title: A low-cost cementite (Fe3C) nanocrystal@N-doped graphitic carbon electrocatalyst for efficient oxygen reduction.
abstract: In this work, chitosan whiskers (CWs) were first extracted using low-cost and earth-abundant crab shells as materials by a series of chemical processes, and then assembled into chitosan whisker microspheres (CWMs) via a simple photochemical polymerization approach. Subsequently, a cementite (Fe3C) nanocrystal@N-doped graphitic carbon (Fe3C@NGC) nanocomposite was successfully fabricated by high temperature pyrolysis of CWMs adsorbed with ferric acetylacetonate (Fe(acac)3) at 900 °C. It was found that a suitable growth atmosphere generated inside CWMs during high temperature pyrolysis is critically important to form Fe3C nanocrystal cores, concurrently accompanying a structural transformation from chitosan whiskers to mesoporous graphitic carbon shells with natural nitrogen (N) doping properties, resulting in the formation of a core-shell structure Fe3C@NGC nanocomposite. The resulting samples were evaluated as electrocatalysts for oxygen reduction reaction (ORR). In comparison with sole N-doped graphitic carbon without Fe3C nanocrystals obtained by direct pyrolysis of chitosan whisker microspheres at 900 °C (CWMs-900), Fe3C@NGC showed significantly improved ORR catalytic activity. The tolerance to fuel cell molecules (e.g., methanol) and the durability of Fe3C@NGC are obviously superior to commercial Pt/C catalysts in alkaline media. The high ORR performance of Fe3C@NGC could be due to its large surface area (313.7 m(2) g(-1)), a synergistic role of Fe3C nanocrystals, N doping in graphitic carbon creating more catalytic active sites, and a porous structure of the nanocomposite facilitating mass transfer to efficiently improve the utilization of these catalytic active sites.
authors.affiliation: Key Laboratory of Materials Physics, Centre for Environmental and Energy Nanomaterials, Anhui Key Laboratory of Nanomaterials and Nanostructures, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, P. R. China. zhanghm@issp.ac.cn gzhwang@issp.ac.cn.
authors.forename: Tianxing
authors.initials: T
authors.lastname: Wu
authors.forename: Haimin
authors.initials: H
authors.lastname: Zhang
authors.forename: Xian
authors.initials: X
authors.lastname: Zhang
authors.forename: Yunxia
authors.initials: Y
authors.lastname: Zhang
authors.forename: Huijun
authors.initials: H
authors.lastname: Zhao
authors.forename: Guozhong
authors.initials: G
authors.lastname: Wang