FULL PAPER In situ X-ray Diffraction Investigation of Hydrogen Storage Alloys During Charge and Discharge

Metal hydride electrodes have shown to be useful both in secondary batteries, e.g. the Ni/metal hydride system, and more recently in fuel cells, especially for direct borohydride fuel cells. This work provides in situ X-ray diffraction (XRD) results aiming at characterizing the phase transitions of the LaNi4.7Sn0.2Cu0.1 metal hydride alloy with and without Pt in the particle surface when charged electrochemically and chemically by exposition to a borohydride solution. Results have shown that the method of alloy charging leads to different phase predominance and different site occupancies, but both methods lead to almost the same discharge capacity. In the electrolysis process, γ-β phase transitions are predominant during the charge/discharge, while in the chemical charging by exposure to a borohydride solution the α-γ phase transition is more important, indicating occurrence of smaller localized stress in the alloy, with benefit on the material lifetime. Essentially the same phenomena were observed for the alloy with Pt, either with respect to the alloy structure and the electrochemical characteristics.