EVALUATION OF H2 STORAGE KINETICS BY PENTAMETALLIC HEA

Hydrogen's sustainability and renewable nature make it a promising fuel for the future. Unfortunately, its low volumetric energy density remains a significant challenge, necessitating high pressure for storage and transport.1 One potential solution is to store H2 in the solid-state in metal alloys or hydrides, which can effectively retain H2 under high T and P conditions. Recently, High Entropy Alloys (HEAs) have been proposed as potential candidates for this application. HEAs consist of five or more elements in near-equiatomic concentrations, ranging from 5 to 35 at.%. HEAs for H2 storage typically contain one hydride-forming metal and exhibit good cyclability.2 In this research work, HEA powders with a MgVAlNiCr equiatomic composition were synthesized by high energy ball milling. The formation of a solid solution with a BCC structure was assessed by XRD, while the chemical homogeneity of the powders was investigated by SEM-EDS analysis. According to literature, a BCC crystal structure is desirable for effective H2 storage, as its low packing density allow for unit cell deformation, leading to high storage capacities ~0.6–3.5 wt.%.2 A Sievert-type device was used to measure H2 sorption at different T (300, 350, and 390 ºC) and P (80 bar for sorption and 0 bar for desorption). After 25 hours at 390 ºC, the HEA's maximum H2 storage capacity was 0.73 wt.%. The powder showed good desorption behavior, releasing all the stored H2 after 24 hours. The HEA released H2 more quickly at the lowest T examined, even though the amount of stored H2 at other T did not exceed the one recorded at 390 ºC. Under such conditions, the HEA released all the stored H2 (0.36 wt.%) in less than one hour. This behavior was confirmed in another test involving sorption at 390 °C and desorption at 300 ºC.