Surface‐enhanced Raman scattering of CO<sub>2</sub> dissolved in aqueous colloidal solutions of silver and gold

Kneipp, Katrin; Wang, Yang; Berger, Andrew J.; Dasari, Ramachandra R.; Feld, Michael S.

doi:10.1002/jrs.1250261006

Cited by 10 publications

(12 citation statements)

References 11 publications

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“…However, at potentials below −0.9 V, significant changes are detected. First of all, the peak intensities decrease at 1300–1400 cm –1 corresponding to CO 2 because surface-adsorbed CO 2 is consumed during the electrochemical reaction. ,, In particular, the bands at 1307 and 1404 cm –1 are assigned to CO 2 vibrational modes. − The CO 2 peak intensity plotted as a function of the applied potential clearly displays its consumption at high turnover rates and its recovery when the electrolyte is exchanged by a freshly CO 2 -saturated solution (Figure S5). During the consumption of CO 2 , different products may be formed with CO and H 2 reportedly being the main product for Ag-based catalysts .…”

Section: Resultsmentioning

confidence: 97%

Optimized Ag Nanovoid Structures for Probing Electrocatalytic Carbon Dioxide Reduction Using Operando Surface-Enhanced Raman Spectroscopy

et al. 2018

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Surface-enhanced Raman spectroscopy is a powerful analytical tool and a strongly surface structure-dependent process. Importantly, it can be coupled with electrochemistry to simultaneously record vibrational spectroscopic information during electrocatalytic reactions. Highest Raman enhancements are obtained using precisely tuned nanostructures. The fabrication and evaluation of a high number of different nanostructures with slightly different properties is time-consuming. We present a strategy to systematically determine optimal nanostructure properties of electrochemically generated Ag void structures in order to find the void size providing highest signal enhancement for Raman spectroscopy. Ag-coated Si wafers were decorated with a monolayer of differently sized polymer nanospheres using a Langmuir–Blodgett approach. Subsequently, bipolar electrochemistry was used to electrodeposit a gradient of differently sized void structures. The gradient structures were locally evaluated using Raman spectroscopy of a surface-adsorbed Raman probe, and the surface regions exhibiting the highest Raman enhancement were characterized by means of scanning electron microscopy. High-throughput scanning droplet cell experiments were utilized to determine suitable conditions for the electrodeposition of the found highly active structure in a three-electrode electrochemical cell. This structure was subsequently employed as the working electrode in operando surface-enhanced Raman measurements to verify its viability as the signal amplifier and to spectroscopically rationalize the complex electrochemical reduction of carbon dioxide.

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Section: Resultsmentioning

confidence: 97%

Optimized Ag Nanovoid Structures for Probing Electrocatalytic Carbon Dioxide Reduction Using Operando Surface-Enhanced Raman Spectroscopy

et al. 2018

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“…Changes in charge distribution upon adsorption on silver that lead to vibrational frequencies that resemble those of the radical rather than the molecule have been reported for several cases. 44,45 Mulliken charge populations are also shown in Table 1. While the absolute charges may not be very meaningful, this method is deemed to be reliable for analyzing trends among similar species.…”

Section: Resultsmentioning

confidence: 98%

Probing Silver Nanoparticles During Catalytic H₂ Evolution

et al. 2008

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Employing silver nanoparticles from a recently developed synthesis [Evanoff, D. D.; Chumanov, G. J. Phys. Chem. B 2004, 108, 13948] and a well-studied probe molecule, p-aminothiophenol, we follow changes at the surface of the particles during the conditioning and eventually the catalytic production of hydrogen from water using strongly reducing radicals. Injection of electrons into the particles causes pronounced variations in the intensity of the surface enhanced Raman scattering (SERS) spectrum of the probe molecule. These spectral changes are caused by changes in the Fermi-level energy that are in turn caused by changes in the silver ion concentrations or in the pH, or by changes in electron density in the particle. This correlation highlights the effect of the chemical potential on the SERS enhancement at the end of the particles synthesis. The intensity of the SERS spectra increases in the presence of the silver ions when excitation at 514 nm is utilized. When the Ag(+) ions in the colloidal suspension are completely reduced by the radicals and the particles operate in the catalytic mode, the SERS spectrum is too weak to record, but it can reversibly be recovered upon the addition of Ag(+). The effect of pH on the SERS intensity is similar in nature to that of the silver ions but is complicated by the pKa of the aminothiol and the point of zero charge (pzc) of the particles. It is hypothesized that as the particles cross the pzc (around neutral pH) the electrostatic interaction between the protonated amine headgroup of the probe and the positively charged surface increases the density of probe molecules in the perpendicular orientation at the expense of a competing species. This conversion results in enhanced SERS signals and is observable during the preconditioning stage of the particles. Indeed, adsorption isotherms of the probe indicate the presence of two species. In analogous previous observations these two species have been attributed to perpendicular and flat adsorption orientations of the deprotonated probe molecule relative to the particle surface. However, preliminary density functional calculations on relevant prototypes raise the possibility that the two species may be the probe molecule and a cationic form produced by charge transfer in the ground state from the chemisorbed probe to the metal. These two forms of the probe have differing electronic structures and vibrational frequencies, with perhaps differing orientations relative to the surface. Whichever is the correct interpretation, a neutral molecule in a flat orientation or a radical cation, this species is easier to replace than the other in competitive adsorption by ethanethiol.

