CN on Pt and Au Electrodes

Daum and coworkers used SPG to study the adsorption and stmcture of GN on Pt(lll) and Pt(110) electrodes [69, 84, 85]. The spectra, shown in Pigs. 5.13 and 5.14, indicate the presence of two adsorption sites for GN. A low frequency peak at 2080cm is assigned to a CN stretch for CN adsorbed on well-ordered Pt sites. This peak exhibits a potential-dependent shift of nearly 30 cm  

The peak at 2145 cm is nearly potential independent and assigned to a CN at disordered Pt sites, which develop after a flame-annealed sample is subjected to oxidation-reduction cycles (see Fig. 5.15) [86]. 

Later SFG [90] and STM [91] experiments attributed the two peaks in the spectrum to CN at different surface sites. FTIR experiments on Pt(lll) and 

Pt(lOO) also indicate that only top-site CN is present but that CN is decomposed to NO and CO2 at high potential on Pt(lOO) [92]. Combined STM and FTIR studies by Weaver et al. indicate that CN binds at an atop site and forms an ordered (2v x2V )R30° stracture that changes to a 2x2 lattice above 0 V vs SCE [91]. 

Tadjeddine s group performed several SFG and DFG [13] measurements on the GN/Au(i/k) system and correlated the results with ab-initio calculations [12, 13, 22, 88, 89, 93]. A particularly noteworthy feature of this work is the use of DFG to minimize the non-resonant contribution to the SFG spectram on Au, resulting in a more easily interpretable spectrum. GN is tightly bound to the Au surface atoms in an atop-site Hnear geometry characterized by a resonance between 2090 and 2130 cm as the potential is changed from -1.2 to 0 V vs SGE. The intensity of the peak reaches a maximum as the potential is increased to more positive values in the order Au(llO), Au(lOO) and Au(lll). This result indicates that the packing density of CN on Au ijk) also increases in this order. 

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