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6CCVD Research

Efficient electrocatalytic reduction of CO2 on an Ag catalyst in 1-ethyl-3-methylimidazolium ethylsulfate, with its co-catalytic role as a supporting electrolyte during the reduction in an acetonitrile medium

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2025-04-09
JournalFrontiers in Chemistry
AuthorsSayyar Muhammad, Asad Ali
InstitutionsIslamia College University, LuleÄ University of Technology
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research details an efficient electrocatalytic pathway for converting carbon dioxide (CO2) into carbon monoxide (CO) using a silver (Ag) catalyst and a specific ionic liquid (IL).

  • Efficient Catalysis: Polycrystalline Ag and Cu electrodes demonstrated superior electrocatalytic activity for CO2 reduction (CO2ERR) in neat 1-ethyl-3-methylimidazolium ethyl sulfate ([emim][EtSO4]), achieving the lowest overpotential compared to Au, Pt, and Boron-Doped Diamond (BDD).
  • Co-Catalytic Role of IL: The ionic liquid [emim][EtSO4] functions as a co-catalyst when used as a supporting electrolyte in acetonitrile (AcN), lowering the CO2 reduction onset potential by approximately 200 mV compared to conventional electrolytes ([TBA][PF6]).
  • Cation-Specific Mechanism: The enhanced co-catalytic activity is specifically attributed to the imidazolium cation ([emim]+), which stabilizes the intermediate CO2- radical anion, facilitating the subsequent reduction step.
  • Product Confirmation: Carbon monoxide (CO) was electrochemically confirmed as the primary reduction product in both the neat IL and the IL/AcN mixed medium using CO stripping voltammetry.
  • Favorable Kinetics: The reaction exhibits a low apparent activation energy (Ea) of 13.04 J mol-1, indicating a fast reaction rate, which is further improved by increasing the system temperature (298 K to 373 K).
  • Process Viability: The resulting CO product is suitable for large-scale conversion into synthetic liquid fuels via the Fischer-Tropsch process or into methane via the Sabatier process, supporting CO2 mitigation strategies.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Best ElectrocatalystsAg, CuN/ALowest CO2ERR overpotential in neat [emim][EtSO4]
CO2ERR Onset Potential (Ag/Cu)-1.8V vs. Fc/Fc+In neat [emim][EtSO4]
CO2ERR Onset Potential (Pt)-2.3V vs. Fc/Fc+In neat [emim][EtSO4] (Highest OP)
Potential Shift (IL vs. Conventional)~200mVReduction potential lowered using [emim][EtSO4] vs. [TBA][PF6] in AcN
Apparent Activation Energy (Ea)13.04J mol-1Calculated from Arrhenius plot (298 K to 373 K)
CO2 Diffusion Coefficient (D)4.78 x 10-6cm2 s-1In [emim][EtSO4] (η = 108 cP)
CO2 Concentration (C)0.0183mol L-1In [emim][EtSO4]
Viscosity of [emim][EtSO4]108cPRoom temperature
Temperature Range Studied298 to 373KTemperature-dependent CO2ERR study
Ag Electrode ECSA4.78 x 10-2cm2Estimated via Pb UPD stripping
Cu Electrode ECSA4.11 x 10-2cm2Estimated via Pb UPD stripping

Key Methodologies

Section titled “Key Methodologies”

The electrochemical reduction and product analysis were performed using a three-necked glass cell and a conventional three-electrode configuration.

  1. Electrolyte Preparation: Experiments utilized either neat 1-ethyl-3-methylimidazolium ethyl sulfate ([emim][EtSO4]) or 0.1 M ILs dissolved in acetonitrile (AcN) for comparative studies.
  2. Electrode Configuration:
    • Working Electrodes: Ag, Cu, Au, BDD, and Pt disks (ECSA determined via Pb UPD or geometric area).
    • Counter Electrode: Pt flag.
    • Reference Electrode: Self-made Ag/Ag+ electrode, calibrated against the IUPAC-recommended ferrocene/ferrocenium (Fc/Fc+) redox couple.
  3. Gas Saturation: Solutions were purged with N2 or Ar for 30 min (blank) or saturated with CO2 for 60 min (reduction experiments).
  4. Electrochemical Characterization: Cyclic Voltammetry (CV) and Linear Sweep Voltammetry (LSV) were used to determine onset potentials and current densities across the temperature range of 298 K to 373 K.
  5. Kinetic Parameter Determination: Chronoamperometry (CA) was performed on an Au microelectrode, and the resulting current-time transients were fitted using the Shoup-Szabo equation to simultaneously determine the CO2 diffusion coefficient (D) and concentration (C).
  6. Product Analysis (CO Stripping):
    • A two-step process was used to confirm CO formation: (1) The Ag working electrode was held at a constant reduction potential (-2.33 V vs. Fc/Fc+) for 2,400 s to generate and adsorb CO. (2) A separate, freshly polished Pt disk was used as a second working electrode to adsorb the generated CO.
    • The Pt disk was then removed, rinsed, and immersed in 0.1 M aqueous HClO4 to voltammetrically strip off the adsorbed CO, confirming its presence via a characteristic oxidative peak.

