Dioxide Materials

Carbon Dioxide electrolyzers are a major part of Dioxide Materials' business.[https://dioxidematerials.com Dioxide Materials website] The work started in response to a Department of Energy challenge to find better catalysts for electrochemical reduction of carbon dioxide.A. Bell et al. Basic research needs catalysts for energy, DOE PNNL-17214 {{URL|https://www.pnnl.gov/science/images/highlights/cmsd/cat_rpt_print.pdf|   }} At the time the overpotential (i.e. wasted voltage) was too high, and the rate too low for practical applications.Halmann and Steinberg, "Greenhouse Gas Carbon Dioxide Mitigation," Lewis Publishers, 1999. {{ISBN|1-56670-284-4}} Workers at Dioxide Materials theorized that a bifunctional catalyst consisting of a metal and an ionic liquid might lower the overpotential for electrochemical reduction of carbon dioxide. Indeed, it was found that the combination of two catalysts, silver nanoparticles and an ionic liquid solution containing equal volumes of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4) and water, reduced the overpotential for CO₂ conversion to carbon monoxide (CO) from about 1 volt to only 0.17 volts.Brian A. Rosen, Amin Salehi-Khojin, Michael R. Thorson, W. Zhu, Devin T. Whipple, Paul J. A. Kenis, Richard I Masel *, Ionic Liquid-Mediated Selective Conversion of CO₂ to CO at Low Overpotentials, Science Vol. 334 no. 6056 pp. 643-644 (2011) {{doi|10.1126/science.1209786 |   }}. Workers from other laboratories have subsequently reproduced the findings on many metals, and with several ionic liquids.Citations for Ionic Liquid-Mediated Selective Conversion of CO₂ to CO at Low Overpotentials [https://scholar.google.com/scholar?oi=bibs&hl=en&cites=13981080967619623958&as_sdt=5  ] Dioxide Materials has shown that a similar enhancement occurs during alkaline water electrolysisR. I. Masel, Z. Liu, and S. D. Sajjad Anion Exchange Membrane Electrolyzers Showing 1 A/cm2 at Less Than 2 V, ECS Transactions, 75 (14) 1143-1146 (2016) {{doi|10.1149/07514.1143ecst}}Zengcai Liu, Syed Dawar Sajjad, Yan Gao, HongzhouYang. Jerry J.Kaczur. Richard I.Masel, The effect of membrane on an alkaline water electrolyzer, International Journal of Hydrogen Energy 42(50), 29661-29665 (2017) {{doi |10.1016/j.ijhydene.2017.10.050}} and the hydrocarboxylation of acetylene Richard I. Masel, Zheng Richard Ni, Qingmei CHEN, Brian A. Rosen, Process for the sustainable production of acrylic acid, US Patent 9790161 [https://patents.google.com/patent/US9790161] ("Reppe chemistry").

File:CO2_electrolysis_pathway.pngAt this point, there is still some question about how the imidazolium is able to lower the overpotential for the electrochemical reduction of carbon dioxide. The first step in the electrolysis of CO₂ is the addition of an electron into the CO₂ or a molecular complex containing CO₂. The resultant species is labeled "CO₂¯" in the figure on the left. It requires at least an electron-volt of energy per molecule to form the species in the absence of the ionic liquid.Chemistry Views (Elsevier) Converting CO₂ with Less Energy {{URL| http://www.chemistryviews.org/details/news/1362657/Converting_CO2_with_Less_Energy.html|  }} That electron-volt of energy is largely wasted during the reaction. Rosen at al postulated that a new complex forms in presence of the ionic liquid so that 1 eV of energy is not wasted. The complex allows the reaction to follow the green pathway on the figure on the right. Recent work suggests that the new complex is a zwitterionMark Pellerite, Marina Kaplun, Claire Hartmann-Thompson, Krzysztof A. Lewinski, Nancy Kunz, Travis Gregar, John Baetzold, Dale Lutz, Matthew Quast, Zengcai Liu, Hongzhou Yang, Syed D. Sajjad, Yan Gao, and Rich Masel Imidazolium-Functionalized Polymer Membranes for Fuel Cells and Electrolyzers, ECS Trans. 2017 80(8): 945-956; {{doi | 10.1149/08008.0945ecst }} Other possible pathways (i.e. non-zwitterions) are discussed in Keith et al.John A. Keith and Emily A. Carter,

