Me-N-C Electrocatalyst Foams for the Oxygen Reduction Reaction in PEFCs

Abstract

Polymer electrolyte fuel cells (PEFCs) will perform the crucial role of energy conversion when society shifts towards the hydrogen economy. However, to perform the the oxygen reduction reaction (ORR) efficiently, a finely dispersed platinum catalyst on a carbon black support is generally utilised. Platinum is an expensive critical raw material (CRM) and is thus susceptible to future shocks, such as bottlenecks in supply or volatile prices. As such it is imperative to investigate alternative platinum-free electrocatalysts.Over the past decade we have developed platinum-free Fe-N-C electrocatalysts with unique properties and microstructure. The basis for our catalysts is a nitrogen-doped carbon foam, which is obtained by thermal decomposition of metal alkoxides. The materials are exceptional in this field due to their unusually large macropores which aid gas diffusion, the very large surface area due to high microporosity, and the fact that the nitrogen content can be systematically varied.Using these electrocatalysts we have with achieved high activity and excellent durability in both acid and alkaline media. One of the advantages of this materials system is that it can be applied as a model catalyst to independently study the effect of different parameters on the catalytic activity. As such we have made important insights into the synthesis mechanisms of Fe-N-C electrocatalysts using techniques such as in situ X-ray absorption spectroscopy (XAS) and in situ X-ray photoelectron spectroscopy (XPS).Furthermore, whilst most research into platinum-free catalysts focusses on iron-containing materials, iron is known to cause degradation in the microporous layer and membrane due to the generation of peroxide-related radicals. As such, a new generation of Me-N-C electrocatalysts are being developed, in which Fe is replaced with e.g., Co or Sn. Here we will discuss the performance of these interesting new Fe-free electrocatalysts.This work was supported by JSPS KAKENHI Grant Number 19H02558.1. Mufundirwa, M. Ismail, G. F. Harrington, B. Smid, K. Sasaki, M. Pourkashanian, A. Hayashi, S. M. Lyth, Nanotechnology 31 (22), 225401 (2020)2. Mufundirwa, B. Smid, G. Harrington, B. V. Cunning, K. Sasaki, and S. M. Lyth, Journal of Power Sources, 375, 244-254 (2018)3. Zitolo, N. Ranjbar-Sahraie, T. Mineva, J. Li, Q. Jia, S. Stamatin, P. Krtil, S. M. Lyth, G. Harrington, S. Mukerjee, E. Fonda, F. Jaouen, Nature Communications, 8, 959 (2017)4. Liu, T. Daio, A. Mufundirwa, B. Cunning, K. Sasaki, S. M. Lyth, Electrochimica Acta, 220, 554-561 (2016)5. Liu, S. Yu, T. Daio, M. Ismail, K. Sasaki, and S. M. Lyth, Journal of the Electrochemical Society, 163 (9), F1049-F1054 (2016)6. Liu, T. Daio, K. Sasaki, S. M. Lyth, Journal of the Electrochemical Society, 161 (9), F838-F844 (2014)7. Liu, T. Daio, D. Orejon, K. Sasaki, S. M. Lyth, Journal of the Electrochemical Society 161 (4), F544-F550 (2014)8. S. M. Lyth*, Y. Nabae, N. M. Islam, T. Hayakawa, S. Kuroki, M. Kakimoto, S. Miyata, eJournal of Surface Science and Nanotechnology, 10, 29-32 (2012)