Synthesis of Polyaniline and Non-Precious Metals on Onion-like Carbon As Catalytic Support for Oxygen Reduction Reaction

Abstract

Oxygen reduction reaction (ORR) is of mayor importance for different life processes and energy converting systems such as fuel cells. The development of economical, efficient, and environmentally friendly electrocatalysts for fuel cells is essential in order to put into action clean energy systems. ORR in aqueous solutions occurs mainly through two different pathways, being a four-electron transfer from O2 to H2O the preferred mechanism. To induce this four-electron reduction, an electrocatalyst is used. Pt is the best electrocatalyst to date, but its large-scale applications are limited by its high cost and limited availability. For this reason, non-precious metal catalysts are currently being studied and developed as a replacement for expensive Pt catalysts. Fe and Co in particular, have been reported to enhance ORR activity and four-electron selectivity of the catalysts. In addition, it is also known that catalyst support is one of the critical components in improving the electrocatalytic activity. Onion-like carbon (OLC) are used as support materials for electrocatalysts, as they have been identified as some of the most promising materials due to their high chemical stability, high surface area and high electric conductivity. Although carbon supports have shown an improved ORR electrocatalytic activity, one of the major causes of failure for fuel cell degradation is due to carbon oxidation or corrosion due to the presence of O2 and/or high electrode potential. Combining carbon compounds with conductive polymers, such as polyaniline (PANI), have been shown to combine high ORR activity with unique performance durability. The purpose of this work is to develop and study FeCo-OLC/PANI nanoparticles and their ORR activity when used as electrocatalysts. In this project, nanodiamonds (NDs) are converted to OLC through a pyrolysis process and then oxidized with sulfuric acid and potassium permanganate. After that, they are dialyzed to remove any residue of acid in the particles and, finally, lyophilized. A synthesis is then carried out with the obtained OLC to polymerize them with the aniline monomer. The presence of PANI in the OLC was confirmed by characterizing the particles with Raman, Scanning Electron Microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and Energy-dispersive X-ray spectroscopy (EDS). The synthesis is then carried out with the non-precious metals Fe and Co, and the particles characterized with the techniques previously mentioned. For the experiments, a three-electrode cell is prepared, where a glassy carbon (GC) rotating ring-disk electrode (RRDE) will be functioning as the working electrode. A FeCo-OLC/PANI ink is made and then pasted to the surface of the RRDE, where it will be characterized with cyclic voltammetry and ORR experiments carried out. In future works, these nanoparticles will also be characterized using synchrotron techniques.