# A Comprehensive Literature Review on Hydrogen Tanks: Storage, Safety, and Structural Integrity
## 6 Summary and Research Perspective  
The general research framework of the authors is built upon three main pillars, each of which is interrelated with the others, concerning hydrogen storage, hydrogen safety, and hydrogen in energy transition [47, 48, 199]. In this context, this paper presents a literature review on hydrogen storage and safety, especially in the automotive field, but also for industrial, aerospace, and marine applications. An important result of this review investigation is highlighting the pivotal role that composite materials are expected to have in the shift toward hydrogen applications relying on thin-walled pressure vessels. The number of scientific publications in this sector has increased threefold compared to the preceding decade. Given this exponential growth in this field, the review conducted in this work was divided into two parts. The first part aimed at providing context by unifying documents, articles, and research up to 2014 through a historical literature review. The second part involved a systematic literature review from 2014 to the present to better understand the current research landscape. To achieve this, bibliometric methods were employed to systematically analyze the research field, identifying key documents, references, and authors. Finally, an in-depth analysis of the collected papers was carried out to categorize and determine the current state of hydrogen storage and safety technology development. To summarize the fundamental outcome of the present study, this review identified three critical issues about hydrogen storage and safety:  
* Designing technology of the tanks to ensure the right balance between pressures, materials, and thermal gradients. * Researching and understanding \(\mathrm{LH_{2}}\) and \(\mathrm{GH_{2}}\) properties to avoid risks such as explosions of the tank, leakage of the hydrogen, material embrittlement, and autofrettage, to improve and guarantee safety. * Managing costs to encourage the development of this technology and allow hydrogen to become the main form of energy of the future. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Storage Parameter** & **Units** & **2020** & **2025** & **Ultimate** \\ \hline System & kWh/kgsystem & 1.5 & 1.8 & 2.2 \\ Gravimetric Capacity & kgH\({}_{2}\)/kgsystem & 0.045 & 0.055 & 0.065 \\ \hline System & kWh/litersystem & 1 & 1.3 & 1.7 \\ Volumetric Capacity & kgH\({}_{2}\)/litersystem & 0.03 & 0.040 & 0.050 \\ \hline Storage & \$/kWh & 10 & 9 & 8 \\ System Cost & \$/kgH\({}_{2}\) & 333 & 300 & 266 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Main DOE Targets [203]. Some possible directions for future research are discussed below, together with an assessment of the open main problems. First, there is a need for enhanced materials that can withstand the high pressures and potential embrittlement associated with hydrogen storage [62; 161; 162]. Research into advanced composite materials and coatings could provide solutions to these challenges [135; 170]. Additionally, developing more efficient and cost-effective hydrogen storage systems remains a critical area of focus, as it directly impacts the feasibility of hydrogen as a mainstream energy source. Innovations in storage methods, such as metal hydrides and cryo-compressed hydrogen, offer promising avenues but require further exploration and optimization [24; 25; 167]. Furthermore, safety protocols and risk mitigation strategies must be continually updated and refined. This includes improving sensor technologies for leak detection and developing more robust containment systems. Collaboration between regulatory bodies and industry stakeholders is essential to establish comprehensive safety standards that keep pace with technological advancements [9; 17]. Another critical area is the infrastructure needed to support widespread hydrogen adoption. This involves the physical infrastructure, such as refueling stations and transportation networks, and the regulatory and economic frameworks that will enable the growth of a hydrogen economy.