On June 24, 2020, Dr. Paul Kenis, 2020 winner of the Energy Technology Division Research Award, presented his talk on “Electrochemical CO2 Reduction: Path Towards a Carbon Neutral Chemical Industry?” via a live webinar presentation.
Dr. Kenis’s talk covered a summary of the status of CO2 electrocatalysis, the techno-economic and life-cycle analysis of CO2 electrolysis to identify remaining hurdles, and the prospects of CO2 electrolysis technology contributing to a future sustainable chemical industry.
View Dr. Kenis’s webinar presentation, here.
Following the talk, attendees were given the opportunity to ask Dr. Kenis questions in a Q&A session, available below.
Q&A with Dr. Paul Kenis
Q: What is the current state of the art in terms of computational modeling of these systems? (Question 1)
A: For the most commonly used catalysts (Ag, Au, Cu), understanding of reaction mechanisms in CO2 reduction is pretty detailed now. Search for work by Marc Koper, Jens Norskov, Karen Chan, …
Q: What method did you use to incorporate Ag on the surface of carbon foam?
A: We use a spray deposition setup (using a spray painter tool from a typical art store), described here: Adv. Energy Mat., 2013, 3 (5), 589-599.
Q: Which of the two species (formic acid, formate) was taken as reference for the calculation of the economic feasibility of the CO2 conversion to formic acid/formate. In other words: Is there a smart way to convert formate to the more valuable formic acid without dramatically altering the business case?
A: Excellent question; this also relates to cost of separation of the formate/formic acid from the electrolyte, both the conversion and separation are related. I don’t recall what we did for the data on my slides, but it should be in our Nature Energy 2019 paper (Verma, Lu, Kenis).
Q: Do you evaporate much water from your cells that you need to recover? What temperatures do you run at?
A: We run at or close to room temperature in most systems. Recent efforts by us and others are looking at cells that can be operated at elevated temperatures.
Q: How do you avoid co2 generation in the GDE? How do you avoid cO2 generation on the GDE as the GDE is graphite made?
A: On the cathode, the problem (side reaction) is H2 generation on the graphite/carbon exposed. On the anode, unless we have massive amounts of carbonate formation at the cathode that diffuses to the anode, we do not have much CO2 production on the anode. This may become an issue in different cell configurations, e.g. a cell based on an anion exchange membrane.
Q: Did you use a composite anode GDE?
A: All GDEs are commercially available carbon papers (e.g., Sigracet 35bc), that we then cover with catalyst via spray coating.
Q: Have you tried alkaline membrane instead of KOH solution? (question #7)
A: This is an active area of research in several labs, including ours. It works.
Q: Do you use the same type of GDE for the anode?
A: Yes, typically the same GDE is used on the anode and cathode, but going forward, tailoring each to the reaction taking place is expected to lead to further performance improvements.
Q: Does the techno-analysis models work the same for a steel plant and a home boiler?
A: The TEA models can be applied to any system; the outcome will be different for these systems; economics work much better at larger scales.
Q: Is it possible that with increasing electrification to reduce CO2 we can increase the impact of the “electricity” component neutralizing the effort to reduce CO2? Slide 8
A: Yes, absolutely. With a higher fraction of renewables in the grid, the electricity component has a lower CO2/kWh burden. In general, electrification of transportation, for example, reduces the impact of the fossil fuels that produce most of the CO2.
Q: What about solid membranes anionic conductors – would it contribute in terms of product separation?
A: Yes, see question 7. Cell configurations based on anion exchange membranes are being developed, and yes, it will help separations, for example, liquids won’t be dissolved in electrolyte anymore.
Q: Was the catalyst used for glycerol oxidation the same used for oxygen evolution – Iridium Oxide? Did you evaluate something else?
A: We use Pt as the catalyst for glycerol, but that is not an optimized system. We and other labs are exploring all kinds of catalyst systems for biomass by-product conversions. Very active area of research, separate from CO2 reduction.
Q: What are the issues of using H2 (g, pure) to get the H protons? in the anode side instead of using water?
A: Yes, one could do this, but water is abundantly available, H2 needs to be produced separately (cost!)
Q: When glycerol is used in the anode side, is the glycerol solution recycled back to the anode?
A: Not right now; need to decide what to do with the effluent stream: treat as a n easier to dispose of waste stream, or try to recover formate, lactate as products and then re-use electrolyte. This is all system optimization; we have not gone this far yet.
Q: In life cycle assessment, the emerging technology is compared with an incumbent technology. What is the GHG emissions and incumbent technology for comparison?
