Infrared Spectroscopic Observation of Adsorbed CO Intermediately Formed in the Electrochemical Reduction of CO2 at a Nickel Electrode

A nickel electrode surface during electroreduction of CO2 in phosphate buffer solution was studied by in situ infrared spectroscopy. SNIFTIRS (subtractively normalized interfacial Fourier transform infrared spectroscopy) technique showed the presence of adsorbed CO on the electrode surface between −0.4 and −0.8 V vs. NHE in CO saturated solution. The adsorbed CO was bonded to the electrode in linear and bridged fashions. Linear and bridged adsorbed CO molecules were also detected on the electrode during the electroreduction of CO2. Linear CO disappeared at relatively negative potential (−0.8 V). Since the reduction of adsorbed CO proceeds below −1.0 V, the electroactive species in the reduction of CO is presumed to be bridged type CO.