Preparation and characterization of PdxAgy/C electrocatalysts for ethanol electrooxidation reaction in alkaline media

Carbon-supported bimetallic PdAg catalysts with Pd/Ag atomic ratios varying from 4/1 to 1/2 were prepared by an impregnation–reduction method. The impregnated black mixture was treated in H2/N2 atmosphere at a temperature varying from 180 to 500 °C. The obtained PdxAgy/C catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV) and chronoamperometry (CA). XRD results show that the lattice constant of Pd is dilated, suggesting the formation of PdAg alloy. The lattice constant of Pd for the PdxAgy/C-500 (reduced at 500 °C by H2) increases linearly and the average metal particle size decreases slightly from 6.8 to 5.1 nm with increasing Ag fractions from 20% to 67% in the PdAg composition. For PdxAgy/C catalysts with a certain specific Pd/Ag atomic ratio, e.g., Pd2Ag1/C, the dilated lattice constant of Pd is independent of the reducing temperature, indicating the alloy degree for the Pd2Ag1/C-t catalysts is comparable. The average metal particle size for the Pd2Ag1/C-t catalysts increases from 3.4 to 5.2 nm with H2 reduction temperature increasing from 180 to 500 °C. The potentiodynamic measurements on ethanol electrooxidation reaction (EOR) show that the catalytic activities for the PdxAgy/C-t catalysts toward the EOR are improved by alloying Pd with Ag. At typical potential of a working fuel cell, e.g., −0.4 V vs. Hg/HgO, the EOR current density presents a volcano shape as a function of the Ag fractions in PdAg with the maximum occurs at the Pd/Ag atomic ratios between 2/1 and 3/1. The CA tests show that the PdxAgy/C-500 catalysts perform high stability than that of Pd/C-500. The improved EOR activity for the PdxAgy/C-t catalysts, compared with whether Pd/C or Ag/C catalyst, may possibly be attributed to the formation of PdAg alloy and the fitted particle size.

• The effects of Pd or PdAg particle size and PdAg alloy degrees on the EOR activity are investigated.
• The Pd lattice constant of the PdAg increases with increasing the Ag content.
• The EOR activity of the PdAg/C presents a “volcano” plot with increasing the Pd lattice constant.
• The optimal Pd/Ag atomic ratio locates between 2/1 and 3/1.
• The EOR activity of the PdAg/C increases with increasing the PdAg particle size from 3.4 to 5.2 nm.