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

Finding an alternative catalysts for the oxygen reduction reaction (ORR) has been a key issue in modern electrocatalysis. Traditional platinum-based catalysts are not viable in the long term and thus much effort has been focused on non-precious metal catalysts. Heteroatom doped and metal-heteroatom co-doped carbon 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 as promising materials to prepare electrocatalysts for ORR in alkaline media [1]. While the development of non-precious metal and non-metal carbon catalysts has gained a lot of attention recently, non-metal phthalocyanines are a less studied topic [2]. In this work a novel catalyst material including multi-walled carbon nanotubes (MWCNT) and silicon phthalocyanine dichloride (SiPcCl2) was synthesized and the electrochemical activity towards the oxygen reduction reaction (ORR) in alkaline media was studied. Different ratios of phthalocyanine-to-nanotubes were pyrolyzed at 800 °C. After optimizing the ratio of phthalocyanine-to-nanotubes, the pyrolysis process was also carried out at different temperatures, but the results showed that the best temperature for pyrolysis is still 800 °C. ORR activity on SiPc/MWCNT catalyst was studied in 0.1 M KOH by employing rotating disc electrode method. Physical characterization was carried out with X-ray photoelectron spectroscopy and transmission electron microscopy. The results showed successful incorporation of silicon and nitrogen into the carbon framework. We show that doping MWCNTs with a non-metal phthalocyanine creates a highly active ORR catalyst rivaling the activity of metal-based catalysts in alkaline conditions. This work clearly demonstrates that non-metal macrocyclic compound modified carbons, similar to the the SiPc/MWCNT can be used as alternative cathode catalysts for the metal-air batteries and alkaline membrane fuel cells. [1] Y. Liu, X. Yue, K. Li, J. Qiao, D.P. Wilkinson, J. Zhang, PEM fuel cell electrocatalysts based on transition 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 carbon nanotubes in alkaline media, J. Electrochem. Soc. 164 (2017) H338-H344.