Palladium and platinum nanocrystals: Facile synthesis and thermal stability

Abstract

New methods for the facile synthesis of palladium nanocrystals were developed, with a focus on reaction conditions amenable to scale-up. A photochemical synthesis of 12-nm Pd cube-like nanocrystals decorated with atomic steps and terraces was achieved at room temperature by using a UV-vis light source to excite and promote the reduction of the metal salt precursor. A one-pot synthesis of 18-nm Pd concave nanocubes was also designed at room temperature. Through careful tuning of reduction kinetics alongside an appropriate selection of reactants, single-crystal seeds were first generated followed by a controlled, seed-mediated growth into concave cubes. Platinum-based nanocrystals were studied using high-resolution in situ electron microscopy. Evaluation of Pd@Pt4L cubes and octahedra revealed a shape-dependence on thermal deformation, with cubes first losing expressed crystal facets and shape before alloying, and octahedra first alloying before losing expressed facets. The energetic rationale for these changes was explained using computational modelling. Platinum cubic, octahedral, and icosahedral nanocages with an average wall thickness of 6 atomic layers were studied to understand their thermal stability through in situ electron microscopy. Results indicated limited durability under thermal stress for all nanocages, with hole enlargement leading to the formation of Pt nanoframes. Enhanced durability may be achieved by more carefully tuning the formation of initial pores on the surface of the nanocages. The broader applications and fundamental understandings derived from these studies for future research is discussed.