Core-shell confinement blocks hydride formation: The impact of surface oxides on hydrogen sorption in nanoporous FeTi

Metal hydrides remain an intriguing alternative to gaseous and liquid hydrogen storage methods, offering high volumetric storage density and enhanced safety for hydrogen storage at ambient conditions. In this regard, TiFe is one of the most promising storage materials. However, its widespread application remains challenging due to the need for activation, slow initial kinetics, large hysteresis, and high material costs. Overcoming these limitations requires an in-depth knowledge of the impact of structure and morphology on the sorption properties of TiFe. In this study, we devise a synthesis pathway to prepare nanoporous and ultrafine porous TiFe with controlled grain and ligament sizes, thereby allowing us to correlate these microstructures with their respective sorption properties. We observe that the oxide layers drastically affect sorption properties, particularly in nanoporous TiFe. The detailed analysis of possible mechanisms indicates that a confinement effect becomes relevant, suppressing hydride formation in nanoscale TiFe. These results are supported by an analytical model that allows the calculation of the absorption pressure as a function of microstructure-dependent elastic stresses. This study lays the groundwork for the systematic study of the processing-structure-properties relations in metal hydrides and TiFe in particular, thereby paving the way to cost-effective and efficient hydrogen storage solutions.