Adsorption phenomena on cyanide-modified Pt(111) surfaces: experiment and theory at the electrochemical interface

MARIA ESCUDERO-ESCRIBANO; PAOLA QUAINO; GERMAN SOLDANO; WOLFGANG SCHMICKLER; ANGEL CUESTA

Niigata

Congreso; 62nd Annual Meeting of the International Society of Electrochemistry (ISE); 2011

International Society of Electrochemistry

Cyanide adsorbs spontaneously and irreversibly on Pt(111) and forms a  highly ordered layer of CNads molecules adopting a (2sqrt(3) x 2sqrt(3))R30° structure. We have used this surface to study atomic ensemble effects and noncovalent interactions, both of them playing an important role in electrocatalysis. We present here a broad, combined experimental and theoretical study, which tries to explain and understand, on the one hand, the structure of adsorbed cyanide on Pt(111) electrodes more deeply and the adsorption of hydrogen on this molecular pattern and, on the other hand, the role of noncovalent interactions in surface electrochemistry.We have carried out cyclic voltammetry, Fourier-transform infrared spectroscopy (FTIRS) and in situ STM experiments on CN-modified Pt(111) in acidic solutions. CVs show that the onset of the H adsorption is positively shifted ca. 0.20 V as compared with unmodified Pt(111) and FTIR spectra show a decrease in the vibration frequency of C-N stretching beginning at the same potential as the H adsorption onset, this behaviour being probably due to the formation of (CNads)x-H clusters. We will show DFT vibration frequency calculations of the C-N stretching of CN-modified Pt(111) which supports this hypothesis. The density of states (DOS) of the Pt atoms which are not bonded to the CNads molecules remains nearly identical to the DOS of the Pt atoms of the clean Pt(111), supporting the notion that CNads acts as an inert site blocker.