Supportting Information for

Bimetallic Thin Film NiCo-NiCoO2@NC as Superior Bifunctional

Electro- catalyst for Overall Water Splitting in Alkaline Media

Yun Xiao,† Pengfang Zhang,† Xin Zhang,†* Xiaoping Dai,† Yangde Ma,† Yao Wang,† Yan Jiang,†

Mengzhao Liu,† Yue Wang†.

†State Key Laboratory of Heavy Oil Processing College of Chemical Engineering, China University of Petroleum Beijing

102249 (China)

‡National Institute of Metrology, Beijing 100013, China

*Corresponding author. E-mail: zhangxin@cup.edu.cn

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

Calculation method

The TOF value (s-1

) was calculated from equation (1):

TOF = J×A

4×F×n (1)

J is obtained at overpotential = 300 mV, normalized by geometric area of GCE (0.07065 cm2), A is the

geometric area of GCE (0.07065 cm2), F is the Faraday constant, n is the mole number of active sites on

the electrode, n(metallic Ni and Co) is the mole number of active sites for HER, n(total Ni and Co

elements) is the mole number of active sites for OER, via equation below:

n(metallic Ni and Co) =mloading×A×rmetallic NiCo/NiCo− NiCoO2@NC×NA

Mw (2)

n(total Ni and Co ) =mloading×A×rtotal NiCo/NiCo− NiCoO2@NC ×NA

Mw (3)

where mloading is the loading mass via drop-casting, A is the geometric area of GCE (0.07065 cm2),

r metallic NiCo/NiCo−NiCoO2@NC is the weight ratio of Ni-Co alloy in NiCo-NiCoO2@NC,

rtotal NiCo/NiCo−NiCoO2@NC is the weight ratio of total Ni and Co elements in NiCo-NiCoO2@NC, NA is

Avogadro's constant, Mw is the molecular weight of active sites.

Mass activity (A·g-1

) values were calculated from the electrocatalyst loading mloading(0.14 mg· cm-2

)

and the measured current densityJ (mA ·cm-2

) at η = 300 mV：

Mass activity = J

mloading (4)

Table S1. Compositions of thin film NiCo-NiCoO2@NC, NiCoO2, Ni-NiO@NC, Co-CoO@NC

determined by ICP-MS and XPS

Sample bulk content(wt%) by ICP-MS Surface content(wt%) by XPS

Co Ni Co : Ni (atom) C N O Co Ni Co : Ni (atom)

Ni-NiO@NC - 65.78 - 83.97 1.48 11.45 - 3.1 -

Co-CoO@NC 60.14 - - 82.23 1.8 13.19 2.79 - -

NiCoO2 29.22 30.52 0.95 26.84 - 46.62 14.82 11.72 1.26

NiCo-NiCoO2@NC 27.25 29.89 0.91 60.96 2.65 25.02 6.48 4.89 1.32

NiCo@NC 37.03 39.84 0.93 66.84 - 26.62 6.82 5.72 1.19

NiCoO2@NC 30.60 31.63 0.97 60.96 2.65 39.02 7.48 6.59 1.14

Table S2. The surface area and pore volume of NiCo-NiCoO2@NC, NiCoO2, Ni-NiO@NC,

Co-CoO@NC

Material Surface area Pore volume Average pore

m2·g-

1 cm

3·g

-1 diameter(nm)

NiCo-NiCoO2@NC 128.7 0.22 3.77

Ni-NiO@NC 208.9 0.21 3.68

Co-CoO@NC 108.4 0.18 3.80

NiCoO2 19.7 0.12 3.40

Table S3. The quantitative results of H2-TPR characterization

Catalyst Weight Reduction Peak area H2

consumption

Ni/Co in

Oxides

content

Metallic

Ni/Co

content

(mg) Temperature (°C) mmol (wt%) (wt%)

NiCo-NiCoO2@NC 10.00 483/526 5011.00 0.05 31 26

Ni-NiO@NC 12.55 490 6894.80 0.07 34 32

Co-CoO@NC 10.00 582 5271.00 0.06 33 27

Table S4. Comparison of the electrocatalytic activity of NiCo-NiCoO2@NC to some

representatively reported OER catalysts in basic solutions.

Material Loading Electrolyte η (V) Tafel slope Reference

mg·cm-2

10 mA·cm-2

mV/decade

NiCo-NiCoO2@NC 0.14 1.0 M KOH 0.31 76 This work

Commercial IrO2/C 0.14 1.0 M KOH 0.36 136 This work

Co3O4/N-rmGO 1 1.0 M KOH 0.31 67 Nat. Mater. 2011, 10, 7801

Co3O4/NiCo2O4 1 1 M KOH 0.34 88 J. Am. Chem. Soc. 2015, 137, 16, 55902

NixCo3-xO4 2.7 1.0 M NaOH 0.42 59 Adv. Mater. 2010, 22, 19263 .

