Bicarbonate Is Not a General Acid in Au-Catalyzed CO<sub>2</sub> Electroreduction

Wuttig, Anna; Yoon, Yong Tae; Ryu, Jaeyune; Surendranath, Yogesh

doi:10.1021/jacs.7b08345

Cited by 229 publications

(278 citation statements)

References 40 publications

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“…Ther ate orders of HCO 3 À for CO formation was much smaller, being 0.19 for l-SnO/C and 0.35 for SnO/C.T his result agrees with previous studies on Au [15] and Ag [8c] where the rate order of HCO 3 À for CO formation was close to zero.Itisconsistent with the reduction of CO 2 to CO 2 C À being the RDS for CO formation. Based on the reaction orders,a10-fold increase of the concentration of HCO 3 À will lead to a4 -fold increase in the selectivity of CO over formate.These results indicate that formate formation is greatly disfavored over CO formation when the concentration of proton source is decreased, consistent with the local pH effect proposed above.…”

Section: Angewandte Chemiesupporting

confidence: 91%

“…[3,6b] Fore ach pathway,i ft he first step,the single electron transfer to CO 2 ,isthe rate determining step (RDS), the Tafel slop should be 118 mV dec À1 .Ifthis step is reversible,f ollowed by ar ate-limiting proton transfer from HCO 3 À ,t he Tafel slop should be 59 mV dec À1 . [14,15] As indicated by the Tafel plots of SnO/C (Figure 4b), the Tafel slopes of formate formation is 64 mV dec À1 ,c lose to 59 mV dec À1 ,s imilar to that reported for other Sn-based catalysts, [4, 5a,b] suggesting that the RDS is the protonation of the adsorbed CO 2 C À .M eanwhile,t he Tafel slope of CO formation is 94 mV dec À1 ,c lose to 118 mV dec À1 ,s uggesting that the formation rate of CO is more limited by the first single electron transfer step.T he Tafel analysis suggests that …”

Section: Angewandte Chemiementioning

confidence: 99%

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Densely Packed, Ultra Small SnO Nanoparticles for Enhanced Activity and Selectivity in Electrochemical CO₂ Reduction

Héroguel

Luterbacher

et al. 2018

Angewandte Chemie

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Controlling the selectivity in electrochemical CO 2 reduction is an unsolved challenge.While tin (Sn) has emerged as apromising non-precious catalyst for CO 2 electroreduction, most Sn-based catalysts produce formate as the major product, which is less desirable than CO in terms of separation and further use.T in monoxide (SnO) nanoparticles supported on carbon black were synthesized and assembled and their application in CO 2 reduction was studied. Remarkably high selectivity and partial current densities for CO formation were obtained using these SnO nanoparticles compared to other Sn catalysts.The high activity is attributed to the ultra-small sizeof the nanoparticles (2.6 nm), while the high selectivity is attributed to al ocal pH effect arising from the dense packing of nanoparticles in the conductive carbon black matrix.Electrochemical reduction of CO 2 to form carbon-based fuels and chemicals has been widely proposed for the storage and utilization of intermittent renewable energies such as solar and wind.[1] However,t wo major deficiencies have prevented CO 2 electroreduction from becoming av iable technology:energy inefficiencyowing to large overpotentials, and poor selectivity leading to separation issues.T herefore, there is tremendous interest in developing active and selective electrocatalysts for CO 2 reduction. In terms of electrochemical activity,n oble-metal catalysts rank the best.[2] Among non-noble metal catalysts,S n-based catalysts stand out. [3,4] However,the major CO 2 reduction product using Sn catalysts is formate (HCOO À ), and CO is generated only in as mall amount.[5] Unlike its acidic form, formic acid which is ahighvalue chemical, formate has no obvious usage and is difficult to separate and convert into other high-value products without adding costly processes.C O, on the other hand, is ah ighly desirable product as it is ag as that can be easily separated and further converted into fuels and bulk chemicals at al arge scale through existing chemical technologies. Achieving high activity and selectivity for CO formation on anon-precious catalyst such as Sn is therefore anotable goal with practical relevance.TheC O 2 electroreduction performance of Sn based catalysts developed recent years is summarized in the Supporting Information, Figure S4. Modulation of size, shape,a nd composition (metal, oxide,o rs ulfide) of monometallic Sn catalysts is effective to achieve high formate formation activity,but these approaches cannot improve CO formation performance.[5a-d] Until now,c ooperative promotion is required to enhance CO formation on Sn-based catalysts.For example,Cu-Sn bimetallic catalysts are reported to favor CO formation; [6] however, Cu also acts as possible catalytic sites.H erein we report an ew strategy that leads to unprecedented activity and selectivity for CO formation among monometallic Sn catalysts.K ey to this performance are the ultra-small size of catalyst nanoparticles and their dense packing in ac onductive matrix, which lead to ah igh density of active s...

