ATOMIC-RESOLUTION STM IMAGING OF ELECTROCHEMICALLY CONTROLLED REVERSIBLE PROMOTER DOSING OF CATALYSTS

Reversible electrochemically controlled dosing (back-spillover) of sod ium on Pt(111) at atmospheric pressure was imaged via atomically resol ved STM. The Pt(111) monocrystal was interfaced with a flat polycrysta lline sample of beta ''-Al2O3, it Na+ conductor. Application of an ele ctrical current between the Pt(111) monocrystal and a counterelectrode also in contact with the beta ''-Al2O3 Na+-conducting solid electroly te causes reversible migration (back-spillover and spillover) of sodiu m, which forms a (12 x 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.