Hydrogen-assisted scalable preparation of ultrathin Pt shells onto surfactant-free and uniform Pd nanoparticles for highly efficient oxygen reduction reaction in practical fuel cells

Concentrating active Pt atoms in the outer layers of electrocatalysts is a very effective approach to greatly reduce the Pt loading without compromising the electrocatalytic performance and the total electrochemically active surface area (ECSA) for the oxygen reduction reaction (ORR) in hydrogen-based proton-exchange membrane fuel cells. Accordingly, a facile, low-cost, and hydrogen-assisted two-step method is developed in this work, to massively prepare carbon-supported uniform, small-sized, and surfactant-free Pd nanoparticles (NPs) with ultrathin ~3-atomic-layer Pt shells (Pd@Pt_3L NPs/C). Comprehensive physicochemical characterizations, electrochemical analyses, fuel cell tests, and density functional theory calculations reveal that, benefiting from the ultrathin Pt-shell nanostructure as well as the resulting ligand and geometric effects, Pd@Pt_3L NPs/C exhibits not only significantly enhanced ECSA, electrocatalytic activity, and noble-metal (NM) utilization compared to commercial Pt/C, showing 81.24 m²/g_Pt, 0.710 mA/cm², and 352/577 mA/mg_NM/Pt in ECSA, area-, and NM-/Pt-mass-specific activity, respectively; but also a much better electrochemical stability during the 10,000-cycle accelerated degradation test. More importantly, the corresponding 25-cm² H₂-air/O₂ fuel cell with the low cathodic Pt loading of ~ 0.152 mg_Pt/cm²_geo achieves the high power density of 0.962/1.261 W/cm²_geo at the current density of only 1,600 mA/cm²_geo, which is much higher than that for the commercial Pt/C. This work not only develops a high-performance and practical Pt-based ORR electrocatalyst, but also provides a scalable preparation method for fabricating the ultrathin Pt-shell nanostructure, which can be further expanded to other metal shells for other energy-conversion applications.