Alkanethiols Adsorbed on Platinum, Palladium and Bimetallic Pd/Au Surfaces

M. FONTICELLI; G. CORTHEY; A. FLORIDIA ADDATO; A.A. RUBERT; G. BENITEZ; R. C. SALVAREZZA

Praga

Congreso; 63rd Annual Meeting of the International Society of Electrochemistry; 2012

International Society of Electrochemistry

Self-assembled monolayers (SAMs) of thiolates on metal surfaces have attracted considerable attention due to their importance on fundamental research and also as far as technological applications are concerned. In contrast to the vast literature of thiolate SAMs on the coinage metals, the information regarding SAMs on platinum group metals is relatively scarce. The study of thiol self-assembly on these metals is difficult since different reaction pathways, involving molecule decomposition and S adsorption, could take place along with SAM formation. In this work, the stability and composition of thiols adsorbed on bulk Pt, Pd and bimetallic Pd/Au, as well as nanoparticles, were studied by electrochemical techniques and X-ray photoelectron spectroscopy (XPS). Alkanethiols on Pd surfaces lead to a complex system composed of thiolates onto a palladium sulfide interface [1], which is possibly responsible for its high stability [2]. On the other hand, the quality of the adlayers grown on Pt is chain length dependent. Butanethiol and hexanethiol SAMs exhibit low thiolate coverage and poor barrier properties, suggesting that thiolates could coexist with adsorbed sulfides and broken hydrocarbon chains. On the contrary, dodecanethiol SAMs exhibit higher thiolate coverage and good barrier properties, similar to those found for the dense phases of thiolates on Au [3]. Finally, the structure and electrochemical behavior of the SAMs grown on Pd deposited in the underpotential regime on Au exhibited very distinctive properties. When thiols adsorb onto about one Pd monolayer the complex thiolate-sulfide adlayer is formed, which stabilizes the thiolates against desorption. As it was shown for Ag-modified Au surfaces [4], the control of the metal adatom coverage permits the tailoring of SAMs’ properties. These results show that SAMs on platinum group metals and bimetallic surfaces have intriguing properties and should be considered from a new perspective. As the pure metals induced the C-S bond scission during adsorption, leading to different surface structures, puzzling experimental and theoretical results were necessary to approach these systems. In this work, a complementary electrochemical and XPS study allowed to gain insights into the structure and phenomena that is involved in SAMs formation and their properties. [1] Love, J. et al. J. Am. Chem Soc. 125 (2003) 2597. [2] Corthey, G. et al J. Phys. Chem. C. 113 (2009) 6735. [3] Floridia Addato, M. A. et al J. Phys. Chem. C, 115 (2011) 17788 [4] Fonticelli, M. et al J. Phys. Chem. C. 112 (2008) 4557.