Surface properties of V 40(TiCr) 51Fe 8Mn alloy during hydrogenation/dehydrogenation cycles

The bcc alloy V40(TiCr)51Fe8Mn shows a high reversible hydrogen capacity of 2.22 mass% at room temperature and is therefore expected to be applied as a hydrogen storage material. During the first 10 hydrogenation/dehydrogenation cycles, the capacity decreases markedly from 2.22 to 1.86 mass%. Possible reasons are both internal (including lattice variation, strain, phase transformation, phase disproportion, etc.) and external factors (poisoning by impurities in the gas after decades of cycles mainly). In this work, the surface properties of the V40(TiCr) 51Fe8Mn alloy during 20 hydrogenation/dehydrogenation cycles were investigated by XPS analysis. During hydrogenation/dehydrogenation cycles, the surface becomes oxidized. Particular oxides were known to block hydrogen uptake and might thus be responsible for the capacity decay. It was found that Cr is enriched at the surface. Dense and passive chromia forms thereafter around alloy particles and hinder further oxidation and therefore stops further degradation of the hydrogen capacity of the alloy. © 2013 Elsevier B.V. All rights reserved.