A sequential hydrogen-adsorption-assisted bond-weakening strategy for preparing sub-2-nm ordered Pt alloy nanocrystals

Abstract

<h2>Summary</h2> Synthesis of highly active sub-2 nm Pt-based alloy nanocrystals for oxygen reduction reaction (ORR), especially by a confinement-free route, remains a challenge. Herein, we report a sequential hydrogen-adsorption-assisted bond-weakening strategy. To Pt₃ clusters deposited on Fe–N₅–C surface, due to stronger Pt–H than N–H interaction, H would firstly adsorb on Pt and then on N, which then weakens Pt–Pt and Fe–N bonds, improves atomic mobility, and thus significantly decreases the kinetic barriers for alloying Pt clusters with single Fe species. As a result, Pt alloys can be prepared at a lower temperature, which largely inhibits the size growth and successfully leads to 1.55 nm Pt₃Fe and 1.25 nm Pt₃Ni intermetallic nanocrystals. Under an ultralow cathodic loading of 0.03 mg_Pt cm^-2, the H₂–O₂ fuel cell assembled with Pt₃Ni cathode delivers extraordinary activity (1.60 A cm^-2@0.67 V; 13.7 W mg_Pt^-1 for the whole cell).