Unusual process of water formation on RuO2(110) by hydrogen exposure at room temperature

The reduction mechanism of the RuO2(110) surface by molecular hydrogen exposure is unraveled to an unprecedented level by a combination of temperature programmed reaction, scanning tunneling microscopy, high-resolution core level shift spectroscopy, and density functional theory calculations. We demonstrate that even at room temperature hydrogen exposure to the RuO2(110) surface leads to the formation of water. In a two-step process, hydrogen saturates first the bridging oxygen atoms to form (O-br-H) species and subsequently part of these O-br-H groups move to the undercoordinated Ru atoms where they form adsorbed water. This latter process is driven by thermodynamics leaving vacancies in the bridging O rows.