The Effect of Sulphate and Chloride Palladium Salt Anions on the Morphology of Electrodeposited Pd Nanoparticles and their Catalytic Activity for Oxygen Reduction in Acid and Alkaline Media

Pd/GC electrodes were prepared by the electrochemical deposition of palladium on glassy carbon (GC) using PdSO4 or PdCl2 salts. As-prepared GC-supported Pd nanoparticles were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). XPS spectra revealed that the depositing palladium salt anion influences the oxidation state of the deposited Pd, while AFM images showed its effect on Pd nanoparticle size and coverage. The deposition from the PdCl2 salt solution resulted in smaller palladium nanoparticles, but much higher GC surface coverage than from PdSO4. The activity of Pd/GC electrodes towards oxygen reduction was examined in acid and alkaline media using the rotation-disc electrode. Among the different Pd/GC electrodes, the one prepared using PdCl2 salt with the full Pd coverage has shown the best ORR activity. The ORR occurs through a 4e-series reaction mechanism like on polycrystalline palladium but exceeds its activity concerning the initial potential.