Negative Reaction Order for CO during CO Electroreduction on Au.

The potential-dependent negative fractional reaction orders with respect to the CO partial pressures were measured for CO electroreduction (COR) 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 COR to CO. This observation enriches the current mechanistic understanding of the COR and could have significant implications not only in the theoretical modeling of the COR but also in the evaluation of intrinsic COR activity at practical current density and high conversion conditions.