Methanol electro-oxidation on Pt-Pd/PTh NFs in DMFCs

A direct methanol fuel cell (DMFC) is an electrochemical device that converts chemical energy into electricity using methanol and oxygen as the anode and cathode reactants, respectively. The usage of liquid fuel is a superior characteristic in that it allows easy handling of fuel with very high specific energy density [1]. It is well understood that the specific activity of the Pt electrocatalyst in the MOR correlates with the carbon support [2]. However, there are some disadvantages related to the use of carbon black such as the attendance of a high amount of micropores, which leads to the inaccessibility of the reactive species to the catalyst, and also some other problems, such as corrosion of the carbon surface in the fuel cell environment that can be caused fuel cell performance losses. Conductive polymers such as PANi, PPy and polythiophene (PTh) as supports for fuel cell catalysts have received considerable attention from researchers due to their suitable features like good electronic and proton conductivity, high surface area, suitable porosity, high stability, nontoxic effects and good resistance to corrosion in fuel cell operating conditions [3]. Although the presence of sulfur atoms in the PTh chains imparts high affinity toward heavy metal ions, they may cause Pt particle aggregation [4]. So, in the present study PTh nanospheres has not been used as a Pt electrocatalyst support and the nanofiber structure of it has been synthesized. In this study a novel polythiophene nanofibers (PTh-NFs) structure (fig1a) was prepared by a facile solution dispersion method (processing of thiophene with ammonium persulfate (APS), triethanolamine (TEA) and sodium dodecyl sulfate (SDS) at 75℃ for 20 hours) and used to support PtPd nanoparticles. The resultant electrocatalysts were extensively characterized by physical and electrochemical techniques including XRD, SEM, and CV tests. The SEM observations (fig1b) showed that the fine Pt nanoparticles prepared by the ethylene glycol (EG) reduction method were distributed on the surface of the PTh NFs successfully. The XRD spectrum (fig1c) showed that the polythiophene nanostructure is semi-crystalline with an amorphous nature (a one broad peak around 2θ equal to 20.84° has appeared in this spectrum, which indicates amorphous polythiophene). Cyclic voltammetry experiments (fig1d) indicate that the Pt-Pd/PTh NFs catalyst is more promising than the Pt/C for DMFC anode applications. As can be seen in fig1d, the first methanol electro-oxidation peak potential in the forward scan located at around 0.71 for Pt-Pd/PTh NFs, which are slightly lower than that of the Pt/C (0.81V), implying higher activity for methanol oxidation on Pt-Pd/PTh NFs catalyst. Also Pt-Pd/PTh NFs catalyst exhibits an especially higher current density of 4.21 mA/cm2 lower onset of 0.37V potential compared with that of 2.16 mA/cm2 and 0.46V for Pt/C catalyst, indicating that Pt-Pd/PTh NFs exhibits a higher catalytic activity for methanol electro-oxidation than Pt/C.