Electronic Supporting Information

Self-assembled Globular Clusters-like Cobalt Hexacyanoferrate /

Carbon Nanotubes Hybrid as Efficient Nonprecious

Electrocatalyst for Oxygen Evolution Reaction

Xiaojuan Zhanga, Bo Yua, Xinqiang Wanga, Dongxu Yang*a, Yuanfu Chen*a

aSchool of Electronic Science and Engineering, and State Key Laboratory of Electronic

Thin Films and Integrated Devices, University of Electronic Science and Technology of

China, Chengdu 610054, PR China

*Corresponding authors.

Emails addresses: dongxu_y@hotmail.com (D.X. Yang), yfchen@uestc.edu.cn (Y.F.

Chen)

1

Details concerning the calculation of mass activity, specific activity, and turnover frequency

(TOF) are shown below.

The values of mass activity (A g-1) were calculated from the catalyst loading m (0.6470 mg

cm-2) and the measured current density j (mA cm-2) at η = 400 mV

Mass activity = jm

(1)

The values of specific activity (mA cm-2) were calculated from the BET surface area SBET (m2

g-1), catalyst loading m (0.6470 mg cm-2) and the measured current density j (mA cm-2) at η =

400 mV

Specific activity = j

m SBET(2)

The TOF is another crucial criteria for estimating the intrinsic OER activity of

electrocatalysts. The values of TOF can be calculated the following equation by assuming

that every active metal atom (Co) is involved in the catalysis (lower limits) [1]： TOF = j

4 F n (3)

where j (mA cm-2) is the measured current density at η = 400 mV, the number 4 means 4

electrons per mole of O2, F is Faraday’s constant (96485.3 C mol-1). And n is the number of

moles of metal on the electrode (mol cm-2). All the Co atoms were assumed to be accessible

for catalyzing the OER. We did not count Fe because normally Co was much more active for

OER catalysis than Fe in alkaline solution. The bulk cobalt content of CCFC revealed by the

ICP-AES measurement was about 1.33 wt% (Table S1). The OER current density for CCF,

CCFC-1, CCFC-2, CCFC-3 and CCFC-4 were 8.52, 83.10, 95.02, 92.23 and 78.03 mA cm -2,

respectively, and the corresponding TOF values were calculated to be

TOFCCF = 8.52 mA cm−2

4 96485.3C mol−1 1.33 mg100 mg

0.6470 mgcm2

158.93

mmolmg

= 0.1511 s-1

TOFCCFC-1 = 83.10 mA cm−2

4 96485.3C mol−1 1.33 mg100 mg

0.6470 mgcm2

158.93

mmolmg

= 1.474 s-1

2

TOFCCFC-2 = 95.02 mA cm−2

4 96485.3C mol−1 1.33 mg100 mg

0.6470 mgcm2

158.93

mmolmg

= 1.686 s-1

TOFCCFC-3 = 92.23 mA cm−2

4 96485.3C mol−1 1.33 mg100 mg

0.6470 mgcm2

158.93

mmolmg

= 1.636 s-1

TOFCCFC-4 = 78.03 mA cm−2

4 96485.3C mol−1 1.33 mg100 mg

0.6470 mgcm2

158.93

mmolmg

= 1.384 s-1

3

Fig. S1 EDX spectra of globular clusters-like CCFC-2 electrocatalyst

4

Fig. S2 SEM images of as-prepared CCFC-1 (A), CCFC-3 (B) and CCFC-1 (C)

electrocatalyst and HRTEM images of CCFC-2 (D)

5

Fig. S3 The effect of CNTs content on the onset potentials and Tafel slope (A) and TOF (B)

of CoHCF electrocatalysts; and the specific activity and mass activity (C) of the as-prepared

CCF and CCFC-2 electrocatalysts

6

Fig. S4 LSV

curves of globular clusters-like CCFC-2 for initially and after

1500 potential sweeps

7

Fig. S5 Co 2p XPS spectra (A), Fe 2p XPS spectra (B), XRD patterns (C) and SEM image

(D) of CCFC-2 electrocatalyst after testing in KOH medium.