A: Incumbent technology: this really depends on which product and process we are talking about. The answer is different for an ethylene cracker than for stream reforming etc. Some incumbent processes produce multiple CO2s per carbon atom converted from a feed to a product; for others, it is less. I alluded to this on slide 36 of the webinar.
Q: How do we ensure that the value added products from eCO2RR don’t end up as CO2 in the atmosphere at the end of their respective lifecycles anyway? Isn’t sequestration the only option to do this?
A: Yes, excellent point. By using (close to) carbon neutral processes, we can produce and use chemicals that eventually turn into CO2 again, but the overall cycle is close to carbon neutral; we are not adding Co2 to the atmosphere. To remove CO2 from the atmosphere, indeed sequestration, ref-forestation, etc. is what is needed.
Q: Very nice talk, Prof. Kenis. For glycerol oxidation, is Pt the only catalyst that worked? Also, what would be the additional cost of separation of products you make with glycerol oxidation?
A: We used Pt for this work and are working on a few other catalysts with collaborators (Baranova group, Ottawa). Don’t know about the additional cost of separation; the best approach is probably to switch to a membrane-based cell configuration (Anion exchange membrane).
Q: Also, did you test the stability of catalyst for glycerol oxidation?
A: We did not. Others have done work in this area, just focusing on glycerol oxidation separate from CO2 reduction
Q: Can you comment on solubility of co2 in water?
A: Co2 solubility in water is low, but it readily reacts with hydroxide in the electrolyte we use, so we lose some CO2 to the electrolyte.
Q: Slide 19: Are you at 1 bar of CO2?
A: Slightly higher than 1 bar, but this is not a pressurized cell.
Q: On cathode, what was the mechanism of CO2 reduction? Was H2 produced first and then reacted with CO2?
A: H2 is formed independently from Co2 reduction. See the literature for the detailed mechanisms of CO2 reduction on Ag, Au, and Cu. See also question 1.
Q: What principles were used/modeling was done to develop the systems analyzed in the TEA and LCA, where one has to make assumptions about the commercial scale equipment, etc.?
A: Easiest to answer by referring to our papers: Nature Energy 2019, and references therein. In general, we use whatever information on commercial systems we can find, and estimate cost if not available yet (e.g. estimate Co2 electrolyzer cost based on cost of water electrolysis systems).
Q: What is the lifetime of the electrode material/catalyst?
A: Depends on exact configuration and reaction and at what potential, current the cell is operated. MAJOR area of research now, to go from tens of hours of operation to thousands of hours of operation.
Q: If we can mitigate CO2 emissions from industry sources, could these methods be used (or inspire new methods) in the other causes such as transportation?
A: That would be hard. Direct Air Capture will be necessary to mitigate CO2 produced by transportation.
Q: Is there enough metal in the world for catalysts to convert co2 on climate relevant scale?
A: Several Co2 reduction reactions can be performed with non-metal catalysts; very active area of research. Also, Ag, Au, and Cu are still abundantly available, even when projecting massive scaling going forward.
Q: What about the energy of the used glycerol?
A: Glycerol is an otherwise discarded byproduct of biomass conversion; hence, we do not take into account the energy to produce glycerol.
Q: What about CO2 electrolysis using solid oxide cells?
A: Yes, works well. Active area of research!
Q: In regards to energy efficiency, what approaches do you endorse for reducing ohmic losses across the electrolyte?
A: Once can run these systems with thinner cells, but the best approach is probably to switch to membrane electrode assembly based cells.
Q: Concentration of CO2 in flue gas (i.e. 96% from NH3) – is this concentration in mol% or vol%?
A: Volume %
Q: Are there currently any electrolysis process that you described for CO2 is at scale or pilot stage?
A: Ongoing work at Siemens, ThyssenKrupp, Covestro, …
Q: Could you please discuss about the hidden reasons that we still cannot find catalyst for CO2 reduction to Methanol? Thank you, sir.
A: See the work by Marc Koper (J. Phys. Chem. Lett., 2015, 6, 4073-4082). Basically, the intermediate that is expected to lead to methanol, more readily produces methane + water.
Q: Do you have any opening postdoc position on this topic in the near future?
A: I might. Send me an e-mail 🙂 kenis@illinois.edu
Q: Have you accounted for CO2 produced from glycerol (production, transportation, etc) in the mass balance of CO2?
A: Good question! No, in this case, the product is an electrolyte stream containing formate and lactate. We don’t continue further than that.
Q: What do you use as an anion exchange membrane in your cells?
A: Any commercial AEM, e.g. fumasep.
