H2-Annealed Core–Shell Pt-Co/C Electrocatalysts with Enhanced Durability for the Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) at the cathode remains a major kinetic bottleneck for proton-exchange-membrane fuel cells, and Pt-Co alloying is a well-established strategy for boosting Pt-mass-normalized ORR activity. However, the long-term durability of such alloys is limited by two largely independent degradation pathways, dealloying-induced Co leaching and nanoparticle coalescence, that are rarely addressed simultaneously. Here, a series of PtxCoy/C-H2 catalysts with varying Pt:Co ratios were synthesized via gel-confined co-reduction of Pt and Co precursors, phosphoric-acid-assisted carbonization into a mesoporous carbon support, and a subsequent H2-annealing step. XRD confirmed Pt-Co alloy formation with composition-dependent lattice contraction, while XPS showed that surface Pt:Co ratios consistently exceeded the nominal feed ratios across all compositions, indicating H2-annealing-induced Pt surface segregation and the formation of a Pt-enriched, core–shell-like architecture, further supported by TEM/EDS line-scan profiles. Among the series, Pt3Co1/C-H2 delivered ORR activity (E1/2, mass activity, and specific activity) essentially comparable to commercial Pt/C while reducing Pt loading by approximately 9 wt%, and retained the intrinsic four-electron ORR pathway (n = 3.78). After accelerated durability testing (10,000 cycles), Pt3Co1/C-H2 exhibited smaller E1/2 decay than Pt/C (48 vs. 52 mV), which is attributed to the concurrent suppression of nanoparticle coalescence by mesopore confinement and of Co leaching by the Pt-enriched surface. These results establish a generalizable design principle for decoupling the dominant degradation pathways of Pt-transition-metal alloy ORR catalysts while reducing precious-metal content.