UC San Diego

Electrochemical CO2 conversion into value-added chemical feedstocks, if powered with renewable electricity, is a promising path to approach carbon neutrality. However, developing active and selective catalysts is necessary to enable energy efficient conversion. In this thesis, I provide strategies to design active electrocatalysts with enhanced selectivity for CO2 electrolysis via tuning of the local reaction environment. First, I show that modulating the surface strain of a model Cu (001) catalyst epitaxially grown on a single-crystal Si substrate results in an increase of the Cu 3d band center position. This change in the electronic structure causes a suppression of the CO production pathway, increasing selectivity to multi-carbon products. I demonstrate that multi-carbon products can be further selected for by an operando restructuring of the micro- and nanoscale morphology of Cu-based catalysts. An electrochemically reduced Cu(OH)2 nanowire catalyst enhances the selectivity of multi-carbon products at moderate electrolysis potentials where a hierarchical morphology evolves. A final level is the tuning of the chemical state of the catalyst surface. By switching the initial surface oxidation state of tin oxide catalysts to be SnII-rich, the selectivity and energy efficiency of formate generation are promoted, offering a possible nearest-term path to carbon-negative CO2 electrolysis. Optimizing electrolyzer design is also crucial to facilitate mass transport of CO2 to reach industrial relevance. The importance of the mass transport of CO2 to enhance overall activity is also demonstrated by controlling flow rate of partially concentrated CO2 stream. These findings reveal the importance of surface strain, morphology and chemical state on designing efficient CO2 catalysts, providing fundamental guidelines and direction toward carbon neutral CO2 conversion.