Novel Electrochemical Raman Spectroscopy Enabled by Water

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Novel Electrochemical Raman Spectroscopy Enabled by Water Immersion Objective Zhi-Cong Zeng, Shu Hu, Sheng-Chao Huang, Yuejiao Zhang, Wei Xing Zhao, Jianfeng Li, Chaoyang Jiang, and Bin Ren Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b02739 • Publication Date (Web): 09 Sep 2016 Downloaded from http://pubs.acs.org on September 11, 2016

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Analytical Chemistry

Novel Electrochemical Raman Spectroscopy Enabled by Water Immersion Objective Zhi-Cong Zeng,†,¶ Shu Hu,†,¶ Sheng-Chao Huang,† Yue-Jiao Zhang,† Wei-Xing Zhao,§ Jian-Feng Li,† Chaoyang Jiang, *‡ and Bin Ren*† †

State Key Laboratory of Physical Chemistry of Solid Surface, Key Laboratory of Analytical Sciences, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China. ‡ Department of Chemistry, University of South Dakota, Vermillion, SD 57069, USA §

Nanjing OPTOTEK Technology Co., Ltd., Nanjing 211100, China

ABSTRACT: Electrochemical Raman spectroscopy is a powerful molecular level diagnostic technique for in situ investigation of adsorption and reactions on various material surfaces. However, there is still a big room to improve the optical path to meet the increasing request of higher detection sensitivity and spatial resolution. Herein, we proposed a novel electrochemical Raman setup based on a water immersion objective. It dramatically reduces mismatch of the refractive index in the light path. Consequently, significant improvement in detection sensitivity and spatial resolution has been achieved from both Zemax simulation and the experimental results. Furthermore, the thickness of electrolyte layer could be expanded to 2 mm without any influence on the signal collection. Such a thick electrolyte layer allows a much normal electrochemical response during the spectroelectrochemical investigations of the methanol oxidation.

Raman spectroscopy is an important non-destructive vibrational spectroscopic method that has been intensively applied to study the interfacial structures and electrochemical reactions, benefited from its broad spectral range and weak signal from water.1-7 There is an everlasting effort to achieve the highest signal to noise ratio for the detection of bulk electrode material, monolayer or submonolayer species, etc.8-12 In addition to the introduction of certain enhancement mechanisms,3,13,14 there have been continuous effort to design new types of electrochemical Raman (EC-Raman) cells to achieve the highest detection sensitivity without distorting the electrochemical response.8,15 This is particular important when the system to be studied is of weak signals, such as those processes occurring on platinum and palladium.16-18 There have been several generations of electrochemical Raman cells since the first type reported by Fleischmann and later by Van Duyne groups, where thick window and ultrathin electrolyte layer were used in their setup.19,20 This type of cell fits for the macro sample chamber with a low numerical aperture and does not work well with the confocal Raman systems. We have systematically investigated the effect of different cell designs on the collection efficiency of Raman signal under electrochemical conditions.8,21,22 In 2000, we developed a new type of EC-Raman cell made of Teflon or Kel-F with a facing up working electrode.21 In such a design, a thin electrolyte

layer, a quartz windows and air were sandwiched between the objective and electrode surface. The quartz window is to form a closed electrochemical system to avoid contamination of electrolyte solutions from airborne species and the corrosion of objective lens by the electrolytes. However, the presence of the electrolyte and quartz window can significantly deteriorate the overall detection sensitivity and spatial resolution due to the mismatch of the refractive indices of these media. Therefore, we have to use a very thin electrolyte layer of 0.2 mm to ensure a strong signal, which can drastically impact the material diffusion to and from the electrode surface.21 An alternative way to reduce the signal loss was to use polymer films instead of quartz window. The objective can be wrapped with a polyvinyl chloride film to protect the objective from the electrolyte.4,8 However, the electrolyte was exposed to air and can be easily contaminated in such an approach. More recently, Bell et al. reported an approach of employing a water immersion objective (with an NA of 1.23) wrapped with a 13µm thin Teflon film to overcome mismatch of the refractive index.15 However, to wrap the Teflon film with an optical quality without any leakage of solution is very challenging and the working distance (0.21-0.31mm) is still too short to maintain the normal electrochemical response. In this note, we report a new design of spectroelectrochemical setup using a water immersion objective with a long work-

