Bi-modified Pd-based/carbon-doped TiO 2 hollow spheres catalytic for ethylene glycol electrooxidation in alkaline medium
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e TiO2 hollow spheres (TiO2HS) were successfully prepared by a hydrothermal method and added to Vulcan XC-72 carbon black as the support materials for Pd nanoparticles. A facile approach to promote ethylene glycol (EG) electrooxidation in alkaline medium was carried out by the PdBi/TiO2HS-C catalyst. The results show that Pd and Bi nanoparticles are uniformly dispersed on the surface of carbon-doped TiO2 hollow spheres, the appropriate amount of Bi modification into Pd/TiO2HS-C catalyst can enhance remarkably the electrocatalytic activity for EG oxidation, in which the PdBi/TiO2HS-C (Pd:Bi 5 1:0.1) catalyst exhibits excellent stability. The high electrochemical performance is attributed to the unique structure and high surface area of the TiO2HS, metal nanoparticles uniform distribution, the electronic effect between Pd and Bi as well as the bifunctional effect between metal nanoparticles and the support TiO2HS-C. The results obtained are significant for the development of new Pd-based TiO2HS-C electrocatalysts for alcohol fuel cells. I. INTRODUCTION
As an alternative power source, direct alcohol fuel cells (DAFCs) is popular due to its high electromotive force, low toxicity, limited fuel crossover as well as high practical power densities.1,2 Among various types of alcohols, ethylene glycol (EG) is one of the most promising candidates as it can be produced directly from biomass.3,4 Moreover, EG has superior energy density (7.56 kW h/L) and higher boiling point (198 °C) than other typical alcohol fuels such as methanol and ethanol.5 So it is very significant to study the application for EG as alcohol fuel cells. Additionally, Pd has certain catalytic effects on alcohol electrooxidation in alkaline medium.6,7 Furthermore, Pd is much more abundant compared to Pt on the earth8 and thus the Pd-based catalysts facilitate their commercialization application. The combination of nanostructured Pd with transition metal oxides has originated a distinctive class of Pd-based electrocatalysts for DAFCs applications.9 It was reported that the addition of transition metal oxides (CeO2, Co3O4, Mn3O4, NiO, MnO2) could obviously improve the activity and the stability of Pd catalyst for alcohol oxidation.6,10 For example, Shen et al.11 found that carbonized TiO2 nanotube supported Pd was not only superior in electrocatalytic activity for ethanol oxidation
Contributing Editor: Xiaobo Chen a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.429
reaction (EOR) but also more stable during the constant current density polarization in alkaline media than Pd/C. Moreover, some studies have been reported that C-doped TiO2 has better catalytic activity.12–14 However, the activity of Pd-based catalysts should be further enhanced to fulfill commercialization as they are used in practical fuel cells. For this purpose, uniform nanocatalysts with large surface area and high activity per unit area are needed to design; and various approaches are proposed to achieve these conditions, such as size control,15 sur
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