Furthermore, microbial activities in the reservoir can lead to the conversion of H\({}_{2}\) to CH\({}_{4}\) and H\({}_{2}\)S, which depends on the availability of electron receptors and the amount of co-injected gas [35]. Hence, potential challenges during UHS in depleted gas reservoirs, such as H\({}_{2}\) leakage and H\({}_{2}\)-reservoir rock interactions, must be thoroughly investigated. The use of deep saline aquifers for geological storage of CO\({}_{2}\) is widely prevalent because of its long-term viability of preventing CO\({}_{2}\) leakage through the caprock, which is typically shale [41; 42; 43; 44]. While saline aquifers have been primarily studied for CO\({}_{2}\) storage, there is a comparative lack of comprehensive studies on these reservoirs for H\({}_{2}\) storage. [PERSON] et al. [45] reported that there are no ongoing pure H\({}_{2}\) storage projects in saline aquifers worldwide and/or mostly unexplored and untested for H\({}_{2}\) storage. Therefore, when considering such reservoirs for H\({}_{2}\) storage detailed research is required [16; 46; 47]. Despite this, various simulation, and modeling studies available in the literature on the feasibility of H\({}_{2}\) storage in deep saline aquifers provide some insight into geological, chemical,and technical issues [48; 49; 50; 51; 52]. These investigations include developing 3D geological models to understand the structure, porosity, and permeability of the saline aquifer, to predict H\({}_{2}\) behavior over time. For instance, [PERSON] et al. [53] conducted pore-scale modeling on H\({}_{2}\) storage in porous media and found that only a small fraction of H\({}_{2}\) is successfully extracted, with recovery factors ranging from 16.2% to 19.1% attributed to capillary trapping in saline porous media. Recently, [PERSON] et al. [54] conducted a study on developing a general workflow using reduced-order models (ROM) to select optimal H\({}_{2}\) storage sites in saline aquifers. Furthermore, saline aquifers require a larger percentage of cushion gas, which is required to maintain the reservoir pressure when injecting and withdrawing H\({}_{2}\) from the subsurface, compared to depleted hydrocarbon reservoirs [16; 46; 47]. Instead, combinations of gasses such as H\({}_{2}\), CO\({}_{2}\), and CH\({}_{4}\), known as town gas, have been stored in various combinations in different saline reservoirs. For instance, in Ketzin, Germany, town gas containing 62% H\({}_{2}\) was stored from 1960 until 2000, after which the site was tested for storing CO\({}_{2}\). In Beynes, France, town gas comprising 50% H\({}_{2}\) was stored from 1983 until 2007. Although the site had a storage capacity of 3.3 \(\times\) 10\({}^{8}\) m\({}^{3}\), changes in the composition of the stored gas were observed due to microbial reactions, after which the storage site was renovated until 2015 and is now used for natural gas storage. Similarly, in Lobodice, Czech Republic, town gas comprising 50% H\({}_{2}\) and 25% CH\({}_{4}\) was injected from 1965 until 1990, after which the site was repurposed for natural gas storage [45]. A decrease in the composition of town gas was observed due to the microbial reactions causing the consumption of H\({}_{2}\) and CO\({}_{2}\)[45]. Thus, while saline aquifers meet the criteria for efficient storage of gasses underground, the storage of pure H\({}_{2}\) has not yet been implemented in these formations [55]. However, they can be used to meet medium- to long-term demand of energy fluctuations. Next, salt caverns are either naturally occurring or built artificially from salt deposits, such as salt beds or salt domes. They are suitable for H\({}_{2}\) storage because of their unique properties, which include minimal microbial activity, steady geochemical interactions, mechanical stability, and large storage capacity [56; 57; 58; 59; 60]. Solution mining in salt deposits creates man-made caverns that provide cost-effectiveness, high storage capacity, and geological stability [61; 62; 63; 64; 65].