16 th International Conference on Environmental Science and Technology Rhodes, Greece, 4 to 7 September 2019 CEST2019_00609 Nitrogen co-doped with fluorine on reduced graphene oxide for enhanced electrocatalytic activity and stability for ORR in alkaline fuel cells Musico Y.L.F. a , Labata M.F.M. a , Chuang P.-Y. A. a,* , Ocon J.D. b a Department of Mechanical Engineering, University of California, Merced, CA, 95343 USA b Department of Chemical Engineering, University of the Philippines, Diliman, Quezon City, 1101 Philippines * corresponding author: e-mail: abel.chuang@ucmerced.edu Abstract Nitrogen co-doped with fluorine on reduced graphene oxide (N-F-rGO) was prepared by one-pot hydrothermal treatment method. The scanning electron microscopy (SEM) images and X-ray photoelectron microscopy (XPS) spectra revealed the successful doping of nitrogen and fluorine into the rGO. The Brunauer-Emmett-Teller (BET) results demonstrated high surface area of N-F-rGO that are favorable for O 2 adsorption. The results show that N- F-rGO catalyst has improved the catalytic performance electrode for the ORR in alkaline environment than the fluorine undoped N-rGO. The Koutechy-Levich (KL) analysis and rotating ring disk electrode (RRDE) measurements suggest that N-F-rGO dominantly favors a 4e- reduction process. The nitrogen co-doped with fluorine on rGO exhibited remarkable long-term stability towards the ORR than Pt/C. These improved electrochemical properties indicate that N-F-rGO will be promising candidates for cost-effective electrode materials for application of non-polluting alternative energy sources. Keywords: electrocatalyst, ORR, N-F-rGO, hydrothermal treatment, fuel cells 1. Introduction The development of cost-effective, efficient and stable electrocatalysts towards oxygen reduction (ORR) has been aimed to overcome the bottleneck of widespread application of fuel cells (Ma, Ma et al. 2016). Pt-based nanomaterials show the greatest promise as electrocatalyst for this reaction among all current catalytic structures (Zhang, Shen et al. 2017). However, Pt-based catalysts are too expensive for making commercially viable fuel cells. The high cost, scarcity and lack of durability of traditional Pt-based electrocatalyst limits the widespread implementation of fuel cells for practical applications (Raj, Samanta et al. 2016). Therefore, the development of earth-abundant, cost-effective, stable, and catalytically active metal-free alternatives is highly desirable for application in renewable energy technologies (Hu, Xiao et al. 2018). While the progress in ORR catalyst has yielded some very attractive material designs, graphene has recently drawn the attention of scientists and engineers due to its some specific properties that can be fine-tuned for electrocatalyst applications (Higgins, Zamani et al. 2016). Different notable methods have been developed to tailor the structure and fine-tune the surface chemistry of graphene which has impact in the field of electrolysis, whereby the properties of graphene and its composites have been shown to provide beneficial activity and stability enhancements for ORR. For these reasons, there is a large body of work done on graphene that has been doped with heteroatoms (Duan, Chen et al. 2015, Marinoiu, Raceanu et al. 2017). The performance of heteroatom-doped on graphene catalysts can be further improved through co-doping with different heteroatoms. This is due to the increased numbers of dopant heteroatoms and electronic interactions between different doped heteroatoms often generate additional synergistic effects than single heteroatom-doped counterparts (Zhang, Qu et al. 2016). In this study, nitrogen was co-doped with the most electronegative element, fluorine, on reduced graphene oxide (rGO) via one-pot hydrothermal treatment method to enhance the stability and activity of ORR in alkaline fuel cells. 2. Methodology Fluorine co-doped on reduced graphene oxide (N-F-rGO) were prepared by hydrothermal method. To evaluate the successful synthesis of the electrocatalysts, the scanning electron microscopy (SEM) images were obtained using Zeiss Gemini 500 scanning electron microscope, pore size distribution and specific surface area were obtained by Brunauer-Emmett-Teller (BET) using Micromeritics Tristar surface area and porosity analyzer, and X-ray photoelectron spectroscopy (XPS) measurements were done using Perkin Elmer PHI 5600 X-ray photoelectron spectrometer equipped with a monochromatic Al K X- ray source. The electrochemical measurements were done by the triple electrode system using Autolab Metrohm PGSTAT128N potentiostat/galvanostat. The as-prepared electrode was used as the working electrode, while Hg/HgO and Pt wire were used as the reference and counter electrodes, respectively. The electrolyte was 0.1 M KOH aqueous solution.