Pt-Pyrrole Complex-Assisted Synthesis of Carbon-Supported Pt Intermetallics for Oxygen Reduction in Proton Exchange Membrane Fuel Cells

Nanosized intermetallic Pt-transition metal alloys with high catalytic activity and stability are considered as promising catalysts for the oxygen reduction reaction (ORR). However, the preparation of intermetallic Pt alloy nanoparticles remains a dilemma due to their pronounced tendency for sintering at high synthesizing temperatures. Here, we have synthesized several Pt intermetallics with an average size of 4 nm by employing carbon-supported Pt--pyrrole complex and transition metal (TM = Fe, Co, Ni) salts as precursors. Transmission electron microscope (TEM) results indicate that not only the uniform pregrowth of the Pt-pyrrole complex onto the carbon support but also the subsequently derived N-doped carbon shells (<1 nm) on the nanoparticles during annealing contribute to the formation of the nanosized intermetallics. Additional characterization suggests that the intermetallic alloy structure endows the catalyst (PtCo@Pt/C-6) with a downshifted Pt d-band center, which implies the weakened adsorption of the ORR intermediates on the Pt alloy, thus facilitating the ORR kinetics. The fuel cell with the as-prepared PtCo@Pt/C-6 catalyst displays a rated peak power density of 1.1 W/cm(2) at 0.67 V (H-2/air) and a mass activity of 0.49 A/mg(Pt) at 0.9 V, exceeding the targets of the US Department of Energy (1.0 W/cm(2) and 0.44 A/mg(Pt), respectively). This method demonstrates great potentials for the scalable synthesis of PtTM/C catalysts with high ORR performance and promoting their applications in PEMFCs.