Hydrogen-assisted reduction of the Ni(1 1 0)(3 × 1)–O surface studied by metastable-induced electron spectroscopy

Hydrogen-assisted reduction reactions at oxidized Ni(1 1 0) surfaces have been studied by metastable-induced electron spectroscopy (MIES). We prepared an O/Ni(1 1 0) surface with the high oxygen-coverage (3 × 1) surface phase, “HC-(3 × 1)”. This surface has been known to show no reactions to molecular hydrogen gas at RT, which differs from other surface phases, low-coverage (3 × 1) and (2 × 1), that undergo prompt reduction reactions at RT. We exposed the HC-(3 × 1) surface to molecular hydrogen while elevating the substrate temperature. In the temperature range from 450 to 550 °C, MIES showed a decrease in the emission intensity of the O2p-induced peak in parallel with a recovery of the Ni3d-induced peak intensity. Evidence of reactions of the HC-(3 × 1) surface to the incident molecular hydrogen was obtained on the MIES spectrum only at temperatures above 500 °C, where a H1s-induced peak appeared at the same energy as the case of initial H adsorption on the clean Ni(1 1 0) surface. This result means that molecular hydrogen takes effect on the HC-(3 × 1) O/Ni(1 1 0) surface but at reduced oxygen-coverages. A surface-structure dependency of the hydrogen-assisted reduction reactions at the O/Ni(1 1 0) surface is discussed.