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Probing the Gold/Water Interface with Surface-Specific Spectroscopy

Piontek, Stefan M.
Naujoks, Dennis
Tabassum, Tadneem
Jaugstetter, Maximilian
Hosseini, Pouya
Corva, Manuel
Ludwig, Alfred
Tschulik, Kristina
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https://doi.org/10.1021/acsphyschemau.2c00044
Abstract
Water is an integral component in electrochemistry, in the generation of the electric double layer, and in the propagation of the interfacial electric fields into the solution; however, probing the molecular-level structure of interfacial water near functioning electrode surfaces remains challenging. Due to the surface-specificity, sum-frequency-generation (SFG) spectroscopy offers an opportunity to investigate the structure of water near working electrochemical interfaces but probing the hydrogen-bonded structure of water at this buried electrode–electrolyte interface was thought to be impossible. Propagating the laser beams through the solvent leads to a large attenuation of the infrared light due to the absorption of water, and interrogating the interface by sending the laser beams through the electrode normally obscures the SFG spectra due to the large nonlinear response of conduction band electrons. Here, we show that the latter limitation is removed when the gold layer is thin. To demonstrate this, we prepared Au gradient films on CaF2 with a thickness between 0 and 8 nm. SFG spectra of the Au gradient films in contact with H2O and D2O demonstrate that resonant water SFG spectra can be obtained using Au films with a thickness of ∼2 nm or less. The measured spectra are distinctively different from the frequency-dependent Fresnel factors of the interface, suggesting that the features we observe in the OH stretching region indeed do not arise from the nonresonant response of the Au films. With the newfound ability to probe interfacial solvent structure at electrode/aqueous interfaces, we hope to provide insights into more efficient electrolyte composition and electrode design.
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Probing the Gold/Water Interface with Surface-Specific Spectroscopy Stefan M. Piontek, Dennis Naujoks, Tadneem Tabassum, Mark J. DelloStritto, Maximilian Jaugstetter, Pouya Hosseini, Manuel Corva, Alfred Ludwig, Kristina Tschulik, Michael L. Klein, and Poul B. Petersen ACS Physical Chemistry Au 2023 3 (1), 119-129 DOI: 10.1021/acsphyschemau.2c00044
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ACS Physical Chemistry Au, Vol. 3, Iss. 1
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