Bridge Sites of Au Surfaces Are Active for Electrocatalytic CO 2 Reduction

Prior in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) studies of electrochemical CO reduction catalyzed by Au, one of the most selective and active electrocatalysts to produce CO from CO , suggest that the reaction proceeds solely on the top sites of the Au surface. This finding is worth updating with an improved spectroelectrochemical system where in situ IR measurements can be performed under real reaction conditions that yield high CO selectivity. Herein, we report the preparation of an Au-coated Si ATR crystal electrode with both high catalytic activity for CO reduction and strong surface enhancement of IR signals validated in the same spectroelectrochemical cell, which allows us to probe the adsorption and desorption behavior of bridge-bonded *CO species (*CO ). We find that the Au surface restructures irreversibly to give an increased number of bridge sites for CO adsorption within the initial tens of seconds of CO reduction. By studying the potential-dependent desorption kinetics of *CO and quantifying the steady-state surface concentration of *CO under reaction conditions, we further show that *CO are active reaction intermediates for CO reduction to CO on this Au electrode. At medium overpotential, as high as 38% of the reaction occurs on the bridge sites.