Co-P film 2.71 1.0 M KOH 0.34 47 Angew. Chem., Int. Ed. 2015, 54, 62514

α-Ni(OH)2/GC 0.2 0.1 M KOH 0.33 42 Chem. Mater. 2014, 26, 41305

NiCo-NS 0.07 1.0 M KOH 0.33 41 Nat. Commun. 2014, 5, 44776

NiCoLDHs 0.17 1.0 M KOH 0.37 40 Nano Lett. 2015, 15, 14217

CoP/C 0.36 1.0 M KOH 0.33 53 J. Mater. Chem. A. 2016, 4, 23, 90728

PNG-NiCo2O4 - 0.1 M KOH 0.35 156 ACS Nano 2013, 7, 101909

Table S5. Comparison of the electrocatalytic activity of NiCo-NiCoO2@NC to some

representatively reported HER catalysts for basic solutions.

Material Loading Electrolyte η (mV) Tafel slope Reference

mg·cm-2

10 mA·cm-2

mV/decade

NiCo-NiCoO2@NC 0.26 1.0 M KOH 0.11 125 This work

Commercial Pt/C 0.26 1.0 M KOH 0.066 90 This work

Co@N-C 4.5 1.0 M KOH 0.21 108 J. Mater. Chem. A 2014, 2, 2006710

Co-NCNT/CC 3.4 1.0 M KOH 0.18 193 ChemSusChem 2015, 8, 185011

CoOx@CN 0.12 1.0 M KOH 0.23 115 J. Am. Chem. Soc. 2015, 137, 268812

CoSe2 nanosheet 0.142 0.1 M KOH 0.32 44 ACS Nano 2014, 4,397013

Ni0.33Co0.67S2 nanowire 0.3 1.0 M KOH 0.088 118 Adv. Mater. 2010, 22,19263

Co-NRCNTs 0.36 1.0 M KOH 0.37 - Angew. Chem., Int. Ed. 2014, 5314

NiCo2S4 4 1.0 M KOH 0.26 141 Nanoscale 2015, 7, 1512215

NiCo2O4 1 1.0 M NaOH 0.11 49.7 Angew. Chem., Int. Ed. 2016, 55, 629016

Co-P film 2.71 1.0 M KOH 0.094 42 Angew. Chem., Int. Ed. 2015, 54, 62514

Table S6. TOF for HER of NiCo-NiCoO2@NC, Ni-NiO@NC, Co-CoO@NC, NiCo@NC and Pt/C

Catalyst

Current

density

(mA•cm-2

)

Current

density

(mA•cm-2

)

TOFH(S-1

) TOFH(S-1

) Mass activity

(A·g-1

)

Mass activity

(A·g-1

)

at η=300 mV at η=500 mV at η=300

mV

at η=500

mV at η=300 mV at η=500 mV

NiCo-NiCoO2@NC -141.4 -745.4 0.63 3.32 539.7 2845.0

Ni-NiO@NC -65.5 -169.9 0.24 0.62 250.0 648.5

Co-CoO@NC -19.7 -181.0 0.08 0.77 75.2 690.8

Pt/C -86.0 -130.0 0.87 1.31 328.2 496.2

NiCo@NC -49.1 -132.3 0.14 0.37 187.4 505.0

Table S7. TOF for OER of NiCo-NiCoO2@NC, Ni-NiO@NC, Co-CoO@NC, NiCo@NC,

NiCoO2@NC and IrO2

Catalyst

Current

density

(mA•cm-2

)

Current

density

(mA•cm-2

)

TOFO(S-1

) TOFO(S-1

) Mass activity

(A·g-1

)

Mass activity

(A·g-1

)

at η=300 mV at η=500 mV at η=300 mV at η=500 mV at η=300 mV at η=500 mV

NiCo-NiCoO2@NC 6.6 181.2 0.013 0.35 47.4 1294.3

Ni-NiO@NC 6.9 129.3 0.011 0.21 49.3 923.6

Co-CoO@NC 6.2 98.2 0.011 0.18 44.3 701.4

IrO2 4.0 79.2 0.0090 0.18 28.6 565.7

NiCo@NC 4.1 138.4 0.0058 0.20 29.3 988.6

NiCoO2@NC 4.0 150.2 0.0070 0.26 28.6 1072.9

Table S8. “theoretical” TOF numbers of NiCo-NiCoO2@NC

TOF TOFcal-H(S-1

) TOFcal-O(S-1

) TOFcalM-H(S-1

) TOFcalM-O(S-1

)

η(mV) η=300 η=500 η=300 η=500 η=300 η=500 η=300 η=500

NiCo-NiCoO2@NC 0.16 0.69 0.01 0.23 0.070 0.18 0.01 0.20

Table S9. Comparison of the electrocatalytic activity of NiCo-NiCoO2@NC to some

representatively reported bifunctional electrocatalysts for overall water splitting in 1.0 M KOH

solution.

