Abstract
Fe-N-C has emerged as a promising noble-metal-free catalyst for the oxygen reduction reaction (ORR). However, achieving a catalytic activity comparable to that of Pt in acidic medium remains a great challenge. Here we report a N-doped carbon nanotube (CNT) catalyst in which a high concentration of single Fe atoms has been dispersed (CNT@Fe-N-PC). The catalyst was prepared by a simple and scalable atomic isolation method, in which a metal isolation agent was introduced to isolate Fe atoms and was then evaporated to produce abundant micropores that host single Fe atom active sites. The CNT@Fe-N-PC catalyst contained a high concentration of single Fe atom active sites and exhibited ultrahigh ORR activity with a half-wave potential of 0.82 V, comparable to that of Pt/C in an acidic medium. A high concentration of Fe-Nx active sites was created on a flexible single-wall CNT film and carbon cloth using this technique, and these materials showed even better ORR performance, that is, 40–60 mV more positive onset potentials than those of a commercial Pt/C catalyst. These catalysts exhibit excellent catalytic activity, good durability and low cost, and show great potential for commercial use as substitutes for current Pt-based catalysts.
Highlights
Fuel cells, proton exchange membrane fuel cells operated in an acidic medium, are considered one of the most promising electrochemical energy storage and conversion devices for transportation applications, due to their high theoretical specific energy, which is sufficient to power electric vehicles over a long driving range.[1,2,3] The sluggish oxygen reduction reaction (ORR) kinetics at the cathode in these devices compels us to use Pt-based catalysts to achieve desirable performance
Evidence shows that the ORR active sites of these catalysts are nitrogen-coordinated single iron atoms of the form Fe-Nx embedded in the basal planes of carbon or at the edges of two graphene planes and the average coordination number ranges from 2 to 4.16–18 The catalyst activity is closely related to the concentration of active single Fe atom sites and previous work has aimed to increase the density of Fe-Nx sites by increasing the Fe concentration in the precursors during synthesis.[19]
The PPy/ carbon nanotube (CNT) hybrid was dispersed in a 0.4 M Zn(NO3)[2] solution containing a small amount of 10 mM FeCl3 so that the hybrid material could adsorb Fe3+ and Zn2+cations, which was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy results (Supplementary Fig. 1a–c)
Summary
Proton exchange membrane fuel cells operated in an acidic medium, are considered one of the most promising electrochemical energy storage and conversion devices for transportation applications, due to their high theoretical specific energy, which is sufficient to power electric vehicles over a long driving range.[1,2,3] The sluggish oxygen reduction reaction (ORR) kinetics at the cathode in these devices compels us to use Pt-based catalysts to achieve desirable performance. Fe-NC catalysts are generally synthesized by pyrolyzing precursors containing carbon, nitrogen, and iron at temperatures above 700 °C, to achieve high activity and a robust structure. It has remained a great challenge to obtain Fe-N-C catalysts containing a high concentration of active Fe atoms that are uniformly dispersed in a carbon matrix with a high specific surface area
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