Supporting Information for

Pseudo-Atomic-Scale Metals Well-Dispersed on Nano-Carbons as Ultra-Low Metal Loading Oxygen-Evolving Electrocatalysts

Jing-Fang Huang* and Wei-Zhe Xie

Department of Chemistry, National Chung Hsing University, Taichung 402, Taiwan, R.O.C.

*Correspondence to: E-mail: jfh@dragon.nchu.edu.tw

This file includes:

The area of single molecule of TA

Coverage of TA on GCE (one monolayer)

Coverage of TA on SWCNT (one monolayer)

pH-controllable TA molecule monolayer on the nano-carbon (NC)

UV-Vis of Fe2+-TA complex determines the Fe loading on the Fe@SWCNT

Figs. S1 to S16

Tables S1

Electronic Supplementary Material (ESI) for Chemical Science.This journal is © The Royal Society of Chemistry 2020

The area of single molecule of TA

The radius of a TA molecule was determined by measuring the length from its center (A) to one of end hydroxyl groups (B). The A-B length was measured to be ca 1.28 nm. Thus, the area of single-molecule of TA (ATA) is calculated as below.

ATA = [2 x (1.28 x 10-9 m)]2 = ca 7 x 10-18 m2

Coverage of TA on GCE (one monolayer)

The surface area of GCE/ATA = 7 × 10-6 m2/ 7 x 10-18 m2

= ~1 × 1012 molecules/GCE

= ~1.66 × 10-12 moles/GCE

Coverage of TA on SWCNT (one monolayer)

The Carbon loading 15.1 μg cm-2 is drop-dried on a GCE (0.07 cm2)

1.06 μg SWCNT on the GCE and the BET SWCNT specific surface area is about 525 m2 g-1

Total surface area of SWCNT on the GCE = 1.06 × 10-6 × 525 = 5.6 × 10-4 m2

Coverage of TA on SWCNT (one monolayer):

Total surface area of SWCNT on GCE/ ATA = 5.6 × 10-4 m2/7 x 10-18 m2

= ~8.1 × 1013 molecules/GCE

= ~1.33 × 10-10 moles/GCE

Fig. S1. Molecule structure of TA

A

B

1.28 nm

S3

Fig. S2 TEM images of well-dispersed (a) TA-SWCNT, (b) TA-MWCNT, and (c)

TA-GE8; Photographs of vials containing 0.12 wt% NCs, including #1 SWCNT, #2

MWCNT, #3 GE8, and #4 GE12 in (d) 0.12 wt% TA aqueous solution and (e) pure

water, respectively.

a

b

c

d

f

#1 #2 #3 #4

#1 #2 #3 #4

TAaq

Pure water

S4

2000 1500 1000 500

2000 1500 1000 500

2000 1500 1000 500

2000 1500 1000 500

plane vibrationsof aromatic C-Hbenzenealkyl benzene bonds

vibrations of the benzene ring

C=C

TA

phenyl group C-H(out of-plane bend)

C-O(acid group)

aromatic -C-C

aromatic C=O

C-O(polyols)

phenolic-OH(bending) C-O-C groupA

bsor

banc

e

SWCNT

TA-SWCNT11

981

195

10

671

078

10

40

87

28

64

756

760

aromatic C=C

wavenumbers(cm-1)

C=O

157

1

17

09

170

117

01 FeNi

3@TA

i-SWCNT

157

716

11

15

34

14

48 132

1

120

3

108

4

10

30

869

75

9

14

44

142

0

134

31

32

3

Fig. S3 FTIR spectra of FeNi3@TAi-SWCNT, TA-SWCNT, SWCNT, and TA.

S5

0.8 1.0 1.2 1.4 1.6 1.8

0.0

0.5

1.0

1.5

2.0

0 20 40 60 80 100 120

0.5

1.0

1.5

2.0

~1 TA layers

TA

on

SW

CN

T (

nm

ol)

tde

(min)

~12 TA layers

j (m

A c

m-2)

E (V vs. RHE)

pH-controllable TA molecule monolayer on the nano-carbon (NC)

TAad on NCs also can be evaluated by CVs recorded in KOHaq (Fig. S4), with TAad

on SWCNT serving as an example. In this case, 4 μl of 0.027 wt% TAm-SWCNTaq

(carbon loading 15.1 μg cm-2) was drop-dried onto a GCE (0.07 cm2)

(TAm-SWCNT@GCE) serving as a working electrode. CVs of TA anodic stripping

were recorded after various periods (tde) before the CV measurement in 1.0 M KOHaq.

