TiFe$_{0.85}$Mn$_{0.05}$ alloy produced at industrial level for a hydrogen storage plant

TL;DR

This study evaluates an industrially produced TiFe$_{0.85}$Mn$_{0.05}$ alloy for hydrogen storage, demonstrating its effective hydrogen sorption, stability over cycles, and resistance to impurities, with insights into microstructure effects.

Contribution

It presents the first industrial-scale synthesis and comprehensive characterization of TiFe$_{0.85}$Mn$_{0.05}$ alloy for hydrogen storage, including microstructural analysis and performance evaluation.

Findings

The alloy stores 1.0 wt.% H$_2$ with fast kinetics.

The alloy shows stability over 250 cycles.

Passive layer formation affects hydrogen sorption properties.

Abstract

In the use of hydrogen as large-scale energy vector, metal hydrides based on intermetallic compounds play a key role, thanks to mild temperatures and pressures required for the storage. It is increasingly necessary to develop hydrogen-based devices, and in this work, the intermetallic compound TiFe$_{0.85}$Mn$_{0.05}$ is evaluated and selected as H$_2$-carrier for a storage system of 50 kg of H$_2$. A batch of 5 kg of alloy was synthesized at industrial level and characterized through scanning electron microscopy and powder X-ray diffraction, to determine the structure and phase abundance. Moreover, the hydrogen sorption properties were investigated through thermodynamic and kinetic analyses, followed by a long-term cycling study and resistance to O$_2$ and H$_2$O poisoning. Comparing results for alloys with same nominal composition, but prepared either under industrial or laboratory conditions, it was found that the alloy synthesis promotes discrepancies in phase abundance and microstructure and promotes the formation of a passive layer that deeply affect the hydrogen sorption properties. A scheme based on Monte Carlo simulation and structural results was developed to explain the key role of the passive layer (Ti$_3$Fe$_3$O) and of the secondary phases (Ti$_4$Fe$_2$O$_{0.4}$ and $\beta$-Ti$_{80}$(Fe,Mn)$_2$0) in promoting the hydrogenation of the TiFe$_{0.85}$Mn$_{0.05}$. A storage system based on this alloy can be integrated with an electrolyser upstream (25 bar) and a fuel cell downstream (1 bar) at 55 $^\circ$C, storing 1.0 H$_2$ wt.%, displaying fast kinetic, resistance to oxygen, water and nitrogen gas impurities, and stability over more than 250 cycles.