Performance Investigation Of Rare Earth-Pd Based Catalysts For Methanol Electrooxidation In Alkaline Media

In this study, Pd-based anode catalysts doped with different rare earth and functionalized catalyst support to improve the Pd-based catalysts for methanol oxidation in alkaline media. The structure and morphology of those catalysts had been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-Ray photoelectron spectroscopy (XPS) and Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The electrocatalytic performance of those catalysts for methanol oxidation in alkaline media was investigated using cyclic voltammetry (CV), chronoamperometry(CA), linear sweep voltammetry (LSV) and CO stripping experiments.The Pd-Tb/C catalysts with different Pd/Tb ratios were synthesized by a simple simultaneous reduction reaction with sodium borohydride in aqueous solution. It can be seen that the nanoparticles are dispersed uniformly on the carbon black substrate by XRD and TEM.The catalytic performance towards methanol electrooxidation in alkaline media was investigated. It was found that the20%Pd-1%Tb/C catalyst has a higher activity than the20%Pd/C catalyst, but this cannot be explained by a bi-functional mechanism. The analysis for XPS spectra indicates that the higher content of metallic Pd caused by the addition of Tb contributes to the better catalytic activity of20%Pd-1%Tb/C. According to the analysis of ICP-AES, the mass ratio of Pd to Tb is19.43%and0.9360%respectively, which is in close proximity to the theoretical value.Carbon black supported bimetallic palladium-yttrium (Pd-Y/C) catalysts with different Pd-Y ratios were prepared by chemical reduction and calcination treatment methods. The structure and morphology of the catalysts were characterized by XRD and TEM, the results indicated that the nanoparticles are dispersed uniformly on the carbon black substrate. Electrochemical characterization techniques, including cyclic voltammetry (CV), chronoamperometry (CA) and CO stripping were carried out to analyze the electrochemical performance of these catalysts for methanol oxidation in alkaline media. All the results show that the20%Pd-5.0%Y/C catalyst has a higher catalytic activity than the20%Pd/C catalyst and the addition of Y also facilitates the oxidative removal of adsorbed CO. The promoting effect of Y is explained by a bi-functional mechanism.The Pd-La2O3/C catalysts with a small amount of La2O3were synthesized by a simple simultaneous reduction reaction with sodium borohydride in aqueous solution. The structure and morphology of those catalysts were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrocatalytic performance of those catalysts for methanol oxidation in alkaline media was investigated using cyclic voltammetry (CV), chronoamperometry (CA) and CO stripping experiments. The results show that the20%Pd-3.0%La2O3/C catalyst has a higher catalytic activity than the20%Pd/C catalyst, but the effect of La2O3cannot be explained by a bi-functional mechanism. X-Ray photoelectron spectroscopy (XPS) analyses suggest that the higher content of metallic Pd caused by the addition of La2O3contributes to the better catalytic activity of20%Pd-3.0%La2O3/C.Based on the good electrocatalytic performance of the20%Pd-1%Tb/C catalyst, the20%Pd-1%Tb catalyst supported on activated carbon nanotubes was synthesized, but its electrocatalytic activity deteriorated, which is ascribed to the high aggregation degree of alloy particles due to the hydrophobility of aCNTs. After aCNTs was functionalized by PDDA, the20%Pd-1%Tb/aCNTs-PDDA catalyst exhibited a better catalytic activity than the20%Pd-1%Tb/C catalyst. The improvement is attributed to the good dispersion status of alloy particles and the further increase of metallic Pd due to the presence of PDDA.