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ing distance for the Raman measurement. We systematically simulated the size of focused beam under various cell parameters using Zemax. Confocal Raman mappings were then performed with the newly designed electrochemical Raman setup, which demonstrates an improvement in both spatial resolution and signal-to-noise ratio. We then employed the setup for studying the electrochemical oxidation of methanol, which shows significantly improved detection sensitivity, spatial resolution, and electrochemical response. EXPERIMENTAL SECTION The EC-Raman measurements were conducted on a confocal Raman microscope (Alpha-300, Witec). A single-mode polarization-maintaining fiber was used to introduce a 632.8 nm laser (He-Ne, Melles Griot) for the sample excitation. A 50 µm multi-mode fiber was used for Raman signal collection and also as a confocal hole. The signal was then sent via an optical fiber port to a UHTS-300 spectrometers (Witec) equipped with an EMCCD detector (1600×200 pixels, Newton, Andor) to achieve the highest sensitivity. An edge filter was equipped to filter the exciting line, and a 600 g/mm grating was employed for the experiments. A dry objective with NA=0.55 (Olympus, 50×, WD=8 mm) and a water immersion objective with NA=1.0 (Nikon, 60×, WD=2.8 mm) were used in this study for comparative purpose. Zemax software was used to estimate the radius of the focused beam and here the geometrical rays were just used for the data analysis. In the confocal Raman mapping, Raman signals were collected while the samples were raster scanned with 100×200 pixels. The integrated area of silicon 520 cm-1 Raman peak was used for the investigation with a 1 mW excitation. The signal collection time for each pixel is 50 ms. The Raman mapping data were then analyzed with Witec Suite 4.1 software to determine the signal to noise ratios and spatial resolutions. In the electrochemical experiments, a glassy carbon (GC) electrode (2 mm in diameter, CH Instruments) and a platinum electrode (2 mm in diameter, CH Instruments) were polished with 0.3 and 0.05 µm of alumina slurry (Buehler, Ltd.) to a mirror finish, and then sonicated in Milli-Q water (18.2 MΩ cm, Millipore). The chemically synthesized gold core (50nm) and platinum shell ([email protected]) nanoparticles were dispersed on the GC electrode for the study of methanol electro-oxidation.9 A large Pt ring served as the counter electrode. The reference electrode was a saturated calomel electrode (SCE) placed in a separate compartment connected to the cell via a capillary. The applied potentials during the ECRaman and cyclic voltammograms were controlled by a CHI660D electrochemical workstation (CH Instruments). The potential-dependent Raman spectra were acquired 5 min after the movement of the potential stepwise in either the positive or negative direction. All experiments were performed at room temperature (23 ± 1 °C). All chemicals used were analytical reagent grade and the solutions were prepared using Milli-Q water. RESULTS AND DISCUSSION Design of the New Spectroelectrochemical Setup A great challenge for electrochemical Raman spectroscopy is to achieve the highest possible sensitivity while maintaining the ideal electrochemical response.4 However, in conventional electrochemical Raman setup, a long-working distance air

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objective (Figure 1a) was usually used.21 Between the objective and electrode surface, there are air, quartz/glass, and electrolyte layer with different refractive index of 1.00, 1.46/1.52 and 1.33, respectively, which may cause severe distortion in the optical path. To minimize such a distortion, a thin electrolyte layer (ca. 0.20 mm) configuration was commonly used, which in turn may distort the electrochemical response. To reconcile the conflict, we proposed in this study a new configuration for electrochemical Raman study by using water immersion objective with a long working distance (Figure 1b). The water immersion objective was working by connecting to the cover glass with a droplet of pure water, and the cover glass completely isolated the objective from the electrolyte. The difference in the refractive indices of the three layers of media, i.e., water (1.33), glass (1.52), and electrolyte (1.33) is small and we would expect a less distortion to the optical path. Furthermore, the objective has a large numerical aperture (NA=1.0), which can potentially provide a higher detection sensitivity and spatial resolution.

