Supporting Information
Highly Efficient Oxygen Reduction Electrocatalysts based on Winged Carbon Nanotubes
Yingwen Cheng1,2 Hongbo Zhang1 Chakrapani V. Varanasi3and Jie Liu1,2,*
1Department of Chemistry, Duke University, Durham, NC 27708 United States
2Center for the Environmental Implication of NanoTechnology (CEINT), Duke University, Durham, NC 27708 United States
3Army Research Office, Research Triangle Park, NC 27703
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Figure S1: Raman spectra of different materials: pristine SC-CNTs, as-oxidized nanotubes and nitrogen doped winged nanotubes.
Figure S2: High resolution TEM image of the as-oxidized carbon nanotube. Note thatwhile the outer graphene layers were heavily oxidized, the inner tubular structure was largely preserved as no obvious change in d-spacing was identified.
Figure S3: A typical TEM image of winged carbon nanotubes after being sonicated for 10 hours. Note that graphene wings were still attached on carbon nanotubes, indicating the interaction between graphene wings and nanotubes was strong.
Figure S4: Set of TEM images of nitrogen doped winged nanotubes. Graphene sheets (mostly single layer) strongly attached to nanotubes is largely preserved after the doping process.
Figure S5: XPS survey spectrum of the N-wNT-Fe sample
Figure S6: Stability of N-wNT at 0.5 V as a function of time (acquired with RDE at 1600 rpm)
Calculations:
The average number of electrons transferred per oxygen molecule involved in the ORR was analyzed on the basis of the Koutecky-Levich equations:
in which J is the measured current density, JL and JK are the diffusion- and kinetic-limiting current densities. ω is the linear rotating speed of RDE in rpm. n is the overall number of electrons transferred in the ORR, F is the Faradic constant 96485 C mol-1, D is the diffusion coefficient of O2 in the electrolyte 1.73×10-5 cm2 s-1, V is the kinematic viscosity of the electrolyte 0.01 cm2s-1,Co is the concentration of oxygen 1.21×10-6 mol L-1.