Amine functionalized holey graphene (AFHG), synthesized by the hydrothermal reaction of GO and ammonia and the subsequent KOH etching, has been used as a metal-free catalyst for the oxygen reduction reaction (ORR). It shows that AFHG is highly active for the ORR and exhibits higher electrocatalytic activity than graphene, nitrogen-doped graphene (NG) and amine functionalized graphene (AFG), which could be demonstrated from its higher current density and more positive halfwave and onset potentials for the ORR. Although AFHG also exhibits a slightly higher overpotential towards ORR, it is indeed more kinetically facile than the commercial JM Pt/C 40 wt%. Its higher electrochemical performance could be attributed to the presence of the electron donating group (e.g. amine) and a large number of holes in its sheet plate and the porous structure in its randomly stacked solid, which provide AFHG with higher electrical conductivity, more active edge N atoms and easier accessibility to oxygen, respectively. The stability measurements show that AFHG is more stable than graphene, NG, AFG and the JM Pt/C 40 wt% and exhibits higher immunity towards methanol crossover and CO poisoning than the JM Pt/C 40 wt%. Over 10 h of the ORR, AFHG loses only <7% of its original activity in the absence of methanol or CO, and the introduction of methanol or CO has no effect on its oxygen reduction activity, which makes it highly desirable as a metal-free catalyst for the ORR.

Development of inexpensive, efficient, and stable nonprecious-metal-based bifunctional catalysts for oxygen reduction (ORR) and evolution (OER) reactions remains an enormous challenge. This work reports on an excellent bifunctional electrocatalyst consisting of ultrathin N-doped carbon (1–3 graphitic carbon layers) coated Fe1.2Co nanoparticles and N-doped carbon nanotubes (Fe1.2Co@NC/NCNTs). The Fe1.2Co@NC/NCNTs have an extremely low Fe/Co content (6.7 wt %), but with highly efficient and durable bifunctionality for ORR and OER. Specifically, the Fe1.2Co@NC/NCNT exhibits onset potential (E onset = 0.842 V vs RHE) and half-wave potential (E 1/2 = 0.82 V vs RHE) for ORR and onset potential of 1.43 V vs RHE and overpotential of 355 mV at 10 mA cm–2 for OER. The potential gap (ΔE) between E 1/2 of ORR and E OER at 10 mA cm–2 (E j=10) for the Fe1.2Co@NC/NCNTs is 0.765 V, which surpasses the commercial Pt/C and Ir/C catalysts and most state-of-the-art bifunctional catalysts previously reported. Most notably, when used in the Zn-air battery, the Fe1.2Co@NC/NCNT exhibits superior efficiency and durability to the Pt–Ir/C catalysts. This strongly suggests that the Fe1.2Co@NC/NCNT can be used as an efficient bifunctional catalyst with potential applications in the field of clean electrochemical energy storage and conversion technologies.

No abstract

No abstract