UC Berkeley

Electrons are the currency of the future energy economy. With a host of renewable sources of electrical energy and steadily decreasing cost of generation, our ability to store that electricity via chemical bonds becomes increasingly paramount. Development of materials that allow the transformation of electrical energy to chemical energy, e.g. the electroreduction of CO2 to value-added chemicals and fuels, will push our energy infrastructure to new heights. Despite considerable progress in thermal gas-phase heterogeneous catalysis of CO2, the heterogeneous electrocatalysis of aqueous CO2 under room temperature and neutral pH has remained challenging. The key gating obstacle has been the development of catalysts that effect efficient and selective formation of higher order products such as methane or multicarbons, for which only copper has emerged as a candidate material. To design next-generation electrocatalysts for CO2 conversion to multicarbons (CO2-to-C2+), the relationship between activity/selectivity and catalyst structure must be better understood, to identify the structural motifs that define CO2-to-C2+ active sites. Recent work has consistently revealed that copper nanomaterials undergo considerable structural change under operating conditions. Thus, a central challenge to the understanding of these active surfaces is their dynamic nature under operation in electrochemical conditions, especially as applied to nanoscale electrocatalysts. Hence, this dissertation centers around structural dynamics of copper-based nanocatalysts under CO2 electroreducing conditions.

After a brief introduction to the problem statement and fundamental concepts related to heterogeneous electrocatalysis of CO2 to value-added products, I discuss the prospects and existing work around Cu structural evolution in Chapter 1. In Chapter 2, I show how the link between structural evolution and catalytic activity change can be clearly shown on a Cu nanowire catalytic platform, and further show how strategies that mitigate structural change also impact selectivity retention. In Chapter 3, I move to a copper nanoparticle ensemble platform with intriguing activity for multicarbon formation, coupled with a striking structural evolution. I illustrate the dichotomy between the apparent evolution and active structure via conventional ex situ measurements, and the structural and catalytic insights revealed by more comprehensive investigation using preservation strategies. In Chapter 4, I discuss how in situ characterization techniques assist the illumination of such structural evolution under electrocatalytic conditions, and further explore what additional advances are needed to harness these insights. Finally, I close in Chapter 5 with an outlook on materials development for CO2 electrocatalysis as it stands at time of writing. Overall, this dissertation seeks to provide a narrative of the relationship between an electrochemical materials scientist and the concept of structural dynamics. Through the works to be described, this dissertation will take the reader on a journey from emphasizing stabilization and mitigating structural change, towards understanding it for the eventual purpose of leveraging such structural change as another dimension of electrocatalyst design.