Exploring new frontiers of carbon dioxide electrolysis at industrially relevant conditions

Carlos Andres Giron Rodriguez

Research output: Book/ReportPh.D. thesis

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Electrochemical CO2 reduction (CO2R) driven by renewable energies has emerged as a promising solution to mitigate greenhouse gas emissions and produce carbon–neutral energy-dense chemicals. In recent years, developments in electrocatalysts for CO2R have resulted in materials with enhanced selectivity toward hydrocarbons and alcohols. Nevertheless, mass transport issues can limit the testing of these materials in traditional electrolyzer configurations, which may be detrimental since parameters such as selectivity and activity strongly depend on reaction rates and microenvironments. Therefore, operations at high current densities should be encouraged to increase production rates while demonstrating their technical and economic feasibility.
Although intensive efforts are being made to increase the efficiency of COelectrolyzers through catalyst development, process intensification, and system design, it is challenging to achieve high selectivity towards a specific product, reaction rates, and long-term stability. This is primarily due to catalyst deactivation, salt precipitation, GDE flooding, inadequate water management, and a lack of components designed specifically for CO2R applications. To enhance performance, research has been undertaken to develop highly efficient and stable CO2R electrocatalysts; however, other engineering factors must also be considered, such as reactor configuration, electrode structure, reaction conditions (temperature, pressure, pH), and electrolyte selection. 
Throughout this thesis, I propose different strategies for addressing the most relevant challenges of operating CO2 electrolyzers at industrially relevant conditions using gasfed reactors. I have attempted to improve catalytic activity, selectivity, and stability by analyzing the effect of operating conditions (through the design and construction of a reaction setup), electrolyzer components (e.g., ion-exchange membranes), and electrocatalysts. As a first step, I investigated the effects of different reaction components on the overall performance of gas-fed reactors. My subsequent work focused on understanding how the operating temperature affected catalyst activity, water management, and product distribution over Cu-based GDEs using a zero-gap cell. This study aimed to investigate the effect of temperature on the kinetics and transport of CO2R, demonstrating its potential to enhance its catalytic performance and emphasizing the importance of appropriate heating during these experiments.
Moreover, I focused on electrocatalysts using tandem catalysts following a two-step electrolysis procedure. This work compared the sputtering with nanoparticulate approaches, the effects of metal loading, and electrode composition ratios during electrode preparation. Additionally, a ”CO- selective” catalyst layer was added to examine how it affects the selectivity of C2+ products. This electrode type showed promising results evaluated during its testing, characterization, and product quantification using a simple preparation method.
Further, I investigated the role of the anion-exchange membrane by testing a new generation of membranes designed explicitly for CO2 electrolysis. In this study, RG-AEM membranes were synthesized with different functionalized head groups. The relationship between their mechanical properties and CO2R performance has been examined through properties like the ion exchange capacity, water uptake, and thickness. Results showed that AEMs with heterocyclic groups exhibited competitive mechanical, thermal, and chemical properties compared to current commercial membranes and provided stable long-term CO2R operation under industrial  conditions. 
Finally, I investigated various other strategies, including adding recycling lines to boost the CO2 conversion, manipulating the backpressure to control CO2 surface coverage, or adding ionomers to the catalyst layer to enhance gas and ionic transport, some of which have shown promising results in CO2R applications. Ultimately, the described alternatives were combined, demonstrating their benefits for a stable and selective long-term operation (>200 hours). Through this research, I have proposed alternatives to address existing CO2R challenges, proposing potential solutions that can be easily scaled up in the industry and showing additional research opportunities in this field.
Original languageEnglish
PublisherDepartment of Physics, Technical University of Denmark
Number of pages234
Publication statusPublished - 2023


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