Protective Surface Amorphization Enabling Electrocatalytic Pt Alloy Synthesis.

We present a silica nanoshell confinement strategy that enables a previously unreported surface-specific amorphization process on ultrathin 2D Pt nanodendrites (2D-PtNDs). By treating silica-encapsulated 2D-PtNDs with NaBH4, only the outer atomic layers transform into an amorphous Pt "skin" rich in high-energy, coordinatively unsaturated sites, while the rigid silica shell decouples surface from bulk reactions and prevents structural collapse. The resulting amorphous surface exhibits extraordinary reactivity, spontaneously reducing and incorporating secondary metal ions (Pd, Ag, Au, Ru) via an off-equilibrium redox exchange (antigalvanic alloying) under ambient conditions, yielding conformal Pt-M surface alloys with tunable compositions without compromising the ultrathin morphology. Using ethanol oxidation as a model reaction, we demonstrate that Ag- and Pd-alloyed trimetallic Pt nanosheets achieve dramatically enhanced electrocatalytic performance, including nearly complete ethanol conversion to CO2 (∼89% Faradaic efficiency) and an order-of-magnitude higher mass activity than commercial Pt/C. Notably, the same surface activation extends to bulk platinum substrates (e.g., Pt foil), doubling their catalytic activity via Ag alloying. Our findings establish a general and scalable route to engineer amorphous alloy skins on noble metals for improved catalysis.