UC Berkeley

Chapter 1 – The rising levels of CO2 in the atmosphere necessitate further investigation into methods of converting CO2 into more valuable products. In this chapter, we introduce the chemistry of CO2 conversion, particularly via electrocatalytic methods, and the strategies and considerations involved in selectively reducing CO2 to desirable products.

Chapter 2 – We describe the effects of the CO2 reduction device on the observed product selectivity and the method used herein to evaluate the performance of metallic catalysts.

Chapter 3 – We develop a predictive framework to understand how organic modifiers on a Cu surface influence the selectivity of the CO2 reduction reaction at the metallic surface. This study of a series of polymeric and molecular modifiers indicates that protic species enhance selectivity for H2, hydrophilic species enhance formic acid formation, and cationic hydrophobic species enhance CO selectivity. The relationship between these structural features of the modifiers and the changes in selectivity yields insights into how these modifiers influence catalytic behavior. We hypothesize that the hydrophilic/hydrophobic modifiers influence the binding strength of surface hydrides, which yield formic acid or H2. This study demonstrates how the selectivity of a single metallic surface may be tuned to favor formic acid or CO simply by changing the properties of the added organic modifier and may aid in the future implementation of organic structures in CO2 reduction devices.

Chapter 4 – The study of cationic ammonium salts on a Ag surface allows a closer investigation of how these salts influence CO formation. The trends observed with these ammonium salts indicate that the selectivity-determining factor is not the hydrophilicity/phobicity, but rather the length of the longest hydrocarbon substituent. This correlation suggests that the ordering of the ammonium salts at the Ag surface plays a key role in obtaining improved CO selectivity. We discuss possible mechanisms by which these ordered ammonium salts may influence the formation of CO. The emergence of the organization of these organic modifiers as an important parameter demonstrates that strategic design of these modifiers requires an understanding of not only the mechanism, but also of ancillary features of the organic species that impact their ability to influence surface processes.