Morphology-Guided Phase-Controlled Synthesis of Nickel Selenide Nanocrystals through Cation Exchange Reactions

The precise control of the crystal phase during the synthesis of nickel selenide (NiSe) nanocrystals is crucial, as crystal structure and composition significantly influence their reactivity, growth kinetics, and properties. The cation exchange (CE) method provides a versatile and robust approach for synthesizing nanomaterials, enabling precise control over phase, composition, and morphology. However, the application of this method for phase-controlled synthesis of NiSe nanocrystals has received limited research attention. Here, we present a morphology-guided CE method for the synthesis of spinel Ni₃Se₄ nanoparticles (NPs) and rhombic Ni₃Se₂ nanorods (NRs), wherein berzelianite Cu_2-Se NPs and NRs are employed as sacrificial templates for CE with Ni²⁺. This phase-controlled behavior, which is guided by morphology and dependent on the stacking length of the close-packed facets, relies on the rearrangement of the Se^2- sublattice accompanied by CE, providing a unique and precise approach to controlling phase during nanocrystal synthesis. Additionally, the obtained Ni₃Se₄ NPs and Ni₃Se₂ NRs exhibit structure-dependent catalytic activities in the oxygen evolution reaction.