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Keywords:

  • alloys;
  • borohydride oxidation reaction;
  • galvanic displacements;
  • hydrogen storage;
  • metal hydrides

Abstract

This work provides insights into the processes involved in the borohydride oxidation reaction (BOR) in alkaline media on metal hydride alloys formed by LaNi4.7Sn0.2Cu0.1 and LaNi4.78Al0.22 with and without deposited Pt, Pd, and Au. The results confirm the occurrence of hydrolysis of the borohydride ions when the materials are exposed to BH4 and a continuous hydriding of the alloys during BH4 oxidation measurements at low current densities. The activity for the direct BOR is low in both bare metal hydride alloys, but the rate of the BH4 hydrolysis and the hydrogen-storage capacity are higher, while the rate of H diffusion is slower for bare LaNi4.78Al0.22. The addition of Pt and Pd to both alloys results in an increase of the BH4 hydrolysis, but the H2 formed is rapidly oxidized at the Pt-modified catalysts. In the case of Au modification, a small increase in the BH4 hydrolysis is observed as compared to the bare alloys. The presence of Au and Pd also leads to a reduction of the rates of alloy hydriding/de-hydriding.