Adsorption of CO on Cu Electrode Voltammetric and Spectroscopic Studies

Carbon monoxide is produced during CO2 reduction, weakly and reversibly adsorbed on Cu electrode surface. Adsorbed CO is easily desorbed from Cu electrode surface by purging CO from the electrolyte solution, whereas HER at Cu electrode is significantly suppressed by the adsorption of CO. 

CO adsorption on Cu electrode surface is interfered with by specifically adsorbed anions. CO can be adsorbed below a certain definite potential, determined by the adsorption strength of CO and the anion. When CO molecules displace the specifically adsorbed anions on Cu electrode, a voltammetric peak is observed as exemplified for Cu(lOO) in CO saturated phosphate buffer solution in comparison with N2 saturated solution (Fig. 29). Subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) spectra in Fig. 30 demonstrates that CO is adsorbed at -0.8 V vs. SHE but not at -0.4 V, and adsorbed phosphate anion vice versa. This process is equivalent to charge displacement adsorption of CO on Pt electrode revealed by Clavilier et al The profile of the voltammogram depends greatly on the crystal 

Infrared absorption spectra would contribute to elucidation of the electrochemical reduction of CO2 as well as CO. However, the potential range of the spectroscopic measurement is restricted the measurement must be made below the potential of the charge displacement adsorption. And the measurement is actually impossible 

The solubility of CO2 in water is as low as 30 mM at 1 atm at the ambient temperature, restricting the transport of CO2 to the electrode. Under moderate experimental conditions, the highest current density will be limited to 20 mA cm or so for formation of CO or HCOO for example. Such a low transport process must be improved by any means, if the CO2 reduction is utilized for a practical process. Various solutions have been proposed, application of 

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