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Supporting Information

Spatially Resolved Electrochemistry Enabled by Thin-Film Optical

Interference

Yafeng Wang, Qian Yang and Bin Su*

Institute of Analytical Chemistry, Department of Chemistry, Zhejiang University, Hangzhou 310058, China

*Corresponding author: subin@zju.edu.cn

Table of Contents

S1. Voltammetric Characterization of SNM S-2

S2. Interferometric Electrochemistry Responses of SNM/ITO in KCl Solution S-3

S3. Interferometric Responses of ITO/glass During Electrochemical Process S-4

S4. Relationship between ΔI and Potential Applied on SNM/ITO S-5

S5. UV-Vis Spectra of Ru(NH3)63+, Ru(NH3)6

2+, Fe(CN)63 and Fe(CN)6

4 S-6

S6. CVs of SNM/ITO and ITO/glass in Ru(NH3)63+ Soution S-7

S7. CVs of SNM/ITO and ITO/glass in Fe(CN)63 Soution S-8

S8. Interferometric Electrochemistry Responses of SNM/ITO and ITO/glass in

Fe(CN)63 Solution S-9

S9. Interferometric Electrochemistry Responses of SNM/ITO in Ru(bpy)32+

Solution S-10

S10. Variations of Gray Values of Different Locations on SNM/ITO S-

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S11. Experimental Section S-12

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

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S1. Voltammetric Characterization of SNM

As shown in Figure S1, no obvious redox current was observed for SNM/ITO with CTAB surfactants in silica

nanochannels (blue curve), indicating that the SNM was integrated and uniform over large area (centimeter scale).

Meanwhile, obvious redox current, similar to that of ITO/glass (Figure S1, red curve), was seen (Figure S1, black

curve) after removal of CTAB surfactants from nanochannels. These results are similar to those reported

previously.1,2

Figure S1. CVs of ITO/glass (red curve), SNM/ITO with CTAB surfactants in nanochannels (blue curve) and

SNM/ITO (black curve) in 50 mM KHP solution (pH = 4) containing 0.5 mM Ru(NH3)63+. The potential scan

rate was 50 mV/s.

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S2. Interferometric Electrochemistry Responses of SNM/ITO in KCl Solution

The concentration of KCl near the electrode surface will change with the sweep of applied potential. To exclude

the effect of concentration of KCl on the value of ΔI, the experiments depicted in Figure 3b were also performed

in 0.1 M and 1 M KCl solution, respectively (Figure S2a and b). The value of ΔI changed slightly with the

concentration of KCl, revealing that the variation of concentration of KCl contributed slightly to the value of ΔI.

Figure S2. Interferometric electrochemistry responses of SNM/ITO in 0.1 M KCl solution (a) and 1 M KCl solution

(b). The potential scan rate was 20 mV/s.

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S3. Interferometric Responses of ITO/glass During Electrochemical Process

Figure S3. Changes of ΔI with the sweep of potential applied to the ITO/glass in 0.5 M KCl solution (a) and 0.5 M

KCl solution (b) containing 10 mM Ru(NH3)63+. The potential was swept from +0.2 V to 0.45 V. The potential scan

rate was 20 mV/s.

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S4. Relationship between ΔI and Potential Applied on SNM/ITO

Figure S4. The variation of ΔI of SNM/ITO with the potential sweep in 0.5 M KCl solution containing 10

mM Ru(NH3)63+. The potential scan rate was 20 mV/s.

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S5. UV-Vis Spectra of Ru(NH3)63+, Ru(NH3)6

2+, Fe(CN)63 and Fe(CN)6

4

Figure S5. UV-Vis spectra of Ru(NH3)63+ (a) and Ru(NH3)6

2+ (b) with different concentrations. (c) UV-Vis spectra of

10 mM Fe(CN)63 and Fe(CN)6

4.

