Recently a major effort in fuel cell research and development have been undertaken to displace platinum with platinum-free or even better, totally metal free catalyst materials. With the possibility of using heteroatom doped carbon-based materials as electrocatalysts for oxygen reduction reaction (ORR) instead of Pt, anion exchange membrane fuel cells (AEMFCs) have big advantage over other low-temperature fuel cells. Beside other carbon nanomaterials, carbon nanotubes and graphene have shown good electrocatalytic and catalyst supporting properties for different fuel cell cathode catalysts. Graphene and/or carbon nanotubtube doping with heteroatoms is a common strategy to increase the electrocatalytic activity of these materials towards the ORR [1]. Different heteroatoms, such as nitrogen, phosphorous, sulfur and boron have been studied as promising dopants to prepare electrocatalysts for ORR in alkaline media [2].

In this work the electrocatalytic activity of nitrogen and sulfur co-doped MWCNT/rGO was studied towards the ORR in alkaline media (0.1 M KOH) using the rotating disc electrode (RDE) method. The catalyst materials were prepared by doping of MWCNT/rGO with N and S via simple one-pot synthesis method using high-temperature pyrolysis in inert gas atmosphere. The resulting catalyst material exhibited excellent electrocatalytic activity towards the ORR in alkaline media. Catalyst samples were characterized also by transmission electron microscopy, X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy methods. Fuel cell experiments were carried out using Fumatech Fumapem® FAA anion-exchange membrane and FAA ionomer. Methanol tolerance and long-term stability tests were performed.

The results revealed remarkable catalytic activity of nitrogen and sulfur co-doped carbon towards the ORR in alkaline media, as well good methanol tolerance. Composition analysis with different physical characterization methods confirmed that nitrogen and sulfur have been grafted onto the carbon support. RDE tests demonstrated highly improved catalytic activity in comparison with undoped MWCNT/rGO and fuel cell tests showed a great potential of N and S doped carbon as alternative cathode catalyst and catalyst carrier for anion exchange membrane fuel cells.

References

[1] S. Ratso, I. Kruusenberg, U. Joost, R. Saar, K. Tammeveski, Enhanced oxygen reduction reaction activity of nitrogen-doped graphene/multi-walled carbon nanotube catalysts in alkaline media, International Journal of Hydrogen Energy 41 (2016) 22510.

[2] J.-C. Li, P.-X. Hou, C. Liu, Small 13 (2017) 1702002.