Factors affecting the catalytic activity of Pd-based electrocatalysts in the electrooxidation of glycerol: element doping and functional groups on the support

Abstract

In this paper, the loaded Pd-based (Pd–Ni, Pd-Co, Pd–Ag, Pd-Pb and Pd-Pr) electrocatalyst was prepared by the method of impregnation-freeze-drying-H2/Ar2 reduction. The crystal structure, spatial distribution and surface chemical state of Pd-based electrocatalysts were characterized by X-ray diffraction, transmission electron microscope, and X-ray photoelectron spectroscopy. The effects of doping elements and functional groups of the support on the electrocatalytic activity of Pd-based electrocatalysts were studied using cyclic voltammetry and chronoamperometry. The results show that when the atomic ratio of Pd to Pr is 1.25, the PdPr/rGO nanocatalyst has the best catalytic activity for the electrooxidation of glycerol, which is 2.76 times that of pure Pd. In comparison to MWCNTs with -COOH, -NH2 and -OH functional groups, nitrogen-doped MWCNTs are more beneficial to increase the reaction rate of glycerol electrooxidation. The reason may be that Pr can produce praseodymium hydroxide in alkaline solution. In the electrooxidation reaction of glycerol, praseodymium hydroxide can act as an electrocatalyst. In addition, the doping of Pr increases the content of Pd0, and there is a synergistic effect between Pd and Pr. These are beneficial for increasing the electrooxidation rate of glycerol on the Pd6Pr4/N-MWCNT catalyst. The functional groups on the support may be affect the adsorption capacity and the degree of reduction for metal ions, and then affect the electrocatalytic activity. The influence of doping in the electrocatalyst is greater than that of the functional groups on the support.