Disproportionation chemistry in K₂PtCl₄ visualized at atomic resolution using scanning transmission electron microscopy

The direct observation of a solid-state chemical reaction can reveal otherwise hidden mechanisms that control the reaction kinetics. However, probing the chemical bond breaking and formation at the molecular level remains challenging because of the insufficient spatial-temporal resolution and composition analysis of available characterization methods. Using atomic-resolution differential phase-contrast imaging in scanning transmission electron microscopy, we have visualized the decomposition chemistry of K₂PtCl₄ to identify its transient intermediate phases and their interfaces that characterize the chemical reduction process. The crystalline structure of K₂PtCl₄ is found to undergo a disproportionation reaction to form K₂PtCl₆, followed by gradual reduction to crystalline Pt metal and KCl. By directly imaging different Pt-Cl bond configurations and comparing them to models predicted via density functional theory calculations, a causal connection between the initial and final states of a chemical reaction is established, showcasing new opportunities to resolve reaction pathways through atomistic experimental visualization.