UC Berkeley

The CO2 carbon building block is essential to sustain life on Earth. However, its excessive emissions driven by anthropological activity have irreversibly affected the environment. Therefore, closing the carbon cycle loop through CO2 recycling using renewably sourced electricity not only addresses the growing threat of climate change but is also a powerful way to synthesize the chemicals necessary for the development of present and future generations. Specifically, the combination of CO2, protons, and electrons into value-added products enables the upcycling of CO2 while storing energy into chemical bonds. Given CO2 worldwide availability on Earth as well as in outer space (e.g., Mars), CO2 will always be a relevant feedstock in the future development of chemicals electrosynthesis. In this thesis, I present the prospects of catalyst materials design targeted for improving the utilization of CO2 through electrocatalysis.I introduce in Chapter 1 the current challenges we face for the CO2 electroreduction reaction to have a sizeable impact. There, I specifically discuss within the field of heterogeneous electrocatalysis the various strengths and drawbacks of utilizing nanomaterials to optimize CO2 electroconversion. Nanomaterials are the preferred platform to achieve catalyst fine-tuning that is essential to the CO2 electroconversion to higher-order products. However, in spite of the specific structural design accessible through their synthesis, nanomaterials’ high surface energy makes their structure and resulting properties especially prone to transformation when subject to external activation. The applied bias and reaction environment necessary to electrocatalysis induce in fact great change to such materials. In Chapter 2, I show that although often associated with the degradation of the catalyst surface and thus activity, the structural dynamics in nanocatalysts simultaneously introduces the possibility to design an incredible variety of catalysts constructed in operando. Furthermore, I present in Chapter 3 how the activity of nanocatalysts is not only driven by their surface properties, but also by the reaction environment formed near their surface during the reaction. The unique physicochemical landscape created at this interface can be exploited to tune the progress of complex reactions such as the electrochemical CO2 reduction reaction (CO2RR). Understanding the driving forces behind the formation of such an interface is therefore crucial in guiding the outcome of CO2RR in a controlled manner. I discuss the tools that can be employed to obtain such insights in Chapter 4, including powerful characterization techniques and the fine tuning catalyst structural properties. I emphasize there the importance of in situ and operando characterization techniques to accurately probe the dynamics of nanocatalysts. In addition, I highlight the synthetic advantages intrinsic to utilizing nanomaterials which can help isolate the driving parameters behind their structural evolution during electrolysis. While CO2 electroreduction is a close parallel to photosynthesis, there is a long way to go before it can replicate its selectivity and produce molecules as complex. In Chapter 5, I introduce a first attempt to bridge the synthetic gap between CO2 and sugars in an abiological catalytic process. I conclude this thesis in the last and 6th chapter with an overview of the breadth of advances done on the CO2 valuation through heterogeneous catalysis approaches.