_applied_  
_sciences_  
_Article_  
Hydrogen Permeability of Epoxy Composites as Liners in Linced Rock Caverns--Experimental Study  
**[PERSON] \({}^{\star}\) and [PERSON] \({}^{\copyright}\)**  
Faculty of Mining, Safety Engineering and Industrial Automation, Silesian University of Technology,  
Akademicka 2, 44-100 Gliwice, Poland; [EMAIL_ADDRESS]  
\({}^{\star}\) Correspondence: [EMAIL_ADDRESS]; Tel. : +48-880-205-614  
**Featured Application: Materials investigated in this paper can serve as a substitute of stainless-steel liners in underground gas/hydrogen storage. **  
**Abstract: Energy production from renewable energy sources is not stable and any fluctuations in energy productions need to be eliminated with underground energy storage. Demand of underground gas storage will be increasing, due to the switching to green energy, while the availability of underground storage sites, especially salt caverns suitable for hydrogen storage, is limited. The purpose of this paper is to compare the hydrogen permeability of different materials and select a proper liner material for hydrogen storage in Liner Rock Caverns or post mine workings. A variety of materials, like concrete, polymer concrete, epoxy resin, salt rock, and mudstone, were tested for gas permeability/hydrogen diffusion, using the combined Steady-State Flow/Carrier Gas methods. Results are shown in different units, providing the opportunity to compare the results with literature data. The permeability value of investigated epoxy resin is comparable to the salt rock (after creep process), which makes the epoxy resin a promising sealing liner for hydrogen and potential substitution of stainless-steel in Linced Rock Cavern (LRC) gas storage. **  
**Keywords: hydrogen storage; sealing liners; Liner Rock Caverns; epoxy resin; hydrogen permeability**  
**1. Introduction**  
Large scale energy storage is essential to increase the share of renewable energy in energy production. Power-to-X, and among them Power-to-gas technologies, could solve some of the problems related to the fluctuations in energy production from renewables, which is the main obstacle in their future implementation [1, 2]. In Power-to-gas technologies, excess renewable energy is converted into hydrogen gas through PEM electrolysis or methane through methanation. This technology is already well developed and in connection with CCU technologies and can contribute to the reduction of CO\({}_{2}\) emissions [3, 4, 5]. Hydrogen can be injected into natural gas grids and existing infrastructure can be used for such purposes [6, 7]. Nevertheless, hydrogen storage is much more challenging than storing natural gas. High mobility and lightness, as well as reactivity in the presence of microorganisms cause nontrivial hydrodynamic effects and cause safety concerns [6, 8]. Large scale hydrogen storage was already proven in salt caverns. A vast amount of research and modelling of salt cavern behavior was made, including the salt rock permeability, sealing properties, and general geomechanics of the cavern. Salt rock remains impermeable for gas in the zones, where the rock properties are not affected by the extraction process. Micro fracturing processes during the salt rock formation are also responsible for the presence of damage zones in salt rock, where the gas impermeability may be limited [9]. An alternative to store hydrogen in salt caverns is Linced Rock Caverns (LRC) technology which was successfully proven in natural gas storage. This technology uses underground hard rocks to store natural gas. The reservoir is fully isolated from the outer environment. Hard rock is only a mechanical base, where the cavern is drilled. Base rock does not need to have any isolating properties (like salt rock). Then, the shotcrete reinforcement, followed by the necessary installations, like drainage, are made. Final layer is the sealing lining. In order to ensure isolation and erosion, proven properties of sealing material are essential.