Surface Ligands in Nanocrystal Electrocatalysis: A Double-Edged Sword

Colloidal nanocrystals with well-controlled sizes, shapes, and facets have found extensive applications in electrocatalysis as model catalysts for fundamental studies of structure-property relationships. Surface ligands are ubiquitously employed in nanocrystal synthesis and play a pivotal role in directing nanocrystal growth to realize precise morphology control, yet the influences of surface ligands on the electrocatalytic properties of nanocrystals remain to be better understood. Here, a survey and perspectives are presented on the double-edged sword effect of surface ligands in nanocrystal electrocatalysis. Surface ligands, depending on circumstances, can either be detrimental to electrocatalysis by poisoning nanocrystal surfaces or be beneficial for creating favorable interfacial microenvironments to synergistically boost electrocatalysis. First, an overview of the surface-ligand chemistry of colloidal nanocrystals is provided, followed by a discussion of the types and binding modes of surface ligands. Subsequently, several strategies for removing surface ligands from nanocrystals are introduced to yield either clean surfaces or ligand-derived carbon coatings suitable for certain electrocatalytic applications. Furthermore, strategies for creating ligand-enabled favorable interfacial microenvironments are discussed by tailoring nanocrystal-ligand interactions via ligand exchange/modification and by tailoring ligand-ligand interactions via nanocrystal/ligand assembly. Finally, the discussion concludes by highlighting future opportunities for in-depth mechanistic understanding and rational design of surface ligands on nanocrystals toward molecular-level control of electrocatalytic processes.