Deconvolution of Degradation Mechanisms Towards Durable Gas Diffusion Electrodes for the Efficient Electrochemical Reduction of CO2
Authors: Cofell Emiliana R. , Nwabara Uzoma O , Henckel Danielle A. , Bhargava Saket , Park Zachary , Kenis Paul J.A. 
Published: May 2020

Anthropogenic CO2 emissions present an immediate and unprecedented threat to our planet. Electroreduction of CO2 (CO2RR) offers the dual benefits of reducing CO2 emissions from point sources and producing valuable chemicals such as CO, formic acid, and ethanol in a carbon-neutral manner1,2. Over the past decade, a significant body of research has focused on improving the product selectivity and activity of CO2RR catalysts, but studies regarding long-term stability and durability of these electrocatalytic systems have been rare3. To date, only a few studies have reported performance durations exceeding 100 hours, and even fewer have reported on possible mechanisms underlying decrease in performance and system failure. Techno-economic analyses suggest a lifetime of 3000 hours or greater is needed for economically feasible CO2RR systems4. Progress in this area will be crucial for further development of CO2RR technology.
The use of gas diffusion electrodes (GDEs) in flow electrolyzer and membrane electrode assembly-based systems has enabled the conversion of a gaseous stream of CO2 into products at a high rate5. However, the layers of the GDE are plagued by a variety of degradation modes, the mechanisms of which are still unclear. By determining the physical and chemical degradation mechanisms present in the catalyst layer, as well as the detrimental role of carbonate deposits within the GDE, we can better understand electrode performance loss and how to design long-lasting electrodes.
In this talk, we will discuss the various mechanisms that cause performance degradation in GDEs over time, investigated via a series of 6-hour tests in our GDE-based alkaline flow electrolyzer. The insights gained from these tests using a broad range of characterization techniques (i.e. SEM, EDS, Micro-CT, XRD, XPS) provide a deeper mechanistic understanding of long-term GDE performance for CO2 electroreduction. This will be followed by a discussion of strategies for overcoming the challenges currently facing GDEs in our system, including the use of durable electrode substrate materials and catalyst layer coatings for improved hydrophobicity and stability for long-term operation. While pursuing these studies, we also developed protocols for durability and stability testing based on those used in the fuel cell, water electrolysis and solid oxide electrolysis communities. This allows tests to be completed in an accelerated fashion while simulating a variety of operating conditions.

Acknowledgement

We gratefully acknowledge financial support from Royal Dutch Shell and I2CNER.

References:

Oerlemans, J. Science
308, 675-677, doi:10.1126/science.1107046 (2005).

Jhong, H. R., Ma, S. C. & Kenis, P. J. A. Curr Opin Chem Eng
2, 191-199, doi:10.1016/j.coche.2013.03.005 (2013).

Hori, Y. Mod Asp Electrochem, 89-189, doi:Book_Doi 10.1007/978-0-387-49489-0 (2008).

Verma, S., Kim, B., Jhong, H., Ma, S. C. & Kenis, P. J. A. Chemsuschem
9, 1972-1979, doi:10.1002/cssc.201600394 (2016).

Kim, B., Hillman, F., Ariyoshi, M., Fujikawa, S. & Kenis, P. J. A. J Power Sources
312, 192-198, doi:10.1016/j.jpowsour.2016.02.043 (2016).