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Electrospun interconnected Fe-N/C nanofiber networks as efficient electrocatalysts for oxygen reduction reaction in acidic media.

Wu N, Wang Y, Lei Y, Wang B, Han C, Gou Y, Shi Q, Fang D - Sci Rep (2015)

Bottom Line: One-dimensional electrospun nanofibers have emerged as a potential candidate for high-performance oxygen reduction reaction (ORR) catalysts.Intriguingly, the resulting Fe-N/C NNs exhibit 34% higher peak current density and superior durability than generic Fe-N/C ones with similar microstructure and chemical compositions.The higher electroactivity is mainly due to the more effective electron transport between the interconnected nanofibers.

View Article: PubMed Central - PubMed

Affiliation: Science and Technology on Advanced Ceramic Fibers and Composites Laboratory, National University of Defense Technology, Changsha 410073, P.R. China.

ABSTRACT
One-dimensional electrospun nanofibers have emerged as a potential candidate for high-performance oxygen reduction reaction (ORR) catalysts. However, contact resistance among the neighbouring nanofibers hinders the electron transport. Here, we report the preparation of interconnected Fe-N/C nanofiber networks (Fe-N/C NNs) with low electrical resistance via electrospinning followed by maturing and pyrolysis. The Fe-N/C NNs show excellent ORR activity with onset and half-wave potential of 55 and 108 mV less than those of Pt/C catalyst in 0.5 M H2SO4. Intriguingly, the resulting Fe-N/C NNs exhibit 34% higher peak current density and superior durability than generic Fe-N/C ones with similar microstructure and chemical compositions. Additionally, it also displays much better durability and methanol tolerance than Pt/C catalyst. The higher electroactivity is mainly due to the more effective electron transport between the interconnected nanofibers. Thus, our findings provide a novel insight into the design of functional electrospun nanofibers for the application in energy storage and conversion fields.

No MeSH data available.


Related in: MedlinePlus

(a) XRD patterns of Fe-N/C NNs and Fe-N/C NMs. SEM images of (b) Fe-N/C NMs and (c,d) Fe-N/C NNs. (e) Typical TEM and (f) HRTEM images of Fe-N/C NNs revealing the iron compound nanoparticles enchased into the carbon nanofibers.
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f2: (a) XRD patterns of Fe-N/C NNs and Fe-N/C NMs. SEM images of (b) Fe-N/C NMs and (c,d) Fe-N/C NNs. (e) Typical TEM and (f) HRTEM images of Fe-N/C NNs revealing the iron compound nanoparticles enchased into the carbon nanofibers.

Mentions: The structure and morphology of the as-prepared nanofiber samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD patterns (Fig. 2a) suggest the presence of Fe3O4 (JCPDS, No. 65–3107), Fe3C (JCPDS, No. 65–2412) and α-Fe (JCPDS, No. 65–4899) in the Fe-N/C hybrid nanofibers. Furthermore, the diffraction peak of α-Fe in Fe-N/C NNs becomes weaker remarkably compared with the peak before acid leaching (Fig. S1†), indicating that the exposed unstable α-Fe phase was efficiently removed after being preleached in hot H2SO4 solution. In addition, the rod-like metal iron crystals on the surface of composite nanofibers (Fig. S2†) disappeared after acid leaching (Fig. 2b-d), which also validated that α-Fe phase was removed. SEM image in Fig. 2b shows that Fe-N/C NMs consist of overlapped, continuous and randomly oriented nanofibers with diameter in the range of 400–500 nm. Interestingly, large numbers of interconnected nodes were obviously observed in the SEM images of Fe-N/C NNs (Fig. 2c,d and Fig. S3†). As analyzed from Fig. S4†, the interconnected system was derived from the exposure of the as-spun Fe(acac)3/PVP nanofibers under moist atmosphere. We deduced that the as-spun nanofibers became softening and possessed a high mobility after the absorption of enough water molecules. Then fusion occurred at the intersections while other parts still maintained the fibrous form. TEM image (Fig. 2e) reveals uniform iron-containing nanoparticles embedded into the nanofibers, which could suppress the agglomeration of nanoparticles. Closer inspection by high-resolution TEM (HRTEM, Fig. 2f) displays that Fe3O4 and Fe3C nanoparticles are surrounded by carbon shell. This core-shell structure will protect the iron-based composition from dissolving in acid. The formation of Fe3C can be attributed to carbothermal reduction of carbon with iron oxide33.


