Structural Transformations Of Multimetallic Nanoparticles

Atomic-level understanding of the structural transformations of multimetallic nanoparticles (NPs) triggered by external stimuli is of vital importance to the enhancement of our capabilities to precisely fine-tailor the key structural parameters and thereby to fine-tune the catalytic properties of the NPs. In this work, I firstly show that Au-Cu bimetallic NPs demonstrate stoichiometry-dependent architectural evolutions during chemical dealloying processes and nanoporosity-evolving percolation dealloying only occurs for Au-Cu alloy NPs with Cu atomic fractions above the parting limit. The electrochemically active surface area and the specific activity of the dealloyed nanoframes can be systematically tuned to achieve the optimal electrocatalytic activity. Both the stability and the activity of the dealloyed Au nanoframes could be remarkably enhanced by incorporation of residual Ag into Au nanoframes through percolation dealloying of Au-Ag-Cu ternary alloy NPs. In addition, the catalytic selectivity of dealloyed porous Au NPs could be realized by precise control over of the surface atomic coordination numbers through percolation dealloying of Au-Cu bimetallic alloys with interior compositional gradients. Besides, nanoscale galvanic replacement reaction induced structural evolutions of Au-Cu bimetallic NPs has also been investigated in this dissertation. I have demonstrated the compositional stoichiometry and the structural ordering function as two key factors dictating the resulting architectures. More sophisticated and intriguing nanostructures have been achieved by coupling galvanic replacement with percolation dealloying or co-reduction. The electrocatalytic activity and the stability of the resulting NPs with controllable geometries have been pushed to a new level. Lastly, I extend the investigation to Au-Ni system with huge lattice mismatch. The success in geometry-controlled syntheses of a series of Au-Ni bimetallic heteronanostructures represents a significant step toward the extension of nanoscale interfacial heteroepitaxy to the ones exhibiting large lattice mismatches and even dissimilar crystalline structures. In summary, the goal of this dissertation is to gain new insights on structural transformations of multimetallic NPs which serve as a central design principle that guides the development of synthetic approaches to controllably fabricate architecturally sophisticated and compositionally diverse multimetallic nanostructures and build the structure-composition-property relationships and eventually optimize their performances