Palladium-based polyelemental nanoparticles for ethanol oxidation reaction

Abstract

Designing efficient and stable catalysts for the anodic oxidation of alcohols is important for the development of high-performance fuel cells. Here, we report the use of colloidal methods to synthesize unary Pd, binary PdAg, PdAu, PdPb, and PdBi, and ternary PdAuAg nanoparticles with a uniform size and well-defined composition. The synthesized alloy nanocatalysts exhibit a larger electrochemically active surface area, higher mass activity, and improved stability compared to monometallic Pd nanoparticles and commercial Pd/C and Pt/C catalysts. Notably, the ternary PdAuAg nanoparticles have a mass activity of 2448.7 mA mg_Pd⁻¹ for ethanol oxidation, which is 4.0 and 3.2 times that of commercial Pd/C and Pt/C, respectively, and the PdAuAg nanoparticles retain 94.5% of the initial activity after 1000 cycles of activity tests. The incorporation of elements with a larger atomic radius into the Pd nanoparticles causes the expansion of the Pd lattice while changing the coordination environment of the surface Pd sites, resulting in tensile-strain effects and ligand effects that contribute to the high electrochemical activity and stability. DFT calculations reveal that the PdAuAg catalyst has a more uniform distribution of reaction energy barriers and a smaller energy barrier of the rate-determining step than the Pd catalyst. In addition, the Pd sites on PdAuAg are responsible for the activation of the reactants, while the Au and Ag sites facilitate the desorption of the poisoning species, thus improving the stability of the catalyst. Taken together, this work provides a simple yet effective strategy for the design of polyelemental nanoparticle catalysts for electrocatalytic oxidation of alcohols.