Supporting Information for

Tuning wettability of carbon nanotube arrays for efficient

bifunctional catalysts and Zn-air battery

Weiliang Tian a,c, Haoyuan Li a, Bangchang Qin a, Yuqi Xu a, Yongchao Hao a, Yaping Li a,

Guoxin Zhang a, Junfeng Liu a*, Xiaoming Sun a, b* and Xue Duana

a State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical

Technology, Beijing 100029, China

b College of Energy, Beijing Advanced Innovation Center for Soft Matter Science and

Engineering, Beijing University of Chemical Technology, Beijing, 100029, China

c Key Laboratory of Chemical Engineering in South Xinjiang, College of Life Science, Tarim

University, Alar 843300, China

*Corresponding Author: E-mail address: ljf@mail.buct.edu.cn, sunxm@mail.buct.edu.cn. Tel.:

+86−10−64438991. Fax: +86−10−64438991.

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Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2017

Video Caption

Video S1: hydrophobicity and hydrophilicity of the CNTAs and N-CNTAs.

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Figures and captions

Figure S1. (a) XRD pattern of VMT/N-CNTAs, N-CNTAs and Co3O4/N-CNTAs (* stands for the (002) peak of CNTs), (b) Raman spectra of CNTAs, N-CNTAs, and Co3O4/N-CNTAs.

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Figure S2. (a) XPS survey spectra of N-CNTAs-0.5, N-CNTAs, Co3O4 and Co3O4/N-CNTAs; (b-d) N binding energy region of N-CNTAs-0.5 (b), N-CNTAs (c), and Co3O4/N-CNTAs (d).

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Figure S3. First principles calculation structure diagram: CNTs-water and N-CNTs-water. Gray spheres stand for C atoms, red for O, white for H and blue for nitrogen.

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Figure S4. Schematic diagram showing the fabrication of 3D structured N-CNTAs decorated with cobalt oxide NPs.

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Figure S5. SEM images of Fe2O3/N-CNTAs composite.

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Figure S6. Electrocatalytic ORR and OER activities of Co3O4/N-CNTAs compared with other

samples. (a, b) OER CV (a) and tafel plots (b) of ACNTs, N-CNTAs and Co3O4/N-CNTAs

compared with IrO2/C 20%. (c, d) Durability tests of ORR (c) and OER (d) at 1600 rpm speed of

rotating disc electrode in 0.1 M KOH solution.

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Rotating-disk voltammetry measurements:

Rotating-disk voltammetry measurements: To further study the ORR electrochemical

procedures of Co3O4/N-CNTAs, we performed rotating-disk electrode (RDE). The RDE current-

potential curves at various rotating speeds are shown in Figure S4a .The limited diffusion currents

are dependent on the rotating rates. The number of electrons involved in the ORR can be

calculated from the Koutecky-Levich (K-L) equation:

(1) J-1=JL-1+JK

-1=(Bω1/2)-1+JK-1

(2) B=0.62nFC0(D0)2/3v-l/6

(3) B=nFkCo

(4) JK-1=J-1-(0.62nFC0(D0)2/3v-l/6ω1/2)-1.

Where J is the measured current density, JK and JL are the kinetic- and diffusion-limiting

current densities, ω is the angular velocity of the disk (ω=2pN, N is the linear rotation speed), n is

the overall number of electrons transferred in oxygen reduction, F is the Faraday constant

(F=96485 C·mol-1), C0 is the bulk concentration of O2, (C0 =1.2x10-6 mo1·cm-3), v is the

kinematic viscosity of the electrolyte (v=0.01 cm2·s-1), Do is the diffusion coefficient of O2 in 0.1

M KOH (1.9x10-5 cm2·s-1). According to Equations (1) and (2), the number of electrons

transferred (n) can be calculated to be 3.93, which indicates that the of Co3O4/N-CNTAs lead to a

four-electron-transfer reaction to reduce directly oxygen into OH-.

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a b

Figure S7. (a) Polarization curves and (d) K-L plots of Co3O4/N-CNTAs.

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a b

c d

Figure S8. The ORR 300 oC (a) and 800 oC (b), and OER 300 oC (c) and 800 oC (d) LSV curves

of Fe2O3/N-CNTAs, Co3O4/N-CNTAs, NiO/N-CNTAs, and MnO/N-CNTAs.

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Figure S9. (a) The galvanostatic discharge curve of the primary zinc-air batteries at the current

density of 5 mA cm-2. (b) Specific capacities of the primary zinc-air batteries normalized to the

mass of the consumed Zn at the current density of 5 mA cm-2.

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Table S1. The element content of N-CNTAs-0.5, N-CNTAs and Co3O4/N-CNTAs obtained by XPS.

N-CNTAs-0.5Atomic

(%)N-CNTAs

Atomic(%)

Co3O4/N-CNTAsAtomic

(%)

C1s 96.13±1.5 C1s 91.99±1.5 C1s 73.72±1.5N1s 3.87±1.5 N1s 8.01±1.5 N1s 6.95±1.5

Co2p3 8.07±1.5O1s 11.26±1.5

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Table S2. The binding energy of water and CNTAs or N-CNTAs with different N doping.

N (at. %) ΔE(ads)/eV

0.000 +0.0101803.125 -0.0870086.250 -0.1471739.375 -0.21149412.500 -0.428177

* 2 2( ) ( ) ( )ads A H O A H OE E E E

where A is CNTs or N-CNTs; E(A+H2O) is the total energy of the A with a water

molecule, E(A) is the total energy of CNTs or N-CNTs, and E(H2O) is the total

energy of the H2O.

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Table S3. The electrochemical performances of the electrocatalysts for bifunctional oxygen

catalysis.

Catalysts EORR/V-3

mA/cm2

EOER/V10

mA/cm2

ΔE/V(EOER-EORR)

CNTAs 0.440N-CNTAs 0.635 1.904 1.269Co3O4/N-CNTAs

0.785 1.662 0.877Pt/C 0.802 1.805 1.003

IrO2/C 0.445 1.700 1.255

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