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CO2 electrochemical reduction in ionic liquid/deep eutectic solvent-based systems: Technology development to process evaluation
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.ORCID iD: 0000-0001-9841-8285
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

CO2 conversion plays an important role in mitigating the issues caused by CO2 emissions. Among different CO2 conversion technologies, CO2 electrochemical reduction (CO2R) is considered as one of the most promising ways, but it still suffers from high overpotential, low reaction rate, and low selectivity. Ionic liquids (ILs) and deep eutectic solvents (DESs), as novel solvents with many unique advantages, such as wide electrochemical window, high stability, and tunable nature, have been widely used as electrolytes for CO2R to reduce the overpotential and improve reaction performance. Currently, numerous studies on CO2R with IL/DES-based electrolytes have primarily focused on fundamental research, providing insights into CO2R performance improvement and reaction mechanism analysis, but research on evaluating the techno-economic and environmental feasibility of CO2R is very limited. Meanwhile, from an experimental viewpoint, how to further improve the performance of CO2R by designing/modifying catalysts and electrolytes is another concern.

This work aims to systematically study the techno-economic and environmental feasibility of the CO2R process under current and future conditions, along with technology development focused on designing novel catalysts and electrolytes for CO2R, where ILs/DESs were used as electrolytes. Since CO2 can be converted to different chemicals/fuels, such as CO, syngas, HCOOH, CH3OH, CH4, and some multi-carbon compounds. The research status, difficulties, as well as the future research focuses for producing different products need to be clear. To this end, a comprehensive literature survey was conducted to highlight recent progress, to offer an overview of the state-of-the-art advancements, and to identify research gaps in CO2R within IL-based systems. Based on the literature survey, CO, syngas, and CH3OH have been identified as particularly attractive products, considering both CO2R performance and the challenges associated with product separation. 

Based on the results from the literature survey, a comprehensive assessment model for the integrated (CO2R + biomass gasification) process was established, enabling the evaluation of key performance parameters and commercialization potential for both stand-alone and combined processes. In terms of technology development, a molecule-regulated Ag catalyst was designed for CO2R in the IL-based system, where its reaction performance and mechanisms were thoroughly analyzed. Additionally, DES-based solvents were selected as electrolytes for CO2R with Ag as the catalyst, and the effect of electrolytes on CO2R performance was studied. The main results are summarized below.

The stand-alone CO2R process for producing CH3OH in IL-based electrolytes was first established and then further integrated with biomass gasification. The economic and environmental viability of these processes under current and future conditions was thoroughly examined. The high total production cost (TPC) of the stand-alone CO2R process is primarily driven by the significant expenses associated with the electrolyzer and electricity. After integration, TPC can be reduced from 1.44 to 1.02 €/kg-CH3OH. In the integrated process, electricity for CO2R constitutes the main portion of energy usage and is the predominant contributor to CO2 emissions.

A techno-economic analysis was conducted on the integrated processes of CO2R to CO/syngas/CH3OH, combined with biomass gasification for CH3OH production. Among these processes, the process combined with CO2R to CO showed the lowest TPC of 0.38 €/kg-CH3OH under current conditions, which is below the market price of CH3OH (0.50 €/kg-CH3OH). Sensitivity analysis revealed that electricity price is a crucial factor affecting TPC for all combined processes. In addition, CO2R performance and stack price significantly impact TPC in processes that involve CO2R to syngas and CH3OH.

Experimental research on CO2R to CO was conducted with a molecule-regulated catalyst in BmimPF6-based electrolytes. Specifically, the molecule with desirable CO2 affinity, 3-mercapto-1,2,4-triazole (m-Triz), was introduced onto the surface of Ag to obtain the Ag-m-Triz catalyst. This catalyst demonstrated desirable performance, achieving a partial CO current density of 85.0 mA/cm2 and a Faradaic efficiency of CO of 99.2% at -2.3 V vs. Ag/Ag+. Mechanism studies revealed that the enhanced performance is due to the increased CO2 adsorption ability and the reduced binding energy for the formation of the COOH* intermediate, resulting from the introduction of m-Triz on the surface of the Ag catalyst. 

