Selenium‐Mediated Sub‐1 nm Amorphous Shell Spatially Confines Platinum Nanocrystal for Efficient Hydrogen Evolution

Abstract Ultrafine nanocatalysts can provide abundant catalytic sites, but typically it is less stable and susceptible to dissolution diffusion. Here, this work reports a selenium‐mediated strategy to construct sub‐nanometers amorphous shell on ultrafine Pt nanocrystal core, forming a Pt@PtSe _x core/shell nanostructure. In this developed strategy, the active Se‐oleylamine precursor after Pt nucleation confines the overgrowth and oriented attachment of Pt, allowing the in situ formation of core/shell nanostructures combining ultrafine size and sub‐nano amorphous shell. Essentially, the sub‐nano amorphous PtSe _x shell can not only optimize the hydrogen adsorption energy and lower the water dissociation energy, but also retard the dissolution of Pt atoms, thus leading to significantly improved activity and durability in both acidic and alkaline electrolytes. The overall water splitting can be driven by a small cell voltage of 1.48/1.53 V at 10 mA cm ⁻² in 0.5 M H ₂ SO ₄ /1.0 M KOH, respectively. Moreover, Pt@PtSe _x ‐1 with ≈0.8 nm thick amorphous shell exhibits ultra‐high mass activity of 75.2 A mg _Pt ⁻¹ in acidic and 18.4 A mg _Pt ⁻¹ in alkaline at −70 mV, as well as a robust durability with stable operation for 1100 h at 100 mA cm ⁻² in alkaline (1300 h at 160 mA cm ⁻² in acidic), superior to the most reported Pt‐based electrocatalysts.