Pt–Pyrrole Complex-Assisted Synthesis of Carbon-Supported Pt Intermetallics for Oxygen Reduction in Proton Exchange Membrane Fuel Cells
Yuting Jiang, Qing Zhang, Junning Qian, Yameng Wang, Yongbiao Mu, Zhiyuan Zhang, Zheng Li, Tianshou Zhao, Bilu Liu, Lin Zeng
Abstract
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.