Surface-adsorbed CO is generally considered a reactive on-pathway intermediate in the aqueous electrochemical reduction of CO2 on Cu electrodes. Though CO can bind to a variety of adsorption sites (e.g., atop or bridge), spectroscopic studies of the Cu/electrolyte contact have mostly been concerned with atop-bound CO. Using surface-selective infrared (IR) spectroscopy, we have investigated the reactivities and coverages of atop- and bridge-bound CO on a polycrystalline Cu electrode in contact with alkaline electrolytes. We show here that (1) a fraction of atop-bound CO converts to bridge-bonded CO when the total CO coverage drops below the saturation coverage and (2) unlike atop-bound CO, bridge-bonded CO is an unreactive species that is not reduced at a potential of −1.75 V vs SHE. Our results suggest that bridge-bonded CO is not an on-pathway intermediate in CO reduction. Using density functional theory (DFT) calculations, we further reveal that the activation barrier for the hydrogenation of bridge-bonded CO to surface-adsorbed formyl on Cu(100) is higher than that of the reduction of atop-bound CO, in qualitative agreement with our experimental findings. The possible modulation of the catalytic properties of the interface by the electrochemically inert bridge-bonded CO population should be considered in future studies involving CO2 or CO reduction on Cu under alkaline conditions.

and selectively produce carbon-containing products from CO 2 with reasonably low overpotentials and low cost.From the theoretical point of view, electrochemical CO 2 reduction, similar to many other electrochemical energy conversion processes on metal surfaces, comprise of multiple concerted or sequential proton-electron transfer reactions. In 2004, Nørskov et al. [2] developed a concise and effective scheme to understand the origin of the overpotential, which was denoted as the computational hydrogen electrode (CHE) model. They claimed that due to the relative low proton transfer barriers, the kinetic aspects in the proton transfer was omitted, and the rate-determining step was the one with the most positive free energy change ΔE max . To make the free energy of the rate-determining step become zero, a limiting potentialneeds to be applied. If we denote the equilibrium potential of a given electrochemical reaction as U eq , the overpotential wouldThe overpotential thereby originates from the relative stability between certain adsorbed intermediates. For example, the overpotential for 4-electron oxygen reduction reaction (ORR) is ascribed to the high adsorption free energy barrier of *OOH on the weak binding materials or the high desorption free energy barrier of *OH on the strong binding materials. [3] Similarly, when excluding the Tafel mechanism, the overpotential for hydrogen evolution reaction (HER) originates from either the high adsorption free energy barrier of *H (Volmer step) or the high desorption barrier of the same intermediate (Heyrovsky step). [4] Based on the Sabatier principle, [5] when the maximum electrocatalytic activity is reached in these reactions, the binding of the reaction intermediates should be neither too strong nor too weak. In HER, where only *H is emerged as the reaction intermediate, it is easier to achieve a maximum reactivity with negligible overpotential because the binding energy of *H is not limited and can be tuned freely. If the binding energy of *H on a certain material renders the adsorption free energy of *H close to zero, the overpotential will be negligible. Such an electroactive electrode for HER indeed exists, say the platinum electrode. However, for electrocatalytic reactions with multiple proton-electron transfer steps, the case is much more complex. The overpotential cannot be lowered to a negligible value because the relative The increasing concentration of CO 2 in the atmosphere, and the resulting environmental problems, call for effective ways to convert CO 2 into valuable fuels and chemicals for a sustainable carbon cycle. In such a context, CO 2 electrocatalytic reduction has been hotly studied due to the merits of ambient operational conditions and easy control of the reaction process by changing the applied potential. Among the various systems studied, Cu and Au are found to possess the highest Faradaic efficiency toward cathodic electrocatalytic conversion of CO 2 to hydrocarbons and CO, respectively. However, both of them suffer from large overpotentials ...

Amino acid functionalized Cu nanowire (NW) film electrode exhibits remarkably enhanced selectivity of hydrocarbons during CO2electroreduction, by stabilizing the key intermediate CHO.

The conversion of CO2 into fuels and useful chemicals has been intensively pursued for renewable, sustainable and green energy. However, due to the negative adiabatic electron affinity (EA) and large ionization potential (IP), the CO2 molecule is chemically inert, thus making the conversion difficult under normal conditions. Novel catalysts, which have high stability, superior efficiency and low cost, are urgently needed to facilitate the conversion. As the first step to design such catalysts, understanding the mechanisms involved in CO2 conversion is absolutely indispensable. In this review, we have summarized the recent theoretical progress in mechanistic studies based on density functional theory, kinetic Monte Carlo simulation, and microkinetics modeling. We focus on reaction channels, intermediate products, the key factors determining the conversion of CO2 in solid-gas interface thermocatalytic reduction and solid-liquid interface electrocatalytic reduction. Furthermore, we have proposed some possible strategies for improving CO2 electrocatalysis and also discussed the challenges in theory, model construction, and future research directions.