Interaction of H2O with the RuO2(1 1 0) surface studied by HREELS and TDS

The adsorption of water on a RuO₂(1 1 0) surface was studied by using high-resolution electron energy loss spectroscopy (HREELS) and thermal desorption spectroscopy (TDS). The first thermal desorption peak observed between 350 and 425 K is attributed to molecular water adsorbed on fivefold coordinated Ru_cus sites. Higher coverages of water give rise to TDS peaks between 190 and 160 K, which we attribute to water in the second layer bound to bridge oxygen, and multilayers, respectively. HREELS shows that H₂O chemisorbs on Ru_cus sites through oxygen inducing a slight red shift of the vibrational frequency of O_bridge atoms. Molecular adsorption is also confirmed by the presence of both the scissor and the libration modes showing the expected isotopic shift for D₂O. The water adsorbed on the Ru_cus sites also forms hydrogen bonds with the bridge oxygen indicated by the broad intensity at the lower frequency side of the O-H stretch mode. HREELS and TDS results suggest that on the perfect RuO₂(1 1 0) surface water dissociation is almost negligible.