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S6. CVs of SNM/ITO and ITO/glass in Ru(NH3)63+ Solution

Figure S6. CVs of SNM/ITO (a) and ITO/glass (b) in 0.5 M KCl solution containing different concentrations of

Ru(NH3)63+. Black curve: 0 mM, red curve: 0.5 mM, blue curve: 1 mM, green curve: 2 mM, purple curve: 3 mM,

yellow curve: 5 mM, brown curve: 10 mM, red dotted curve: 20 mM, black dotted curve: 30 mM. The potential

scan rate was 20 mV/s.

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S7. CVs of SNM/ITO and ITO/glass in Fe(CN)63 Soution

Figure S7. CVs of SNM/ITO (blue curve) and ITO/glass (red curve) in 0.5 M KCl solution containing 10 mM Fe(CN)63.

The potential scan rate was 20 mV/s.

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S8. Interferometric Electrochemistry Responses of SNM/ITO and ITO/glass in

Fe(CN)63 Solution

Figure S8. The variation of ΔI with the potential sweep for the ITO/glass (a) and SNM/ITO (b) in 0.5 M KCl

solution containing 10 mM Fe(CN)63. The potential scan rate was 20 mV/s.

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S9. Interferometric Electrochemistry Responses of SNM/ITO in Ru(bpy)32+ Solution

Figure S9. The variation of ΔI with the potential sweep for the SNM/ITO in 0.5 M KCl solution containing 10 mM

Ru(bpy)32+. The potential scan rate was 20 mV/s. Note that the Intensity of light reflected from SNM/ITO at 800 nm

was recorded during electrochemical reaction to exclude the effect of light absorption and fluorescence of

Ru(bpy)32+ on the intensity of interferometric light.

The intensity of interferometric light at 800 nm changes significantly during the

electrochemical reactions, indicting the versatility of the method for studying different

molecules.

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S10. Variations of Gray Values of Different Locations on SNM/ITO

Figure S10. (a) Interferometric image of ITO/glass partially coated by SNM. (b) Changes of mean gray values of the

entire SNM/ITO region during CV. (cf) Changes of mean gray values of different locations (marked in (a), 2 × 2

pixels, ca. 800 nm × 800 nm) on SNM/ITO electrode during CV in 0.5 M KCl solution containing 10 mM Ru(NH3)63+.

The potential scan rate was 20 mV/s.

The variations of gray value of the entire SNM/ITO (Fig. S10a and b) during CV were compared with that of different locations (2 × 2 pixels, ca. 800 nm × 800 nm, Fig. S10cf) on SNM/ITO. The tendencies of the curves were different, indicating the heterogeneity of the electrode. Moreover, the mean gray value of different locations began to increase at different times, implying that the EC reactions at different locations began to occur under different potentials. The slope of the curves was also different, revealing the difference of reaction rates at different locations.

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S11. Experimental Section

Chemicals and Materials. Hexaammineruthenium(II) chloride ([Ru(NH3)6]Cl2, 99.9%) was obtained from

Alfa Aesar. Hexaammineruthenium(III) chloride ([Ru(NH3)6]Cl3, 98%), cetyltrimethylammonium bromide

(CTAB), concentrated ammonia aqueous solution (25 wt%), poly(methyl methacrylate) (PMMA, Mw =

996000), tris(2,2’-bipyridine)dichlororuthenium(II) hexahydrate ([Ru(bpy)3]Cl2·6H2O) and

tetraethoxysilane (TEOS) were bought from Sigma. Potassium ferricyanide (III) (K3Fe(CN)6, 99.95 %) and

Potassium ferricyanide (II) trihydrate (K4Fe(CN)63H2O, 99.99 %) were received from Aladdin. Ethanol,

acetone, potassium chloride, sodium hydroxide, potassium hydrogen phthalate (KHP) were ordered from

Sinopharm. All chemicals and materials were used as obtained without further purification. And ultrapure

water (18.2 M cm) was used for preparing all aqueous solutions. ITO coated glass (ITO/glass) was

obtained from Kaivo.

