Soft template-assisted method for synthesis of nitrogen and sulfur co-doped three-dimensional reduced graphene oxide as an efficient metal free catalyst for oxygen reduction reaction

Developing earth-abundant materials to replace platinum (Pt)/Pt-based materials is an inevitable tendency for the progress of fuel cells due to the practical application limits. Recently, heteroatoms doped (N, S et al.) carbon materials, such as carbon nanotubes and graphene, have attracted great interests because of their amazing electrochemical activity towards oxygen reduction reaction (ORR). Herein, nitrogen and sulfur dual-doped three-dimensional reduced graphene oxide (NS-3DrGO) catalysts have been synthesized by a soft template-assisted approach followed by heat-pyrolysis treatment. Results indicate that with high specific surface area, sufficient porous structures, as well as the well-dispersed and doped atoms of N and S, the NS-3DrGO catalysts possess high onset/half-wave potentials together with large diffusing-limiting current density and present a four-electron transfer process in alkaline media. Specifically, at a relatively higher annealing temperature of 950 °C, the NS-3DrGO catalyst presents the optimal ORR activity compared with the others, which may be due to its highest amount (74.8 at. %) of the two active nitrogen species (pyridinic N and graphitic N) and the highest amount (79.8 at. %) of active thiophene-S together with the desirable specific surface (391.9 m2 g-1) area and multi-porous structure. Furthermore, the NS-3DrGO catalysts also exhibit superior methanol tolerance and favorable durability.

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