Q: What about H2 evolution and how long catalysts works without losing stability?
A: H2 evolution is typically most of the FE that does not go to the desired product. Catalyst/electrode stability: tens of hours now. Area of active research to improve this.
Q: Didn’t you test the catalysts in a 3 electrode system? So that you can know about the kinetics of the process.
A: For some catalysts we have done so. And yes, for some catalyst we have kinetic information. LOTS of literature by other research groups.
Q: Can you use formate or lactate? Are these more valuable than glycerol? Do you have to worry about transportation of glycerol to the point of use for production of your value added chemicals?
A: Yes, to determine economic viability, one would need to determine whether the produced formate/lactate solution is discarded as a waste, or whether one would like to separate the products so the present value. We have not done that yet. And yes, transportation (Cost and CO2 produced) comes in as well when looking at specific sites.
Q: How have you addressed issues of flooding of the Gas diffusion layers?
A: That is one of several issues preventing long-term operation. Multiple strategies are being researched by us and others to overcome the issue.
Q: Can carbon production and carbon capture be comparable in future scale wise, sir?
A: Indeed, the vision for a sustainable plant is that there is a balance between the two, so net we are not adding CO2 to the atmosphere. Many studies and reports indicate that we need to go to a net carbon negative situation for many decades to achieve global sustainability over hundreds of years.
Q: What are the oxidation products for glycerol? Would it considered a byproduct or waste stream? Reduction processes in general produce higher value products (e.g. CO2RR, Nitrogen reduction, HER). Are there any valuable oxidation products?
A: Both scenarios could be useful: glycerol waste stream to a dilute solution of formate and lactate that can be disposed; OR trying to separate lactate and formate to deliver a valuable product. Both scenarios could be valuable (economically and life cycle). Lost of research to be done here.
Q: What are Prof. Kenis’s views on converting CO2 directly captured from air into valuable products?
A: That would be great. Lots of impressive progress in direct air capture.
Q: You have demonstrated current density of >100 ma/cm2. What strategies did you use to improve the current density ?
A: Better catalyst layers, so more catalyst surface available, improved transport to/from electrode surface etc. Most critical is the use of gas diffusion electrodes.
Q: What are the challenges of using acidic system instead of alkaline?
A: Kinetics of the desired conversions in acidic media is much works.
Q: What is the global production quantity of glycerol and how does it compare to the scale of the CO2 to X you propose?
A: In countries with a lot of biofuel production (e.g. Brazil), large supplies of glycerol. Note that the same concept of lowering the cell potential would work with oxidation of any other organic waste stream.
Q: Is it possible for the FE to reach more than 100% as it can be seen on page 19?
A: It is on slide 20: indeed some FE’s appear to be larger than 100%, but that is a result of experimental error, in both the measurement itself and the calibration curve.
Q: Your research has focused on aqueous-based electrolysis. Would you comment on Solid Oxide Electrolysis Cell technology? Haldor Topsoe offers a small commercial SOEC.
A: Yes, a very active area of research. SOEC approach will work well for some of the CO2 to X reactions. Haldor-Topsoe’s effort is a prime example!
Q: I wonder how much is the net CO2 reduction on the cathode while it is the product of Gly-OH oxidation on the anode?
A: Even if you would completely oxidize glycerol, there is a net more CO2 consumed than produced. However, note that the idea is NOT to oxidize glycerol all the way, but instead to produce lactate and formate.
Q: Hi Paul, can you still go to high current densities when using Glycerol oxidation at the anode?
A: Not as high yet as when using OER, but we are working on improving this. The challenge is that glycerol is a much larger reactant, lower diffusion, and lower concentration than water. Also, the catalyst layer has not been optimized for conversion of biomass byproducts. Active area of research!
Q: Are you also looking at CO as a feedstock?
A: Yes, for example, you can run a cascade of first Co2 to CO and then a next reactor that uses CO as a reactant to form another product. Active area of research.
Q: What is the prospect of co2 to formic acid? Which kind of the metal oxide catalysts are suitable for this kind of co2-HCOOH?
A: Yes, this conversion can already be done very well and is already being used by a few food companies to provide them with the FA solution they need. World market is small though.
Q: What do you think is current heterogeneous catalysis comparing to electrocatalysis of CO2 reduction economically?
A: At scale, right now the heterogeneous processes using fossil fuel feeds are more economical. They have been developed and improved over decades. For some processes, electrocatalytic reduction of CO2, with a lot more development, may become competitive in an economic sense, while being close to carbon neutral or even carbon negative.
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