Morphology-GuidedPhase-Controlled Synthesis of NickelSelenide Nanocrystals through Cation Exchange Reactions

The precise control of the crystal phase during the synthesis of nickel selenide (Ni_<i>x</i>Se_<i>y</i>) 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 Ni_<i>x</i>Se_<i>y</i> 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‑<i>x</i>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.