Advances in Solid–Gas Reaction-Based Thermochemical Energy Storage Systems

Thermochemical energy storage (TCES) has emerged as one of the pivotal technologies for enhancing the stability and efficiency of energy systems, owing to its advantages including high energy storage density, low heat loss and long-term energy storage capability. Among various TCES technologies, solid–gas reaction-based TCES exhibits tremendous potential in medium- and high-temperature applications. This paper first overviews the research progress of solid–gas reaction-based TCES technologies. Focusing on four major TCES material systems, namely hydroxides, carbonates, metal oxides and metal hydrides, it discusses their energy storage mechanisms, material modification strategies, and reaction kinetics, as well as approaches to improve thermal conductivity and cycling stability. Subsequently, reactor types (including fixed bed, moving bed and fluidized bed reactors) applicable to different materials and the latest research progress of diverse reaction systems are elaborated in detail, and the optimal designs of heat transfer performance for the four reaction materials in corresponding reactors are clarified. Based on the comparative analysis, the Ca(OH)2/CaO system is identified as the most promising material system for engineering deployment, owing to its moderate operating temperature, low material cost, and validated pilot-scale performance. The intrinsic complementarity between material modification strategies and reactor heat transfer enhancement is also elucidated, providing a theoretical foundation for scalable implementation.