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 areas and the specific activity of the dealloyed nanoframes can be systematically tuned to achieve the optimal electrocatalytic activities. Both the stability and 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 trimetallic alloy NPs. In addition, catalytic selectivity of dealloyed porous Au nanoframes could be realized by precise control over of the surface atomic coordination numbers of the dealloyed porous Au NPs 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 details. The compositional stoichiometry and the structural ordering function as two key factors dictating the resulting architectures. Much more sophisticated and fantastic structures have been achieved by coupling galvanic replacement reaction 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.