Highly Dispersed and Small-Size Pd–Cu Nanoparticles Supported on N-Doped Graphene for Oxygen Reduction Reaction Catalysts

Carbon-based material-supported precious metal catalysts have important applications in fuel-cell cathode electrocatalysis due to the excellent conductivity and abundance of active sites. Here, a nitrogen-doped graphene-supported bimetallic palladium–copper composite catalyst (Pd₃Cu₁/N-rGO) was prepared by heat-treating the aniline monomer and graphene oxide polymer, followed by supporting palladium–copper metal particles. The change in the structure and surface state of the carbon matrix can effectively control the particle size and dispersion of alloy particles and improve the catalytic performance of the catalyst to reduce the amount of palladium. The alloy nanoparticles of the prepared Pd₃Cu₁/10N-rGO-800 composite catalyst material are about 1.75 nm in size and the Pd content is less than 10%, which demonstrates an excellent oxygen reduction reaction (ORR) catalytic performance with a mass-normalized current density of 2.35 times that of commercial Pt/C (20 wt % Pt), mainly a four-electron transfer process, and higher catalytic stability than commercial platinum carbon (Pt/C). Most importantly, the prepared catalyst showed better methanol tolerance and much higher stability, and Pd₃Cu₁/10N-rGO-800 is used as a cathode catalyst material in a zinc–air battery; it presents a higher peak power density (164.39 mW/cm²) and faster discharge performance. The N-doped graphene facilitated the dispersion of the Pd–Cu nanoparticles, effectively reduced the size of alloy particles, maximized the exposure of active sites on the surface, and improved the electrocatalytic activity of oxygen reduction. Pd–Cu nanoparticles supported on N-doped graphene will potentially offer an alternative approach to utilize non-platinum metal catalysts in electrocatalyst applications of oxygen reduction.