Oxygen Reduction Reaction Catalyzed By Silicon and Nitrogen Co-Doped Carbon

Abstract

Finding an alternative catalysts for the oxygen reduction reaction (ORR) has been a key issue in modernelectrocatalysis. Traditional platinum-based catalysts are not viable in the long term and thus much efforthas been focused on non-precious metal catalysts. Heteroatom doped and metal-heteroatom co-dopedcarbon materials have emerged as the main candidate for replacing the platinum-based catalysts.Different MN4 macrocycles, such as metal phthalocyanines and porphyrins, have been studied aspromising materials to prepare electrocatalysts for ORR in alkaline media [1]. While the development ofnon-precious metal and non-metal carbon catalysts has gained a lot of attention recently, non-metalphthalocyanines are a less studied topic [2].In this work a novel catalyst material including multi-walled carbon nanotubes (MWCNT) and siliconphthalocyanine dichloride (SiPcCl2) was synthesized and the electrochemical activity towards the oxygenreduction reaction (ORR) in alkaline media was studied. Different ratios of phthalocyanine-to-nanotubeswere pyrolyzed at 800 °C. After optimizing the ratio of phthalocyanine-to-nanotubes, the pyrolysis processwas also carried out at different temperatures, but the results showed that the best temperature forpyrolysis is still 800 °C. ORR activity on SiPc/MWCNT catalyst was studied in 0.1 M KOH by employingrotating disc electrode method. Physical characterization was carried out with X-ray photoelectronspectroscopy and transmission electron microscopy. The results showed successful incorporation ofsilicon and nitrogen into the carbon framework. We show that doping MWCNTs with a non-metalphthalocyanine creates a highly active ORR catalyst rivaling the activity of metal-based catalysts inalkaline conditions. This work clearly demonstrates that non-metal macrocyclic compound modifiedcarbons, similar to the the SiPc/MWCNT can be used as alternative cathode catalysts for the metal-airbatteries and alkaline membrane fuel cells.[1] Y. Liu, X. Yue, K. Li, J. Qiao, D.P. Wilkinson, J. Zhang, PEM fuel cell electrocatalysts based ontransition metal macrocyclic compounds, Coord Chem Rev. 315 (2016) 153-177.[2] K.-K. Türk, K. Kaare, I. Kruusenberg, M. Merisalu, U. Joost, L. Matisen, V. Sammelselg, J.H. Zagal, K.Tammeveski, Oxygen electroreduction on zinc and dilithium phthalocyanine modified multiwalled carbonnanotubes in alkaline media, J. Electrochem. Soc. 164 (2017) H338-H344.