Supporting Information

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1 Supporting Information Bamboo-Like Carbon Nanotube/Fe 3 C Nanoparticle Hybrids and Their Highly Efficient Catalysis for Oxygen Reduction Wenxiu Yang a,b, Xiangjian Liu a,b, Xiaoyu Yue a,b, Jianbo Jia, a * and Shaojun Guo c * a State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin , China b University of Chinese Academy of Sciences, Beijing , China c Physical Chemistry and Applied Spectroscopy, Los Alamos National Laboratory, Los Alamos, NM 87545, USA Corresponding Authors: jbjia@ciac.ac.cn (J. Jia); sguo@lanl.gov (or shaojun.guo.nano@gmail.com) (S. Guo) Experimental Section Materials. Melamine was purchased from the East China Chemical Reagent Company (Tianjin, China). Iron nitrate and methanol were obtained from Beijing Chemical Reagent Company (Beijing, China). Pt catalyst (20 wt %, Pt/C) was purchased from Johnson Matthey. PEG-PPG-PEG Pluronic P123 (Mw = 5800), Pluronic F127, and Nafion (5.0 wt %) were purchased from Sigma-Aldrich. Single-walled carbon nanotube (SWCNT) was bought from Shenzhen Nanotechnology Port Co. Ltd., and treated with 2.3 M HNO 3 for 24 h before use. 1 All aqueous solutions were prepared with ultrapure water from a Water Purifier System (Sichuan Water Purifier Co. Ltd., China). Apparatus. High resolution transmission electron microscopy (HRTEM) images were obtained with a JEM-2100F high-resolution transmission electron microscope (JEOL Ltd., Japan). X-Ray diffraction (XRD) data were obtained with model D8 ADVANCE (BRUKER, Cu K α radiation, λ = Å). Nitrogen sorption isotherms were measured with an ASAP 2020 Physisorption Analyzer (Micrometrics Instrument Corporation). X-Ray photoelectron spectroscopy (XPS) analysis was performed on an ESCALABMKII X-ray photoelectron spectrometer (VG Scientific, UK). S1

2 Thermogravimetric analysis (TGA) was performed with NETZSCH STA 449F3. Raman spectra were measured with a Renishaw 2000 model confocal microscopy Raman spectrometer with a CCD detector and a holographic notch filter (Renishaw Ltd., Gloucestershire, U. K.). The electrochemical experiments were performed using a CHI842B electrochemical workstation (CH Instruments, Shanghai). Rotating ring-disk electrode (RRDE) techniques were employed on a Model RRDE-3A Apparatus (ALS, Japan) with a CHI842B electrochemical workstation. The electrochemical experiments were carried out via a three electrode system with a modified glassy carbon electrode (GCE, φ = 3.0 mm) as the working electrode, an Ag/AgCl (saturated KCl) electrode as the reference electrode, and a platinum foil as the counter electrode, respectively. The potential, measured against a Ag/AgCl electrode, was converted to the potential versus the reversible hydrogen electrode (RHE) according to E(vs. RHE) = E(vs. Ag/AgCl) pH. All the measurements were carried out at room temperature Synthesis of bamboo-like carbon nanotube/fe 3 C nanoparticles composites. In a typical synthesis of PMF-800, 0.75 g melamine was dissolved into 7.5 ml ultrapure water under stirring at room temperature, followed by the addition of 5.0 ml homogenous P123 (0.10 g/ml) and 7.5 ml 1.0 wt.% Fe(NO 3 ) 3 aqueous solution. The mixture was stirred for 2 h, and further sonicated for 5 h. Then, the solvent was slowly evaporated at 80 C. The remaining powder was converted into the PMF-800 by heated at 180, 240, and 800 C for 2, 2, and 1 h at a heating rate of 2 C/min, respectively in a quartz boat in nitrogen. To clarify, the resulting sample was labeled as PMF-800 considering the use of P123, melamine, Fe(NO 3 ) 3 and the pyrolysis temperature (800 C). As a comparison, the nanocomposites without P123 or melamine or Fe(NO 3 ) 3 prepared at 800 C under the same conditions were named as MF-800, PF-800, and PM-800, respectively. Meanwhile, the composite made from Pluronic F127, melamine, and Fe(NO 3 ) 3 at 800 C under the same conditions were named as FMF-800. And the composite produced by heating to 800 C for 0 h was labeled as i-pmf-800. Electrocatalytic activity evaluation. The as-prepared nanocomposites were treated with 0.10 M H 2 SO 4 for 24 h to remove the unstable and ORR-nonreactive substance, then washed with water for three times and then dried before use. 6.0 mg of the PMF-800 or Pt catalyst (20 wt %, Pt/C) were dissolved in a mixture (3.0 ml) of water, isopropyl alcohol, and Nafion (5.0 wt %) with a ratio of S2

