This study investigates the effects of different sealing materials, steel lining and Fiber-Reinforced Polymer (FRP), on the thermodynamic properties of hydrogen storage in lining rock caverns (LRCs). A thermodynamic coupling equation for hydrogen storage in LRCs was developed, and its validity was confirmed by comparison with simulations and data from the Huntorf power station. The leakage rate, temperature changes, and stress distribution of steel and FRP sealing layers with varying thicknesses were analyzed over a 30-day period. The results show that the leakage rate of the FRP layer decreases significantly with thickness, with a peak leakage of 1.3 g/s for the 10 mm layer, stabilizing at around 0.1 g/s for the 100 mm layer. Temperature fluctuations within the cavern are periodic, with more pronounced changes in the FRP layer as its thickness increases. Steel lining experiences minimal temperature changes. Additionally, increasing the FRP thickness results in larger fluctuations in the principal stress of both the sealing and lining layers, impacting the surrounding rock mass. The FRP lining experiences higher tensile stress, while the steel lining shows smaller changes. A thicker FRP layer also increases normal and shear stresses in the surrounding rock, potentially affecting cavern stability. These findings emphasize the importance of selecting appropriate sealing materials and thicknesses to improve the efficiency and stability of hydrogen storage systems.

Underground hydrogen storage (UHS) in geological formations offers a promising solution for large-scale energy buffering, but its long-term safety and mechanical stability remain concerns, particularly in fractured rock environments. This study develops a fully coupled thermo-mechanical model to investigate the cyclic response of a dual-cavern hydrogen storage system with polymer-based sealing layers. The model incorporates non-isothermal gas behavior, rock heterogeneity via a Weibull distribution, and fracture networks represented through stochastic geometry. Two operational scenarios, single-cavern and dual-cavern cycling, are simulated to evaluate stress evolution, displacement, and inter-cavity interaction under repeated pressurization. Results reveal that simultaneous operation of adjacent caverns amplifies tensile and compressive stress concentrations, especially in inter-cavity rock bridges (i.e., the intact rock zones separating adjacent caverns) and fracture-dense zones. Polymer sealing layers remain under compressive stress but exhibit increased residual deformation under cyclic loading. Contour analyses further show that fracture orientation and spatial distribution significantly influence stress redistribution and deformation localization. The findings highlight the importance of considering thermo-mechanical coupling and rock fracture mechanics in the design and operation of multicavity UHS systems. This modeling framework provides a robust tool for evaluating storage performance and informing safe deployment in complex geological environments.