To investigate the effect of electrolytes on CO2R, a DES-based non-aqueous electrolyte, 0.5 M 1-butyl-3-methylimidazolium chloride/ethylene glycol (BmimCl-EG) with a mole ratio of 1:2 in acetonitrile (AcN), was used as catholyte for CO2R to CO over Ag. The results showed that the highest Faradaic efficiency could reach 100% within the potential range of -2.0 to -2.4 V vs. Ag/Ag+, which is 1.43 times higher than the maximum Faradaic efficiency achieved in 0.5 M KHCO3. Additionally, the overpotential was reduced by 150 mV, and the current densities increased significantly across various applied potentials compared to the results obtained using 0.5 M BmimCl in AcN. In situ ATR-SEIRA measurements confirmed that EG, acting as a hydrogen bond donor, participated in the CO2R process, thereby enhancing the reaction performance.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2024.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords [en]
CO2 electrochemical reduction, Ionic liquid, Deep eutectic solvent, Catalyst, Biomass gasification, Techno-economic analysis, Environmental assessment
National Category
Energy Engineering
Research subject
Energy Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-110331ISBN: 978-91-8048-664-4 (print)ISBN: 978-91-8048-665-1 (electronic)OAI: oai:DiVA.org:ltu-110331DiVA, id: diva2:1904973
Public defence
2024-12-12, E632, Luleå University of Technology, Luleå, 09:00 (English)
Opponent
Supervisors
Available from: 2024-10-11 Created: 2024-10-10 Last updated: 2024-10-11Bibliographically approved
List of papers
1. Ionic liquids for CO2 electrochemical reduction
Open this publication in new window or tab >>Ionic liquids for CO2 electrochemical reduction
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2021 (English)In: Chinese Journal of Chemical Engineering, ISSN 1004-9541, E-ISSN 2210-321X, Vol. 31, p. 75-93Article, review/survey (Refereed) Published
Abstract [en]

Electrochemical reduction of CO2 is a novel research field towards a CO2-neutral global economy and combating fast accelerating and disastrous climate changes while finding new solutions to store renewable energy in value-added chemical and fuels. Ionic liquids (ILs), as medium and catalysts (or supporting part of catalysts) have been given wide attention in the electrochemical CO2 reduction reaction (CO2RR) due to their unique advantages in lowering overpotential and improving the product selectivity, as well as their designable and tunable properties. In this review, we have summarized the recent progress of CO2 electro-reduction in IL-based electrolytes to produce higher-value chemicals. We then have highlighted the unique enhancing effect of ILs on CO2RR as templates, precursors, and surface functional moieties of electrocatalytic materials. Finally, computational chemistry tools utilized to understand how the ILs facilitate the CO2RR or to propose the reaction mechanisms, generated intermediates and products have been discussed.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
Carbon dioxide, ionic liquids, electro-reduction, electrolyte, electrocatalytic material, computer simulation
National Category
Energy Engineering
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-81828 (URN)10.1016/j.cjche.2020.10.029 (DOI)000651052400010 ()2-s2.0-85101008472 (Scopus ID)
Note

Validerad;2021;Nivå 2;2021-06-07 (alebob)

Available from: 2020-12-03 Created: 2020-12-03 Last updated: 2024-10-10Bibliographically approved
2. Energy, Cost, and Environmental Assessments of Methanol Production via Electrochemical Reduction of CO2 from Biosyngas
Open this publication in new window or tab >>Energy, Cost, and Environmental Assessments of Methanol Production via Electrochemical Reduction of CO2 from Biosyngas
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2023 (English)In: ACS Sustainable Chemistry and Engineering, E-ISSN 2168-0485, Vol. 11, no 7, p. 2810-2818Article in journal (Refereed) Published
Abstract [en]

Electrochemical reduction of CO2 removed from biosyngas into value-added methanol (CH3OH) provides an attractive way to mitigate climate change, realize CO2 utilization, and improve the overall process efficiency of biomass gasification. However, the economic and environmental feasibilities of this technology are still unclear. In this work, economic and environmental assessments for the stand-alone CO2 electrochemical reduction (CO2R) toward CH3OH with ionic liquid as the electrolyte and the integrated process that combined CO2R with biomass gasification were conducted systematically to identify key economic drivers and provide technological indexes to be competitive. The results demonstrated that costs of investment associated with CO2R and electricity are the main contributors to the total production cost (TPC). Integration of CO2R with CO2 capture/purification and biomass gasification could decrease TPC by 28%-66% under the current and future conditions, highlighting the importance of process integration. Energy and environmental assessment revealed that the energy for CO2R dominated the main energy usage and CO2 emissions, and additionally, the energy structure has a great influence on environmental feasibility. All scenarios could provide climate benefits over the conventional coal-to-CH3OH process if renewable sources are used for electricity generation.

