Growth Pathway and Phase Transition From Quasi-layered Pt₅Se₄ to Layered PtSe₂ Nanocrystals

The discovery and control of phases is a significant endeavor for materials science. PtSe₂, as a stable Pt─Se phase, is controllably synthesized for electronic, optoelectronic, and electrocatalytic applications, while research on another stable Pt─Se phase, Pt₅Se₄, is limited to calculations. Moreover, the growth mechanisms and phase transition of Pt─Se compounds remain unclear. Here, we report a two-step growth pathway of PtSe₂ with a stable Pt₅Se₄ phase as intermediate and reveal the Pt-Pt₅Se₄-PtSe₂ transition process. The synthesis of PtSe₂ and Pt₅Se₄ nanocrystals is achieved by controlling the degree of selenization. Theoretical calculations prove that Pt₅Se₄ phase is thermodynamically favorable under Se-deficient conditions and PtSe₂ nanocrystals are formed along with the diffusion of Pt and Se atoms. This work greatly enriches the knowledge on the growth mechanism and phase transition of Pt─Se compounds, and offers insights into the controlled synthesis of Pt₅Se₄ for future electrocatalysis and electronic devices.