Electrochemical reduction of carbon dioxide

This article is about the electrochemical system. For related systems, see Photoelectrochemical reduction of carbon dioxide and Photochemical reduction of carbon dioxide.

The electrochemical reduction of carbon dioxide, also known as CO2RR, is the conversion of carbon dioxide (CO₂) to more reduced chemical species using electrical energy. It represents one potential step in the broad scheme of carbon capture and utilization.<ref>"Dream or Reality? Electrification of the Chemical Process Industries". www.aiche-cep.com. Retrieved 2021-08-22.</ref>

CO2RR can produce diverse compounds including formate (HCOO^-), carbon monoxide (CO), methane (CH₄), ethylene (C₂H₄), and ethanol (C₂H₅OH).<ref name="Jitaru">Appel AM, Bercaw JE, Bocarsly AB, Dobbek H, DuBois DL, Dupuis M, et al. (August 2013). "Frontiers, opportunities, and challenges in biochemical and chemical catalysis of CO2 fixation". Chemical Reviews. 113 (8): 6621–58. doi:10.1021/cr300463y. PMC 3895110. PMID 23767781.</ref> The main challenges are the relatively high cost of electricity (vs petroleum) and that CO₂ is often contaminated with O₂ and must be purified before reduction.

The first examples of CO2RR are from the 19th century, when carbon dioxide was reduced to carbon monoxide using a zinc cathode. Research in this field intensified in the 1980s following the oil embargoes of the 1970s. As of 2021, pilot-scale carbon dioxide electrochemical reduction is being developed by several companies, including Siemens,<ref>"CO2 is turned into feedstock". siemens-energy.com Global Website. Archived from the original on 2021-07-09. Retrieved 2021-07-04.</ref> Dioxide Materials,<ref>"CO2 Electrolyzers With Record Performance". Dioxide Materials. Retrieved 2021-07-04.</ref><ref>Masel, Richard I.; Liu, Zengcai; Yang, Hongzhou; Kaczur, Jerry J.; Carrillo, Daniel; Ren, Shaoxuan; Salvatore, Danielle; Berlinguette, Curtis P. (2021). "An industrial perspective on catalysts for low-temperature CO 2 electrolysis". Nature Nanotechnology. 16 (2): 118–128. Bibcode:2021NatNa..16..118M. doi:10.1038/s41565-020-00823-x. ISSN 1748-3395. OSTI 1756565. PMID 33432206. S2CID 231580446.</ref> Twelve and GIGKarasek. The techno-economic analysis was recently conducted to assess the key technical gaps and commercial potentials of the carbon dioxide electrolysis technology at near ambient conditions.<ref>Jouny, Matthew; Luc, Wesley; Jiao, Feng (2018-02-14). "General Techno-Economic Analysis of CO2 Electrolysis Systems". Industrial & Engineering Chemistry Research. 57 (6): 2165–2177. doi:10.1021/acs.iecr.7b03514. ISSN 0888-5885. OSTI 1712664.</ref><ref>Shin, Haeun; Hansen, Kentaro U.; Jiao, Feng (October 2021). "Techno-economic assessment of low-temperature carbon dioxide electrolysis". Nature Sustainability. 4 (10): 911–919. Bibcode:2021NatSu...4..911S. doi:10.1038/s41893-021-00739-x. ISSN 2398-9629. S2CID 235801320.</ref>

Chemicals from carbon dioxide

In carbon fixation, plants convert carbon dioxide into sugars, from which many biosynthetic pathways originate. The catalyst responsible for this conversion, RuBisCO, is the most common protein. Some anaerobic organisms employ enzymes to convert CO₂ to carbon monoxide, from which fatty acids can be made.<ref>Fontecilla-Camps JC, Amara P, Cavazza C, Nicolet Y, Volbeda A (August 2009). "Structure-function relationships of anaerobic gas-processing metalloenzymes". Nature. 460 (7257): 814–22. Bibcode:2009Natur.460..814F. doi:10.1038/nature08299. PMID 19675641. S2CID 4421420.</ref>