Preparation and Transfer of SNM. The Stöber-solution growth approach with CTAB used as the

surfactant template was employed to fabricate SNM.3 Typically, the ITO/glass was first washed

ultrasonically in ethanol solution (1 M NaOH), acetone, ethanol and ultrapure water for 20 min,

respectively. Then, the ITO/glass was soaked in the solution containing ethanol (70 mL), ammonia aqueous

solution (10 µL), CTAB (0.16 g), TEOS (80 µL) and ultrapure water (30 mL). The solution was kept at 60 °C

for 24 h. Lastly, the SNM/ITO/glass/SNM (SNM can grow on both sides of ITO/glass) was washed using

deionized water and aged in an oven overnight at 100 °C. The as-prepared electrode was immersed in

ethanol solution containing 0.1 M HCl under magnetic stirring for 15 min to remove the CTAB surfactants

in silica nanochannels.

SNM on the ITO side was transferred to a fresh ITO/glass using the approach reported previously,4 in

order to avoid the effect of SNM (grown on the opposite glass side) on the optical interference. In brief,

PMMA solution (one drop) was spin-coated on the SNM/ITO/glass/SNM slide at 2000 rpm for 0.5 min.

Then, the solvent was evaporated at room temperature, followed by heating the slide at 115 °C for 15 min.

The ITO layer was etched by soaking the slide in aqueous solution containing 2 M HCl at room temperature

overnight. The fabricated free-standing PMMA/SNM, which could be fished out by another ITO/glass, was

immersed in ultrapure water (three times) to remove HCl. The membrane was desiccated at room

temperature for 1 h and heated at 100 °C for 2 h. Finally, the PMMA layer was dissolved by soaking the

slide in acetone for 6 h to obtain the double-layer film electrode, SNM/ITO.

Characterization of SNM. A HT7700 transmission electron microscope was used for attaining

transmission electron microscopy (TEM) images. A SU8010 field-emission scanning electron microscope

was used for obtaining scanning electron microscopy (SEM) images (performed at 5 kV).

Interferometric Electrochemistry Experiments. A CHI 440a EC workstation (CH Instrument, Shanghai) was used

for performing EC experiments. And a conventional three-electrode configuration with ITO/glass or SNM/ITO,

platinum wire and Ag/AgCl electrode (saturated KCl) served as working electrode, counter electrode and reference

electrode, respectively, was used. The exposure size of working electrode used in optical interference coupled EC

experiments is 6 mm in diameter. And the exposure size of working electrode used for other EC experiments was

1 cm × 1 cm. White light from a halogen tungsten lamp (HL-2000-LL, Ocean Optics) was projected onto the

electrode surface at the normal incidence by a Y-branch bifurcated optical fiber and a collimating lens (Figure

S11a). The spectrum of bare glass was measured as the reference to obtain the RIS of SNM/ITO. The RIS was

recorded at a frequency of 5 Hz using an optical fiber CCD-array miniature spectrometer (QEPro, Ocean Optics).

The experimental setup for studying local electrochemistry was shown in Figure S11b. A halogen tungsten lamp

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was chosen as the light source. And a bandpass filter (center wavelength = 532 nm, full width at half maximum = 4

nm) was employed to narrow the wavelength of incident light. The EC cell was mounted under an optical

microscope equipped with a water-immersion objective (40×, NA = 0.8). An electron multiplying charge coupled

device (EMCCD) camera (Andor, iXon Ultra 897) was employed to image the surface of the electrode during EC

experiments. The images were recorded each 0.35 s (exposure time 50 ms).

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Figure S11. (a) The experimental setup for measuring the RIS. (b) The experimental setup for studying local

electrochemistry.

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ReferenceS1 F. Yan, Y. He, L. Ding and B. Su, Anal. Chem., 2015, 87, 4436-4441.

S2 Q. Sun, F. Yan, L. Yao and B. Su, Anal. Chem., 2016, 88, 8364-8368.

S3 Z. Teng, G. Zheng, Y. Dou, W. Li, C.-Y. Mou, X. Zhang, A. M. Asiri and D. Zhao, Angew. Chem. Int. Ed., 2012, 51,

2173-2177.

S4 X. Lin, Q. Yang, L. Ding and B. Su, ACS Nano, 2015, 9, 11266-11277.