Atomic resolution STM imaging of electrochemically controlled reversible promoter dosing of catalysts

Reversible electrochemically controlled dosing (back-spillover) of sodium on Pt(111) at atmospheric pressure was imaged via atomically resolved STM. The Pt(111) monocrystal was interfaced with a flat polycrystalline sample of β″-Al 2 O 3 , a Na + conductor. Application of an electrical current between the Pt(111) monocrystal and a counterelectrode also in contact with the β″-Al 2 O 3 Na + -conducting solid electrolyte causes reversible migration (back-spillover and spillover) of sodium, which forms a (12 × 12) hexagonal structure on the Pt(111) surface. In addition to explaining the phenomenon of electrochemical promotion in heterogeneous catalysis, these observations provide the first STM confirmation of spillover phenomena which play a key role in numerous catalytic systems.