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

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 mgPt 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 mgPt-1 for the whole cell).