Tri-(Fe/F/N)-doped porous carbons as electrocatalysts for the oxygen reduction reaction in both alkaline and acidic media

One-Step Synthesis of a Non-Precious-Metal Tris (Fe/N/F)-Doped Carbon Catalyst for Oxygen Reduction Reactions

Advancements in inexpensive, efficient, and durable oxygen reduction catalysts is important for maintaining the sustainable development of fuel cells. Although doping carbon materials with transition metals or heteroatomic doping is inexpensive and enhances the electrocatalytic performance of the catalyst, because the charge distribution on its surface is adjusted, the development of a simple method for the synthesis of doped carbon materials remains challenging. Here, a non-precious-metal tris (Fe/N/F)-doped particulate porous carbon material (2₁P₂-Fe₁-850) was synthesized by employing a one-step process, using 2-methylimidazole, polytetrafluoroethylene, and FeCl₃ as raw materials. The synthesized catalyst exhibited a good oxygen reduction reaction performance with a half-wave potential of 0.85 V in an alkaline medium (compared with 0.84 V of commercial Pt/C). Moreover, it had better stability and methanol resistance than Pt/C. This was mainly attributed to the effect of the tris (Fe/N/F)-doped carbon material on the morphology and chemical composition of the catalyst, thereby enhancing the catalyst's oxygen reduction reaction properties. This work provides a versatile method for the gentle and rapid synthesis of highly electronegative heteroatoms and transition metal co-doped carbon materials.

The synergistic effect of carbon edges and dopants towards efficient oxygen reduction reaction

Decoration with alien atoms and increasing the edge content are two valid ways to activate the oxygen reduction reaction (ORR) property of nanocarbons. To further enhance their intrinsic activity and explore the underlying ORR mechanism, graphene nanoribbons (GNRs) were selected as an ideal catalyst model. Theoretical simulations have predicted that with the synergistic effect between heteroatom-doping and edge sites, the ORR activity can be significantly improved. Inspired by this, N-GNRs were synthesized via the oxidative unzipping of CNTs followed by nitrogen incorporation with urea. Ample edges and nitrogen doping sites were detected by high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy, respectively. As a result, N-GNRs exhibited remarkably higher ORR properties in terms of onset and half-wave potentials, Tafel slopes, electron transfer number and methanol tolerance than either GNRs, the control sample without doping, or N-CNTs, the control sample without abundant edges, simply clarifying the significance of synergy between dopants and edges. Thus, this work provides a simple but efficient strategy to fabricate high-performance oxygen reduction catalysts.