Insight into CO Activation over Cu(100) under Electrochemical Conditions

Abstract

Sun, Insight into CO Activation over Cu(100) under Electrochemical Conditions, Electrochimica Acta http://dx.doi.org/10. 1016/j.electacta.2016.01.037 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. (ii) For the formation of COH ads , the reaction energy is endothermic by 0.34 eV and the free energy barrier is 0.38 eV, and the feasible route of proton transfer is illustrated. Insight into CO Activation over Cu(100) under Electrochemical Conditions(iii) A linear relationship is revealed between the C-O bond distance and the negative charge in CO.(iv) The formation of CHO ads is endothermic by 0.46 eV with the free energy barrier of 0.64 eV. Before the coupling, H adsorbs first with a reaction energy of -0.24 eV and the free energy barrier of 0.56 eV.(v) The formation of COH ads has been found to be more favorable than that of CHO ads kinetically, but CHO ads has been shown to be more stable thermodynamically. AbstractThe reduction of CO 2 on copper electrodes has attracted great attentions in the last decades, since it provides a sustainable approach for energy restore. During the CO 2 reduction process, the electron transfer to CO ads is experimentally suggested to be the crucial step. In this work, we examine two possible pathways in CO activation, i.e. to generate COH ads and CHO ads , respectively, by performing the state-of-the-art constrained ab initio molecular dynamics simulations on the charged Cu (100) electrode under aqueous conditions, which is close to the realistic electrochemical condition. The free energy profile in the formation of COH ads via the coupled proton and electron transfer is plotted. Furthermore, by Bader charge analyses, a linear relationship between C-O bond distance and the negative charge in CO fragment is unveiled. The formation of CHO ads is identified to be a surface catalytic reaction, which requires the adsorption of H atom on the surface first. By comparing these two pathways, we demonstrate that kinetically the formation of COH ads is more favored than that of CHO ads , while CHO ads is thermodynamically more stable. This work reveals that CO activation via COH ads intermediate is an important pathway in electrocatalysis, which could provide some insights into CO 2 electroreduction over Cu electrodes.

Electrochemical interfacial influences on deoxygenation and hydrogenation reactions in CO reduction on a Cu(100) surface

“…From our previous calculation, one can see that the corresponding electrode potential in neutral system (potential of zero charge) is -0.63 (vs SHE), comparing with the experimental value of -0.54 V (vs SHE). 25 For the charged interface model including H + , the corresponding electrode potential is -2.04 V (vs SHE), more negative than the onset potential of -1.4 V (vs SHE) in CO 2 electroreduction on Cu(100). 8 Using the water/Cu(100) interface and the charged water/Cu(100) interface can help to decouple the effects of aqueous surrounding and electrode potential for investigating them respectively.…”

“…23, 24 We previously revealed that adsorbed COH was favorable kinetically but CHO was favorable thermodynamically in CO activation on Cu(100). 25 In fact, the mechanism to explain how copper catalyzes CO 2 to hydrocarbons still remains controversial and requires further studies. Hori et al carried out the CO 2 electroreduction over a series of Cu single crystal planes, it was found that the activity on Cu(100) and Cu(111) single crystal surfaces is comparable, e.g., a current density of 5 mA cm -2 was achieved at a reduction potential of -1.4 V (vs SHE) on Cu(100) and -1.5 V (vs SHE) on Cu(111), respectively.…”

“…Since the H atoms could separate into protons and electrons, one may vary the surface charge and the potential by changing the concentration of protons. 25,36,37 DFT calculations performed in aqueous surrounding would be extremely challenging and extraordinary time-consuming since the water structures would be fluctuating in dynamics at the interface. In fact, it has been proved that without the appropriate dynamics for water structure, calculation of the work function hardly matched the experiments.…”

“…[10][11][12][13][14][15] To advance our understanding of the experimental findings, density functional theory (DFT) calculations were employed widely for investigating the mechanisms in CO 2 reduction at the atomic level. [16][17][18][19][20][21][22][23][24][25] Norskov's group has developed a computational hydrogen electrode model to map out the free energy diagrams from CO 2 to CH 4 including about 40 elementary steps on Cu(111). 17 Nie et al described the roles of the kinetics of elementary steps and the whole reaction network on Cu(111).…”

“…[22][23][24][25][28][29][30][31][32][33][34][35][36][37][38] To avoid the introduction of artificial counter-charge, H atoms were usually introduced into the water layer. Since the H atoms could separate into protons and electrons, one may vary the surface charge and the potential by changing the concentration of protons.…”