In and Out: Shuttling Atoms in Covalent Nanocrystals, from Synthesis in Molten Salts to Water-Splitting Electrocatalysis

Postsynthetic transformations are key to the colloidal synthesis of functional nanocrystals by offering a way to complex shapes, heterostructures, and chemical compositions. They however remain inaccessible to whole families of solids, especially those relying on covalent bonds, which crystallize at temperatures that common solvents cannot stand. Herein we show that in inorganic molten salts above 500 °C, such transformations can be triggered to deliver metallo-covalent nanocrystals previously unattainable. By incorporating silicon and phosphorus into metal nanoparticles, we synthesize nickel silicophosphide nanocrystals and demonstrate how distinct chemical bonds involving silicon or phosphorus drive their electrocatalytic properties for alkaline water oxidation and hydrogen evolution. These bonds also determine the synthesis pathway, from sequential incorporation of p-block elements to topotactic transformations not reported before. The ability to run such complex postsynthetic reactions of nanoparticles into molten salts paves the way to increasing complexity in compositions and chemical bonding in nanocrystals for energy conversion.