Figure 1. Schematic of the conventional setup using an air objective (a) and the newly designed electrochemical Raman setup utilizing a water immersion objective (b). Both objectives are of long working distance.

Smaller Spot Sizes and Higher Raman Intensities In order to quantitatively understand the impacts of objective lens, cover glass and electrolyte layer, we conducted a simulation using the Zemax software. Figure 2a shows the radii of laser spots on the electrode surface with the water immersion objective (60×, NA=1.0) at different thicknesses of cover glass and electrolyte layer. The radius of the laser spot is about 2.5 µm with a 0.5 mm thick cover glass, and it can be reduced to 0.84 µm with a 0.17 mm cover glass. In both cases, the radius does not change with the thickness of electrolyte layer. This is understandable since both sides of the cover glass are aqueous solutions with similar refractive indices. However, the radius dramatically increases with the increasing thickness of the electrolyte layer with an air objective (Figure 2c). The radius of laser spot increases linearly from 1.25 µm in the absence of the electrolyte layer to about 15 µm in the presence of a 2 mm electrolyte layer, with a slope of 6.7 µm per mm of the electrolyte layer. In this case, a 0.17 mm thick cover glass was placed in between the objective and the electrode surface. The laser spots are even larger with a thicker cover glass of 0.5 mm. Clearly, the Zemax simulation indicates that a smaller spot size can be achieved with the use of water immersion objective in the EC-Raman setup. Such a small spot is critical to achieving a high spatial resolution. We then experimentally investigated the impacts of objective lens and the thicknesses of cover glass and electrolyte


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layer on the collection efficiency of the EC-Raman system using the integrated intensity of silicon 520 cm-1 peak. We used a water immersion objective with a long working distance of 2.8 mm. When a 0.17 mm cover glass is used, the intensity of Raman signal is decreased to 47.5% of the signal in the absence of the cover glass (Figure 2b). When the thickness of the cover glass is further increased to 0.5 mm, the signal experiences additional 50% decrease. Similar to the simulation result, the electrolyte layer thickness does not affect the signal. In comparison, the signal intensity is much weaker using the air objective and decreases almost linearly with the increase of the electrolyte layer thickness, due to the large mismatch between the refractive indices of air and glass (Figure 2d).

Figure 2. Zemax simulation and experimental data for EC-Raman setup with a water immersion objective (a and b) or an air objective (c and d). (a) Dependence of the radius of beam focus on the thickness of electrolyte layer. (b) The integrated intensity of silicon 520 cm-1 Raman peak under different thicknesses of the electrolyte layer. (c) Radius of beam focus with an air objective. (d) The integrated intensity of silicon Raman peak with an air objective. Cover glasses with thicknesses of 0.17 and 0.5 mm were used in the simulation.

The above result shows that we can use an electrolyte layer as thick as 2 mm while still having sufficient flexibility for operation when a water immersion objective with a long working distance is used and a cover glass with thickness of 0.17 mm is used as the optical window. The use of cover glass as the optical window also has additional advantages, including minimum contamination and rigid configuration, compared with the plastic wrapping methods.8,15 The signals obtained by this method are at least one-order of magnitude larger than that using an air objective, which can make the EC-Raman more applicable for weak signal detections. Improved Spatial Resolution with Confocal Raman Mapping As shown from the Zemax simulation, the use of water immersion objective will significantly reduce the size of the laser spot, which may drastically improve the spatial resolution. Here, we used a patterned silicon chip with sub-micrometer features to evaluate the spatial resolution of the EC-Raman setup experimentally. The surface of patterned silicon chip consists of gold film and bare Si squares. The top view and side view of chip are shown in Figure 3a and 3b, respectively.

