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Plasmon-Promoted Electrocatalytic Water Splitting on Metal-Semiconductor Nanocomposites: the Interfacial Charge Transfer and the Real Catalytic SitesLili Du, Guodong Shi, Yaran Zhao, Xiang Chen, Hongming Sun, Fangming Liu, Fangyi Cheng and Wei Xie*

Dedicated to 100th anniversary of Nankai University

Key Lab of Advanced Energy Materials Chemistry (Ministry of Education)

Renewable Energy Conversion and Storage Center,

College of Chemistry, Nankai University

Weijin Rd. 94, Tianjin 300071, China

*Correspondence: wei.xie@nankai.edu.cn

This PDF file includes:

Supplementary Figures S1 – S20.

Supplementary Calculations S2-S3

Supplementary Scheme S1.

Supplementary Tables S1-S4.

Electronic Supplementary Material (ESI) for Chemical Science.This journal is © The Royal Society of Chemistry 2019

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S1. Supplementary Figures

Figure S1. (a) Schematic illustration of the preparation of Au/NiCo LDH nanocomposite. SEM

images of Ni foam (b), NiCo LDH nanosheet (c-d) and Au/NiCo LDH (e). Inserts are the

corresponding optical images.

Figure S2. TEM images of the NiCo LDH.

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Figure S3. TEM image of the Au NPs. Insert shows the diameter distribution of the particles.

Figure S4. Zeta potentials of NiCo LDH (a) and Au NPs (b) dispersed in water.

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Figure S5. X-ray diffraction (XRD) patterns of NiCo LDH and Au/NiCo LDH.

Figure S6. (a) XPS spectrum of Au/NiCo LDH. High-resolution XPS spectra of Au 4f (b), Ni 2p

(c) and Co 2p (d) of Au/NiCo LDH.

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Figure S7. XRD patterns of Au/Ni(OH)2 (a) and Au/Co(OH)2 (d). SEM and TEM images of

Au/Ni(OH)2 (b & c) and Au/Co(OH)2 (e & f), respectively.

Figure S8. High-resolution XPS spectra of (a) Ni 2p and (b) Co 2p in NiCo LDH (green curve)

and Au/NiCo LDH (pink curve).

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Figure S9. Polarization curves of the corresponding electrocatalysts toward (a) OER and (b) HER.

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Figure S10. (a) Tafel plots derived from the OER polarization curves (Figure 3a) of Au/NiCo

LDH (pink), NiCo LDH (green), Au NPs (blue), and Ni foam (black) with (solid curves) and

without (dashed curves) light illumination. (b) Overpotentials of Au/NiCo LDH, NiCo LDH and

Au NPs for OER at the current density of 10 mA/cm2 with (red) and without (blue) light

illumination. (c) Tafel plots derived from the HER polarization curves (Figure 3b) of Au/NiCo

LDH (pink), NiCo LDH (green), Au NPs (blue), and Ni foam (black) with (solid curves) and

without (dashed curves) light illumination. (d) Overpotentials of Au/NiCo LDH, NiCo LDH and

Au NPs at -10 (red) and -100 mA/cm2 (blue) for HER.

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Figure S11. (a) Electrochemical impedance spectroscopy (EIS) Nyquist plots (overpotential = 250

mV) for the many different electrocatalysts with and without light illumination. (b) The equivalent

circuit model for EIS analysis.

Figure S12. (a) OER and (b) HER polarization curves of Au/NiCo LDH with different Au

contents (0%, 1.7%, 3.3%, and 5.1%). (c) Summary of the overpotentials using the Au/NiCo LDH

samples at current densities of 10 and 100 mA/cm2.

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Figure S13. (a) OER and (b) HER polarization curves of Au/NiCo LDH under illumination (red

dashed curves) and control experiment where only the working electrode is illuminated (red solid

curves) and only the counter electrode is illumination (blue curves).

Figure S14. (a) Chronopotentiometry curves at a fixed current of 10 mA/cm2 in OER for 6 h. (b)

Time dependence of the current density for Au/NiCo LDH in HER. (c) XPS survey and high-

resolution XPS spectra of Ni 2p (d), Co 2p (e) and Au 4f (f) of Au/NiCo LDH before and after the

test.

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Figure S15. (a) Experimental and theoretical amounts of H2 and O2 by the Au/NiCo LDH

electrode at a constant current density. (b) Chronopotentiometry curves of Au/NiCo LDH in

overall water splitting at a constant current density of 10 and 20 mA/cm2 by using a two-electrode

configuration.

Figure S16. SEM (a, b) and TEM (c, d) images of the Au/NiCo LDH after the overall water

splitting experiment.

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Figure S17. (a) OER polarization curves under the illumination of different lights. (b)

Chronoamperomertic i-t curves of the Au/NiCo LDH at an applied potential of 1.23 V vs. RHE

under illumination of visible light at 420, 500, 550, 600, and 700 nm with 30 s light on/off cycles.

(c) OER polarization curves in the darkness at different reaction temperatures.

Figure S18. OER polarization curves of Au/NiCo LDH and Au@SiO2/NiCo LDH under

illumination. Insert is the TEM images of Au@SiO2.

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Figure S19. (a-c) HER polarization curves of Au NPs, NiCo LDH and Au/NiCo LDH with and

without TP under the illumination; (d-f) OER polarization curves of Au NPs, NiCo LDH and

Au/NiCo LDH with and without TP under the illumination.

