The Role of Carbonate Formation on the Long-Term Performance of Gas Diffusion Electrodes for Carbon Dioxide Electrolysis in Alkaline Media

Abstract

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 manner.1,2 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 rare.3 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.4 Techno-economic analyses suggest a lifetime of 3000 hours or greater is needed for economically feasible CO2RR systems5. 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, which have not been extensively studied to date. Our study investigates the detrimental role of carbonate deposits on the catalyst layer and within the GDE; by understanding the conditions that promote or inhibit their formation, we can better understand electrode performance loss and how to design long-lasting electrodes.In this talk, we will discuss the role of electrolyte concentration and composition in carbonate deposit formation, 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 (SEM, EDS, Micro-CT, XRD) provide a deeper mechanistic understanding of long-term GDE performance for CO2 electroreduction in alkaline media. This will be followed by a discussion of strategies for overcoming the challenges currently facing GDEs in our system, including the use of durable and hydrophobic electrode substrate materials, and electrolyte engineering-based solutions. 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 Shell’s New Energies Research & Technology - Dense Energy Carriers Program and I2CNER.