# A Comprehensive Literature Review on Hydrogen Tanks: Storage, Safety, and Structural Integrity
## 1 Introduction
### Problem Statement and Formulation of the Research Questions  
Throughout history, lots of studies have focused on hydrogen safety and storage. [PERSON] et al. [8] gave an overview of the potential hazards of hydrogen use in storage systems for different applications: vehicles, trains, aircraft, ships, and stationary applications. The most relevant dangers of using hydrogen are the possibility of explosion, its invisible flames, instantaneous ignition, embrittlement, and its high permeation rate. It has to do with how hydrogen behaves differently from hydrocarbons: it can burn and explode at a broad range, requires little energy to ignite and explode, produces a non-luminous flame, and is highly diffusive and buoyant, which causes flammable clouds to spread quickly. In more detail, [PERSON] et al. [9] investigated the importance of using sensors to ensure the safe usage of hydrogen and prevent leaks. [PERSON] et al. [10] and [PERSON] et al. [11] analyzed the problem of explosions that can occur in non-well-ventilated areas. [PERSON] et al. [12] and [PERSON] et al. [13] focused on embrittlement due to the hydrogen-aluminum alloy liner contact. Other significant problems such as ignition ([PERSON] et al. [14], [PERSON] et al. [15], [PERSON] et al. [16]), hydrogen leakage and diffusion ([PERSON] et al. [17], [PERSON] et al. [18], [PERSON] et al. [19], [PERSON] et al. [20]) have been conducted to deeply understand how hydrogen can be the energy of the future. In this context, it is easy to recognize that hydrogen storage can be a critical technology for successfully commercializing hydrogen-based energy applications. Hydrogen can be stored in various ways, depending on application fields and several other factors [5; 21]. For the automotive field, there are two primary ways in which hydrogen can be utilized to produce mechanical energy in a vehicle: Hydrogen Internal Combustion Engine Vehicles (HICEVs) use hydrogen as fuel in a traditional internal combustion engine, while Fuel Cell Electric Vehicles (FCEVs) generate electricity through fuel cells where hydrogen reacts with oxygen, producing water vapor as the only emission [22]. A significant challenge for FCEVs is hydrogen storage due to hydrogen's low density. One method involves Liquid Hydrogen (LH\({}_{2}\)) storage, where hydrogen is liquefied at temperatures below 20 K, significantly increasing its density. This method offers high volumetric capacity and lower system costs, but requires high energy for liquefaction and suffers from fuel losses due to boil-off [23; 24]. Another method is Gaseous Hydrogen (GH\({}_{2}\)) storage, which compresses hydrogen at high pressures (generally 350 bar or 700 bar). This mature technology has low energy consumption, but lower volumetric capacity and higher specific costs, with significant safety concerns due to high pressure [25]. A third method is cryo-compressed hydrogen storage, which combines high pressure and low temperature to enhance density and reduce boil-off [26; 27]. While this approach offers high storage capacities and refueling flexibility, it involves high costs and energy consumption [24; 25; 28]. Using composite materials is fundamental for reducing weight and improving efficiency [29; 30], especially in aerospace applications [31; 32; 33]. Hydrogen storage technology, particularly in the automotive sector, has made significant advancements over recent years, but several critical challenges remain before widespread commercial adoption can be realized [34]. Current high-pressure hydrogen tanks are relatively mature in design, and have been successfully integrated into fuel cell \begin{table}
\begin{tabular}{c c c} \hline \hline
**Fuel** & **HHV [M/kg]** & **LHV [M/kg]** \\ \hline Hydrogen & 141.7 & 120.0 \\ \hline Methane & 55.5 & 50.0 \\ \hline Butane & 49.1 & 45.3 \\ \hline Gasoline & 46.4 & 43.4 \\ \hline Diesel & 45.6 & 42.6 \\ \hline Methanol & 23.0 & 19.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Higher Heating Values (HHV) and Lower Heating Values (LHV) for the most common fuels [7].