Abstract
For the case where oxygen is present as an impurity in hydrogen, a hydriding mechanism is proposed along with hydriding cycling of the Mg2Ni alloy. The large chemical affinity of magnesium for oxygen leads to the selective oxidation of magnesium and to the segregation of the more noble nickel component. The consequence is a progressive decrease in hydrogen storage capacity of Mg2Ni along with hydriding cycling. The segregated nickel provides active sites for chemisorption of oxygen and hydrogen. The chemisorbed oxygen accelerates the surface segregation of nickel or can form water vapour with hydrogen, or (least favourably) directly oxidizes nickel. The chemisorbed hydrogen can form water vapour with oxygen, can hydride Mg2Ni or can reduce the nickel oxide eventually formed. All these reactions are exothermic, causing an increase in temperature during the hydriding process.
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Song, M.Y., Pezat, M., Darriet, B. et al. Hydriding mechanism of Mg2Ni in the presence of oxygen impurity in hydrogen. J Mater Sci 20, 2958–2964 (1985). https://doi.org/10.1007/BF00553060
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DOI: https://doi.org/10.1007/BF00553060