Anodic waves appear due to TA oxidation to TA-quinone through 2e-/2H+ in the first

cycle of CVs, then disappear in the second cycle of CVs, indicating TA anodic

stripping from TA-SWCNT. The SWCNT specific surface area is ~525 m2 g-1,

evaluated from nitrogen adsorption data calculated by the Brunauer-Emmett-Teller

method, and is consistent with the data provided by the manufacturer (400–600 m2

g-1). TAad in one monolayer on SWCNT is ~8.1 × 1013 molecules. The TAad on the

as-prepared TAm-SWCNT is ~12 TA molecule layers, which is then reduced to 1–1.5

TA molecule layers after immersion in KOHaq for over 30 min (Fig. S4). These

results demonstrate that pH-tunable TA monolayer formation occurs on NCs

(TAi-NCs).

Fig. S4 CVs of TA anodic stripping were recorded on (black solid circle) a GCE, (red

solid circle) a TAm-SWCNT@GCE, and (blue solid circle) a TAm-SWCNT@GCE

incubated in 1.0 M KOHaq for tde = 20 min before the CV measurement with a scan

rate of 50 mV/s. Inset: TAad on the TA-SWCNT vs. tde.

S6

300 295 290 285 280 275

C=OC-O

FeNi3@TA

i-SWNCT

Inte

nsi

ty (

a.u

.)

Binding Energy (eV)

C 1s

FeNi3@SWNCT

C-C

a

540 535 530 525

FeNi3@TA

i-SWNCT

FeNi3@SWNCT

O 1s

Inte

nsi

ty (

a.u

.)

Binding Energy (eV)

M-OHH

2O

C=OC-OH

b

Fig. S5 C 1s and O 1s spectra of the FeNi3@SWCNT and FeNi3@TAi-SWCNT.

S7

400 500 600 700 800 9000.0

0.2

0.4

0.6

0.8

1.0

Abs

orba

nce

Wavelength (nm)

[TA-Fe2+]/M 280 140 70 35 18

b

200 300 400 500 600 700 800 9000

2

4

6

8

10

Abs

orba

nce

Wavelength (nm)

[TA-Fe2+]/M 280 140 70 35 18

a

UV-Vis of Fe2+-TA complex determines the Fe loading on the Fe@SWCNT

Two peaks of TA were observed at 218 and 275 nm, which correspond to the *

and n-* transitions of TA, respectively (Fig. S6a). After the addition of Fe2+, other

peaks appeared at 317 and 550 nm. The peak at 317 nm was assigned to the TA

absorption peaks coordinated to the Fe2+, and the broad peak near 550 nm corresponds

to a coordinated TA to Fe2+-charge transfer band in the Fe2+-TA complex. In the

UV-Vis spectra, the absorbance at 550 nm (A550) is dependent on the concentration of

the Fe2+-TA complex (Fig. S6b). The Fe loading on the Fe@SWCNT was determined

by tracking the reduction in A550 after SWCNT adsorption (Fig. S7).

Fig. S6 UV-Vs absorption spectra a) 200–900 nm and b) 350–900 nm recorded in

various of [TA-Fe2+].

S8

0.00 0.05 0.10 0.15 0.20 0.25 0.300.0

0.3

0.6

0.9

Abs

orba

nce

[TA-Fe2+]/(mM)

A=2.65[TA-Fe2+] + 0.003

± 

b

400 500 600 700 800 9000.0

0.2

0.4

0.6

0.8

1.0

Abs

orba

nce

Wavelength (nm)

Pre SWCNT adsorption Post SWCNT adsorption

a

|

Fig. S7 (a) Tracking the reduction in A550 before and after SWCNT adsorption in

TA-Fe2+-complex-containing aqueous solution. (b) Calibration curve was recorded as

A550 vs. [TA-Fe2+].

S9

0.1 0.2 0.3 0.4 0.50.20

0.25

0.30

0.35

0.40

36.3 mV dec-1

46.2 mV dec-1

35.4 mV dec-1

31.2 mV dec-1

(V

)

Log (j/mA cm-2)

FeNi3

FeNi Fe

3Ni

Ni Fe

30.4 mV dec-1

Fig. S8 Tafel plots are transferred from the data shown in Fig. 6a.

S10

0 5000 10000 15000 20000 250001.2

1.3

1.4

1.5

1.6

E (

V v

.s R

HE

)

Time (s)

jOER

=10 mA cm-2a

Fig. S9 (a) Chronopotentiometry curves at a current density of 10 mAcm-2 and (b)

gram-scale production of FeNi3@SWCNT.

b

S11

Fig. S10 HR-TEM images of (FeNi)x@SWCNT including Ni@SWCNT,

FeNi3@SWCNT, Fe3Ni@SWCNT, and Fe@SWCNT.

Ni@SWCNT

Fe3Ni@SWCNT

FeNi3@SWCNT

Fe@SWCNT

S12

Fig. S11 TEM images of (FeNi)x@MWCNT including Ni@MWCNT,

FeNi3@MWCNT, Fe3Ni@MWCNT, and Fe@MWCNT.

