Near-Surface Accumulation of Hydrogen and CO Blocking Effects on a Pd–Au Alloy

Abstract

Alloying Pd with Au has remarkable features of enhancement of hydrogen solubility compared to Pd and catalytic activity for reactions such as partial hydrogenation of unsaturated hydrocarbons. A key to understanding these phenomena is clarification of hydrogen behavior in the near-surface region. In the present work, by applying nuclear reaction analysis for high-resolution depth profiling of hydrogen in combination with thermal desorption spectroscopy, we show that hydrogen substantially accumulates in the near-surface region and is absorbed in the bulk of a single-crystal Pd70Au30(110) alloy. We also demonstrate a molecular cap effect of CO, where a small amount of CO adsorption greatly changes the hydrogen absorption and desorption behavior by blocking the entrance/exit channel for hydrogen. These findings lead to understanding and controlling the catalytic activity of the Pd–Au alloy and Pd-related surfaces and also open up a new method to control hydrogen transport across metal surfaces.