In industry, a few products are made from CO₂, including urea, salicylic acid, methanol, and certain inorganic and organic carbonates.<ref>Susan Topham, "Carbon Dioxide" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a05_165</ref> In the laboratory, carbon dioxide is sometimes used to prepare carboxylic acids in a process known as carboxylation. An electrochemical CO₂ electrolyzer that operates at room temperature has not yet been commercialized. Elevated temperature solid oxide electrolyzer cells (SOECs) for CO₂ reduction to CO are commercially available. For example, Haldor Topsoe offers SOECs for CO₂ reduction with a reported 6-8 kWh per Nm³<ref group="note">Normal Cubic Meter - the quantity of gas that occupies one cubic meter at standard temperature and pressure.</ref> CO produced and purity up to 99.999% CO.<ref>"Produce Your Own Carbon Monoxide - on-site and on-demand". www.topsoe.com. Haldor Topsoe. Archived from the original on 28 February 2021.</ref>

Electrocatalysis

The electrochemical reduction of carbon dioxide to various products is usually described as:

Reaction	Reduction potential Eo (V) at pH = 7 vs SHE <ref>Zhu D, Liu J, Qiao S (2016). "Recent Advances in Inorganic Heterogeneous Electrocatalysts for Reduction of Carbon Dioxide". Advanced Materials. 28 (18): 3423–3452. Bibcode:2016AdM....28.3423Z. doi:10.1002/adma.201504766. PMID 26996295.</ref>
CO2 + 2 H+ + 2 e− → CO + H2O	−0.52
CO2 + 2 H+ + 2 e− → HCOOH	−0.61
CO2 + 8 H+ + 8 e− → CH4 + 2 H2O	−0.24
2 CO2 + 12 H+ + 12 e− → C2H4 + 4 H2O	−0.34

The redox potentials for these reactions are similar to that for hydrogen evolution in aqueous electrolytes, thus electrochemical reduction of CO₂ is usually competitive with hydrogen evolution reaction.<ref name= Jitaru/>

Electrochemical methods have gained significant attention:

1. at ambient pressure and room temperature;
2. in connection with renewable energy sources (see also solar fuel)
3. competitive controllability, modularity and scale-up are relatively simple.<ref>Lee S, Lee J (February 2016). "Electrode Build-Up of Reducible Metal Composites toward Achievable Electrochemical Conversion of Carbon Dioxide". ChemSusChem. 9 (4): 333–44. Bibcode:2016ChSCh...9..333L. doi:10.1002/cssc.201501112. PMID 26610065.</ref>

The electrochemical reduction or electrocatalytic conversion of CO₂ can produce value-added chemicals such methane, ethylene, ethanol, etc., and the products are mainly dependent on the selected catalysts and operating potentials (applying reduction voltage). A variety of homogeneous and heterogeneous catalysts<ref>Hori Y (2008). "Electrochemical CO2 Reduction on Metal Electrodes". Modern Aspects of Electrochemistry. Vol. 42. pp. 89–80. doi:10.1007/978-0-387-49489-0_3. ISBN 978-0-387-49488-3.</ref> have been evaluated.<ref name="Centi" /><ref name='Jitaru'/>

Many such processes are assumed to operate via the intermediacy of metal carbon dioxide complexes.<ref>Benson EE, Kubiak CP, Sathrum AJ, Smieja JM (January 2009). "Electrocatalytic and homogeneous approaches to conversion of CO2 to liquid fuels". Chemical Society Reviews. 38 (1): 89–99. doi:10.1039/b804323j. PMID 19088968. S2CID 20705539.</ref> Many processes suffer from high overpotential, low current efficiency, low selectivity, slow kinetics, and/or poor catalyst stability.<ref name="B">Halmann MM, Steinberg M (May 1998). Greenhouse gas carbon dioxide mitigation: science and technology. CRC press. ISBN 1-56670-284-4.</ref>