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Section: Angewandte Chemiesupporting

confidence: 91%

Section: Angewandte Chemiementioning

confidence: 99%

Densely Packed, Ultra Small SnO Nanoparticles for Enhanced Activity and Selectivity in Electrochemical CO₂ Reduction

Héroguel

Luterbacher

et al. 2018

Angewandte Chemie

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“…Therefore, our observation (see Figure ) that the partial currents for the formation of C 2 H 4 and CH 3 CH 2 OH formation are independent of buffer concentration when the rates are compared on an SHE scale is what should be expected. Similarly, the production of CO and HCOO ‐ have previously been shown to be independent of pH, suggesting that the rate limiting step does not involve a concerted proton‐coupled electron‐transfer step, but rather electron transfer to form a CO 2 δ− ,. We note here that the effects of pH and buffer concentration on the formation of CO and HCOO ‐ can be observed more readily on metals selective for these products.…”

Section: Resultssupporting

confidence: 64%

“…The observed differences in selectivity with buffer concentration and buffer capacity were attributed to changes in the pH at the electrode surface; however, these changes in pH were not quantified nor was it explained how the electrolyte pH might cause the observed changes in product distribution ,,. Recent studies have also discussed the possibility of HCO 3 − acting as a carbon source . Given the lack of a clear interpretation of the effects of anion composition on the activity and selectivity of Cu for the CO 2 RR, we undertook an effort to develop a complete picture of the role of anionic species on the electrochemical reduction of CO 2 .…”

Section: Introductionmentioning

confidence: 99%

Effects of Anion Identity and Concentration on Electrochemical Reduction of CO₂

et al. 2018

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The electrochemical reduction of CO2 is known to be influenced by the concentration and identity of the anionic species in the electrolyte; however, a full understanding of this phenomenon has not been developed. Here, we present the results of experimental and computational studies aimed at understanding the role of electrolyte anions on the reduction of CO2 over Cu surfaces. Experimental studies were performed to show the effects of bicarbonate buffer concentration and the composition of other buffering anions on the partial currents of the major products formed by reduction of CO2 over Cu. It was demonstrated that the composition and concentration of electrolyte anions has relatively little effect on the formation of CO, HCOO−, C2H4, and CH3CH2OH, but has a significant effect on the formation of H2 and CH4. Continuum modeling was used to assess the effects of buffering anions on the pH at the electrode surface. The influence of pH on the activity of Cu for producing H2 and CH4 was also considered. Changes in the pH near the electrode surface were insufficient to explain the differences in activity and selectivity observed with changes in anion buffering capacity observed for the formation of H2 and CH4. Therefore, it is proposed that these differences are the result of the ability of buffering anions to donate hydrogen directly to the electrode surface and in competition with water. The effectiveness of buffering anions to serve as hydrogen donors is found to increase with decreasing pKa of the buffering anion.

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“…They claimed that bicarbonate species had an active role as a carbon source in the CO production, possibly through a dynamic chemical equilibrium between CO 2 and bicarbonates species. The theory that bicarbonate is involved in the CO production on gold surfaces was, however, recently questioned by Wutting et al . as well as by Singht et al .…”

Section: Structure Sensitivity In Co2 Reductionmentioning

confidence: 99%

Structure‐Sensitivity and Electrolyte Effects in CO₂ Electroreduction: From Model Studies to Applications

et al. 2019

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Aiming to reduce anthropogenic CO2 emissions, there is an urgent demand to develop more efficient and affordable technologies which convert CO2 into valuable feedstock molecules. The use of renewable electricity is a promising and sustainable approach to overcome this environmental issue, while producing valuable chemicals and clean fuels. However, the CO2 electroreduction reaction (CO2RR) still shows two main gaps: poor selectivity and required large overpotentials make the process not profitable enough. To overcome these challenges, model studies on single‐crystalline surfaces aiming to find the relations between surface structure/electrolyte interactions and activity/selectivity are necessary. In these model studies, tuning the electrolyte composition is also key for the fundamental understanding of the CO2RR. In this review, we first discuss the structure‐activity‐selectivity relations from studies on well‐ordered surfaces, i. e., single crystalline electrodes, for the CO2RR. We then summarise the role of the electrolyte, presenting work on classical aqueous solvents as well as non‐aqueous electrolytes such as ionic liquids. We illustrate the importance of carrying out studies on well‐defined electrified interfaces in order to get deep fundamental insights on the mechanism of the CO2RR, as well as scaling the process for real applications. Ultimately, this knowledge will be essential to rationally design the catalyst with tailored activity and selectivity for CO2 reduction.

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Bicarbonate Is Not a General Acid in Au-Catalyzed CO₂ Electroreduction

Cited by 229 publications

References 40 publications

Densely Packed, Ultra Small SnO Nanoparticles for Enhanced Activity and Selectivity in Electrochemical CO₂ Reduction

Densely Packed, Ultra Small SnO Nanoparticles for Enhanced Activity and Selectivity in Electrochemical CO₂ Reduction

Effects of Anion Identity and Concentration on Electrochemical Reduction of CO₂

Structure‐Sensitivity and Electrolyte Effects in CO₂ Electroreduction: From Model Studies to Applications

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Bicarbonate Is Not a General Acid in Au-Catalyzed CO2 Electroreduction

Cited by 229 publications

References 40 publications

Densely Packed, Ultra Small SnO Nanoparticles for Enhanced Activity and Selectivity in Electrochemical CO2 Reduction

Densely Packed, Ultra Small SnO Nanoparticles for Enhanced Activity and Selectivity in Electrochemical CO2 Reduction

Effects of Anion Identity and Concentration on Electrochemical Reduction of CO2

Structure‐Sensitivity and Electrolyte Effects in CO2 Electroreduction: From Model Studies to Applications

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Product

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Bicarbonate Is Not a General Acid in Au-Catalyzed CO₂ Electroreduction

Densely Packed, Ultra Small SnO Nanoparticles for Enhanced Activity and Selectivity in Electrochemical CO₂ Reduction

Densely Packed, Ultra Small SnO Nanoparticles for Enhanced Activity and Selectivity in Electrochemical CO₂ Reduction

Effects of Anion Identity and Concentration on Electrochemical Reduction of CO₂

Structure‐Sensitivity and Electrolyte Effects in CO₂ Electroreduction: From Model Studies to Applications