Ion Selective Membranes in CO2 Electrolysis

By: Johnny Kung

29 Jul, 2019

July 29, 2019

One promising strategy for mitigating the environmental effects of CO₂ emissions is to convert the CO₂ via electrochemical reduction into high value-added molecules such as methanol and ethylene. These commercially valuable products could help ensure the economic viability of deploying carbon capture and conversion technologies to offset CO₂ emissions, while simultaneously reducing our reliance on new fossil sources to produce fuel and petrochemicals. The ion selective membrane is a key component that needs to be optimized to achieve highly efficient and stable CO₂ reduction devices, as current offerings do not meet key specifications for industrial scale applications.

On May 15, 2019, CIFAR convened a roundtable to discuss developments in ion selective membranes for CO₂ electrolyzers. This workshop brought together leaders from across the fields of electrochemistry, polymer chemistry and energy research, including Fellows from CIFAR’s program in Bio-inspired Solar Energy, as well as experts from other academic institutions, national labs and industry. Through brief primer talks and moderated discussions, attendees explored a number of properties of polymeric membranes that are subject to optimization, including membrane chemistry, conductivity, stability and permeability. This meeting is the first in a series that will work towards a roadmap for the research and development of commercial-scale CO₂ reduction systems, one that takes account of membranes, catalysts and other relevant technologies.

Impacted Stakeholders

Commercial developers of carbon electrolyzers
National energy and materials labs
Manufacturers of polymeric membranes
Energy companies with interests in: carbon capture and conversion, production of carbon-neutral or -negative fuels, storage of intermittent energy from renewable sources
Energy and climate policy practitioners

Key Insights

The chemical and physical composition of the polymers that comprise electrolytic membranes affect membrane properties such as ion conductivity, reactant/product diffusion and mechanical strength, in turn strongly impacting the efficiency of CO₂reduction devices.
Key problems in the optimization of membranes, such as product crossover, conductivity, stability (in alkaline conditions or moderate-high temperatures) and water management, are intrinsically interconnected. As such, a systems-level approach should be used rather than tackling each problem in isolation. Other factors that need to be taken into account when moving from lab to industrial scale include the purity of the CO₂ source and the cost of separating desired products from byproducts.
Because of the low solubility and diffusibility of CO₂ in aqueous electrolytes, one approach to increasing the efficiency of CO₂ electrolysis is to use gas diffusion electrodes. Current experimental gas-fed CO₂ reduction devices have achieved high current densities, but it will be important to better characterize the triple phase boundary (the interface of the gas phase reactants, aqueous electrolyte, and solid polymers and catalysts) in such devices.
The economics of CO₂ electrolysis is sensitive to faradaic efficiency (the selectivity of CO₂reduction to the desired product), energetic efficiency (the proportion of energy input stored in the desired product) and the price of electricity, among other factors. At current economic conditions, 2-electron products (molecules whose conversion from CO₂ requires two electrons, such as CO and formate) may be profitable.
Scaling up electrolytic devices to industrial scale will require standards or benchmarks against which researchers can compare their experimental membranes. Industrial membrane manufacturers have the capability to produce at scale to reduce batch-to-batch variability, but will need a market with sufficient demand to justify investments.

Priorities and Next Steps

There are lessons for CO₂ electrolysis from the fuel cell community, which has decades of research on relevant membranes. However, hurdles to straightforward knowledge translation between the fields include the fact that fuel cell designs converge on one goal, whereas CO₂ electrolyzers have multiple products or objectives.
Continued study of CO₂ electroreduction reactions will be needed to fully characterize the radicals and other minor / exotic intermediate species and their effects on membrane degradation.
Electrochemists should collaborate with membrane scientists to arrive at optimal designs of electrolytic membranes, e.g., by deciding on specific performance parameters for the electrolyzers that membrane scientists can work towards.
Researchers and industry must maintain close conversation to achieve standards and benchmarks for electrolytic membranes. Governments and other funders can play an important role by providing the resources to facilitate scaled up production and set industry standards.

Roundtable Participants

Shane Ardo, University of California, Irvine
Chulsung Bae, Rensselaer Polytechnic Institute
Bamdad Bahar, Xergy Inc.
Curtis Berlinguette, University of British Columbia / CIFAR
Phil De Luna, National Research Council Canada
Todd Deutsch, National Renewable Energy Laboratory
Jonathan Edwards, University of Toronto
Christine Gabardo, University of Toronto
Claire Hartmann-Thompson, 3M
Michael Hickner, Pennsylvania State University
Winston Ho, Ohio State University
Steven Holdcroft, Simon Fraser University
Shaffiq Jaffer, Total / CIFAR
Feng Jiao, University of Delaware
Kendra Kuhl, Opus-12
Tom Mallouk, University of Pennsylvania / CIFAR
Kenneth Neyerlin, National Renewable Energy Laboratory
Peter Pintauro, Vanderbilt University
Angelica Reyes, University of British Columbia
Danielle Salvatore, University of British Columbia
Ted Sargent, University of Toronto / CIFAR
Stafford Sheehan, The Air Company
Ken Shi, National Research Council Canada
Lihui Wang, Opus-12
Joshua Wicks, University of Toronto
Zhifei Yan, University of Pennsylvania
Fan Yang, Giner Inc.

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