Mechanistic Insights into the Electrochemical Reduction of CO₂ to CO on Nanostructured Ag Surfaces

Abstract

Electroreduction of CO2 in a highly selective and efficient manner is a crucial step towards CO2 utilization. Nanostructured Ag catalysts have been found to be effective candidates for CO2 to CO conversion. In this report, we combine experimental and computational efforts to explore the electrocatalytic reaction mechanism of CO2 reduction on nanostructured Ag catalyst surfaces in an aqueous electrolyte. In contrast to bulk Ag catalysts, both nanoparticle and nanoporous Ag catalysts show enhanced ability to reduce the activation energy of the CO2 to intermediate step through the low coordinated Ag surface atoms, resulting in a reaction mechanism involving a fast first electron and proton transfer followed by a slow second proton transfer as the rate limiting step. Experimental SectionComputational Modeling

Effect of Chloride Anions on the Synthesis and Enhanced Catalytic Activity of Silver Nanocoral Electrodes for CO2 Electroreduction

“…2) is the rate-determining, followed by another electron transfer. 51,53,54 The effects of halides present at the electrode surface or in the electrolyte have been previously reported for CO 2 electroreduction on copper surfaces 55 , and substantial improvement in current efficiency and selectivity was observed. It appears that the presence of chloride ions on the Ag electrode surface or in the electrolyte solution in proximity to the electrode promotes selectivity and activity for the CO 2 reduction reaction.…”

“…52 Under experimental conditions similar to those described in this work, HCO 3 − is the most likely source of protons, since the pK a of bicarbonate is much lower as compared to that of water. 51 The step (3) is an electrochemical step coupled to a chemical reaction involving proton and electron transfer, and the step (4) is the desorption of CO product. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 As shown in Figure 4, the polycrystalline Ag foil exhibited a Tafel slope of 137 mV dec −1 , which is close to 140 mV dec −1 for polycrystalline Ag under similar experimental conditions, 24 and comparable to 132 mV dec −1 measured in 0.5 M KHCO 3 .…”

Tuning of Silver Catalyst Mesostructure Promotes Selective Carbon Dioxide Conversion into Fuels

“…Thes pecific activity for CO production declines by about 15 %upon increasing the rotation rate from 700 to 3500 rpm (Figure 4b). While we cannot rule out several competing effects, [25] we note that the local activity of K + and CO 3 2À must rise in tandem with elevated local pH, and that these species may serve to promote CO production in this system. These results are also in contrast to observations on Au electrodes,f or which the rate of CO production is largely independent of the electrode rotation rate.…”

Enhanced Carbon Dioxide Reduction Activity on Indium-Based Nanoparticles

“…Studies on tin 5,6 and indium 7,8 have demonstrated the importance of a hydrated oxide layer, either native or anodized, which can interact with CO 2 to form a surface-bound carbonate species that is implicated as an essential intermediate. Other research has shown that a size-dependence exists on gold, 9,10 palladium, 11 silver, 10,12,13 and tin oxide 14 nanoparticles for the conversion of CO 2 , with an optimum diameter less than 10 nm but typically greater than 2 nm. Such nanoparticles have a high proportions of edge and corner sites, which, because of their lower * Electrochemical Society Student Member.…”