3 20:1:0.075 (v/v/v) under sonication to get 2 mg/ml ink. The GCE was polished carefully with 0.3 μm alumina slurries, followed by sonication in acetone, ethanol and ultrapure water successively, and then allowed to dry at room temperature. Then, a certain amount of the PMF-800 suspension was casted onto the pretreated GCE surface with a loading amount of 1.2 mg/cm. The modified electrodes were dried under the infrared lamp before use. As a comparison, the Pt/C catalyst was prepared according to the same procedure with a loading amount of catalyst (25 μg Pt/cm 2 ). For RRDE experiments, the polarization curves were obtained by performing a negative-direction sweep of potential at a rate of 5 mv/s from V to (vs. RHE) in 0.10 M KOH or from V to V in 0.50 M H 2 SO 4. The ring potential was set at V in 0.10 M KOH or V in 0.50 M H 2 SO 4, respectively. Before experiments, all the electrodes were activated by potential cycling in 0.50 M H 2 SO 4 from V to V for 30 cycles at a scan rate of 50 mv/s. To prevent deactivation caused by bisulfate adsorption, the Pt/C was tested in 0.10 M HClO 4 rather than 0.50 M H 2 SO 4. S3

4 Figures Fig. S1 (A) XRD survey of the PMF-700, PMF-800, PMF-900 and PMF Fig. S2 Raman spectra of the (a) PMF-700, (b) PMF-800, (c) PMF-900, (d) PMF-1000, (e) PF-800, (f) MF-800 and (g) SWCNT. S4

5 Fig. S3 (a) N 2 adsorption-desorption isotherm of the PMF-700, PMF-900 and PMF a b c d Fig. S4 (a) XPS survey for the PMF-800, and high-resolution (b) C 1s, (c) N 1s and (d) Fe 2p spectra. S5

6 a b c d Fig. S5 TEM images of the resultant nanocomposites annealed at different temperatures in the final step. (a) PMF-700, (b) PMF-800, (c) PMF-900 and (d) PMF a b c d Fig. S6 TEM images of the nanocomposites prepared with different constituents at 800 C. (a) MF-800, (b) PF-800, (c) PM-800 and (d) FMF-800. S6

7 a b c Fig. S7 The comparison on (a) Raman, (b) XRD, and (c) TGA of the FMF-800 and PMF-800. a b c d e f Fig. S8 TEM images of the nanocomposites prepared at different instant high temperatures, (a) i-pmf-650, (b) i-pmf-700, (c) i-pmf-750, (d) i-pmf-800, (e) i-pmf-850 and (f) i-pmf-900. S7

8 Fig. S9 TEM images of the nanocomposites prepared with different constituents and instant temperatures, (a) i-mf-700, (b) i-mf-750, (c) i-pf-700 and (d) i-pm-750. Fig. S10 Cyclic voltammograms (CVs) of the PMF-700, PMF-800, PMF-900 and PMF-1000 in O2-saturated (a) 0.10 M KOH and (b) 0.50 M H2SO4. Scan rate: 50 mv/s. S8

9 Fig. S11 RRDE voltammograms of the PMF-800, FMF-800, MF-800, and PF-800 in O 2 -saturated (a) 0.10 M KOH and (b) 0.50 M H 2 SO 4 solutions at a scan rate of 5 mv/s, rotation rate = 1600 rpm. Electron transfer number (n) for the different electrodes in O 2 -saturated (c) alkaline and (d) acidic solutions. Table Table S1 The I D /I G values of the PMF-700, PMF-800, PMF-900, PMF-1000, PF-800, MF-800 and SWCNT by Raman spectroscopy. Materials PMF-700 PMF-800 PMF-900 PMF-1000 PF-800 MF-800 SWCNT I D /I G Reference 1. Guo, S.; Dong, S.; Wang, E., Constructing Carbon Nanotube/Pt Nanoparticle Hybrids Using an Imidazolium-Salt-Based Ionic Liquid as a Linker. Advanced Materials 2010, 22 (11), 126 S9