8

Fig. S6 CV curves of CCF, CCFC-1, CCFC-2, CCFC-3 and CCFC-4 in KOH solution

9

Fig. S7 CV curves of CCF (A) and globular clusters-like CCFC-2 electrocatalyst (B) at

different scan rates

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Table S1. Lattice space of CCFC-2 hybrid from XRD measurement based on the Bragg's

equation (2dsinθ =n λ)

Sample Crystal planes 2θLattice space (d, calculated from

XRD measurement)

CCFC-2

(200) 17.5° 0.51 nm

(220) 24.8° 0.36 nm

(400) 35.6° 0.25 nm

(420) 39.6° 0.23 nm

(422) 50.6° 0.18 nm

(600) 53.9° 0.17 nm

(620) 57.1° 0.16 nm

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Table S2. ICP-AES results of CoHCF/CNTs hybrid

sample Content (%) of Co Content (%) of Fe

CoHCF 1.51% 0.40%

CCFC-1 1.41% 0.38%

CCFC-2 1.35% 0.37%

CCFC-3 1.29% 0.33%

CCFC-4 1.11% 0.31%

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Table S3 Performance comparison of OER activities of CoHCF/CNT hybrid and other

recently reported OER Co-based electrocatalysts

CatalystTafel slope

(mV dec-1)

η10 (mV

vs. RHE)

KOH

electrolyte

(M)

References

CoFe2O4@N-CNFsa 80 349 0.1 [2]

NiCo2S4/CCb 86 - 1.0 [3]

Co3O4/Fe2O3 67.0 310 1.0 [4]

Co3O4 76.0 307 1.0 [5]

Li0.7Co0.75Fe0.25PO4/rGO 52.8 430 0.1 [6]

NiCo2O4/NFc 172 271 1.0 [7]

Co3O4/Thin film 58.1 377 1.0 [8]

Co-B/C 75 320 1.0 [9]

CoO 65 306 1.0 [10]

CoS2/N,S-GO 75 280 0.1 [11]

N-Co9S8/Gd 82.7 409 0.1 [12]

Ni-Co2-O HNSse 64.4 362 1.0 [13]

Mesoporous CoPi 58.7 380 1.0 [14]

ZnCo2O4/NCNTf 70.6 430 0.1 [15]

Pristine Co-PBA 67 334

1.0 [16]Plasma treated Co-PBA-1 h 72 285

Plasma treated Co-PBA-2 h 53 274

Co-HCF film 84.97 / phosphate buffer (pH = 7) [17]

1-D structured CoHCF film

/ 450 1.0

[18]/ 880

phosphate buffer

electrolyte (pH = 7)

globular clusters-like

CoHCF/CNTs hybrid62.43 274 1.0 This work

Note: aN-CNFs: N-doped carbon nanofibers; bCC: carbon cloth; cNF: nickel foam;dG: grapheme; eHNSs: hollow nanosponges; fNCNT: nitrogen-doped carbon nanotubes.

13

Table S4 The optimum fit parameters and values of equivalent Randles circuit elements (Rs +

Cf/Rf + Cdl/Rct) for electrochemical impedance spectroscopy measured from 100 kHz to 0.01

Hz for CCF, CCFC-1, CCFC-2, CCFC-3 and CCFC-4 electrode

SampleRs

()

Rf

()

Cf

(S-sec0.5)

Rct

()

Cdl

(S-sec0.5)

CCF 0.7895 28.07 0.004608 51.27 1.991× 10-6

CCFC-1 0.7018 10.41 0.00496 44.11 2.656 × 10-6

CCFC-2 0.6778 11.06 0.005623 42.27 2.625 × 10-6

CCFC-3 0.7331 10.19 0.004469 42.09 2.655 × 10-6

CCFC-4 0.792 11.37 0.004839 39.52 2.381 × 10-6

14

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