Hydrogen needs innovative storage solutions. Metal hydrides are promising, but challenges persist due to slow kinetics, inadequate thermo-chemical stability, or unfavorable pressure-temperature conditions.

A well-studied material is FeTi, which qualifies as an excellent candidate to overcome these limitations.

We intend to achieve this by prototyping a nanoporous FeTi foam. FeTi and Cu powders were blended and deformed via high-pressure torsion, whereby the latter acts as a sacrificial phase to be removed after processing. Detailed exploration of the FeTi-Cu system, including varying deformation temperature and Cu content, identified optimal conditions for obtaining a homogeneous nanocomposite.

Removing the metallic Cu transforms the nanocomposite into a foam. The structure of the foam and respective precursor nanocomposites were characterized by electron microscopy and synchrotron X-ray diffraction.

In particular, the characterization via nitrogen sorption at 77 K highlighted a foam structure with a specific surface area of up to ~50 m2/g and a well-defined mesoporous structure with an average pore size < 20 nm.

Hydrogen absorption measurements show hydrogen uptake and hydride formation without the otherwise required activation (up to 400 °C under H2) but at a drastically reduced capacity.

The absorption without activation suggests a hydrogen-permeable surface and is corroborated by electrochemical charging experiments demonstrating faster outgassing and hydride decomposition in FeTi foams with nanoscale ligaments.

Transmission electron microscopy of the foam revealed that FeTi grains were covered by a thick amorphous oxide layer originating from the selective etch process.

We propose that this oxide layer confines FeTi, limiting the hydride formation typically associated with volume expansion. This shows that hydride formation can become blocked at the nanoscale. Nevertheless, the now well-understood FeTi-Cu system, with its highly tailorable structure (ligament/grain size, pore size/fraction), constitutes a vantage point for further investigations into this potential size-effect. Optimizing the foam’s hydrogen storage properties through heat treatments presents a promising path forward.