Molecular chemisorption at well-defined Pd(111) electrode surfaces: hydroquinone sulfonate studied by UHV-EC-STM

The chemisorption of 2,5-dihydroxybenzenesulfonate (hydroquinone sulfonate, HQS) from dilute aqueous solutions, onto a well-defined Pd(111) electrode surface has been studied by a combination of Auger electron spectroscopy, h igh-resolution electron energy loss spectroscopy, scanning tunneling micros copy and electrochemistry. The results indicate that HQS is oxidatively che misorbed and exists on the surface as benzoquinone sulfonate (BQS); it is o riented essentially parallel to the surface with a slight tilt due to the b ulky SO3- group. The H+ counter-ions in the ionic adlayer can be exchanged reversibly and quantitatively by K+ or Cs+ ions without changes in the stru cture and coverage of the surface-anchored species. (C) 2001 Elsevier Scien ce B.V. All rights reserved.