Nitrogen-doped three-dimensional graphene-supported palladium nanocomposites: High-performance cathode catalysts for oxygen reduction reactions

This study reports an effective strategy for fabricating three-dimensional nitrogen-doped graphene supports for palladium nanoparticles (Pd-N/3D-GNS) and studying the electrochemical activity of the synthesized nanocomposites toward oxygen electroreduction in alkaline media as well as implementing the nanocomposite as cathode catalysts in anion exchange membrane fuel cells (AEMFC). It was demonstrated that by embedding and etching an amorphous sacrificial silica template into the reduced graphene matrix, the as-prepared nanocomposites pyrolyzed into hierarchically porous 3D-nanosheets composed of interconnected nitrogen-doped graphene nanostacks, which was confirmed using transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. Palladium nanoparticles were then deposited on the N/3D-GNS supports using a surfactant-free technique and characterized using various surface analysis and potentiodynamic techniques. By analyzing the linear sweep voltammograms obtained from rotating ring disc electrodes, it was demonstrated that the Pd-N/3D-Graphene nanocomposites efficiently catalyzed the four-electron reduction of oxygen, with onset potentials closer to theoretical values and negligible peroxide yields. The nanocomposites were then integrated into a catalyst-coated membrane and tested in H₂/O₂ fed AEMFC. Owing to its unique morphological features and the desirable chemical composition, the Pd/3D-GNS catalysts exhibited much enhanced performance as cathode materials for AEMFCs. The enhanced electrochemical kinetics and high current/power densities of up to 250 mW cm^-2 obtained from the cathodes materials described in this study will lead to further advancements in AEMFC technology.