**4.2 Application of ceramic-based CPCMs**

Medium-high temperature ceramic-based CPCMs could charge or discharge a large amount of heat in the form of sensible and latent heat to solve the conflict between the supply and demand of renewable energy. It could be seen that ceramicbased CPCMs have high heat storage capacity, long cycle thermal life, excellent corrosion resistance, and fast heat transfer rate at medium-high temperatures. This ensures the prospect of a wide application in TES systems, mainly including solar thermal utilization, and waste heat recovery.

Solar thermal technology is severely limited by its instability and discontinuity, so it is necessary to be coupled with a PLTES system to achieve dynamic regulation of heat [63]. Ceramic-based CPCMs have excellent thermal properties and corrosion resistance and are suitable for continuous-dynamic input of high-temperature heat flow in concentrating solar heat collection systems. Xu et al. [64] prepared porous SiC with excellent thermal toughness by biomorphic loofah as a template, and its porosity could be adjusted between 64% and 87%. Then the CPCMs are further obtained by encapsulating NaCl-NaF through the SiC skeleton, which realizes broadband solar energy capture, rapid thermal transfer, and compact latent heat energy storage. 95.25% solar absorption and 20.7 W/m∙K high thermal conductivity are the composites that can quickly realize solar-heat transfer and storage. Excellent solar absorption (95.25%) and thermal conductivity (20.7 W/(m∙K)) enable CPCMs to quickly realize solarheat transfer and storage. Zhang et al. [65] developed a novel microcapsule CPCM with Ti4O7/SiO2 as the encapsulating shell. CPCMs have a high photo-thermal storage efficiency of 85.36%, which efficiently realizes the conversion of photo-conductive heat and preserves most of the heat. Our group initially used stainless steel spheres to encapsulate ternary nitrate for system-level charging-discharging experiments [58]. A schematic diagram of the experimental platform is shown in **Figure 10b** But this approach suffers from the defects of low thermal conductivity and easy leakage.

#### **Figure 10.**

*Diagram of the experimental platform, the arrangement structure, and temperature evolution of SiC-based CPCMs [23, 58] (Reprinted with permission from Elsevier [OR APPLICABLE SOCIETY COPYRIGHT OWNER]).*

**Figure 11.**

*The schematic diagram of the industrial waste heat recovery system based PLTES.*

Therefore, we subsequently developed a simple preparation process for SiC-based CPCMs using starch as a pore-forming agent [23], which could be prepared on a large scale and operated stably for a long lifetime. The CPCMs were verified to have high heat transfer efficiency by systematic experiments.

Traditional thermal power plants and other heavy industries directly discharge a large amount of medium-high temperature waste heat during the production process, resulting in a serious waste of energy. Based on PLTES, the collection and storage of waste heat could be realized, effectively improving the efficiency of energy utilization, and reducing greenhouse gas emissions. The schematic diagram of the industrial waste heat recovery system-based PLTES is shown in **Figure 11**. Due to the continuous fluctuations, high temperatures, and high impacts of industrial waste heat emissions, ceramic-based CPCMs are a key option for the realization of waste heat recovery. Li et al. [66] developed a dynamic optimization model based on CPCMs to solve the dynamic thermal management of industrial waste heat. CPCMs were prepared by using nitrate PCM, silica carrier material, and graphite conductive addictive, and then filled in steel tubes. They developed an intelligent algorithm to study the dynamic optimization of the waste heat recovery system and built a waste heat recovery platform for steel production to verify the reliability of the shell-and-tube heat storage model.