Commercial Applications

Section titled “Commercial Applications”

This technology provides a highly efficient electrochemical route for CO2 utilization, relevant to industries focused on sustainable chemical production and climate mitigation.

  • Carbon Capture and Utilization (CCU): Provides a high-efficiency method for converting captured industrial CO2 emissions (e.g., from steel or cement fabrication) directly into valuable chemical intermediates (CO).
  • Synthetic Fuel Manufacturing: The primary product, CO, is a critical feedstock for synthesizing liquid fuels. This process can be integrated with:
    • Fischer-Tropsch Synthesis: Coupling CO production with green hydrogen (H2) to generate synthetic petrol and other liquid hydrocarbons.
    • Sabatier Process: Converting CO2 (via CO intermediate) and H2 into synthetic natural gas (methane, CH4).
  • Electrolyzer Technology: The use of imidazolium-based ionic liquids as co-catalytic electrolytes offers a pathway to reduce energy consumption (lower overpotential) and improve mass transport kinetics in industrial CO2 electrolyzer designs.
  • Renewable Energy Integration: The electrochemical nature of the process allows for direct coupling with intermittent renewable energy sources (solar, wind), enabling the storage of excess electricity in the form of chemical bonds (Power-to-X).
View Original Abstract

CO 2 electrochemical reduction reactions (CO 2 ERR) has shown great promise in reducing greenhouse gas emissions while also producing useful chemicals. In this contribution, we describe the CO 2 ERR at different catalysts using 1-ethyl-3-methylimidazolium ethyl sulfate [emim][EtSO 4 ] ionic liquid (IL) as a solvent and as a supporting electrolyte. CO 2 ERR occurs at Ag and Cu catalysts at a lower overpotential than that at Au, Pt, and boron-doped diamond (BDD) catalysts. In addition, we report that ILs play a better co-catalytic role when used as a supporting electrolyte during CO 2 ERR in an acetonitrile (AcN) medium than the conventional supporting electrolyte, tetrabutylammonium hexafluorophosphate [TBA][PF 6 ] in AcN. Furthermore, it is found that imidazolium-based cations ([emim] + ) play a significant co-catalytic role during the reduction compared to [TBA] + and pyrrolidinium [empyrr] + cations, while anions of the ILs play no such role. The formation of CO from the CO 2 ERR was detected using cyclic voltammetry at an Ag catalyst both in [emim][EtSO 4 ] as well as in an AcN solvent containing [emim][EtSO 4 ] as a supporting electrolyte. The product of the CO 2 reduction in this IL medium at the Ag catalyst is CO, which can be converted to synthetic liquid fuels by coupling the process with the Fischer-Tropsch process or through the conversion of CO 2 into fuels based on green hydrogen by the Sabatier process, that is, methanation of CO 2 on industrial scale, in the future.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2017 - CO2 activation over catalytic surfaces [Crossref]
  2. 2019 - Electrochemical reduction of CO2 to formate on easily prepared carbon-supported Bi nanoparticles [Crossref]
  3. 2010 - Inner-sphere heterogeneous electrode reactions. Electrocatalysis and photocatalysis: the challenge [Crossref]
  4. 2013 - Cation exchange on the nanoscale: an emerging technique for new material synthesis, device fabrication, and chemical sensing [Crossref]
  5. 2010 - Voltammetry in room temperature ionic liquids: comparisons and contrasts with conventional electrochemical solvents [Crossref]
  6. 2016 - High performance Fe porphyrin/ionic liquid Co‐catalyst for electrochemical CO2 reduction [Crossref]
  7. 2018 - Solar fuels: tailoring surface frustrated lewis pairs of In2O3−x(OH)y for gas‐phase heterogeneous photocatalytic reduction of CO2 by isomorphous substitution of In3+ with Bi3+ (adv. Sci. 6/2018) [Crossref]
  8. 2019 - CO2 electroreduction in ionic liquids [Crossref]
  9. 2018 - Homogeneously catalyzed electroreduction of carbon dioxide—methods, mechanisms, and catalysts [Crossref]
  10. 2024 - Modulating water hydrogen bonding within a non-aqueous environment controls its reactivity in electrochemical transformations [Crossref]

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