Figure S20. (a) UV–Vis absorption spectra of NiCo LDH. The inset shows the band gap. (b) UPS

spectrum of NiCo LDH. Insert is the high binding energy range.

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S2. Calculations of Faradaic efficiencies of photoanode and photocathode

Faraday efficiency can be calculated as following: 1,2

Faraday efficiency (photoanode) (%) =

𝑂2 (𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑)

𝑂2 (𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙) × 100%

Faraday efficiency (photocathode) (%) =

𝐻2 (𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑)

𝐻2 (𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙) × 100%

Where O2 (measured) and H2 (measured) are measured by the gas chromatography and O2

(theoretical) and H2 (theoretical) are calculated as following: 3

O2 (theoretical) = H2 (theoretical) =

𝑄 𝑛𝑜𝑥𝑦𝑔𝑒𝑛 𝐹

𝑄

𝑛ℎ𝑦𝑑𝑟𝑜𝑔𝑒𝑛 𝐹

Q is the integrated charge, noxygen is the number of electrons transferred per oxygen molecule (4 in

this case), nhydrogen is the number of electrons transferred per hydrogen molecule (2 in this case),

and F is the Faraday's constant (96485 C/mol).

As shown in Figure S15a, 0.552 mmol of O2 and 1.107 mmol of H2 are produced after 3 h of

illumination. So the Faradaic efficiencies of photoanode and photocathode are calculated as

following:

Faraday efficiency (photoanode) (%) = = 98.63%

0.552 𝑚𝑚𝑜𝑙

( 216

4 × 96485× 103 )𝑚𝑚𝑜𝑙

× 100%

Faraday efficiency (photocathode) (%) = =

1.107 𝑚𝑚𝑜𝑙

(216

2 × 96485× 103 )𝑚𝑚𝑜𝑙

× 100%

98.92%

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S3. Calculations of incident photon-to-current efficiency (IPCE) of the Au/NiCo LDH at

single wavelengths.

The IPCE is defined as the following equation: 4, 5

IPCE (%) = Where 1240 V·nm represents a

|𝑗𝑝ℎ (𝑚𝐴/𝑐𝑚2)| × 1240 𝑉·𝑛𝑚

𝑃𝑚𝑜𝑛𝑜 (𝑚𝑊/𝑐𝑚2) × 𝜆 (𝑛𝑚)× 100%

multiplication of h (Planck’s constant) and c (the speed of light), Pmono is the monochromated

illumination power intensity, and λ is the wavelength.

So the IPCE at different wavelengths can be calculated:

IPCE (420 nm) = ×100% = 0.732 %

|0.0196 𝑚𝐴/𝑐𝑚2| × 1240 𝑉·𝑛𝑚

7.9 𝑚𝑊/𝑐𝑚2 × 420 𝑛𝑚

IPCE (500 nm) = ×100% = 0.975% |0.070 𝑚𝐴/𝑐𝑚2| × 1240 𝑉·𝑛𝑚

17.8 𝑚𝑊/𝑐𝑚2 × 500 𝑛𝑚

IPCE (550 nm) = ×100% = 1.087%

|0.1075 𝑚𝐴/𝑐𝑚2| × 1240 𝑉·𝑛𝑚

22.3 𝑚𝑊/𝑐𝑚2 × 550 𝑛𝑚

IPCE (600 nm) = ×100% = 0.10% |0.0118 𝑚𝐴/𝑐𝑚2| × 1240 𝑉·𝑛𝑚

24.4 𝑚𝑊/𝑐𝑚2 × 600 𝑛𝑚

IPCE (700 nm) = ×100% = 0.0284% |0.0041 𝑚𝐴/𝑐𝑚2| × 1240 𝑉·𝑛𝑚

25.6 𝑚𝑊/𝑐𝑚2 × 700 𝑛𝑚

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S4. Supplementary scheme

Scheme S1.

HER in alkaline media：

Cat. + H2O + e- → Cat. -H* + OH- (Volmer step)

H2O + Cat. -H* + e- → H2+ Cat. + OH- (Heyrovsky step)

Where Cat. refers to catalysts and H* stands for H atoms adsorbed on surface of catalysts.

OER reaction path in alkaline electrolyte：

1) * + OH- →OH*+ e-

2) OH* + OH- →O* + H2O + e-

3) O* + OH- →OOH*+ e-

4) OOH* + OH- →* +O2 + H2O + e-

Summary OER 4OH- →O2 +2H2O+4e-

Where * stands for an active site on the surface, OH*, O*, OOH* are the adsorbed intermediates.

Step 1, 2 and 3 are reversible and determine the overall OER rate. Step 4 is the path of generating

oxygen in the end, which is fast and irreversible.

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S5. Supplementary Tables

Table S1. Summary of the electrochemical properties of the as-prepared electrodes.

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Table S2. Comparison of the OER performance between Au/NiCo LDH and other catalysts.

* stands for the values calculated from the data shown in the literatures.

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Table S3. Comparison of the HER activity between Au/NiCo LDH and other catalysts.

* stands for the values calculated from the data shown in the literatures.

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Table S4. Summary of the overall water splitting performance of Au/NiCo LDH and other

catalysts. Here V10 corresponds to the voltage to achieve a current density of 10 mA/cm2.

* stands for the values calculated from the data shown in the literature.

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