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“…[14] A weak band at 1380 cm À 1 is due to the CO 2 vibration mode. [15,16] Even at small applied currents, for example of À 1 and À 5 mA, a weak band appeared in the lower wavenumber region at 348 cm À 1 , corresponding to CuÀ CO stretch vibration modes (on-top geometry). [17] Concomitantly, a strong band at 2124 cm À 1 from linearly coordinated on-top bound νC�O (intramolecular) of the CO molecule was detected.…”

Section: In-situ Raman Measurementsmentioning

confidence: 99%

Redox Replacement of Silver on MOF‐Derived Cu/C Nanoparticles on Gas Diffusion Electrodes for Electrocatalytic CO₂ Reduction

Sikdar

Junqueira

Öhl

et al. 2022

Chemistry A European J

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Bimetallic tandem catalysts have emerged as a promising strategy to locally increase the CO flux during electrochemical CO 2 reduction, so as to maximize the rate of conversion to CÀ C-coupled products. Considering this, a novel Cu/CÀ Ag nanostructured catalyst has been prepared by a redox replacement process, in which the ratio of the two metals can be tuned by the replacement time. An optimum Cu/Ag composition with similarly sized particles showed the highest CO 2 conversion to C 2 + products compared to non-Ag-modified gas-diffusion electrodes. Gas chromatography and in-situ Raman measurements in a CO 2 gas diffusion cell suggest the formation of top-bound linear adsorbed *CO followed by consumption of CO in the successive cascade steps, as evidenced by the increasingνCÀ H bands. These findings suggest that two mechanisms operate simultaneously towards the production of HCO 2 H and CÀ C-coupled products on the Cu/Ag bimetallic surface.

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Surface‐enhanced Raman scattering of CO₂ dissolved in aqueous colloidal solutions of silver and gold

Cited by 10 publications

References 11 publications

Optimized Ag Nanovoid Structures for Probing Electrocatalytic Carbon Dioxide Reduction Using Operando Surface-Enhanced Raman Spectroscopy

Optimized Ag Nanovoid Structures for Probing Electrocatalytic Carbon Dioxide Reduction Using Operando Surface-Enhanced Raman Spectroscopy

Probing Silver Nanoparticles During Catalytic H₂ Evolution

Redox Replacement of Silver on MOF‐Derived Cu/C Nanoparticles on Gas Diffusion Electrodes for Electrocatalytic CO₂ Reduction

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Surface‐enhanced Raman scattering of CO2 dissolved in aqueous colloidal solutions of silver and gold

Cited by 10 publications

References 11 publications

Optimized Ag Nanovoid Structures for Probing Electrocatalytic Carbon Dioxide Reduction Using Operando Surface-Enhanced Raman Spectroscopy

Optimized Ag Nanovoid Structures for Probing Electrocatalytic Carbon Dioxide Reduction Using Operando Surface-Enhanced Raman Spectroscopy

Probing Silver Nanoparticles During Catalytic H2 Evolution

Redox Replacement of Silver on MOF‐Derived Cu/C Nanoparticles on Gas Diffusion Electrodes for Electrocatalytic CO2 Reduction

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Product

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Surface‐enhanced Raman scattering of CO₂ dissolved in aqueous colloidal solutions of silver and gold

Probing Silver Nanoparticles During Catalytic H₂ Evolution

Redox Replacement of Silver on MOF‐Derived Cu/C Nanoparticles on Gas Diffusion Electrodes for Electrocatalytic CO₂ Reduction