| Popis: |
The structure, composition, thermal stability, and electrochemical reactivity of the chemisorbed layer formed when a clean and ordered Pd(111) electrode is exposed to a dilute solution of Na 2 S buffered at pH 10 have been studied. Under these adsorption conditions, the predominant solution species is the bisulfide ion, HS (aq) − . Experimental measurements were based upon low-energy electron diffraction, Auger electron spectroscopy, and thermal desorption mass spectrometry in conjunction with classical electrochemical methods. The bisulfide ion is oxidatively chemisorbed onto Pd(111) as zerovalent sulfur which forms a highly ordered structure upon slight heating, Pd(111) and coverage Γ = 1.07 ± 0.06 nmol cm 2 . This particular adiattice is thermally stable up to 1100 K, the highest temperature investigated, or up to 900 K in the presence of 10 −6 Torr of O 2(g) . On the other hand, it is easily oxidized electrochemically to aqueous SO 4 2− ions. Application of negative potentials has no effect either on the structure or the composition of this chemisorbed layer. However, if copious amounts of electrogenerated H 2(g) are present at the applied negative potentials, all the sulfur is hydrogenatively desorbed from the surface, most likely back to HS − (ag) species. |
