Highly Porous Nitrogen-Doped Carbon Nanofibers as Efficient Metal-Free Catalysts toward the Electrocatalytic Oxygen Reduction Reaction

Abstract

Citation: Y. Chen, Q. Liu and J. Wang, Nano Adv., 2016, 1, 79−89.Activated N-doped carbon nanofibers (ANCNFs) were successfully prepared by the combination of electrospinning and following chemical activation of polyacrylonitrile (PAN) as metal-free electrocatalysts for oxygen reduction reaction (ORR). The increase in the activation temperature leads to not only increased specific surface areas and pore volume, and larger percentage of microporosity, but also the gradual loss of nitrogen and continuous increase in the percentage of graphitic nitrogen species. The activation evidently improves the ORR activity of nanofibers in both alkaline and acidic medium. Among the activated samples, ANCNF-800 prepared by KOH activation at 800 °C showed the best electrocatalytic activity, which is comparable but has superior long-life stability and tolerance to methanol crossover to commercial Pt/C for the ORR with an inherit four-electron-transfer pathway in alkaline medium. It should be mainly ascribed to the largest percentage of graphitic nitrogen groups and increased exposure of catalytic sites resulting from significant increase in the specific surface area.

Controlled synthesis of mesoporous nitrogen-doped carbons with highly ordered two-dimensional hexagonal mesostructures and their chemical activation

“…In contrast, the percentage of graphitic-N increased from 49.60% for OMNC-800 to 53.96% for OMNC-800A. These findings are consistent with the fact that graphitic N is more stable than pyridinic N. 39 In general, pyridinic N and graphitic N in carbons are regarded as electroactive sites, which would benefit the enhancement of electrical conductivity as well as capacitances. 40,41 Based on the analysis of N 2 adsorption-desorption isotherms ( Fig.…”

Facile Synthesis of N-Doped Graphene-Like Carbon Nanoflakes as Efficient and Stable Electrocatalysts for the Oxygen Reduction Reaction

“…In contrast, PC showed a type-I isotherm (Fig. 5 a), which is a typical of microporous materials [ 13 , 51 – 53 ]. The BET surface areas ( S BET ) for NC-1, NC-3, and NC-6 were 22, 80, and 86 m 2 g −1 , respectively, which was much lower than the S BET of PC (529 m 2 g −1 ), as shown in Table 2 .…”

Electrospun Inorganic Nanofibers for Oxygen Electrocatalysis: Design, Fabrication, and Progress

“…ENFs-based materials for high surface area and better mass transfer property. To date, various strategies have been reported to successfully realize the desired porous structure, which mainly includes: hard-template methods (e.g., Si nanoparticles), [66] soft-template methods, [67] chemical activation (e.g., KOH) [68] and ultralow-oxygen-etching, [69,70] etc. Besides, CO 2 and water vapor also act as activating agents to generate porous structure of ECNFs-based materials.…”

“…The activation parameters (e.g., activation temperature and amount of KOH) have an important influence on the catalytic performance. Wang et al [68] reported activated N-doped CNFs (ANCNFs) by the combination of electrospinning and following KOH activation at elevated temperature. They found that the BET surface area of the resultant ANCNFs increased with the rise of the activation temperature.…”

“…The formed pyridinic-NH raised from the strong interaction between the positively charged protons and the lone-pair electrons of the pyridinic-N invalidate the N-containing active sites, thus limiting their applications in proton exchange membrane fuel cells. [68] These problems could be partially addressed by introducing transition metal into NCNFs composite nanofibers. Importantly, these ECNFsbased catalysts containing metals exhibit higher electrocatalytic ORR activity and stability compared to their unsupported counterparts.…”