Oxygen reduction reaction of Pt-Pd on poly thiophene nanofibers in PEMFCs

Polymer electrolyte membrane fuel cells (PEMFCs) are increasingly gaining acceptance as a clean, efficient, and silent energy conversion technology, and are seen as a future alternative energy source . However, the sluggish kinetics of the oxygen reduction reaction (ORR) and the instability of platinum electrocatalysts for ORR significantly hinder the commercialization of PEMFCs [1]. It is well understood that the specific activity of the Pt electrocatalyst in the ORR 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. On this basis, various alternative catalyst supports such as conductive polymers (e.g. polythiophene (PTh)) to improve the stability and catalytic activity of the catalyst have been studied [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, polythiophene nanospheres have not been used as a Pt electrocatalyst support and the nanofiber structure has been synthesized. Since the catalytic capability of Pd is analogous to that of platinum extensive research [5, 6] has been devoted to its application in incorporation into Pt catalyst material in recent years. 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 FTIR, SEM, and RDE. The SEM results 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 results of FTIR spectroscopy(fig1c) confirmed the formation of polythiophene composition (the characteristic peaks of polythiophene can be observed at 709.75 cm-1 for C–S bending and 617.17 cm-1 for C–S–C ring deformation stretching). RDE experiments(fig1d) indicate that the Pt-Pd/PTh NFs catalyst is more promising than the Pt/C for PEMFC cathode applications. As can be seen in Fig.1d the electrochemical reaction occurred under mixed control, which was a combination of kinetic and diffusion control, ranging from 0.9V to 0.3V (vs RHE). The results showed that the onset potential of Pt-Pd/PTh NFs was shifted by 35mV, to a positive direction, when compared to Pt/C.