Effects of Ligands on Synthesis and Surface-Engineering of Noble Metal Nanocrystals for Electrocatalysis

Noble metal nanocrystals are a family of important catalysts for a broad range of processes (especially electrocatalytic ones), which are usually obtained as a hybrid each containing a metallic core and a ligand shell. It is well recognized that the ligand plays a critical role in regulating the crystal growth into different shapes and maintaining the colloidal stability of the nanocrystals. Recently, more effects of the ligand were revealed in controlling both the synthesis and the surface property of noble metal nanocrystals, which could be maneuvered to achieve distinctive catalytic properties. In this review, we present a summary of the roles of the ligand based on typical results from the literature. The review begins with a discussion on the roles of the ligand in the controlled synthesis of noble metal nanocrystals, including the shape control, the reduction potential control for suppressing self-nucleation and galvanic replacement reaction, and the electroless plating effect for noble metal/non-noble metal co-reduction. The following section includes a discussion of the effects of the ligand on the surface property of noble metal nanocrystals, including the ensemble size engineering, the ligand-metal electron transfer, and the local microenvironment construction, toward designable electrocatalytic properties. At the end, we provide our perspectives on the future research of ligand engineering as an advanced technique for tailoring electrocatalytic properties of noble metal nanocrystals.