Electrospun interconnected Fe-N/C nanofiber networks as efficient electrocatalysts for oxygen reduction reaction in acidic media.

Wu N, Wang Y, Lei Y, Wang B, Han C, Gou Y, Shi Q, Fang D - Sci Rep (2015)

(a) XRD patterns of Fe-N/C NNs and Fe-N/C NMs. SEM images of (b) Fe-N/C NMs and (c,d) Fe-N/C NNs. (e) Typical TEM and (f) HRTEM images of Fe-N/C NNs revealing the iron compound nanoparticles enchased into the carbon nanofibers.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663764&req=5

f2: (a) XRD patterns of Fe-N/C NNs and Fe-N/C NMs. SEM images of (b) Fe-N/C NMs and (c,d) Fe-N/C NNs. (e) Typical TEM and (f) HRTEM images of Fe-N/C NNs revealing the iron compound nanoparticles enchased into the carbon nanofibers.
Mentions: The structure and morphology of the as-prepared nanofiber samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD patterns (Fig. 2a) suggest the presence of Fe3O4 (JCPDS, No. 65–3107), Fe3C (JCPDS, No. 65–2412) and α-Fe (JCPDS, No. 65–4899) in the Fe-N/C hybrid nanofibers. Furthermore, the diffraction peak of α-Fe in Fe-N/C NNs becomes weaker remarkably compared with the peak before acid leaching (Fig. S1†), indicating that the exposed unstable α-Fe phase was efficiently removed after being preleached in hot H2SO4 solution. In addition, the rod-like metal iron crystals on the surface of composite nanofibers (Fig. S2†) disappeared after acid leaching (Fig. 2b-d), which also validated that α-Fe phase was removed. SEM image in Fig. 2b shows that Fe-N/C NMs consist of overlapped, continuous and randomly oriented nanofibers with diameter in the range of 400–500 nm. Interestingly, large numbers of interconnected nodes were obviously observed in the SEM images of Fe-N/C NNs (Fig. 2c,d and Fig. S3†). As analyzed from Fig. S4†, the interconnected system was derived from the exposure of the as-spun Fe(acac)3/PVP nanofibers under moist atmosphere. We deduced that the as-spun nanofibers became softening and possessed a high mobility after the absorption of enough water molecules. Then fusion occurred at the intersections while other parts still maintained the fibrous form. TEM image (Fig. 2e) reveals uniform iron-containing nanoparticles embedded into the nanofibers, which could suppress the agglomeration of nanoparticles. Closer inspection by high-resolution TEM (HRTEM, Fig. 2f) displays that Fe3O4 and Fe3C nanoparticles are surrounded by carbon shell. This core-shell structure will protect the iron-based composition from dissolving in acid. The formation of Fe3C can be attributed to carbothermal reduction of carbon with iron oxide33.

Bottom Line: One-dimensional electrospun nanofibers have emerged as a potential candidate for high-performance oxygen reduction reaction (ORR) catalysts.Intriguingly, the resulting Fe-N/C NNs exhibit 34% higher peak current density and superior durability than generic Fe-N/C ones with similar microstructure and chemical compositions.The higher electroactivity is mainly due to the more effective electron transport between the interconnected nanofibers.

View Article: PubMed Central - PubMed

Affiliation: Science and Technology on Advanced Ceramic Fibers and Composites Laboratory, National University of Defense Technology, Changsha 410073, P.R. China.

ABSTRACT
One-dimensional electrospun nanofibers have emerged as a potential candidate for high-performance oxygen reduction reaction (ORR) catalysts. However, contact resistance among the neighbouring nanofibers hinders the electron transport. Here, we report the preparation of interconnected Fe-N/C nanofiber networks (Fe-N/C NNs) with low electrical resistance via electrospinning followed by maturing and pyrolysis. The Fe-N/C NNs show excellent ORR activity with onset and half-wave potential of 55 and 108 mV less than those of Pt/C catalyst in 0.5 M H2SO4. Intriguingly, the resulting Fe-N/C NNs exhibit 34% higher peak current density and superior durability than generic Fe-N/C ones with similar microstructure and chemical compositions. Additionally, it also displays much better durability and methanol tolerance than Pt/C catalyst. The higher electroactivity is mainly due to the more effective electron transport between the interconnected nanofibers. Thus, our findings provide a novel insight into the design of functional electrospun nanofibers for the application in energy storage and conversion fields.

No MeSH data available.


Related in: MedlinePlus