Electrocatalytic Applications of Atomically Precise Gold Nanoclusters

Colloidal nanoparticles are emerging as a novel class of materials and have received intense research interest. With the advances of chemical synthetic methods, scientists are pushing the envelope of fine-tuning the quality of colloidal
nanoparticles. However, their crystal structures still remain mysterious due to the inevitable polydispersity. It is thus desirable to control the quality of colloidal nanoparticles with atomic precision. Recently, thiolate-protected gold nanoclusters [Au_n(SR)_m, where n represents the number of gold atoms and m represents the number of thiolate protecting ligands, respectively] have successfully achieved atomic level precision and their crystal structures have been solved. This novel class of material offers unique
opportunities for fundamental investigations and practical applications in catalysis, sensing, optics and so on. Due to the ultrasmall size regime (1-3 nm), gold nanoclusters show molecular-like properties such as single electron HOMOLUMO transition due to the strong quantum confinement effect. Furthermore, the crystal structures of gold nanoclusters can provide detailed information on the
bonding between gold and sulfur atoms, which can significantly benefit the understanding of surface catalytic processes. These unprecedented advantages make gold nanoclusters a well-defined platform to investigate the electrocatalytic applications and probe the structure-property correlations. This thesis explores the catalytic applications of atomically precise gold nanoclusters, especially in the field of electrocatalysis. Specifically, gold
nanoclusters are employed as effective catalysts for the reduction of 4-nitrophenol (chapter 2) and electroreduction of CO₂ to CO (chapter 3). Mechanistic understandings are achieved owing to the solved crystal structures of gold nanoclusters. In chapters 4 and 5, the strategies of constructing hybrid nanocomposites with gold nanoclusters are proposed and demonstrated in catalyst design. Gold nanoclusters are loaded onto two dimensional CoSe₂ and
MoS₂ nanosheets. The interface between gold nanoclusters and CoSe₂ (or MoS₂) nanosheets is found to be the active sites for electrocatalytic water splitting. In chapter 6, the focus of this thesis moves from gold to palladium.
Ultrasmall palladium nanoclusters are successfully synthesized with excellent performance for electrocatalytic oxygen reduction reaction. The exciting opportunities of gold nanoclusters in electrocatalysis lie not only in their extraordinary performance but also in the atomic-level monodispersity. It is because of the well-defined nature of gold nanoclusters compared to conventional plasmonic nanoparticles that probing mechanistic understanding in
electrocatalysis and understanding structure-property correlations both become possible. Therefore, gold nanoclusters hold high promise for electrocatalysis, and
future endeavors are expected for further explorations in this field.