Electrochemical nucleation and growth of Pd/PdCo core-shell nanoparticles with enhanced activity and durability as fuel cell catalyst

This work presents an innovative approach for the preparation of a promising nano-sized catalyst, Pd/PdCo core-shell nanoparticles (NPs), with enhanced catalytic activity and durability for formic acid electro-oxidation. By addressing the kinetics of nucleation during electrodeposition we developed a method for synthesizing Pd/PdCo core-shell NPs with a shell thickness of ca. 2 nm. During the initial stages of step potential electrodeposition, Pd was deposited to form the core due to the higher nucleation rate of Pd compared to that of Co, and then the co-electrodeposition of Pd and Co led to the formation of a thin PdCo shell. The results of formic acid (FA) electro-oxidation by the synthesized Pd/PdCo core-shell NPs revealed a mass activity of 1580 mA mg(Pd)(-1) at the peak potential, which is three times higher than that of Pd NPs (j(P) = 540 mA mg(Pd)(-1)). Based on X-ray photoelectron spectroscopy (XPS) studies, the variations in activity and durability were attributed to the change of electronic band structure of the Pd/PdCo core-shell, which resulted in the weakened chemisorption of intermediate anion species. The material synthesized herein is a promising catalyst for fuel cell applications and the facile synthesis method can be readily adapted to other core-shell catalyst systems, facilitating screening of high efficiency catalysts.