Article pubs.acs.org/JPCC
Nitrogen-Deficient ORR Active Sites Formation by Iron-Assisted Water Vapor Activation of Electrospun Carbon Nanofibers Beomgyun Jeong,†,‡ Dongyoon Shin,†,‡ Myounghoon Choun,† Sandip Maurya,† Jaeyoon Baik,§ Bongjin Simon Mun,∥,⊥ Seung-Hyeon Moon,†,⊥ Dangsheng Su,⊥,# and Jaeyoung Lee*,†,⊥ †
School of Environmental Science and Engineering (SESE), ∥Department of Physics and Photon Science, and ⊥Ertl Center for Electrochemistry and Catalysis, SESE, Gwangju Institute of Science and Technology (GIST), Gwangju 500-712, South Korea § Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang 37673, South Korea # Shenyang National Laboratory of Material Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China S Supporting Information *
ABSTRACT: Fe- and N-modified carbon nanofibers (Fe−CNF) were synthesized via electrospinning and pyrolysis as electrocatalysts for oxygen reduction reaction (ORR). In order to increase the exposed surface area with the active sites buried inside Fe−CNF, we attempted water vapor activation for Fe−CNF and observed a substantial improvement of ORR activity up to the comparable level with Pt/C. Unlike what was expected, however, water vapor activation did not significantly increase the specific surface area of Fe− CNF; instead, it induced a depletion of surface N content, which makes it difficult to explain the improved ORR activity with the increase of surface area with N-based active sites. In water vapor activation, the chemical phase of embedded particles is changed from Fe3C to Fe3O4 and nitrogen-free Feand C-based ORR active sites were exposed, which seemed to be related with hierarchical macro/mesopore structure and graphitic edge defects. This study demonstrates a facile activation method for better ORR activity of Fe-modified CNF and suggests a potential relationship of surface carbon structure with the catalytic activity toward ORR rather than the type and concentration of N in Fe−CNF, which should be investigated further.
1. INTRODUCTION Platinum (Pt) is the best electrocatalyst to accelerate the sluggish kinetics of the oxygen reduction reaction (ORR) in fuel cells, but the extremely high price of Pt is a formidable hurdle in commercialization of especially low-temperature (
