Characterization of Fe/N-doped graphene as air-cathode catalyst in microbial fuel cells

This work proposed a simple and efficient approach for synthesis of durable and efficient non-precious metal oxygen reduction reaction (ORR) electro-catalysts in MFCs. The rod-like carbon nanotubes (CNTs) were formed on the Fe–N/SLG sheets after a carbonization process. The maximum power density of 1210 ± 23 mW•m⁻² obtained with Fe–N/SLG catalyst in an MFC was 10.7% higher than that of Pt/C catalyst (1080 ± 20 mW•m⁻²) under the same condition. The results of RDE test show that the ORR electron transfer number of Fe–N/SLG was 3.91 ± 0.02, which suggested that ORR catalysis proceeds through a four-electron pathway. The whole time of the synthesis of electro-catalysts is about 10 h, making the research take a solid step in the MFC expansion due to its low-cost, high efficiency and favorable electrochemical performance. Besides, we compared the electrochemical properties of catalysts using SLG, high conductivity graphene (HCG, a kind of multilayer graphene) and high activity graphene (HAG, a kind of GO) under the same conditions, providing a solution for optimal selection of cathode catalyst in MFCs. The morphology, crystalline structure, elemental composition and ORR activity of these three kinds of Fe–N/C catalysts were characterized. Their ORR activities were compared with commercial Pt/C catalyst. It demonstrates that this kind of Fe–N/SLG can be a type of promising highly efficient catalyst and could enhance ORR performance of MFCs.