Mechanisms of hydrogen absorption by cerium with various surface conditions

摘要

Cerium (Ce) thin films were prepared under UHV condition, and each reactivity of H_2, O_2 or H_2O with the Ce surface was quantitatively measured at 298 K and pressures ranging from 10~(-8) to 10~(-2) Pa for the reaction probability r and the gas amount reacted N. A Ce film with a clean surface exhibited the highest reactivity, r = 1, for H_2, O_2 and H_2O [J Alloys Compounds, 2002;330-332:498; J Alloys Compounds, 2003;356-357:368]. The CeH_(2+x) hydride exhibited a higher O_2 reactivity than the clean Ce surface, suggesting a high metallic feature of the Ce hydride [J Alloys Compounds, 2002;330-332:498]. The hydroxidized Ce surface exhibited strongly reduced H_2 reactivities in comparison with the oxidized Ce surface [J Alloys Compounds, 2002;330-332;498]. The oxidized Ce surface exhibited a higher H_2 reactivity than that of La, indicating a stronger metallic feature of Ce oxides than La oxides [J Alloys Compounds, 1999;293-295:403].