A comparison of bright-field images and confocal Raman mappings of the silicon chip was shown in Figure 3 when the air objective and water immersion objective were used with various thicknesses of the cover glass. For the air objective, one can easily observe an improvement of the image resolution from the bright-field microscopic images with the decrease of the cover glass thickness (Figure 3c and 3e). When the water immersion objective was used, the image shows very good contrast and gives much-detailed features, especially for sub-micrometer structures, as shown in Figure 3g. It is worth noting that here a electrolyte layer of 2 mm was used, which is much thicker than that of thin layer (0.2 mm) in the case of air objective.

Figure 3. The schematic top view (a) and side view (b) of the patterned silicon chip. Optical bright-field images (c, e, g) and confocal Raman mapping (d, f, h) of a silicon chip under various experimental conditions. Air objective is used in c, d, e, and f, and water immersion objective is used in g and h. Cover glasses with 0.5 mm thickness were used in c and d, and with 0.17 mm thickness were used in e, f, g, and h. The electrolyte layers were controlled at 0.2 mm for c, d, e, f, and at 2.0 mm for g and h.

The confocal Raman mappings of silicon 520 cm-1 peak, as shown in Figure 3d, 3f, and 3h, demonstrated experimentally the collection efficiency and the spatial resolution of these ECRaman setups. For the air objective, the Raman images show an improved spatial resolution when a thinner cover glass was used (Figure 3d and Figure 3f are for cover glass with a thickness of 0.5 mm and 0.17 mm, respectively), which is consistent with the theoretical simulation. When the water immersion objective is used, the improvement is quite remarkable. The barely separable Si squares can now be easily resolved, indicating a significant improvement in the spatial resolution. We could even clearly observe a much stronger Raman signal at the corners than the other regions on each silicon square, due to the enhancement by the localized surface plasmon resonance from the gold films around these patterns. Such an immersed feature in solution is not possible to be observed with the air objective. EC-Raman Spectroscopic Study of Methanol Oxidation The signal intensity and electrolyte layer thickness are the two important issues but can be hardly taken into account sim-



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ultaneously in conventional electrochemical Raman experiments. Similar to other spectroelectrochemical methods, a very thin electrolyte layer was usually used in conventional setups to acquire Raman spectra with a high signal intensity.4 Such a thin layer structure may not influence the response in an adsorption-related system. However, it will significantly distort the electrochemical response when a large reaction current occurs.21 In this work, we applied the newly designed electrochemical Raman setup with water immersion objective to study the process of methanol electrochemical oxidation on Pt surfaces, an extensively studied system in surface electrochemistry. In conversional EC-Raman setup, the electrolyte layer is rather thin (usual about 0.2 mm), which can significantly hinder the diffusion of chemical species to and from the electrode surface.4,15,21 Figure 4 shows the cyclic voltammograms of a platinum electrode in 1 M methanol + 0.1 M H2SO4 solution with various thicknesses of the electrolyte layer. With a thick layer (2.0 mm), the electrochemical response is similar to that obtained in the bulk solution, showing an oxidation current peak at 0.6 V. However, with the decrease of the layer thickness, the oxidation peak is shifted to higher potentials. Meanwhile, the ohmic resistances increase from 3.4 to 19.5 Ω. The estimated maximal ohmic potential drop will be about 80 mV considering the maximal current of 4 mA. This potential drop is much smaller than the potential shift observed in Fig. 4. Therefore, we think the increased hindrance of the cover glass on the diffusion of reactant (methanol) is the main reason for the distortions of CV curves. When the electrolyte layer is as thin as 0.2 mm, no obvious peak can be observed because of a large solution ohmic resistance and the extreme difficulty for methanol to diffuse into such a thin layer. It means that the electrochemical response will be severely distorted at the thickness of 0.2 mm that was commonly used in EC-Raman study. Therefore, it is necessary to have sufficiently thick layer (2 mm) so that the experimental conditions can represent the true electrochemical reactions in the practical applications.

