Precise synthesis of sub-3 nm platinum-based intermetallic alloys with a freeze-microwave confinement strategy for the hydrogen evolution reaction

Intermetallic compounds (IMCs) with atomically ordered crystal structures exhibit unique electrochemical catalytic properties attributed to their well-defined structure–activity correlations. However, the precise synthesis of sub-3 nm IMCs with highly active surface area remains challenging. Herein, we propose a “freeze-microwave confinement” strategy that precisely regulates crystal nucleation kinetics to widely synthesise sub-3 nm platinum-based IMCs. Significantly, the obtained sub-3 nm Pt–Fe intermetallic alloy (L1₂-Pt₃Fe/KB) achieves overpotentials as low as 27 mV in 0.5 M H₂SO₄ and 35 mV in 1.0 M KOH at 10 mA cm^−2, together with exceptional durability after 20 h of electrolysis. More importantly, this synthesis strategy can be further applied to various Pt–M alloys (M = Cr, Mn, Co, Ni and Zn), demonstrating widely applicable ability for controllable synthesis of sub-3 nm IMCs. This work provides a feasible strategy for constructing sub-3 nm IMCs and offer a fundamental understanding of crystal nucleation kinetics control toward exploring advanced Pt-based electrocatalysts. This journal is © The Royal Society of Chemistry, 2026