Synergistic salt hydrates and advanced porous matrix composites for high-performance thermochemical heat storage: A review

Thermochemical heat storage (TCHS) is a technology that stores thermal energy through reversible chemical reactions, providing high energy density and long-term storage with minimal losses. This review highlights recent advancements in the use of salt hydrates and porous matrix composites as sorbents in TCHS systems, with a focus on their synergistic effects. It begins with an overview of heat storage systems and adsorption concepts. This discussion then addresses key challenges related to salt-hydrated and composite adsorbent materials. In practical applications, salt hydrates for thermochemical heat storage face issues such as deliquescence, agglomeration, poor kinetics, and low thermal conductivity. Consequently, this review systematically categorizes hygroscopic salts embedded in porous host matrices, including zeolite-based materials, silica gel, carbon-based composites, minerals, metal–organic frameworks (MOFs), and mixed-salt composites. These findings highlight that high-conductivity carbon-based materials are utilized to enhance heat transfer, and that MOFs and zeolite 13X can improve sorption performance. Composite materials are analyzed to prevent agglomeration, enhance cyclic efficiency, and increase energy density. Additionally, binary salts confined within porous matrices exhibit notable synergistic effects on overall performance. Finally, the review discusses current limitations and suggests future research directions for developing suitable material–adsorbate pairs.