Figure 4. Cyclic voltammograms of 1M methanol in 0.1 M H2SO4 solution with various thicknesses of the electrolyte layer and their corresponding ohmic resistance measured at open circuit potentials. Scan rate: 200 mV/s.

EC-Raman spectra were recorded during methanol electrochemical oxidation by using an [email protected] core-shell nanoparticle modified glassy carbon electrode. The cyclic voltammograms of the methanol oxidation using water immersion objective and air objective were shown respectively in Figures 5a and 5c for comparison. We can clearly tell that a thicker

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electrolyte layer can significantly eliminate the impact of diffusion hindrance and ohmic drop. Figure 5b and 5d shows the surface Raman spectra recorded at different potentials using the water immersion and air objectives, respectively. The band at ~2050 cm-1 can be assigned to the stretching vibration of linearly bonded CO molecules and the one at ~490 cm-1 belongs to the Pt-C vibration.21 The signal intensities obtained with water immersion objective are about 5 times stronger than that of the air objective, confirming an improved collection efficiency with the water immersion objective. Furthermore, we found that both CO band and Pt-C band disappear at 0.5 V in Figure 5b with the water immersion objective compared with that at 0.6 V in Figure 5d with the air objective. The 0.1 V up-shift of the potential with conventional setup again confirmed the difficulty of methanol oxidation due to the impact of thin electrolyte layer.

Figure 5. Cyclic voltammogram of 1M methanol in 0.1 M H2SO4 solution obtained with water immersion objective and a thick electrolyte layer of 2.0 mm (a) and with air objective and thin electrolyte layer of 0.2 mm (b). Potential-dependent SERS spectra on Au@Pt core-shell nanoparticle modified carbon glass electrode with the water immersion objective (c) and air objective (d). Excitation line: 632.8 nm. Scan rate: 20 mV/s.

Furthermore, a broad band centered at ~580 cm-1 can be observed at potentials more positive than 0.8 V in Figure 5b, which can be assigned to Pt surface oxides.21 However, this band is absence in Figure 5d when the air objective is used. This result further confirms the importance of using a sufficiently thick electrolyte layer to retain the normal electrochemical response. It is no doubt that our new spectroelectrochemical setup assisted by water immersion objective can allow the use of a much thicker electrolyte layers and can make the experimental conditions more similar to real applications. Most importantly, the 2 mm thickness may allow the combination of Raman spectroscopy with the rotating disk electrode technique, which has far reached significance for both electrochemistry and Raman spectroscopy. Conclusion In this work, we designed a novel spectroelectrochemical setup based on the use of water immersion objective. This setup allows the use of a thick electrolyte layer and can achieve high detection sensitivity for electrochemical Raman spectroscopy. Specifically, we extended the electrolyte layer


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thickness to 2.0 mm, which can effectively avoid the impact of thin layer to the real electrochemical reaction, such as the hindered diffusion and ohmic drop. Furthermore, we obtained significant improvements in intensity and spatial resolution of Raman signals. All these are critical for extending the electrochemical Raman studies to specific electrochemical reactions or transition metal surface with extremely weak signal, such as tracking the intermediate species of reactions.

ASSOCIATED CONTENT AUTHOR INFORMATION Corresponding Author * E-mail: [email protected] * E-mail: [email protected]

Present Addresses † Zhi-Cong Zeng’s current address is the Department of Chemistry and Biochemistry, University of Notre Dame, 244 Nieuwland Science Hall, Notre Dame, IN 46556, USA.

Author Contributions Zhi-Cong Zeng and Shu Hu contributed equally to this work.

Note The authors declare no competing financial interest.