Place, publisher, year, edition, pages
American Chemical Society, 2023
Keywords
carbon dioxide, economic analysis, Electrochemical reduction, energy, environmental assessment, methanol production
National Category
Energy Engineering
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-95680 (URN)10.1021/acssuschemeng.2c05968 (DOI)000929071000001 ()2-s2.0-85147820420 (Scopus ID)
Funder
Swedish Energy Agency, P47500-1
Note

Validerad;2023;Nivå 2;2023-02-22 (hanlid)

Available from: 2023-02-22 Created: 2023-02-22 Last updated: 2024-10-10Bibliographically approved
3. Combination of CO2 electrochemical reduction and biomass gasification for producing methanol: A techno-economic assessment
Open this publication in new window or tab >>Combination of CO2 electrochemical reduction and biomass gasification for producing methanol: A techno-economic assessment
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2024 (English)In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 307, article id 118380Article in journal (Refereed) Published
Abstract [en]

Combining CO2 electrochemical reduction (CO2R) and biomass gasification for producing methanol (CH3OH) is a promising option to increase the carbon efficiency, reduce total production cost (TPC), and realize the utilization of byproducts of CO2R system, but its viability has not been studied. In this work, systematic techno-economic assessments for the processes that combined CO2R to produce CO/syngas/CH3OH with biomass gasification were conducted and compared to stand-alone biomass gasification and CO2R processes, to identify the benefits and analyze the commercialization potential of different pathways under current and future conditions. The results demonstrated that the process that combined biomass gasification with CO2R to CO represents a viable pathway with a competitive TPC of 0.39 €/kg-CH3OH under the current condition. For all the combined cases, electricity usage for CO2R accounts for 36–76% of total operating cost, which plays a key role for TPC. Sensitivity analysis confirmed that the process that combined biomass gasification with CO2R to CO is sensitive to the price of electricity, while both CO2R performance and prices of stack and electricity are important for the processes that combined with CO2R to syngas/CH3OH.

Place, publisher, year, edition, pages
Elsevier, 2024
Keywords
Biomass gasification, Carbon dioxide, Combination, Electrochemical reduction, Methanol production, Techno-economic analysis
National Category
Energy Engineering
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-105085 (URN)10.1016/j.enconman.2024.118380 (DOI)2-s2.0-85189673723 (Scopus ID)
Funder
Swedish Energy Agency, P47500-1The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), CH2019-8287
Note

Validerad;2024;Nivå 2;2024-04-15 (hanlid);

Full text license: CC BY 4.0

Available from: 2024-04-15 Created: 2024-04-15 Last updated: 2024-10-10Bibliographically approved
4. Boosting electrochemical reduction of CO2 to CO using molecule-regulated Ag nanoparticle in ionic liquids
Open this publication in new window or tab >>Boosting electrochemical reduction of CO2 to CO using molecule-regulated Ag nanoparticle in ionic liquids
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2024 (English)In: Green Energy & Environment, E-ISSN 2468-0257Article in journal (Refereed) Epub ahead of print
Abstract [en]

Electrochemical reduction of CO2 is a promising approach to convert CO2 to high-valued chemicals and fuels. However, developing efficient electrocatalysts featuring desirable activity and selectivity is still a big challenge. In this work, a strategy of introducing functionalized molecules with desirable CO2 affinity to regulate Ag catalyst for promoting electrochemical reduction of CO2 was proposed. Specifically, 3-mercapto-1,2,4-triazole was introduced onto the Ag nanoparticle (Ag-m-Triz) for the first time to achieve selectively converting CO2 to carbon monoxide (CO). This Ag-m-Triz exhibits excellent performance for CO2 reduction with a high CO Faradaic efficiency (FECO) of 99.2% and CO partial current density of 85.0 mA/cm2 at -2.3 V vs. Ag/Ag+ in H-cell when combined with the ionic liquid-based electrolyte, 30 wt% 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6])-65 wt% acetonitrile (AcN)-5 wt% H2O, which is 2.5-fold higher than the current density in Ag-powder under the same condition. Mechanism studies confirm that the significantly improved performance of Ag-m-Triz originates from (i) the stronger adsorption ability of CO2 molecule and (ii) the weaker binding energy to form the COOH* intermediate on the surface of Ag-m-Triz compared with the Ag-powder catalyst, which boosts the conversion of CO2 to CO. This research provides a facile way to regulate electrocatalysts for efficient CO2 reduction by introducing functionalized molecules.

Place, publisher, year, edition, pages
Elsevier, 2024
Keywords
CO2 reduction, CO, electrochemical, molecule-regulated, silver, ionic liquid
National Category
Materials Chemistry Physical Chemistry
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-110294 (URN)10.1016/j.gee.2024.07.005 (DOI)
Note

Funder: Swedish Energy Agency (P47500-1); National Key R&D Program of China (2020YFA0710200); National Natural Science Foundation of China (22378401 and U22A20416);

Available from: 2024-10-09 Created: 2024-10-09 Last updated: 2024-10-10
5. Efficient CO2 electrochemical reduction to CO facilitated by deep eutectic solvents
Open this publication in new window or tab >>Efficient CO2 electrochemical reduction to CO facilitated by deep eutectic solvents
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(English)Manuscript (preprint) (Other academic)
National Category
Other Chemical Engineering
Research subject
Energy Engineering
Identifiers
urn:nbn:se:ltu:diva-110329 (URN)
Available from: 2024-10-10 Created: 2024-10-10 Last updated: 2024-10-11

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1617181920212219 of 25
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