The composition of the electrolyte can be decisive.<ref>Li, Fengwang; et al. (2020). "Molecular tuning of CO2-to-ethylene conversion". Nature. 577 (7791): 509–513. doi:10.1038/s41586-019-1782-2. PMID 31747679. S2CID 208217415.</ref><ref>Rosen BA, Salehi-Khojin A, Thorson MR, Zhu W, Whipple DT, Kenis PJ, Masel RI (November 2011). "Ionic liquid-mediated selective conversion of CO₂ to CO at low overpotentials". Science. 334 (6056): 643–4. Bibcode:2011Sci...334..643R. doi:10.1126/science.1209786. PMID 21960532. S2CID 31774347.</ref><ref>Service RF (1 September 2017). "Two new ways to turn 'garbage' carbon dioxide into fuel". Science Magazine. doi:10.1126/science.aap8497.</ref> Gas-diffusion electrodes are beneficial.<ref>Thorson MR, Siil KI, Kenis PJ (2013). "Effect of Cations on the Electrochemical Conversion of CO 2 to CO". Journal of the Electrochemical Society. 160 (1): F69–F74. doi:10.1149/2.052301jes. ISSN 0013-4651. S2CID 95111100.</ref><ref>Lv JJ, Jouny M, Luc W, Zhu W, Zhu JJ, Jiao F (December 2018). "A Highly Porous Copper Electrocatalyst for Carbon Dioxide Reduction". Advanced Materials. 30 (49): e1803111. Bibcode:2018AdM....3003111L. doi:10.1002/adma.201803111. OSTI 1712663. PMID 30368917. S2CID 53093014.</ref><ref>Dinh CT, Burdyny T, Kibria MG, Seifitokaldani A, Gabardo CM, García de Arquer FP, et al. (May 2018). "CO₂ electroreduction to ethylene via hydroxide-mediated copper catalysis at an abrupt interface". Science. 360 (6390): 783–787. doi:10.1126/science.aas9100. PMID 29773749.</ref>

Catalysts

Catalysts can be grouped by their primary products.<ref name="Centi">Centi G, Perathoner S (2009). "Opportunities and prospects in the chemical recycling of carbon dioxide to fuels". Catalysis Today. 148 (3–4): 191–205. doi:10.1016/j.cattod.2009.07.075.</ref><ref>Qiao J, Liu Y, Hong F, Zhang J (January 2014). "A review of catalysts for the electroreduction of carbon dioxide to produce low-carbon fuels". Chemical Society Reviews. 43 (2): 631–75. doi:10.1039/c3cs60323g. PMID 24186433.</ref><ref>Vayenas, Constantinos G.; White, Ralph E.; Gamboa-Aldeco, Maria E., eds. (2008). Modern Aspects of Electrochemistry. Vol. 42. doi:10.1007/978-0-387-49489-0. ISBN 978-0-387-49488-3.</ref> Several metal are unfit for CO₂RR because they promote to perform hydrogen evolution instead.<ref>Lin, Jiayi; Zhang, Yixiao; Xu, Pengtao; Chen, Liwei (2023-05-01). "CO2 electrolysis: Advances and challenges in electrocatalyst engineering and reactor design". Materials Reports: Energy. CO2 Reductions to Fuels and Carbon Feedstocks (Part 2). 3 (2): 100194. doi:10.1016/j.matre.2023.100194. ISSN 2666-9358.</ref> Electrocatalysts selective for one particular organic compound include tin or bismuth for formate and silver or gold for carbon monoxide. Copper produces multiple reduced products such as methane, ethylene or ethanol, while methanol, propanol and 1-butanol have also been produced in minute quantities.<ref>Ting LR, García-Muelas R, Martín AJ, Veenstra FL, Chen ST, Peng Y, et al. (November 2020). "Electrochemical Reduction of Carbon Dioxide to 1-Butanol on Oxide-Derived Copper". Angewandte Chemie. 59 (47): 21072–21079. doi:10.1002/anie.202008289. PMC 7693243. PMID 32706141.</ref>

Three common products are carbon monoxide, formate, or higher order carbon products (two or more carbons).<ref>Mok, Dong Hyeon; Li, Hong; Zhang, Guiru; Lee, Chaehyeon; Jiang, Kun; Back, Seoin (2023-11-11). "Data-driven discovery of electrocatalysts for CO2 reduction using active motifs-based machine learning". Nature Communications. 14 (1): 7303. doi:10.1038/s41467-023-43118-0. ISSN 2041-1723. PMC 10640609. PMID 37952012.</ref>

Carbon monoxide-producing

Carbon monoxide can be produced from CO₂RR over various precious metal catalysts.<ref>Marcandalli, Giulia; Monteiro, Mariana C. O.; Goyal, Akansha; Koper, Marc T. M. (2022-07-19). "Electrolyte Effects on CO 2 Electrochemical Reduction to CO". Accounts of Chemical Research. 55 (14): 1900–1911. doi:10.1021/acs.accounts.2c00080. ISSN 0001-4842. PMC 9301915. PMID 35772054.</ref> Steel has proven to be one such catalyst.,<ref>"How does coke and coal play into steel making? - Federal Steel Supply". 2016-06-22. Retrieved 2023-11-21.</ref> or hydrogen.<ref>"Hydrogen Production: Natural Gas Reforming". Energy.gov. Retrieved 2023-11-21.</ref>

