First-Principles Study on CO Hydrogenation Promoted By Oxygen Atoms Adsorbed Onto Cu(100)
Authors: Nagita Kaito , Kamiya Kazuhide , Nakanishi Shuji , Hamamoto Yuji , Morikawa Yoshitada 
Published: December 2024

In order to close the carbon cycle, the carbon dioxide (CO2) reduction reaction (CO2RR) using copper as a electrochemical catalyst is gaining much more attention. When considering the social implementation of the technology, the gaseous CO2 used for the CO2RR should be collected from the atmosphere. However, the gas inevitably contains a number of impurities such as oxygen, NOx and SOx. Among them, the possibility of oxygen contamination is high, and the reactivity of oxygen is higher than that of CO2. Therefore, the oxygen would affect the reaction selectivity of CO2RR. To demonstrate the effect of oxygen on the CO2RR, oxygen-contaminated CO2 gas was used as the feed gas for the system in previous reports.1,2 For the positive effect of oxygen, the twenty percent of oxygen in the CO2 gas decreased the overpotential for the CO2RR, thus increasing the reactivity of the reaction. On the other hand, for the negative effect of oxygen, the selectivity for CO2RR was largely decreased with only four percent of oxygen in the gas under high pressure conditions. The discrepancies in the reported results are due to various factors at different scales, such as current density, type of electrode, concentrations of reactants, surface pH, surface orientation of the catalyst, and oxidation number of the surface metal atoms. Among these factors, those related to the surface reactivity of the catalyst have the greatest effect on the reactivity and selectivity for CO2RR. The presence of reaction intermediates on the catalyst surface, such as O* and OH*, has been demonstrated during oxygen reduction reactions (ORR) using Raman spectroscopy.1

In the present work,3 we perform first-principles calculations for the CO2RR in the presence of oxygen species (O* or OH*) on the Cu(100) surface to focus on the effect of the adsorption of ORR intermediates (Figure 1a) while excluding macroscale differences, such as surface pH, local concentration of reactants, and other factors. In the results of the calculation, we identified the most stable structure of the Cu(100) surface on which zero to five of one kind of oxygen reduction intermediates were adsorbed. Using the obtained surface, the activation energy for CHO* formation by CO hydrogenation was calculated. In the results, the activation energy was 0.74 eV on the clean Cu(100) surface, increased on the OH*/Cu(100) surface (Figure 1b), and decreased to a maximum of 0.15 eV on the O*/Cu(100) surface (Figure 1c). This is because the initial state of CO hydrogenation was activated by the oxygen atoms adsorbed onto the Cu(100) surface.

References

(1) He, M.; Li, C.; Zhang, H.; Chang, X.; Chen, J. G.; Goddard, W. A., 3rd; Cheng, M.-J.; Xu, B.; Lu, Q. Oxygen Induced Promotion of Electrochemical Reduction of CO2 via Co-Electrolysis. Nat. Commun.
2020, 11 (1), 3844.
(2) Xu, Y.; Edwards, J. P.; Zhong, J.; O’Brien, C. P.; Gabardo, C. M.; McCallum, C.; Li, J.; Dinh, C.-T.; Sargent, E. H.; Sinton, D. Oxygen-Tolerant Electroproduction of C2 Products from Simulated Flue Gas. Energy Environ. Sci.
2020, 13 (2), 554–561.
(3) Nagita, K.; Kamiya, K.; Nakanishi, S.; Hamamoto, Y.; Morikawa, Y. CO Hydrogenation Promoted by Oxygen Atoms Adsorbed onto Cu(100). J. Phys. Chem. C
2024, 128 (11), 4607–4615.

Figure 1. (a)Schematic image of the simulation of CO* hydrogenation reaction on the oxygen atoms adsorbed Cu(100) surface. Activation and reaction free energy on the (b)OH*/Cu(100) surface as a function of OH* coverage, (c) O*/Cu(100) surface as a function of O* coverage.

Figure 1