UCLA

The design and synthesis of multicomponent Pt-based nanomaterials with highly controlled structures have attracted extensive research attention, mainly due to their highly active catalytic properties. The performance enhancement of these catalytic systems largely requires the precise control over the structure with the lowest Pt amount yet high activity to mitigate the high cost of Pt-based nanomaterials. Specific surfactant molecules have been widely employed to manipulate the morphologies and assemblies of nanostructures. Thus rational designs of the surfactants become very significant. In nature, a lot of biomaterials evolved well-developed nanostructures with unique properties through long-time natural selection using biomolecules as the surfactant. Compared with traditional trial-and-error design, biomimetic design provides more rational controls leading to new synthetic design for nanostructures. In this thesis, synthesis and assembly of Pt-based nanocrystals and the mechanisms were studied.

Chapter 2 introduces one-step synthesis of single-crystal PtNi octahedron with in situ developed highly concave feature and self-confined composition was studied which is optimal for oxygen reduction reaction (ORR). The combination of Ni facet segregation and oxygen etching of Ni-rich surface lead to the concave feature and confined Ni content. The concave PtNi nanocrystal exhibited a very high activity as well as a remarkable stability in ORR.

Chapter 3-4 explores biomimetic approaches to achieve functional Pt nanostructures and their hierarchical assembly. In Chapter 3 a rational designed peptide was utilized to prepare an ultrathin Pt multiple-twinned nanowire network (MTNN) as an efficient electrocatalyst. In Chapter 4 we further demonstrate a biomimetic approach to explore the impact of higher order structures of surfactants on NC formation and alignment. Results show that at low concentration T7 peptide molecules (Ac-TLTTLTN-CONH2) form ST-turns and benefit the selective formation of cubic Pt NCs, and that β-sheets favored under high concentration readily promote linear self-assembly of the cubic NCs along [100] direction. Tailoring the formation conditions of the secondary structures of biomolecules can realize better tuning of peptide concentration controlled NC behaviors via a process that is analogous to biological regulations in organisms. Great potential in regulating in vivo performance of non-biological substances and derived applications become possible.