Effects of *CO Coverage on Selective Electrocatalytic Reduction of CO₂ to Ethylene over Cu₂O with Undercoordinated Cu Sites

Abstract

Cu 2 O surface with the coordinatively unsaturated Cu sites reveals advantages in the electroreduction of CO 2 toward C 2 H 4 production. Understanding the role of *CO coverage and veritable active sites is of great significance for a good command of the catalytic mechanism. Herein, based on density functional theory, the effects of *CO coverage during the reduction of CO 2 to C 2 H 4 on various active sites of Cu 2 O(111) surface, in terms of the adsorption and structural changes of *CO and key intermediates; the energy profiles of the C−C coupling steps; and the subsequent reaction mechanisms were investigated. Results show that Cu CUS on the Cu 2 O(111) surface is especially reactive toward the *CO adsorption and subsequent reactions, being the preferred site owing to the unsaturated Cu atoms. The *CO coverage obviously tunes the adsorption stability of *COH and *CHO intermediates by affecting the adsorbent−adsorbent interactions. Higher coverage of *CO within 0.13−0.25 promotes the C−C coupling by lowering the energy barrier of *CH 2 dimerization, favoring the C 2 H 4 production. Due to the more facile generation of *CHO than *COH, the rate-determining step is speculated to be the C−C coupling with the highest barrier energy occurring in the *CHO pathway. Results provide a fundamental understanding of the CO 2 reduction mechanism on Cu-based surfaces, favoring novel catalysts, rational design, and chemical fuel production.

Electrochemical CO2reduction towards formic acid and methanol on transition metal oxide surfaces as a function of CO coverage

“…At 75% CO coverage, the repulsion between the CO adsorbates increases significantly in agreement with other studies showing the advent of the repulsion forces as a result of increasing CO coverage. [64][65][66][67] This results in weakening of the binding free energy of other intermediates adsorbed on the surface and forcing the OCHO intermediate that binds bidentately at low CO coverage to bind monodentately. Therefore, as discussed in more detail in the next section, this leads to the release of formic acid rather than reducing it further to methanol.…”

Ag–Sb/Cu by Galvanic Replacement: Electrochemical CO2 Reduction and Unveiling C3+ Hydrocarbon Pathways

“…Subsequent steps include CHO + n H + + n e – → *CH x + H 2 O (or *OH) and CH x + n *H → CH 4 . ,, CH 4 production occurs at a relatively higher negative potential. The methanol process involves *COH + 3H + + 3e – → CH 3 OH …”

“…As discussed earlier, ethanol production was substantially enhanced for Sb/Cu, Ag/Cu, AgSb/Cu, and SbAg/Cu compared to that for pure Cu, Ag, and Sb. Hence, an interfacial effect seems to be at play, involving *CO and *CH x and their subsequent coupling. , The coupling between *CO and *CO is a well-known process for initiating C 2+ products. − The reaction for C 2 H 4 generation involves *CO–*CO + 8H + + 8e – → C 2 H 4 + 2H 2 O. − ,, However, this process requires a high density of neighboring *CO on the surface . When the *CO density is low, the hydrogenation process occurs kinetically faster, and the coupling takes place later.…”

“…The methanol process involves *COH + 3H + + 3e − → CH 3 OH. 59 For the major C 2 reduction products, namely, C 2 H 4 , ethanol, and acetate, coupling is initiated from C 1 surface species such as *COOH, *CO, *CHO, *COH, and *CH x , all plausibly formed on the electrode surface, albeit with different thermodynamic and kinetic rates. 14 A coupling between *CO and *CH x (where x = 1, 2) leads to ethanol formation via *CH x CO + nH + + ne − → C 2 H 5 OH.…”

“…11−29 The reaction for C 2 H 4 generation involves *CO−*CO + 8H + + 8e − → C 2 H 4 + 2H 2 O. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]59,61 However, this process requires a high density of neighboring *CO on the surface. 59 When the *CO density is low, the hydrogenation process occurs kinetically faster, and the coupling takes place later.…”