Negative Reaction Order for CO during CO 2 Electroreduction on Au.

The potential-dependent negative fractional reaction orders with respect to the CO partial pressures were measured for CO 2 electroreduction (CO 2 R) on Au under mass-transfer-controlled conditions using a rotating ring-disk electrode setup. At high overpotentials, the CO reaction order approaches -1 due to enhanced CO adsorption on Au, which is supported by kinetic analysis and density functional theory (DFT) simulations. This work illustrates that the CO site-blocking effect cannot be ignored, even on a weak CO-binding metal such as Au in the electrochemical environment. The CO site-blocking effect can greatly hamper the activity and the selectivity of the CO 2 R to CO. This observation enriches the current mechanistic understanding of the CO 2 R and could have significant implications not only in the theoretical modeling of the CO 2 R but also in the evaluation of intrinsic CO 2 R activity at practical current density and high conversion conditions.