Synergy of Pt-Free Single Metal Sites for Promoting Pt and Pt3co Ordered Intermetallic Catalysts for Fuel Cells: Performance and Durability Improvements

The reduction of platinum use and improvement of its catalytic performance has become the most critical steps to accelerate the development of proton-exchange membrane fuel cells (PEMFCs). Here we report a novel and facile method to boost the performance of the Pt-cased catalyst by integrating with an atomic platinum-group metal (PGM)–free active sites. Using iron-doped zeolitic imidazolate framework-8 (ZIF-8) derived carbon as support, we achieved a uniform deposition of Pt and intermetallic Pt-Co nanoparticles (NPs) through one-step synthesis, with average particle size 2.4 nm for Pt, 3.4 nm for L10 PtCo, and 4.2 nm for L12 Pt3Co. Besides, easy phase transfer during synthesis between ordered intermetallic structures L10 PtCo and L12 Pt3Co was achieved, and a comprehensive comparison between their catalytic performance was established. Synergistic catalysis between Pt or Pt-Co NPs over a PGM–free catalytic substrate derived from iron-doped ZIF-8 led to excellent oxygen reduction reaction (ORR) performance under both rotating disk electrode (RDE) and membrane electrode assembly (MEA) testing. Resulting pure Pt catalysts achieved ORR mass activities of 0.451 A/mgPt and retained 80% initial values after 30,000 voltage cycles in a fuel cell, superior to the DOE 2020 targets without using Pt alloy. Both PtCo and Pt3Co catalysts achieved better performance and exhibited all-sided excellence among mass activity, stability, and power density. Among them, Pt3Co reached the power density at 0.67 V of 923 mW/cm2 and retained 86% initial mass activity after 30,000 voltage cycles in a fuel cell. Their performance dependences on support material particle size and ionomer content were discussed and optimized in MEAs.