Mechanisms of hydrogen absorption by cerium with various surface conditions

Cerium (Ce) thin films were prepared under UHV condition, and each reactivity of H 2 , O 2 or H 2 O 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 2 O [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].