Mechanistically, carbon monoxide arises from the metal bonded to the carbon of CO₂ (see metallacarboxylic acid). Oxygen is lost as water.<ref name=":0">Feaster, Jeremy T.; Shi, Chuan; Cave, Etosha R.; Hatsukade, Toru; Abram, David N.; Kuhl, Kendra P.; Hahn, Christopher; Nørskov, Jens K.; Jaramillo, Thomas F. (2017-07-07). "Understanding Selectivity for the Electrochemical Reduction of Carbon Dioxide to Formic Acid and Carbon Monoxide on Metal Electrodes". ACS Catalysis. 7 (7): 4822–4827. doi:10.1021/acscatal.7b00687. ISSN 2155-5435. OSTI 1390311.</ref>

Formate/formic acid-producing

Formic acid is produced as a primary product from CO₂RR over diverse catalysts.<ref>Valenti G, Melchionna M, Montini T, Boni A, Nasi L, Fonda E, et al. (2020). "Water-Mediated ElectroHydrogenation of CO2 at Near-Equilibrium Potential by Carbon Nanotubes/Cerium Dioxide Nanohybrids". ACS Appl. Energy Mater. 3 (9): 8509–8518. doi:10.1021/acsaem.0c01145. hdl:11368/2972442.</ref>

Catalysts that promote Formic Acid production from CO₂ operate by strongly binding to both oxygen atoms of CO₂, allowing protons to attack the central carbon. After attacking the central carbon, one proton attaching to an oxygen results in the creation of formate.<ref name=":0" /> Indium catalysts promote formate production because the Indium-Oxygen binding energy is stronger than the Indium-Carbon binding energy.<ref>Guo, Weiwei; Tan, Xingxing; Bi, Jiahui; Xu, Liang; Yang, Dexin; Chen, Chunjun; Zhu, Qinggong; Ma, Jun; Tayal, Akhil; Ma, Jingyuan; Huang, Yuying; Sun, Xiaofu; Liu, Shoujie; Han, Buxing (2021-05-12). "Atomic Indium Catalysts for Switching CO 2 Electroreduction Products from Formate to CO". Journal of the American Chemical Society. 143 (18): 6877–6885. doi:10.1021/jacs.1c00151. ISSN 0002-7863. PMID 33856799. S2CID 233257736.</ref> This promotes the production of formate instead of Carbon Monoxide.

C_>1-producing catalysts

Copper electrocatalysts produce multicarbon compounds from CO₂. These include C₂ products (ethylene, ethanol, acetate, etc.) and even C₃ products (propanol, acetone, etc.)<ref>Kuhl, Kendra P.; Cave, Etosha R.; Abram, David N.; Jaramillo, Thomas F. (2012-04-26). "New insights into the electrochemical reduction of carbon dioxide on metallic copper surfaces". Energy & Environmental Science. 5 (5): 7050–7059. doi:10.1039/C2EE21234J. ISSN 1754-5706.</ref> These products are more valuable than C1 products, but the current efficiencies are low.<ref name=":1">Kong, Qingquan; An, Xuguang; Liu, Qian; Xie, Lisi; Zhang, Jing; Li, Qinye; Yao, Weitang; Yu, Aimin; Jiao, Yan; Sun, Chenghua (2023-03-06). "Copper-based catalysts for the electrochemical reduction of carbon dioxide: progress and future prospects". Materials Horizons. 10 (3): 698–721. doi:10.1039/D2MH01218A. ISSN 2051-6355. PMID 36601800.</ref>

See also

• Electromethanogenesis
• Biobattery
• Electrofuel
• Lemon battery
• Photoelectrochemical reduction of carbon dioxide
• Photochemical reduction of carbon dioxide
• Electrolysis of water
• Electrochemical energy conversion
• Bioelectrochemical reactor

Further reading

• LaConti AB, Molter TM, Zagaja JA (May 1986). Electrochemical Reduction of Carbon Dioxide. Online: Information for the Defense Industry. Archived from the original on 27 March 2012.
• Fujita E (January 2000). Carbon Dioxide (Reduction). Upton, NY (United States): Brookhaven National Lab. (BNL).
• Neelameggham NR. "Carbon Dioxide Reduction Technologies: A Synopsis of the Symposium at TMS 2008". The Minerals, Metals & Materials Society (TMS).