Nanostructured Carbon-based materials as efficient electrocatalysts for application in Direct Alcohol Fuel Cells

Abstract: Given the increasing demands in environmental protection issues, direct alcohol fuel cells (DAFCs) which use alcohol as fuel have emerged as promising renewable power devices. The fabrication of electro-catalyst materials dictates the efficiency, stability, the cost of a stack of fuel cells. Palladium (Pd) and its alloys are known as the best electro-catalysts for alcohol oxidation reaction in alkaline media. The support material has a significant impact on how well electro-catalysts function. For better metal dispersion, suitable support material should have a large surface area. It must also have oxygen-containing functional groups for bonding and interacting with the electro-catalysts. Furthermore, the support material should be corrosion resistant in the severe fuel cell environment. In this study, the effect of carbon nanofibers (CNFs) and carbon nano-onions (CNOs) support materials and composition on the structure, stability, and activity of Pd and palladium tin (PdSn) nanoparticles for electro-oxidation of methanol and ethanol have been discussed. The structures of electro-catalysts were studied using a variety of physicochemical techniques (FTIR, Raman spectroscopy, HR-TEM, XRD, XPS, TGA, and BET analysis). CNFs and CNOs were synthesized via flame pyrolysis and chemical vapor deposition respectively and the Pd-CNFs, Pd-CNOs, Pd-Sn-CNFs, and Pd-Sn-CNOs electro-catalysts were prepared by the alcohol reduction method. Carbon nanofibers and nano-onions were functionalized with carboxylic acid functional groups, which improved the dispersion of Pd and Sn nanoparticles, according to FTIR findings. The synthesized CNFs and CNOs have two Raman peaks, D and G, which correspond to a disordered carbon peak (D) and a graphite peak (G) respectively. The nanoscale nature of the synthesized nanomaterials was verified by TEM images, which showed that the size of the nanomaterials was not uniform. The carbon nanofibers and nano-onions were confirmed to be amorphous by XRD peaks, and Pd (111) was found in the electro-catalysts. In addition, Pd diffraction peaks shifted to lower angles upon the addition of Sn. XPS was used to determine the composition of the prepared samples as well as the oxidation states of Pd and Sn in the electro-catalysts. As compared to the Pd-C electro-catalyst, all the prepared electro-catalysts perform better in both methanol and ethanol oxidation reactions. Keywords: DAFCs – CNFs – CNOs – Electro-catalysts – Methanol – Ethanol.M.Sc. (Nanoscience