Negative Reaction Order\nfor CO during CO<sub>2</sub> Electroreduction on Au

The potential-dependent negative\nfractional reaction\norders with\nrespect to the CO partial pressures were measured for CO<sub>2</sub> electroreduction (CO<sub>2</sub>R) on Au under mass-transfer-controlled\nconditions using a rotating ring-disk electrode setup. At high overpotentials,\nthe CO reaction order approaches −1 due to enhanced CO adsorption\non Au, which is supported by kinetic analysis and density functional\ntheory (DFT) simulations. This work illustrates that the CO site-blocking\neffect cannot be ignored, even on a weak CO-binding metal such as\nAu in the electrochemical environment. The CO site-blocking effect\ncan greatly hamper the activity and the selectivity of the CO<sub>2</sub>R to CO. This observation enriches the current mechanistic\nunderstanding of the CO<sub>2</sub>R and could have significant implications\nnot only in the theoretical modeling of the CO<sub>2</sub>R but also\nin the evaluation of intrinsic CO<sub>2</sub>R activity at practical\ncurrent density and high conversion conditions.