Mechanistic Study of Plasmon-Assisted In Situ Photoelectrochemical CO₂ Reduction to Acetate with a Ag/Cu₂O Nanodendrite Electrode

Abstract

Electrochemical and, more recently, photoelectrochemical CO2 reductions have been widely investigated to convert atmospheric CO2 into other useful chemicals. However, understanding the mechanism and selectivity of materials capable of reducing CO2 remains a challenge. Using plasmonic dendritic electrodes of silver and cuprous oxide (Ag/Cu2O) and employing Raman spectroelectrochemistry detection, we observe the selective photoelectroreduction mechanism from CO2 to acetate as a value-added compound instead of the more commonly reported products like methanol, ethylene, or ethane. The selectivity, efficiency, and low overpotential (−0.4 V vs Ag/AgCl) in the CO2 reduction is favored by the basic microenvironment, the semiconductor properties of the Cu2O, and the accumulation of hot electrons from the localized surface plasmon resonance of the Ag nanostructure. Lateral surface interactions between adsorbed CO species are the key to the formation of acetate. The rate-determining step of the reaction is the single transfer of an electron from the electrode to the CO2 molecule to reduce it to the *CO2 – radical anion and subsequently form adsorbed CO, which is a key intermediate in the formation of the carbon–carbon bond during the reduction process.

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

“…While this product is briefly discussed in Section , it is not extensively addressed throughout the paper. For bare Cu, CO, CH 4 , and C 2 H 4 were notably produced, aligning with expectations from literature reports (refer to Figure a). − For bare Ag, a CO FE of 69.2% was observed, and C 2 hydrocarbons were minimal, registering below an FE of 0.2%. Sb, on the other hand, produced CO with an FE of only 1%.…”

“…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 enhancement of C 2 H 4 production with the proper loading of Sb, Ag, or both on Cu indicates an increased coupling at the interfacial sites. Minor acetate production involves *COH + *CO → CH 3 COO – . In addition to the electrode-specific mechanism, the involvement of electrolyte effects in electrochemical processes introduces a multitude of factors that significantly impact the overall system dynamics. − These effects encompassed parameters such as pH, buffering capability, CO 2 solubility, local CO 2 concentration, cation/anion ratio, CO 2 /HCO 3 – /CO 3 2– equilibrium, and cation size, adding complexity to the overall process.…”

“…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.…”

“…Copper (Cu) is one of the most extensively studied pure metals in electrochemical (EC) CO 2 reduction, − and Ag/Cu has been among the most researched bimetallic electrode configurations. − Ag/Cu electrodes exhibit unique synergistic effects in C–C coupling, enhancing the productivity of C 2+ reduction products like C 2 H 4 , ethanol, and propanol in EC CO 2 reduction. The preparation methods of Ag/Cu electrodes influence C–C coupling, with different methodologies altering the balance, favoring either more CO or CH 4 production. − The selectivity and productivity of CO, formate, CH 4 , and C–C coupled reduction products are strongly influenced by the characteristics of the electrode surfaces.…”