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

Metadata	Details
Publication Date	2025-04-09
Journal	Frontiers in Chemistry
Authors	Sayyar Muhammad, Asad Ali
Institutions	Islamia College University, Luleå University of Technology
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for CO₂ Electroreduction

Executive Summary

This research demonstrates the use of various electrode materials, including Boron-Doped Diamond (BDD), for the efficient electrocatalytic reduction of carbon dioxide (CO₂ERR) in ionic liquid (IL) media. While Ag and Cu showed the lowest overpotentials in this specific [emim][EtSO₄] IL, the study validates the use of diamond materials in highly corrosive, high-temperature electrochemical environments.

Application Validation: Confirms the viability of MPCVD diamond (BDD) electrodes for CO₂ERR and synthetic fuel production (CO via Fischer-Tropsch or Sabatier processes).
Material Stability: BDD electrodes were successfully tested in the highly viscous, high-temperature ionic liquid [emim][EtSO₄] (up to 373 K), leveraging diamond’s inherent chemical and thermal stability.
Electrochemical Performance: BDD exhibited an onset potential of -2.2 V vs. Fc/Fc⁺ for CO₂ reduction, confirming its wide electrochemical window (EW) capability essential for non-aqueous electrochemistry.
Key Kinetic Data: The study determined the CO₂ diffusion coefficient (D) in the IL medium (4.78 x 10⁻⁶ cm² s⁻¹) and the low apparent activation energy (Ea) on Ag (13.04 J mol⁻¹), providing critical design parameters for future reactor development.
Co-Catalytic Role: The research highlights the crucial co-catalytic role of the imidazolium cation ([emim]⁺) in stabilizing the intermediate CO₂ radical anion, a mechanism potentially transferable to optimized BDD surfaces.
6CCVD Value Proposition: 6CCVD provides the high-purity, custom-dimension BDD wafers and specialized metalization required to replicate and advance high-stability electrocatalysis research.

Technical Specifications

The following hard data points were extracted from the electrochemical analysis of CO₂ERR in [emim][EtSO₄] ionic liquid.

Parameter	Value	Unit	Context
BDD Onset Potential	-2.2	V vs. Fc/Fc⁺	CO₂ERR in neat [emim][EtSO₄]
Ag/Cu Onset Potential	-1.8	V vs. Fc/Fc⁺	Lowest overpotential observed in neat IL
Pt Onset Potential	-2.3	V vs. Fc/Fc⁺	Highest overpotential observed in neat IL
CO₂ Diffusion Coefficient (D)	4.78 x 10⁻⁶	cm² s⁻¹	In [emim][EtSO₄] at room temperature
CO₂ Concentration (C)	0.0183	mol L⁻¹	In [emim][EtSO₄] at room temperature
Apparent Activation Energy (Ea)	13.04	J mol⁻¹	For CO₂ERR on Ag catalyst
Temperature Range Tested	298 to 373	K	Temperature-dependent LSV profiles
BDD Geometrical Surface Area	7.07 x 10⁻²	cm²	Working electrode dimension
CO₂ Reduction Product	CO	N/A	Confirmed via CO stripping peak

Key Methodologies

The electrochemical experiments utilized standard three-electrode configurations, focusing on precise material preparation and controlled atmospheric conditions, which are critical for IL and non-aqueous electrochemistry.

Electrode Preparation:
- Working electrodes (Ag, Cu, Au, Pt, BDD disks) were polished using soft pads and 0.05 µm alumina suspension.
- Electrodes were thoroughly rinsed with deionized water and dried under N₂ stream.
Electrochemical Cell Setup:
- Three-necked glass cell configuration used for Cyclic Voltammetry (CV), Linear Sweep Voltammetry (LSV), and Chronoamperometry (CA).
- Reference Electrode: Self-made Ag/Ag⁺ reference electrode, calibrated against the IUPAC-recommended ferrocene/ferrocenium (Fc/Fc⁺) redox couple.
Atmospheric Control:
- Solutions were purged with N₂ or Ar for 30 minutes to eliminate dissolved oxygen (blank measurements).
- CO₂ saturation was achieved by purging the IL or AcN solution for 60 minutes prior to measurement.
Temperature Control:
- Temperature-dependent studies were conducted on the Ag electrode at 298 K, 323 K, 353 K, and 373 K to analyze kinetic effects.
Product Analysis:
- Chronoamperometry was used to generate CO, which was then adsorbed onto a secondary Pt working electrode.
- CO formation was verified by voltammetrically stripping the adsorbed CO in 0.1 M aqueous HClO₄, observing a characteristic CO stripping peak.

6CCVD Solutions & Capabilities

The research highlights the need for robust, high-purity electrode materials capable of operating reliably in aggressive, high-viscosity ionic liquids and at elevated temperatures. 6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials necessary to replicate and scale this CO₂ERR research.

Applicable Materials

To replicate the BDD electrode performance and explore optimization pathways for CO₂ERR, 6CCVD recommends the following materials:

6CCVD Material	Specification	Application Relevance
Heavy Boron-Doped Diamond (BDD)	Polycrystalline (PCD) or Single Crystal (SCD) options. Doping levels up to 10²¹ atoms/cm³.	Provides the widest electrochemical window and superior stability required for IL and high-temperature electrochemistry (up to 373 K).
Optical Grade SCD	SCD plates, Ra < 1 nm polishing. Thickness 0.1 µm - 500 µm.	Ideal for fundamental studies requiring ultra-low surface roughness and high crystal purity, minimizing background currents.
High-Purity PCD Wafers	Plates up to 125 mm diameter. Ra < 5 nm polishing for inch-size wafers.	Suitable for scaling up electrode surface area for industrial feasibility studies and high-current density applications.

Customization Potential

The paper utilized specific disk geometries and required precise surface preparation. 6CCVD’s in-house engineering capabilities directly address these needs:

Custom Dimensions and Geometry: The paper used BDD disks with a geometrical surface area of 7.07 x 10⁻² cm². 6CCVD offers custom laser cutting and shaping of BDD plates and wafers up to 125 mm to meet exact reactor specifications (e.g., specific disk, ring, or mesh geometries).
Advanced Polishing: The study required careful polishing (0.05 µm alumina). 6CCVD guarantees ultra-smooth surfaces (Ra < 1 nm for SCD, Ra < 5 nm for PCD) essential for reproducible electrochemical measurements and minimizing non-catalytic surface effects.
Integrated Metalization: The experiment required Ag, Au, and Pt electrodes, as well as an Ag/Ag⁺ reference electrode. 6CCVD offers internal metalization services (Au, Pt, Pd, Ti, W, Cu) directly onto diamond substrates, enabling the creation of integrated, stable reference electrodes or multi-catalyst arrays on a single diamond platform.

Engineering Support

The finding that BDD exhibited a higher overpotential (-2.2 V) compared to Ag (-1.8 V) suggests that the BDD surface chemistry or doping profile used in the study was not optimized for the [emim]⁺ co-catalytic mechanism.

Surface Optimization: 6CCVD’s in-house PhD team specializes in tailoring BDD surface termination (e.g., hydrogen, oxygen, or fluorine) and optimizing boron doping concentration to enhance specific catalytic pathways, such as stabilizing the CO₂ radical anion intermediate.
Material Selection for CO₂ERR: We provide expert consultation on selecting the optimal diamond type (SCD vs. PCD) and doping level to maximize Faradaic efficiency and lower overpotential for similar CO₂ mitigation projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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

Original Source

DOI: https://doi.org/10.3389/fchem.2025.1515903

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