Facile Synthesis of Nitrogen and Sulfur Codoped Carbon from Ionic Liquid as Metal-Free Catalyst for Oxygen Reduction Reaction

Abstract

Developing metal-free catalysts for oxygen reduction reaction (ORR) is a great challenge in the development of fuel cells. Nitrogen and sulfur codoped carbon with remarkably high nitrogen content up to 13.00 at % was successfully fabricated by pyrolysis of homogeneous mixture of exfoliated graphitic flakes and ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bimi][Tf2N]). The exfoliated graphite flakes served as a structure-directing substance as well as additional carbon source in the fabrication. It was demonstrated that the use of graphite flakes increased the nitrogen doping level, optimized the composition of active nitrogen configurations, and enlarged the specific surface area of the catalysts. Electrochemical characterizations revealed that the N and S codoped carbon fabricated by this method exhibited superior catalytic activities toward ORR under both acidic and alkaline conditions. Particularly in alkaline solution, the current catalyst compared favorably to the conventional 20 wt % Pt/C catalyst via four-electron transfer pathway with better ORR selectivity. The excellent catalytic activity was mainly ascribed to high nitrogen doping content, appropriate constitution of active nitrogen configurations, large specific surface area, and synergistic effect of N and S codoping.

A review of exfoliated graphite

“…Functionalization of the edge of the carbon layers with the carboxyl group enhances the formation of self-assembled EG structures in a polymer-matrix composite [44]. The doping of EG with nitrogen and sulfur (by the pyrolysis of a mixture of EG and an ionic liquid) provides a metal-free catalyst for the oxygen reduction reaction, which is relevant to fuel cells [45]. The volume of the EG (not just the surface) can be modified by fluorination [46].…”

A Hydrogen‐Bonded Organic‐Framework‐Derived Mesoporous N‐Doped Carbon for Efficient Electroreduction of Oxygen

“…Thus, it is extremely desirable to produce highly porous carbon through direct carbonization without the implantation of sacrificial templates from the point views of both scientific research and industry. However, the reported carbons prepared by direct carbonization are mostly microporous and of low surface area, which disfavor mass transfer and usually have low electrocatalytic activity . Therefore, examples successfully illustrating this straightforward strategy are rare.…”

Non-Precious Electrocatalysts for Oxygen Reduction Reaction in Alkaline Media: Latest Achievements on Novel Carbon Materials

“…Non-precious alternative precursors' ORR electrocatalysts. [80] According to the literature review, the composition of single-source molecular precursor affects the properties of any adopted metal and carbon and consequently the ORR electrocatalyst's activity. For example, Fe/Fe 3 C NPs encapsulated in nitrogen-doped carbon using ammonium ferritic citrate as single molecular precursor exhibited the highest according to half-wave potential, E 1/2 = 0.881 V vs. RHE ( Figure 5), ORR activity as well as an excellent methanol tolerance [74].…”

“…Fe/N co-doped graphitic carbon bulb electrocatalyst was prepared using only Prussian blue as precursor; exhibiting 0.81 V vs. RHE half-wave potential [76]. [74], [75], [77], [73], [76], [78], [80], [79]). …”

“…By pyrolyzing a homogeneous mixture of exfoliated graphitic flakes and ionic liquid, a very active ORR electrocatalyst was fabricated performing 0.768 V vs. RHE [80]. The great ORR activity was ascribed to the exfoliated graphite flakes which aid to the increased nitrogen doping and consequently the increased active surface area as well as to the co-doping of nitrogen and sulfur.…”