Research Of Binary And Ternary Pd-based Nanoparticles As Anodic Catalysts

As palladium (Pd) shows high catalytic activity toward methanol and ethanol electro-oxidation in alkaline medium and formic acid electro-oxidation in acid medium, researchers always decorate palladium to find new catalysts. One of the most common ways is to synthesize Pd-based nanoparticle catalysts. The additional transition elements obviously increase the activity of the catalysts through synergistic effect or by leaching away to enlarge the electrochemical active surface area (EASA). We successfully synthesized three groups of catalysts by liquid phase reduction method and do some research accordingly. These catalysts are characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and chronoamperometry (CA).The first group are Pd/CNTs, PdCu(molar ratio1:1)/CNTs, PdSn(1:1)/CNTs and PdCuSn(1:1:1)/CNTs nanoparticle catalysts. The additive Cu and Sn both obviously increase the activities of the catalysts toward methanol and ethanol electro-oxidation in alkaline medium, and Cu perform better for methanol electro-oxidation while Sn better for ethanol. We find that the improvement of electro-activity is quite different between Cu and Sn from the CVs and EDX results. While Cu improves the activity through leaching way and exposes the inside Pd to enlarge the EASA but Sn through the synergistic effect. When both Cu and Sn are add to Pd, ternary PdCuSn(1:1:1)/CNTs shows much better electrochemical activity and stability toward methanol, ethanol and formic acid electro-oxidation.The second group are PdSn (molar ratio1:1)/C, PdSnCo(2:2:1)/C, PdSnNi(2:2:1)/C and PdSnAg(2:2:1)/C nanoparticle catalysts. We use Co, Ni and Ag as additives add to PdSn/C catalyst and observe that Ag shows much better synergistic effect with PdSn and PdSnAg/C shows the best electrochemical activity and stability among the four catalysts. The XPS results reveal that during the electro-oxidation progress, Ni and Co are obviously leaching away on the surface while Ag does not.The third group is use Pt which own high electrochemical activities itself as the additive, to research the PdSn-based/C catalysts. Through the different amount of Pt add to PdSn we find the variation tendency from typical Pd to typical Pt toward ethenol and formic acid electro-oxidation both in acid medium. The ternary PdSnPt/C catalyst shows much better electrochemical activity, stability and even CO resistance.