Hydrogen as an energy vector: challenges in storage and transport with special emphasis on metal-based solutions

Hydrogen has long been considered a potential cornerstone of the future energy system, especially in the context of the transition away from fossil fuels. Its appeal lies in its abundance, its clean combustion (producing only water as a by-product), and its versatility as both a fuel and a feedstock. However, the practical use of hydrogen as an energy vector is hindered by fundamental challenges related to its physical and chemical properties. Its very low atomic mass makes hydrogen an energy carrier with low volumetric density; liquefaction is energetically costly due to the extremely low boiling point, and compression requires pressures of several hundred atmospheres, raising issues of safety and efficiency. Furthermore, hydrogen transport is problematic: its tiny molecular size leads to permeation through pipes, and it can induce embrittlement and cracking in metals such as steel. Alternative strategies, such as binding hydrogen into compounds like ammonia, provide partial solutions but bring their own limitations, including energy-intensive synthesis. A promising avenue of research involves solid-state hydrogen storage using metals or alloys, notably palladium, which exhibits exceptional absorption properties. The aim of this article is to discuss these issues from a mathematical and physical perspective, highlighting the analytical and modeling challenges that arise when hydrogen is considered as a key element of the energy transition .