Revealing the Role of Phase Structures of Bimetallic Nanocatalysts in the Oxygen Reduction Reaction

The ability to tune the atomic-level structure of alloy nanoparticles (NPs) is essential for the design and preparation of active and stable catalysts for fuel cell reactions such as the oxygen reduction reaction (ORR), which is highly sensitive to the structure of the catalysts. We report here structurally tunable PdCu nanoparticle catalysts for the ORR obtained by varying the thermochemical treatment conditions. The phase type and the atomic structure of the nanoalloy catalysts strongly depend on the thermochemical treatment temperature and atmosphere, especially at low temperatures. While PdCu nanoalloys feature both body-centered cubic (bcc) and face-centered cubic (fcc) phase structures, a pure fcc structure, prepared at an unusually low thermochemical treatment temperature, showed the highest catalytic activity for the ORR. This was evidenced by a mass activity 8 times higher than that of commercial Pd catalyst. This activity enhancement was shown to be linked to the nanostructural tuning between fcc and bcc structures, as supported by systematic characterization using X-ray diffraction (XRD) coupled with pair distribution function (PDF) analysis. The impact of phase structure on the catalytic properties of the nanocatalyst is further substantiated by computational modeling based on density functional theory (DFT). These findings provide a fresh insight into the nanostructure–activity correlation at the atomic scale, which has significant implications for the design, synthesis, and processing of highly active nanoalloy catalysts.