A comparative study of elemental additives (Ni, Co and Ag) on electrocatalytic activity improvement of PdSn-based catalysts for ethanol and formic acid electro-oxidation

In this study, we have synthesized a series of carbon supported PdSn(molar ratio 1:1), PdSnAg(2:2:1), PdSnNi(2:2:1) and PdSnCo(2:2:1) catalysts by a borohydride reduction method. These catalysts were 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). As compared with PdSn/C, the trimetallic catalysts show a significant activity enhancement for ethanol and formic acid electro-oxidation. Moreover, the PdSnAg/C catalyst exhibits the highest activity together with much better stability. The activity enhancement of PdSnAg/C can be rationalized by the synergistic effect of Pd-SnO2-Ag clusters on the superficial surface of catalyst, such as bi-functional mechanism, superior electronic structure, excellent electric conductivity, etc. In addition, both ethanol and formic acid electro-oxidation reactions on the PdSnAg/C catalyst are diffusion-controlled and represent good linear correlation with ethanol and formic acid concentrations.