Catalyst Catalyst Substrate Overall Voltage

(V) Reference

Cathode (H2) Athode (O2) at j=10 mA·cm-2

NiCo-NiCoO2@NC NiCo-NiCoO2@NC Ni foam 1.44 This work

NiFeLDH NiFeLDH Ni foam ~1.70 Science 2014, 345, 159317

CoOx@CN CoOx@CN Ni foam 1.62 J. Am. Chem. Soc. 2015, 137, 268812

NiSe NWs NiSe NWs Ni foam 1.63 Angew. Chen. Int. Ed. 2015, 54, 935118

Ni-Fe-O Ni-Fe-O Ni foam 1.51 Nat. Commun. 2015, 6, 726119

Ni0.33Co0.67S2 NiCo2O4 Ti foam ~1.73 Adv. Energy Mater. 2015, 5, 140203120

Ni2P nanoparticle Ni2P nanoparticle Ni foam 1.63 Energy Environ. Sci. 2015, 8, 234721

Ni4P5 film Ni4P5 film Ni foam 1.7 Angew. Chem. Int. Ed. 2015, 54, 1236122

Co-P film Co-P film Ni foam 1.63 Angew. Chen. Int. Ed. 2015, 54, 62514

EG/Co0.85Se/NiFe-LDH EG/Co0.85Se/NiFe-LDH EG foam 1.67 Energy Environ. Sci. 2016, 9, 47823

CoP nanorod CoP nanorod Ni foam 1.62 Adv. Funct. Mater. 2016, 25, 733724

Figure S1. (a) SEM image and (b) TEM image of NiCo-NiCoO2@NC obtained by directly calcination

under 600 oC

1 μm 200 nm

a b

Figure S2. XRD pattern of NiCoDH precursor [Ni(OH)2 (JCPDS no. 14-0117); Co(OH)2 (JCPDS no.

30-0443)]

Figure S3. (a) XRD patterns of NiCo@NC, NiCoO2@NC and NiCo-NiCoO2@NC; (b-d) XPS patterns

of NiCo@NC and NiCoO2@NC: (b) Ni 2p; (c) Co 2p; (d) O 1s.

b

c

a

d

Figure S4. SEM images of (a) Ni-NiO@NC; (b) Co-CoO@NC and c) NiCoO2.

Figure S5. TEM images of (a) Ni-NiO@NC with the inset showing the corresponding particle-size

distribution histogram; (b) Co-CoO@NC with the inset showing the corresponding particle-size

distribution histogram; c) NiCoO2.

ba

100 nm

c

34 36 38 40 42 440

10

20

30

40

Diameter(nm)

Fre

qu

en

cy(%

)

39.1±3.6 nm

27 30 33 360

20

40

60

Diameter(nm)

Fre

qu

en

cy

(%) 32.8±3.2 nm

Figure S6. (a) XPS patterns of N 1s of NiCo-NiCoO2@NC; (b) HER linear sweep voltammetry

(LSV) curves of NiCo-NiCoO2@NC and NiCo-NiCoO2@C; (c) OER LSV curves of

NiCo-NiCoO2@NC and NiCo-NiCoO2@C.

a cb

Figure S7. (a) XPS patterns of N 1s of Ni-NiO@NC; (b-f) CV measurements in a non-faradic

current region (0.1-0.2 V vs. RHE, no iR-corrected) at scan rates of 5, 10, 25, 50 and 100 mV s-1

of b) NiCo-NiCoO2@NC, c) Ni-NiO@NC, d) Co-CoO@NC, e) NiCoO2 and f) NC in 1 M

KOH.

b c

e f

a

d

Figure S8. TEM images of (a) NiCo@NC and (b) NiCoO2@NC

a b

Figure S9. (a) Cyclic voltammetry (CV) curves of NiCo@NC recorded at a scan rate of 50 mV s-1

in

1.0 M KOH solution; (b-d) XPS spectrum of CV conditioned species: (b) Ni 2p; (c) Co 2p; (d) O 1s.

b

c

a

d

Figure S10. XPS spectrum of OER conditioned NiCo- NiCoO2@NC: (a) Ni 2p; (b) Co 2p; (c) O 1s.

