Anion effects and the mechanism of Cu UPD on Pt(111): X-ray and electrochemical studies

摘要: Abstract We propose a mechanism for the underpotential deposition of Cu on Pt(111) in 0.1M H 2 SO 4 presence and absence halides. The is based recent results from electrochemical situ surface EXAFS X-ray standing wave (XSW) studies UPD Pt halides with emphasis Cl − , Br I . data were obtained at potential +0.1 V corresponding to coverage approximately 0.75 ML. In chloride, consistent an incompletely discharged copper adlayer. copper—copper bond distance was found be 2.85A. chloride suggest fully layer distance, 2.59A, approached bulk value (2.56A). no oxygen present as backscatterer plane However, (from either bisulfate or water) giving rise copper—oxygen 2.16A. It appears that acts protective overlayer precluding solvent electrolyte) adsorption. Qualitatively similar iodine treated surface. addition, XSW this last system electrochemically inactive (solvated) ions vicinity but not contact platinum which we describe representing “pre-adsorbed” state. From low (10 μM) concentrations, find submonolayer amounts induces enhanced adsorption bromide reflected exceedingly sharp voltammetric peaks are transient nature. adsorbed anions believed electrodeposited copper. ascribe formation CuX adlayer electrode. These increase amplitude coverages up half monolayer subsequently decrease so upon completion they absent. Based these findings previous investigations, involves state, CuAn (An −x =anion) turn gives itself covered by anion-adlayer.