Atomic layer deposition enabled PtNi alloy catalysts for accelerated fuel-cell oxygen reduction activity and stability

Structuring Pt-based alloy catalysts with uniform, dense dispersion, and low loading is a challenging work for efficient and relatively low-cost catalysts to promote oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs). Herein, we present a strategy of active PtNi alloy structure formation with uniform metal alloy nanoparticles (NPs) using fluidized bed reactor atomic layer deposition (FBR-ALD). The compositions of the PtNi alloys were controlled by the ALD super-cycle method, where Pt75+XNi25-X alloy catalysts were successfully synthesized by tuning the super-cycle ratio. The as-deposited alloy catalysts consisted of well-dispersed and dense metal NPs, whose characteristics were maintained even after heat treatment at 700 °C with H2 to produce a well-mixed PtNi alloy. During heat treatment, the Pt-rich Pt3Ni alloy converted into the Pt skin-Pt3Ni alloy structure from the ALD growth mechanism, which is evidenced by spherical aberration (Cs)-corrected transmission electron microscopy (TEM), line profiling, X-ray photoelectron spectroscopy (XPS), and electron energy loss spectroscopy (EELS). The ALD synthesized Pt skin-Pt3Ni alloy structure featured a significantly higher electrochemical surface area (ECSA) as well as ORR activity, durability, and PEMFC performance compared to the commercial Pt and Pt3Ni catalysts due to their excellent uniformity, density, and well dispersity as well as the Pt skin-Pt3Ni structure. This study focuses on an atomic scale strategy for a new alloy architecture and marks a step toward a modern high-performing alloy catalyst for future PEMFC technology.