Existence of an Electrochemically Inert CO Population on Cu Electrodes in Alkaline pH

Abstract

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.

Hydrogen bonding steers the product selectivity of electrocatalytic CO reduction

“…CO is only weakly adsorbed on Cu and The results suggest that the interfacial field at the Cu/ electrolyte interface under the experimental conditions used in this work is too small to have a significant effect on the CO adsorption energy. This conclusion is consistent with DFT calculations demonstrating that an electric field of 0.1 V·Å −1 has negligible effect on the adsorption energy of CO on Cu (99).…”

“…A surface roughness factor of ≈3 compared with a smooth Cu surface (128) was determined on the basis of electrochemical capacitance measurements. The electrochemical protocols are detailed in our prior report (99).…”

“…Cu Thin-Film Preparation for SEIRAS. Thin polycrystalline Cu films were deposited on a reflecting facet of a 60 • Si prism (Pike Technologies) by an electroless deposition procedure and characterized as described in our previous report (99). The film roughness factor was ≈13.…”

Molecular tuning of CO2-to-ethylene conversion

“…The asymmetric region at the range of 1900-2120 cm -1 is attributed to the C≡O stretch of *CO 34,35 . This band is sensitive to the coordination of the *CO on the metal surface [35][36][37] , which, in turn, may affect the activity and selectivity of the CO2RR.…”

Changing the Product Selectivity for Electrocatalysis of CO2 Reduction Reaction on Plated Cu Electrodes

“…Waegele et al. used the same technique and clarified that atop‐bound CO rather than bridge‐bonded CO is an on‐pathway intermediate for C1 and C2+ products . It is thus of particular interest to extend in situ spectroscopic study of CO 2 reduction from monometallic Cu to metalloid‐doped Cu electrodes.…”