Coverage- and potential-dependent binding geometries of carbon monoxide at ordered low-index platinum- and rhodium-aqueous interfaces: comparisons with adsorption in corresponding metal-vacuum environments

ATR-SEIRAS study of CO adsorption and oxidation on Rh modified Au(111-25 nm) film electrodes in 0.1 M H2SO4

“…observed both ν COL and ν COB bands during CO oxidation on both Rh(110) and Rh(100) surfaces [11,12]. The discrepancies with results reported here might be caused by the different surface quality of the Rh electrodes used.…”

“…[45,46]. In comparison with stepped gold single crystals Au(n,n,n-2) [42] , the electrochemical features of the Au(111-25 nm) film ( The 2024 and 1900 cm -1 bands correspond to the stretching modes of CO adsorbed on Rh atop (ν COL ) and bridge (ν COB ) sites, respectively [12,32,51]. As mentioned above, the observation of the ν COL (Au) band indicates that the Au(111-25 nm) film surface was not completely covered by the Rh film and there were some free Au sites exposed to the electrolyte solution.…”

“…The spectrum acquired at 0.10 V after complete removal of CO from Rh surface was chosen as the reference. In Figure 6B, two positivegoing bands are specified at 0.10 V, the one at 2029 cm -1 is attributed to CO bound to atop sites (ν COL ) and the one at lower frequency 1797 cm -1 is attributed to multi-fold bonded CO on Rh sites (ν COM ) [9,12,32,64]. Atop CO stretching band exists in the entire potential region from 0.10 V to 0.90 V while the multi-fold CO band disappears at potentials around 0.79 V, which is consistent with observations in Refs.…”

“…2A) resembles that on the Rh(110). Finally, the presence of defects at the surface of the Rh film electrodes is witnessed by the faster electro-oxidation of adsorbed CO, which, in contrast to the behavior of well-ordered Rh (111) Note that multi-bonded CO M has been observed only on a well-defined Rh(111) surface [9,12,32,66], indicating that CO M is preferentially formed on well-ordered Rh (111) terrace sites. In this way, it can be recalled that a potential excursion up to 0.90 V with the Rh(111) electrode leads to the formation of surface oxide, which could drastically change the surface morphology of well-ordered Rh(111) terrace site after the reduction of surface oxides.…”

“…Importantly, the CO molecules adsorbed on different surface sites (atop, bridge, multi-fold) can be distinguished by their vibration frequencies. In situ infrared reflection absorption spectroscopy (IRRAS) studies of CO chemisorption and electro-oxidation on the lowindex Rh single crystal surfaces by Weaver's group demonstrated a strong dependence of the preferable adsorption site on the surface orientation, CO coverage and applied potential [9][10][11][12][13][14]. A combined IRRAS and in situ scanning tunneling microscopic (STM) study revealed two distinctly different potential-dependent CO adlayer structures on smooth Rh(111) in aqueous electrolyte [15].…”