Infrared spectroscopic observation of intermediate species on Ni and Fe electrodes in the electrochemical reduction of CO2 and CO to hydrocarbons

Adsorbed species on Ni and Fe electrodes were investigated by in-situ infrared spectroscopy in the electrochemical reduction of CO2 or CO. Two types of adsorbed CO on the Ni electrode and one type on the Fe electrode were detected in a CO atmosphere. The two types, assigned to linear and bridged CO molecules, were also formed on the Ni electrode in CO2 reduction. The negative polarization decreased the coverage of the adsorbed CO on Ni. The decay rate constants were evaluated from the spectroscopic data; the rate constant for the linear type was three times higher than that fur the bridge one. Both constants agreed well with those determined from the formation rate of hydrocarbons in CO reduction, confirming that both adsorbed CO molecules were intermediate species to hydrocarbons. The high electrocatalytic activity of Cu in hydrocarbon formation from CO2 and CO was rationalized in terms of the adsorption strength of CO on metals by comparing the activity of Ni, Fe, and Cu electrodes with the infrared bands of adsorbed CO on these electrodes. The weaker adsorption of CO on Cu led to higher activity.