Preparation Of Highly Stable Pd-based Catalysts And Their Electrocatlytic Properties For Ethanol Oxidation

Direct ethanol fuel cells are highly efficient power generators that directly convert chemical energy into electrical energy.They can provide a high theoretical energy density with little harm to the environment.In addition,ethanol that is non-toxic and easy to store and transport,has a wide range of sources and its production process is mature.So,the development of direct ethanol fuel cells is of strategic significance to alleviate the energy crisis and environmental pollution.However,the process of ethanol electrooxidation is complex,which involves a 12-electron transfer process.Besides,the C-C bond is difficult to break and the anode catalysts are easily poisoned because of the presence of various intermediate products.Another problem that hinders the commercialization of direct ethanol fuel cells is the extremely high price of commonly used Pt catalysts.Consequently,enormous efforts have been devoted to the development of non-Pt catalysts.Among them,Pd catalyst has caused wide attention due to its low price and relatively high catalytic activity and stability to ethanol electrooxidation in alkaline media.In this work,we successfully synthesized two kinds of Pd-based materials in order to further increase the catalytic activity and stability of Pd-based catalysts.1.Pd embedded in graphene doped carbon nanfibers?Pd@G-CNFs?were prepared by electrospinning and heat treatment.The average diameter of the nanofibers is 500 nm.Furthermore,the rough surface of the carbon nanofibers is decorated with some small-sized Pd nanoparticles.XRD,SEM,TEM and XPS were used to characterize the morphology,crystalline structure and composition of the as-prepared catalysts.We also utilized cyclic voltammetry and chronoamperometry to test its electrochemical performance.The results verified that: compared with Pd@CNFs,Pd@G-CNFs which possesses relatively small-sized nanoparticles has a large electrochemically active surface area and excellent catalytic activity and stability towards the electrooxidation of ethanol.The onset potential of electrooxidation of ethanol on Pd@G-CNFs is 0.46 V and its mass activity is caculated to be 869 mA mg^-1 which is 2.6 times that of Pd@CNFs.2.Based on the above experiments,we then prepared a series of PdFe catalysts by electrospinning and heat treatment: Pd₃Fe₁@G-CNFs,Pd₂Fe₁@G-CNFs and Pd₁Fe₁@G-CNFs.Electrochemical tests show that Pd₂Fe₁@G-CNFs exhibits the most excellent electrochemical performance and its electrochemically active surface area is as high as 30.9 m²g^-1,which is about 1.2 times and 3.6 times that of Pd₃Fe₁@G-CNFs and Pd₁Fe₁@G-CNFs,respectively.The current density of electrooxidation of ethanol is 1896 mA mg^-1 that is 1.3 times and 7.2 times that of Pd₃Fe₁@G-CNFs and Pd₁Fe₁@G-CNFs,respectively.Pd₂Fe₁@G-CNFs possesses some merits: i)the carbon coated structure can effectively prevent the nanoparticles from agglomeration or detachment from the support.ii)the introduction of appropriate amount of iron not only reduces the particle size of Pd particles,but also increased the electrochemical active area.In addition,the synergistic effect and electronic effect of Fe greatly increase the catalytic activity and stability of the catalyst.