a b c

Reference

1 Liang, Y.; Li, Y.; Wang, H.; Zhou, J.; Wang, J.; Regier, T.; Dai, H., Nat. Mater. 2011, 10 (10), 780-6. 2 Hu, H.; Guan, B.; Xia, B.; Lou, X. W., J. Am. Chem. Soc. 2015, 137 (16), 5590-5. 3 Li, Y.; Hasin, P.; Wu, Y., Adv. Mater. 2010, 22 (17), 1926-1929. 4 Jiang, N.; You, B.; Sheng, M.; Sun, Y., Angew. Chem., Int. Ed. 2015, 54 (21), 6251-4. 5 Lim, C. S.; Chua, C. K.; Sofer, Z.; Jankovsk, O.; Pumera, M., Chem. Mater. 2014, 26 (14), 4130-4136. 6 Song, F., Nat. Commun. 2014, 5, 4477. 7 Liang, H.; Meng, F.; Cabánacevedo, M.; Li, L.; Forticaux, A.; Xiu, L.; Wang, Z.; Jin, S., Nano Lett.

2015, 15 (2), 1421. 8 Bai, Y.; Zhang, H.; Feng, Y.; Fang, L.; Wang, Y. J. Mater. Chem. A 2016, 4 (23), 9072-9079. 9 Chen, S.; Qiao, S. Z., Acs Nano 2013, 7 (11), 10190-6. 10 Wang, J.; Gao, D.; Wang, G.; Miao, S.; Wu, H.; Li, J.; Bao, X., J. Mater. Chem. A 2014, 2 (47),

20067-20074. 11 Xing, Z.; Liu, Q.; Xing, W.; Asiri, A. M.; Sun, X., Chemsuschem 2015, 8 (11), 1850. 12 Jin, H.; Wang, J.; Su, D.; Wei, Z.; Pang, Z.; Wang, Y., J. Am. Chem. Soc. 2015, 137 (7), 2688-94. 13 Liu, Y.; Cheng, H.; Lyu, M.; Fan, S.; Liu, Q.; Zhang, W.; Zhi, Y.; Wang, C.; Xiao, C.; Wei, S.; Ye, B.;

Xie, Y., J. Am. Chem. Soc. 2014, 136 (44), 15670-5. 14 Zou, X.; Huang, X.; Goswami, A.; Silva, R.; Sathe, B. R.; Mikmeková, E.; Asefa, T., Angew. Chem.,

Int. Ed. 2014, 53 (17), 4372. 15 Liu, D.; Lu, Q.; Luo, Y.; Sun, X.; Asiri, A. M., Nanoscale 2015, 7 (37), 15122. 16 Gao, X.; Zhang, H.; Li, Q.; Yu, X.; Hong, Z.; Zhang, X.; Liang, C.; Lin, Z., Angew. Chem., Int. Ed.

2016, 55 (21), 5872-5872. 17 Luo, J.; Im, J. H.; Mayer, M. T.; Schreier, M.; Nazeeruddin, M. K.; Park, N. G.; Tilley, S. D.; Fan, H.

J.; Grätzel, M., Science 2014, 345 (6204), 1593-1596. 18 Tang, C.; Cheng, N.; Pu, Z.; Xing, W.; Sun, X., Angew. Chem., Int. Ed. 2015, 54 (32), 9351-9355. 19 Wang, H.; Lee, H. W.; Deng, Y.; Lu, Z.; Hsu, P. C.; Liu, Y.; Lin, D.; Cui, Y., Nat. Commun. 2015, 6,

7261. 20 Peng, Z.; Jia, D.; Al‐Enizi, A. M.; Elzatahry, A. A.; Zheng, G., Adv. Energy Mater. 2015, 5 (9). 21 Feng, L.; Song, F.; Hu, X., Energy Environ. Sci. 2015, 8 (8), 2347-2351. 22 Ledendecker, M.; Krick Calderón, S.; Papp, C.; Steinrück, H. P.; Antonietti, M.; Shalom, M., Angew.

Chem., Int. Ed. 2015, 54 (42), 12361. 23 Hou, Y.; Lohe, M. R.; Zhang, J.; Liu, S.; Zhuang, X.; Feng, X., Energy Environ. Sci. 2015, 9 (2),

478-483. 24 Zhu, Y. P.; Liu, Y. P.; Ren, T. Z.; Yuan, Z. Y., Adv. Funct. Mater. 2016, 25 (47), 7337-7347.