Ni@MWCNT FeNi3@MWCNT

Fe@MWCNTFe3Ni@MWCNT

S13

Fig. S12 TEM images of (FeNi)x@GE8 including Ni@GE8, FeNi3@GE8,

Fe3Ni@GE8, and Fe@GE8.

Ni@GE8

Fe@GE

FeNi3@GE

Fe3Ni@GE8

S14

20 30 40 50 60 70 80 90

Fe@SWCNT

Fe3Ni@SWCNT

FeNi@SWCNT

FeNi3@SWCNT

Ni@SWCNT

SWCNT Inte

nsi

ty (

a.u

.)

2

Ti

Fig. 13 X-ray diffraction of (FeNi)x@SWCNT on a Ti sample holder.

S15

Fig. S14 FeNi3@SWCNT ink loaded in a sprayer can homogeneously spray catalysts

onto any conducting substrates for OER application.

FeNi3@SWCNTaq

Ti mesh

S16

0.8 1.0 1.2 1.4 1.6 1.8 2.0-20

0

20

40

60

c1

Fe Fe

3Ni

FeNi FeNi

3

Ni

j (m

A c

m-2)

E (V vs. RHE)

a1

a2

Fig. S15 OER CVs for the (FeNi)x@SWCNT series recorded in 1.0 M KOH with a

scan rate of 10 mV/s.

S17

0.4 0.6 0.8 1.0 1.2 1.4

0

20

40

60

80

100

Cou

nts

The size of metal nanocluster (nm)

b

Fig. S16 HR-TEM images of (a) FeNi3@SWCNT and (b) Histograms of metal

nanocluster size constructed by counting 200−300 nanoclusters on the SWCNT in

TEM images of FeNi3@SWCNT

a

S18

Table S1. Comparisons of OER performance for various transition metal-based electrocatalysts.

Catalyst Catalyst

loading TOF Tafel slope Jm

* Jm@η* η10* Refs.

mg cm-2 s-1 mV dec-1 A mg-1 A g-1 V

FeNi3@SWCNT 0.00042 14.03 30.2 23.81 92249.6@0.3V 0.275

this work

FeNi@SWCNT 0.00041 8.2 31.2 24.39 53925.8@0.3V 0.280

Fe3Ni@SWCNT 0.00045 1.25 35.4 22.22 8247.3@0.3V 0.329

Fe@SWCNT 0.00046 0.02 36.3 21.74 0.0066@0.3V 0.442

Ni@SWCNT 0.00040 0.31 46.2 25.00 0.86@0.3V 0.360

Fe3Co(PO4)4@rGO 1.0 0.54 57 0.01 0.54@0.237V 0.237 27

NiMoN@NiFeN 1270 0.09 58.6 0.0079 0.163@0.3V 0.277 28

AN-CuNiFe 0.025 3.3 44 0.4 1464.5@0.3V 0.224 26

Au/NiFe LDH 2 0.11 36 0.005 64.9@0.28V 0.237 25

FeP/Ni2P 8 0.16 22.7 0.00125 159.6@0.3V 0.154 24

Fe(TCNQ)2/Fe 0.49 N/A 110 0.0204 NA 0.340 23

Fe-Co-2.3Ni-B 0.3 N/A 38 0.0333 N/A 0.274 22

Ni3Fe0.5V0.5 1.27 0.09 58.6 0.0079 0.163@0.3V 0.264 21

Fe-NiSe2 ~0.2 0.071 41 0.05 124.3@0.29V 0.268 20

Ni2Fe1-O 0.15 N/A 39 0.0667 N/A 0.244 19

Ni@NC-800 0.31 N/A 45 0.0323 N/A 0.280 18

P-Co3O4 0.4 0.0158 51.6 0.025 N/A 0.280 17

Ultrathin CoFe LDHs 0.2 4.78 37.9 0.05 190@0.3V 0.266 42

Ni45Fe55/XC-72r 0.01 0.2 36 1 2000@0.3V N/A 37

NiFe-MOF N/A 3.8 34 N/A N/A 0.24 15

S19

Gelled FeCoW 0.21 0.46 N/A 0.05 1175@0.3 0.223 14

Fe0.5V0.5 0.143 0.02 36.7 0.07 6.99@0.292V 0.39 16

CP/CTs/Co-S 0.32 0.016 72 0.0313 31.3*0.306 0.306 29

FeOOH/Co/FeOOH 0.5 2.33 32 0.02 40@0.25 0.25 13

NiFe LDH/GO 0.25 0.1 42 0.04 40@0.23 0.23 11

NiFe-LDH/CNTs 0.2 0.56 31 0.05 47.63@0.3 0.26 10

Ni0.75V0.25-LDH 0.143 0.054 50 0.07 70@0.35 0.35 12

* Jm: Mass activity at 10 mA cm-2geo; Jm@η: Mass activity @specific η; η10: Overpotential for 10 mA

cm-2geo