepared into paste, screen-printed, and then heat-treated at a uniform temperature to form an electrode layer. The specific resistivities of these heat-treated electrodes were measured and compared through the four-point probe method.
