Electrodeposition Of Pd-Sn Alloy Electrocatalytic Activity Toward Ethanol Oxidation

Direct ethanol fuel cells (DEFCs) convert the chemical energy of ethanol fuel directly into electrical energy. Ethanol is biodegradable with high energy density. Compared with the traditional Pt catalyst, Pd catalyst shows higher electrocatalytic activity toward the ethanol oxidation reaction (EOR) in alkaline media. Moreover, Pd is much cheaper and more abundant than Pt. Although Pd is a more active catalyst for the EOR in alkaline media, it cannot completely avoid CO poisoning. Alloyed Pd-Sn binary electrocatalysts with enhanced catalytic activities and stability have been widely reported in the literature. The enhanced catalytic activity toward ethanol electroxidation of Pd-Sn catalysts can be attributed to changes of geometric and electric structure of Pd by forming alloy with Sn. It is well known that catalytic activity is related to properties of the catalyst, such as component, support, morphology, size and so on. By tuning the the morphology of binary electrocatalysts can enhance their catalyst activities. Recently, nanodendrites have been extensively studied as an electrocatalyst for DEFCs. Nanodendritic structure is constructed with numerous subbranches, and a large number of edges and corner atoms are favorable for its catalytic activity. Up to date, several methods have been developed for the preparation of various bimetallic nanodendrites, such as electrodeposition, wet-chemical synthesis and so on. Among them, electrochemical deposition represents a simple, quick, and method for the preparation of dendritic structures by tuning its deposition conditions.Coordination agent have important influence on tuning nanodendrites growth, and tartaric acid is chosen, because as an electron donor with coordination ability it can coordinate with metal ions and tuning the morphology of nanodendrites, thus enhance Pd-Sn catalyst activity towards ethanol oxidation.1.Single crystal hierarchical Pd-Sn alloy nanodendrites are prepared via electrodeposition method in the presence of tartaric acid for the first time. Furthermore, the effects of ratios of PdCl2 to SnCl2, deposition time, current density, and tartaric acid concentrations on the morphology of the Pd-Sn deposits are also investigated. Its optimum preparation conditions were in 0.02 mol/L tartaric acid and 2 mol/L HC1 at 1.5 mA/cm2 for 60 min with a 1:4 concentration ratio of PdCl2 to SnCl2.2.The formation mechanism of hierarchical Pd-Sn alloy nanodendrites were investigated:the electrodeposition condition of Pd-Sn alloy nanodendrites is far from the thermodynamic equilibrium, and under diffusion control the hierarchical Pd-Sn alloy nanodendrites preferentially grow along PdiSn4 (131) directions. And Sn atoms can be treated as "foreign impurities" with respect to Pd matrix and consistent with the so-called foreign-particles-induced growth mechanism. As a protecting agent, tartaric acid can prevent the crystals from aggregation.3.The electrocatalytic activities of Pd-Sn with different atom ratios are are characterized. All of Pd-Sn catalysts showed better activities towards ethanol oxidation and Pd1Sn4 showed best electrocatalytic activity. Moreover, hierarchical Pd-Sn alloy nanodendrites (Pd1Sn4-1) exhibit better electrocatalytic activities than unhierarchical Pd-Sn alloy nanodendrites (Pd1Sn4-2).4. The reasons for enhanced catalytic activity toward ethanol electroxidation of Pd1Sn4-1 are investigated. It is maybe that Pd1Sn4-l possess more surface-area-to-volume ratio and more catalytic sites. By forming alloy with Sn, geometric and electric structure of Pd has changed and Pd1Sn4-1 surface can support more-OH, which is good for enhancement of catalytic activity.