Theoretical Insights into Electrochemical CO2 Reduction Mechanisms Catalyzed by Surface-Bound Nitrogen Heterocycles, J. Phys. Chem. Lett., 2013, 4 (23), pp 4058–4063 {{doi | 10.1021/jz4021519}} Rosen at al.Jonathan Rosen, Gregory S. Hutchings, Qi Lu, Sean Rivera, Yang Zhou, Dionisios G. Vlachos, and Feng Jiao, Mechanistic Insights into the Electrochemical Reduction of CO2 to CO on Nanostructured Ag Surfaces, ACS Catal., 2015, 5 (7), pp 4293–4299 {{doi| 10.1021/acscatal.5b00840}} Verdaguer-Casadevall et al.Arnau Verdaguer-Casadevall, Christina W. Li‡, Tobias P. Johansson, Soren B. Scott, Joseph T. McKeown, Mukul Kumar, Ifan E. L. Stephens, Matthew W. Kanan*, and Ib Chorkendorff* Probing the Active Surface Sites for CO Reduction on Oxide-Derived Copper Electrocatalysts, J. Am. Chem. Soc., 2015, 137 (31), pp 9808–9811

{{doi | 10.1021/jacs.5b06227}} and Shi et al.Chuan Shi, Heine A. Hansen, Adam C. Lauscheb, and Jens K. Nørskov, Trends in electrochemical CO2 reduction activity for open and close-packed metal surfaces, Phys. Chem. Chem. Phys., 2014,16, 4720-4727 {{doi | 10.1039/C3CP54822H }}

File:Sustainion_37_labeled.pngUnfortunately, ionic liquids were found to be too corrosive to be used in practical carbon dioxide electrolyzers. Ionic liquids are strong solvents. They dissolve/corrode the seals, carbon electrodes and other parts in commercial electrolyzers. As a result, they were difficult to be used in practice.

In order to avoid the corrosion, Dioxide Materials switched from ionic liquid catalysts to catalytic anion exchange polymers.R. I. Masel, Qingmei Chen, Zengcai liu, Robert Kutz, Ion Conducting Polymers, US patent 9580824 {{ URL|https://patents.google.com/patent/US9580824B2 |   }}Richard I. Masel, Amin Salehi-Khojin, Robert Kutz, Electrocatalytic process for carbon dioxide conversion, US Patent 981501 {{URL | https://www.google.com/patents/US9815021 |   }} A number of polymers were tested and the imidazolium functionalized styrene polymer shown in the figure on the right showed the best performance.Robert Brian Kutz, Qingmei Chen, Hongzhou Yang, Syed Dawar Sajjad, Zengcai Liu, Richard Masel, Sustainion Imidazolium-functionalized Polymers for Carbon Dioxide Electrolysis, Energy Technology 5, (6) 929-936 (2017) {{doi| 10.1002/ente.201600636 }} The membranes were trade named Sustainion. The use of Sustainion membranes raised the current and lifetime of the CO₂ electrolyzer into the commercially useful range.R.F. Service, Two new ways to turn ‘garbage’ carbon dioxide into fuel Science, Sept 1, 2017 {{URL| http://www.sciencemag.org/news/2017/09/two-new-ways-turn-garbage-carbon-dioxide-fuel |   }}Steven K Ritter, CO₂ Electrolyzer Nears Commercialization, C&E News, Volume 93 Issue 13 | p. 30 . March 30, 2015{{URL|https://cen.acs.org/articles/93/i13/CO2-Electrolyzer-Nears-Commercialization.html |  }}Mark Harris, The entrepreneurs turning carbon dioxide into fuels, The Guardian, 14 Sept 2017 {{URL| https://www.theguardian.com/sustainable-business/2017/sep/14/entrepreneurs-turn-carbon-dioxide-into-fuels-artificial-photosynthesis |   }}SAVVY: Turning Carbon Dioxide into products New Straitus Times, Dec 3, 2017. {{URL| https://www.nst.com.my/lifestyle/sunday-vibes/2017/12/310154/savvy-turning-carbon-dioxide-products |  }}Michael Foertsch, These methods turn CO2 into cheap energy, Wired, Sept 24, 2017{{URL| https://www.wired.de/collection/science/wissenschaft-co2-energie|   }} Sustainion membranes have shown conductivities above 100 mS/cm under alkaline conditions at 60 °C, stability for thousands of hours in 1M KOH, and offer a physical mechanical stability that is useful for many different applications. The membranes showed a lifetime over 3000 hours in CO₂ electrolyzers at high current densities.Syed D. Sajjad, Yan Gao, Zengcai Liu, Hongzhou Yang and Rich Masel Tunable-High Performance Sustainion™ Anion Exchange Membranes for Electrochemical Applications ECS Transactions, 77(11): 1653-1656 (2017) {{ doi| 10.1149/07711.1653ecst |  }} More recent research has noted that a cell membrane that has an optimized cathode has the capability of running for up to 158 days at 200 mA/cm² .Zengcai Liu et al 2018 J. Electrochem. Soc. 165 J3371

DOI 10.1149/2.0501815jes

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