PdZn nanoparticle electrocatalysts synthesized by solution combustion for methanol oxidation reaction in an alkaline medium

Abstract

Herein, we report the synthesis of PdZn nanoparticle (NP) electrocatalysts for the methanol oxidation reaction (MOR). The PdZn NPs were synthesized by solution combustion synthesis in the presence of Pd(NO₃)₂·xH₂O, Zn(NO₃)₂·6H₂O and glycine in H₂O, where glycine acted as a fuel. In this synthesis, the glycine amount was varied with a fixed stoichiometric ratio of Pd- and Zn-precursors at 1 : 1 to obtain two electrocatalysts (PdZn/C) of fuel-high (glycine to metal nitrate ratio = 1.75), PdZn/C (1.75) and fuel-low (glycine to metal nitrate ratio = 0.5), PdZn/C (0.5). The NPs were characterized by X-ray diffractometry, transmission electron microscopy and scanning electron microscopy for the crystallite size, morphology and elemental composition of the electrocatalysts. High-angle annular dark-field-scanning transmission electron microscopy coupled to energy dispersive X-ray spectroscopy was used to obtain the elemental distribution maps of the aggregated NPs, which confirmed the NPs with Pd and Zn in the alloyed state. X-ray photoelectron spectroscopy was performed to analyze the electronic structures of the elements in the samples. The NPs were then applied in the electrocatalysis for MOR in an alkaline medium. We found that PdZn/C showed an improved electrocatalytic activity by a factor of ∼1.4–1.9 in comparison with Pd/C synthesized using the same method. The MOR on PdZn/C (1.75) began at an earlier onset potential and higher current density than for Pd/C and PdZn/C (0.5). Stability tests were performed by chronoamperometry on PdZn/C and Pd/C, and the results showed a higher stability of PdZn/C (1.75) compared to PdZn/C (0.5) and Pd/C. The fuel amount affected the NP sizes, reaction yield and electrocatalytic properties.