Schematic of the design approach for new hydrogen storage CCAs; synchrotron radiation powder X-ray diffraction (SR-PXD) measurements of the dehydrogenation process; and the hydrogen storage properties of the new CCAs.A new family of TiMgLi-based compositionally complex alloys (CCAs) have extremely low alloy densities and promise sizable hydrogen storage capacity at room temperature [Shang et al., Materials Today (2023), https://doi.org/10.1016/j.mattod.2023.06.012].
Hydrogen is a crucial part of the transition to sustainable, low-carbon energy and is particularly attractive for transportation. The practical deployment of hydrogen, however, rests on solid-state storage media. Currently, metals or alloys are used for hydrogen storage because they are easy to synthesize for large-scale application.
“Despite the benefits of conventional metal hydrides for storing hydrogen, a good balance between energy density and thermodynamic stability is still difficult to achieve,” says Claudio Pistidda of the Institute of Hydrogen Technology at Helmholtz-Zentrum hereon GmbH.
So, together with colleagues at the Institute of Materials Mechanics, Hunan University, University of Sassari, DESY, University of Science and Technology Beijing, and Helmut Schmidt University, Pistidda has designed a series of low-density, ultra-lightweight CCAs with high hydrogen storage capacity at room temperature. CCAs are a new family of alloys that contain several major elements in approximately equimolar amounts. The researchers chose Ti, Mg, and Li as lightweight materials with high affinities for hydrogen, along with V for its fast hydrogen kinetics and ability to absorb hydrogen under moderate conditions, and Fe for its rapid dehydrogenation kinetics and abundance.
“Through computer simulations and experiments, we explored different compositions and created several ultra-light alloys with some of the highest hydrogen storage capacities ever reported,” explains Pistidda. “Tuning the alloy composition allows for tailoring of the material’s storage properties.”
The team used ball milling to prepare alloys of TiVFeMgLi, TiVFeMg, and TiVMgLi, which demonstrate hydrogen storage capacities of up to 2.62 wt% at 50°C and 100 bar. Following the approach of multi-principal-lightweight element alloying produces materials with record-low alloy densities as well.
Analysis of the new CCAs using powder X-ray diffraction measurements from in-situ synchrotron radiation and kinetic modelling reveals that the alloys’ numerous phases make it easier to achieve large hydrogen storage capacities compared with single-phase materials.
“We have developed TiMgLi-based CCAs that can store over 30% more hydrogen at room temperature than some of the most commonly utilized materials for hydrogen storage,” says Pistidda, “[and they are] barely 1g/cm3 heavier than pure Mg – the lightest utility material in the world.”
The team believe the alloys could be the building blocks of future hydrogen storage facilities and have the potential for large-scale manufacturing.