ACKNOWLEDGMENT We acknowledge the support from the MOST (2013CB933703, 2016YFA0200601, and 2011YQ03012406), NSFC (21227004, 21321062, and J1310024), and MOE (IRT13036). C.J. thanks the support from the PCOSS Fellowship program.

REFERENCES (1) Brolo, A. G.; Irish, D. E.; Smith, B. D. J. Mol. Struct. 1997, 405, 29-44.

(2) Lombardi, J. R.; Birke, R. L. Acc. Chem. Res. 2009, 42, 734742. (3) Stiles, P. L.; Dieringer, J. A.; Shah, N. C.; Van Duyne, R. P. Annu. Rev. Anal. Chem. 2008, 1, 601-626. (4) Tian, Z. Q.; Ren, B. Annu. Rev. Phys. Chem. 2004, 55, 197229. (5) Pemberton, J.; Abruna, H. In-situ Studies of Electrochemical Interfaces: A Prospectus, VCH, Berlin, 1991, p 328. (6) Weaver, M. J.; Kizhakevariam, N.; Jiang, X.; Villegas, I.; Stuhlmann, C.; Tolia, A.; Gao, X. J. Electron. Spectrosc. Relat. Phenom. 1993, 64, 351-362. (7) Pettinger, B.; In: Lipkowski, J.; Ross , P.; (eds). Adsorption of Molecules at Metal Electrodes, VCH, New York, 1992, p 285-345. (8) Ren, B.; Lin, X. F.; Jiang, Y. X.; Cao, P. G.; Xie, Y.; Huang, Q. J.; Tian, Z. Q. Appl. Spectrosc. 2003, 57, 419-427. (9) Tian, Z. Q.; Ren, B.; Li, J. F.; Yang, Z. L. Chem. Commun. 2007, 3514-3534. (10) Williams, K.; Pitt, G.; Batchelder, D.; Kip, B. Appl. Spectrosc. 1994, 48, 232-235. (11) Zou, S.; Weaver, M. J.; Li, X. Q.; Ren, B.; Tian, Z. Q. J. Phys. Chem. B 1999, 103, 4218-4222. (12) Oberst, J. L.; Kenis, P. J.; Gewirth, A. A. J. Solid State Electrochem. 2016, 20, 1149-1154. (13) Lin, X. M.; Cui, Y.; Xu, Y. H.; Ren, B.; Tian, Z. Q. Anal. Bioanal. Chem 2009, 394, 1729-1745. (14) Moskovits, M. J. Raman Spectrosc. 2005, 36, 485-496. (15) Yeo, B. S.; Klaus, S. L.; Ross, P. N.; Mathies, R. A.; Bell, A. T. ChemPhysChem 2010, 11, 1854-1857. (16) Tian, Z. Q.; Ren, B.; Mao, B. W. J. Phys. Chem. B 1997, 101, 1338-1346. (17) Yao, J. L.; Yuan, Y. X.; Fan, X. M.; Ren, B.; Gu, R. A.; Tian, Z. Q. J. Electroanal. Chem. 2008, 624, 129-133. (18) Hu, J. W.; Chen, S.; Johnson, R. P.; Lin, X. D.; Yang, Z. L.; Russell, A. E. J. Phys. Chem. C 2013, 117, 24843-24850. (19) Fleischmann, M.; Hendra, P. J.; McQuillan, A. Chem. Phys. Lett. 1974, 26, 163-166. (20) Jeanmaire, D. L.; Van Duyne, R. P. J. Electroanal. Chem. Interfacial Electrochem. 1977, 84, 1-20. (21) Ren, B.; Li, X. Q.; She, C. X.; Wu, D. Y.; Tian, Z. Q. Electrochim. Acta 2000, 46, 193-205. (22) Tian, Z. Q.; Ren, B. Raman Spectroscopy of Electrode Surfaces. In Encyclopedia of Electrochemistry, Wiley-VCH: Weinheim, 2003, p 572-659.


Novel Electrochemical Raman Spectroscopy Enabled by Water

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