Comparative analysis of the efficiencies of hydrogen storage systems utilising solid state H storage materials

Abstract

Evaluation of the performances of hydrogen storage systems accommodating solid H storage materials should include characteristics on their reversible hydrogen storage capacity, operating pressures and temperatures, packing densities, and heat effects of hydrogen uptake and release. We have conducted a performance evaluation of the systems accumulating 5 kg of hydrogen in a containment of cylindrical geometry filled with a solid H storage material including such hydrides and reactive hydride composites as AlH 3 , MgH 2 , "low-temperature" (inter)metallic hydrides, NaAlH 4 , Na 3 AlH 6 , LiBH 4 + MgH 2 , and MOFs. The analysis yielded gravimetric and volumetric H storage capacities, and energy efficiencies of hydrogen stores. We conclude that the weight efficiency of hydrogen stores, apart from the gravimetric H storage capacity of the material, is greatly affected by its packing density, and by the pressure-temperature conditions which determine type and dimensions of the containment. The materials with low heat effects of H exchange, operating close to the ambient conditions, should be targeted in the course of the development of new hydrogen stores as offering the best energy efficiency of their operation.

Energetic evaluation of hydrogen storage in metal hydrides

“…Figure 4 gives an overview on the respective energy shares. The total energy demand to release the hydrogen is 50 MJ/kg H2 (42 % of LHV), corresponding well to the calculations published in [19]. About 92 % of the total energy demand is heat; the remaining 8 % is electric energy to operate the compression unit.…”

“…Obviously—as also clearly stated in —the main energy demand occurs during the hydrogen release step. Therefore, the following sensitivity analysis focuses on parameters influencing the energy required during hydrogen release.…”

Progress Towards Direct Hydrogen Peroxide Fuel Cells (DHPFCs) as an Energy Storage Concept

“…Although this statistic may favour the use of compressed H 2(g) , it is not only the volume of the fuel that needs to be considered in the practical application of these systems. As mentioned above, pressurisation inevitably requires additional and specialised equipment for compressing the gas [13] and to prevent leakage and relieve pressure in case of faults. [9] In total, the gravimetric capacity of compressed H 2(g) is ,13 wt-%, [17] meaning that most of the weight of the system is taken up by the storage vessel.…”

“…There is also a certain amount of energy required to pressurise the H 2 in the first place, all of which lowers the efficiency of these types of storage systems. Other options are physiochemical storage (using materials such as a metal-organic frameworks) [10][11][12][13] or chemical storage (such as in metal hydrides) [14,15] to adsorb or chemically bind H 2 . These materials are certainly safer than pressurised or liquid storage of H 2, but usually necessitate energy losses such as heating to release H 2 from the storage material during operation [16] and may suffer from impurities that lower their performance over time.…”

Mechanical stresses originating from metal hydride composites during cyclic hydrogenation

“…In most metal hydride tank systems, free space inside the pressure vessel is reserved, so that the macroscopic volume expansion of the hydrogen absorbing powder bed or of an MHC is fully or partly possible [28]. However, this free volume, which in some cases occupies up to 70% of the volume available inside the vessel, reduces the volumetric hydrogen storage capacity of the metal hydride tank drastically.…”