EVIDENCE FOR THE FORMATION OF SURFACE CARBONATES ON SOME HYDROGEN STORAGE INTERMETALLIC COMPOUNDS - AN XPS STUDY

X-Ray photoelectron spectroscopic (XPS) studies of air exposed samples of LaNi5, CaNi5, Mg2Ni, Mg2Cu and FeTi indicate that the interaction of atmospheric carbon dioxide results in the formation of surface carbonates in addition to the usual oxides and hydroxides. The reaction of carbon dioxide, in fact, is favoured by the oxidized surface which in turn produces the carbonate species on the top few layers, hitherto not reported. In particular, the carbonates seem to be predominant in the case of CaNi5. The adsorption of carbon dioxide also gives an idea of the segregated elements of the different systems. Even though such carbonate species on the alloy surfaces seem to be expected rather than surprising, there is no evidence available in the literature. To our knowledge, this forms the first report on such a problem. The results also provide valuable information concerning the understanding of various surface reactions and the nature of activation processes which often differ between materials involved in hydrogen uptake. © 1990.