Thomas F. Vogt

The correlation between composition and electrochemical properties of metal hydride electrodes

This paper is concerned with an overview of the properties of metal hydride electrodes used for battery applications. The emphasis is on the properties of AB5 electrodes but others are treated as well. The review begins with a brief discussion of the pertinent chemistry of hydrogen in metals, the properties of intermetallic hydrides and their relation to electrochemical behavior. Systematic guidelines which permit the modification of such properties for electrochemical applications are discussed. The electrochemical behaviors of certain specific AB5 alloy electrodes are covered in detail, emphasizing the effects of composition changes with respect to both the A and the B components. The consequences of electrode expansion and contraction with respect to hydride formation and decomposition are discussed quantitatively. Novel alloy compositions and phases are noted and evaluated. The attractive properties of cobalt-free, non-stoichiometric AB5+x electrodes are noted.

Degradation behavior of LaNi5−xSnxHz (x=0.20–0.25) at elevated temperatures

Abstract Systematic studies of the hydriding behavior of LaNi 5− x Sn x alloys with tin contents in the range 0.20 x P – C – T ) isotherms measured after heating the hydrides above 450 K. Some loss in reversible capacity was observed along with reductions in the plateau pressures and hysteresis ratios while the slopes of the plateaus became greater. These changes are indications of degradation processes and increased disorder within the alloy structure. Additional experiments were performed for long periods (i.e. >1000 h) at elevated temperatures and hydrogen pressure to produce further degradation in the P – C – T isotherms. The impact of alloy composition on the isotherms has been determined. The crystal lattice properties of the alloys before and after hydrogen reactions have been studied using high-resolution X-ray powder diffraction with synchrotron radiation. Changes in these X-ray diffraction patterns are correlated to various structural modifications resulting from hydride formation and degradation.

The magnetic structure of TbNiAlD1.1

Abstract The magnetic structure of orthorhombic TbNiAlD 1.1 was determined by powder neutron diffraction at 3.8 and 10 K, below the antiferromagnetic ordering temperature T N =11 K. The unit cell is doubled in b and c directions compared to the nuclear unit cell (space group Amm 2; at 3.8 K a =3.6554; b =12.3954; c =7.6316 A), and the magnetic moments are confined to the bc plane with main component along c . The magnetic structure is different from TbNiAl and TbNiAlD 0.3 which both have ordered magnetic moments along the corresponding a axis. The magnetic moments of Tb1 and Tb2 at 3.8 K are 6.8 and 5.7 μ B , respectively. On heating to 10 K, the type of magnetic structure is not changed, however, μ (Tb) are decreased to 2.9 μ B (Tb1) and 5.4 μ B (Tb2).