Chemisorption and anodic oxidation of aromatic molecules on Pd electrode surfaces: studies by UHV-EC-STM
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The chemisorption and anodic oxidation of hydroquinone (H2Q) and benzoquinone (BQ) at palladium electrode surfaces was studied by a combination of electrochemistry (EC), Auger electron spectroscopy (AES), high-resolution electron- energy loss spectroscopy (HREELS) and electrochemical-scanning tunneling microscopy (EC-STM) on a smooth polycrystalline and well-defined (single-crystalline) Pd(100) electrode surface. The results point to the following more critical conclusions: (i) Chemisorption of H2Q from dilute (less than or equal to 0.1 mM) aqueous solutions forms surface- coordinated BQ oriented parallel albeit with a slight tilt. (ii) At high concentrations (greater than or equal to 1mM), chemisorption yields an edge-vertical oriented diphenolic species. (iii) The extent of anodic oxidation of the chemisorbed organic strongly depends upon its initial orientation; only the flat-adsorbed species are oxidized completely to carbon dioxide. (iv) The rate of anodic oxidation is likewise dependent upon the initial adsorbate orientation; the rate for vertically-oriented species is more than twice that of flat- adsorbed species. (v) The chemisorbed species are not oxidized (to the same extent) simultaneously; instead, oxidation occurs one molecule at a time. That is, molecules that survive the anodic oxidation and remain on the surface retain their original identities.
Pd single crystals
Chen, Xiaole (2004). Chemisorption and anodic oxidation of aromatic molecules on Pd electrode surfaces: studies by UHV-EC-STM. Doctoral dissertation, Texas A&M University. Texas A&M University. Available electronically from