Core-Shell Confinement Blocks Hydride Formation: The Impact of Surface Oxides on Hydrogen Sorption in Nanoporous FeTi

TL;DR

This paper investigates how surface oxides affect hydrogen storage in nanoporous FeTi, revealing microstructure-dependent effects on sorption properties and hysteresis, and proposes a model to predict absorption pressures.

Contribution

It introduces a novel synthesis method for nanoporous FeTi and demonstrates how surface oxides and microstructure influence hydrogen sorption behavior.

Findings

Surface oxides confine FeTi, affecting hydrogen sorption.

Elastic stresses influence absorption pressure and hysteresis.

Microstructure control can optimize hydrogen storage properties.

Abstract

Metal hydrides remain an intriguing alternative to conventional gaseous and liquid hydrogen storage methods, offering high volumetric storage density and enhanced hydrogen storage safety at ambient conditions. In this regard, the intermetallic compound FeTi is one of the most promising storage materials. However, its widespread industrial application remains challenging due to the need for activation, slow initial kinetics, large hysteresis, and high material costs. In this study, we aim to overcome these limitations by devising an alternative synthesis pathway to prepare nanoporous and ultra-fine porous FeTi with controlled grain and ligament sizes, allowing us to study the obtained well-defined microstructures in detail. In particular, we observe the confinement of the FeTi phase by surface oxides, which can be correlated with the hydrogen sorption properties of the respective material. These experimental results are further supported by an analytical model allowing the calculation of the absorption pressure as a function of microstructure-dependent elastic stresses. Additionally, we show that such stresses also influence the absorption-desorption hysteresis. This study lays the groundwork for the controlled and systematic study of the processing-structure-properties relations in metal hydrides and FeTi in particular, thereby paving the way to cost-effective and efficient hydrogen storage solutions based on metal hydrides.