HYDROGEN ADSORPTION ON IRIDIUM SINGLE-CRYSTAL SURFACES

Following the previous report on hydrogen adsorption on Pt single-crystal surfaces [Surf. Sci. 220 (1989) 18], results of a similar investigation on Ir are presented. Clean and well-defined surfaces were produced as in the case of Pt. Voltammograms obtained for these Ir planes are shown together with the corresponding ones of Pt. Surface-dependent sharp peaks are observed in most cases. These are attributed to the formation of molecule-like units of HM3 or HM, M standing for Ir of Pt, via covalent bonding between the hydrogen 1s and the metal 5d orbitals. An exception is the broad plateau seen in the case of the Pt(111) plane. It is suggested that this broadening of the peak may be due to the itinerant nature of the 5dγ electrons in the densely arranged Pt(111) surface atoms. This character may disappear in the Ir(111) plane because of the lower number of 5dγ electrons in Ir than in Pt. © 1990.