Interaction of CO with Gold in an Electrochemical Environment

We present a joint theoretical-experimental study of CO coverage and facet selectivity on Au and under electrochemical conditions. With in situ attenuated total reflection surface enhanced IR spectroscopy (ATR-SEIRAS), we investigate the CO binding in an electrochemical environment. At 0.2V vs. SHE, we detect a CO band that disappears upon facet selective partial Pb underpotential deposition, suggesting that Pb blocks certain CO adsorption sites. With Pb underpotential deposition on single crystals and theoretical surface Pourbaix analysis, we eliminate (111) terraces as a possible adsorption site of CO. Ab initio molecular dynamics simulations of explicit water at the Au surface, shows the adsorption of CO on (211) steps to be significantly weakened relative to the (100) terrace due to competitive water adsorption. This result suggests that CO is more likely to bind to the (100) terrace than (211) steps in an electrochemical environment, even though Au steps in gas phase conditions bind CO* more strongly. The competition between water and adsorption can result in different binding sites for CO* on Au in gas phase and electrochemical environments.

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