UC San Diego

The availability of renewable energy sources (solar and wind) provides opportunities to replace many traditional chemical reactions by the electrochemical processes to achieve industrial upgrading, including direct ethanol fuel cells (DEFCs), hydrogen peroxide (H2O2) production, and carbon dioxide (CO2) conversion. However, the rates of many important reactions involved in electrochemical processes are too slow and the selectivity of targeted products also needs to be improved. The key to solve these challenges is to design better electrocatalysts. In this thesis, some strategies to design advanced electrocatalysts are investigated. The first strategy is to control the morphology and surface composition of the Platinum (Pt) nanocube-based electrocatalyst in DEFCs to selectively cleave the C-C bond in ethanol to improve its energy utilization. The (100)-exposed Pt38Ir nanocubes with one-atom-thick Ir-rich skin exhibited unprecedented EOR activity, high CO2 selectivity and long-term stability, due to the promotion of C-C bond cleavage and CO desorption from the catalyst surface. Furthermore, we show that the complete oxidization of ethanol to CO2 was achieved by the Rh single atom on the Pt(100) surface, demonstrating the great potential of the decoration of single atom catalysts on the metallic surface in electrochemical reactions. The second example is to tune the local chemical coordination between atomic catalyst clusters (metal) and their support materials (defect carbons) using a composite approach to achieve the synergistic effect in H2O2 electrochemical production. A catalyst composed of oxidized carbon nanotubes and clusters of three to four partially oxidized palladium (Pd) atoms was prepared, forming a special coordination (Pd-O-C) between carbon material and partially oxidized Pd atoms. This coordination can significantly enhance its H2O2 production rate with > 90% selectivity and shorten the production time. The third strategy is to control the intermediate state of catalyst to promote CO2 reduction. In previous studies, Pd was found to transform into palladium hydride (PdH) during the reaction and the latter was believed to be beneficial for syngas production. Based on this finding, the electrocatalyst was directly designed to partially hydridize Pd nanocubes. In comparison with pure metallic Pd, partial hydridization of Pd structure (PdH0.40) showed an earlier transformation to the key intermediate, leading to enhanced syngas production. As a result, the suitable operation potential range can be extended, resulting in a more flexible working condition for potential industrial applications. Overall, the above three strategies for designing electrocatalysts are explored in this thesis work. The results will provide fundamental understanding and guidance for rational design of highly efficient electrocatalysts for crucial electrochemical reactions, getting one step closer to the industrial applications related to sustainable and green chemical engineering.