As demonstrated in this paper, magnetic and electronic measurements can be used to quantify hydrogen availability, absorption, and desorption in materials for nickel metal-hydride batteries and hydrogen storage. The ability of a metal alloy to absorb and desorb hydrogen depends on the interaction of the metal's electronic d- and f-bands with electrons donated or accepted by the hydrogen. The tendency of alloys to dissolve hydrogen and form hydrides depends on their performance as electron acceptors. Absorbed hydrogen may exist in either soluble (protonic) or bound phases. Magnetization and thermoelectric (Seebeck) coefficient were measured as functions of hydrogen content in powdered AB5- and AB2-type alloys. Magnetization decreases with increasing soluble hydrogen in ferromagnetic AB5-type (La-Ce)(Ni-Mn)5 and (La-Nd)(Ni-Co-Mn)5. However, magnetization increases with increasing soluble hydrogen in AB2-type (Zr-Ti)(Cr-Fe)2. Finally, magnetization does not change with increasing bound hydrogen in AB2-type (Zr-Ti)(Ni-Mn-V-Cr)2. The Seebeck coefficient for AB5-type (La-Nd)(Ni-Co-Mn)5 is a monotonically decreasing function of hydrogen content. However, the effect of absorbed hydrogen on the Seebeck coefficient of the AB2 alloys depends on whether the hydrogen is soluble or bound.
Citation: Journal of Alloys and Compounds
Pub Type: Journals
electronic structure, hydrogen absorption, magnetic measurements, magnetization, metal hydrides, Seebeck effect, thermopower