The authors review available experimental information on the existence, thermodynamic stability and physical properties of hydrides formed by the absorption of hydrogen gas in intermetallic compounds of two transition metals. The emphasis is on stability. It is shown that empirical models for the stability of ternary hydrides can be reconciled with ideas based on the results of band structure calculations of (binary) metallic hydrides. It is concluded that metallic hydrides can be looked upon as alloys of metallic hydrogen. In addition to the thermodynamic properties of ternary metallic hydrides the authors discuss experimental information on electronic properties (magnetic, super-conductivity, band structure features) and on crystallographic and metallurgical properties (neutron scattering, nuclear and electron spin resonance, Mossbauer spectroscopy, diffusion). Applications are briefly reviewed.

https://iopscience.iop.org/article/10.1088/0034-4885/45/9/001/pdf

Hydrides formed from intermetallic compounds of two transition metals: a special class of ternary alloys

Metal hydrides, as energy storage media, are receiving considerable attention. The amount of literature concerning the properties of these materials has increased markedly over the past few years. In this paper, we conduct a review of the alloy groups which absorb large quantities of hydrogen. These alloy classes are designated as AB5, AB, AB2, AB3 and A2B7 and Mg-based compounds. These materials are discussed with emphasis placed on thermodynamic and kinetic properties, activation and deactivation, poisoning effects and storage capacity.

Storing energy in metal hydrides: a review of the physical metallurgy

FeTi is an interesting hydrogen storage material which has to be activated at ≈670 K for the absorption of hydrogen. We review critically the great number of previously published results and models on this activation process and emphasize the controversial points. To eliminate the controversy we analysed the variation of the surface composition of FeTi upon activation in the high-pressure cell of a photoelectron spectrometer. The initially passivating surface oxide is shown to be converted into a mixture of TiO2 and Fe by surface segregation and chemical reduction. No evidence for the formation of Fe2Ti4O
 x
 , FeTiO
 x
 , and TiH
 x
 is found. H2/D2 exchange reactions show that H2 dissociates rapidly on Fe and FeTi, but not on TiO2. The surface of FeTi is activated easily at 670 K. Difficulties encountered with the initial hydrogen absorption by virgin high purity FeTi are probably related to bulk (H diffusion, fracture toughness) rather than surface properties.

The activation of FeTi for hydrogen absorption

The physics, chemistry, and possible applications of the storage of hydrogen in intermetallic reservoirs are discussed. Storage in the form of intermetallic hydrides can be safe and, where hydrogen has some special value as a fuel, economical. New pumps and refrigerators based on the heat of sorption of the hydrogen into the intermetallic are approaching commercial viability.

https://science.sciencemag.org/content/sci/214/4525/1081.full.pdf

Hydrogen storage materials: properties and possibilities

The activation of FeTi for hydrogen storage: A different view

By means of Conversion Electron Mossbauer Spectroscopy (CEMS) Fe clusters have been found on the surface of activated TiFe specimens. The magnetic moments of the Fe precipitates order ferromagnetically with a field of 328 KOe and are aligned parallel to the surface. The Fe precipitates are produced by the thermal treatment under hydrogen atmosphere and can be regarded as catalysts for the dissociation of the H2 molecules.

U. Gonster

Papers

Mössbauer surface studies on Tife hydrogen storage material