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Probing the Gold/Water Interface with Surface-Specific Spectroscopy
DOI:10.1021/acsphyschemau.2c00044.png)
Abstract
En 中文
Water is an integral component in electrochemistry, inthe generationof the electric double layer, and in the propagation of the interfacialelectric fields into the solution; however, probing the molecular-levelstructure of interfacial water near functioning electrode surfacesremains challenging. Due to the surface-specificity, sum-frequency-generation(SFG) spectroscopy offers an opportunity to investigate the structureof water near working electrochemical interfaces but probing the hydrogen-bondedstructure of water at this buried electrode-electrolyte interfacewas thought to be impossible. Propagating the laser beams throughthe solvent leads to a large attenuation of the infrared light dueto the absorption of water, and interrogating the interface by sendingthe laser beams through the electrode normally obscures the SFG spectradue to the large nonlinear response of conduction band electrons.Here, we show that the latter limitation is removed when the goldlayer is thin. To demonstrate this, we prepared Au gradient filmson CaF2 with a thickness between 0 and 8 nm. SFG spectraof the Au gradient films in contact with H2O and D2O demonstrate that resonant water SFG spectra can be obtainedusing Au films with a thickness of similar to 2 nm or less. The measuredspectra are distinctively different from the frequency-dependent Fresnelfactors of the interface, suggesting that the features we observein the OH stretching region indeed do not arise from the nonresonantresponse of the Au films. With the newfound ability to probe interfacialsolvent structure at electrode/aqueous interfaces, we hope to provideinsights into more efficient electrolyte composition and electrodedesign.
Keywords:
interfacial water structure
hydrogen-bonded network
gold interface
electrochemistry
sum-frequencygeneration
atomic force microscopy
sputter deposition
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