A Happy Get‐Together – Probing Electrochemical Interfaces by Non‐Linear Vibrational Spectroscopy

Abstract

Electrochemical interfaces are key structures in energy storage and catalysis. Hence, a molecular understanding of the active sites at these interfaces, their solvation, the structure of adsorbates, and the formation of solidelectrolyte interfaces are crucial for an in-depth mechanistic understanding of their function. Vibrational sum-frequency generation (VSFG) spectroscopy has emerged as an operando spectroscopic technique to monitor complex electrochemical interfaces due to its intrinsic interface sensitivity and chemical specificity. Thus, this review discusses the happy get-together between VSFG spectroscopy and electrochemical interfaces. Methodological approaches for answering core issues associated with the behavior of adsorbates on electrodes, the structure of solvent adlayers, the transient formation of reaction intermediates, and the emergence of solid electrolyte interphase in battery research are assessed to provide a critical inventory of highly promising avenues to bring optical spectroscopy to use in modern material research in energy conversion and storage.

Direct Observation of Surface-Bound Intermediates in CO/CO2 Reduction on a Polycrystalline Cu Electrode Using Broad-Band SFG Spectroscopy

“…It is worth noting that, in Figure a,b, the SFG line shapes change from downward negative bands (valleys on NR) to upward positive peaks from −0.5 to −0.6 V for COR and −0.7 to −0.8 V for CO 2 R (comparison with the enlarged portion of the spectra in Figure S6). The SFG signal is generated from the second-order responses at the interface to the incident light fields. , Here, the SFG spectra are a coherent sum of contributions of the Cu surface (NR) and the surface-adsorbed species ( R ): when the NR and R are in the same phase (relative phase angle of the induced polarization θ = 0), constructive interference leads to superimposition of positive peaks (when the relative phase θ = π/2, simple summation of the NR and R also gives positive peaks); when the two contributions are in the opposite phase (θ = π), destructive interference occurs, and the SFG spectra appear as inverted or negative peaks . The broad-band feature is the SFG contribution of the Cu electrode, and the superimposed narrow bands are from the possible intermediates of the COR and CO 2 R. The line shape reversal of the R bands is caused by either the orientation flip-flop of the adsorbed species or the absolute phase change of the Cu electrode.…”

“…SFG is a powerful vibrational spectroscopic technique to investigate electrode/electrolyte interfaces under potential control . SFG originates from a 3-wave mixing process by the induced second-order polarization.…”

“…SFG is a powerful vibrational spectroscopic technique to investigate electrode/electrolyte interfaces under potential control. 35 SFG originates from a 3-wave mixing process by the induced second-order polarization. In BB-SFG spectroscopy, the SFG signal is induced by the electric fields of a tunable femtosecond IR pulse ω IR and a picosecond visible pulse with a fixed frequency, ω vis .…”

Design of 2D nanomaterials (photo-)electrocatalysts for biomass valorization coupled with H2 production

“…In this context, a clear understanding of catalyst interfacial processes such as dynamic chemical/structural/electronic evolution, formation/interaction of key electroactive intermediates, and dominant reaction pathways, is required to rationalize the selection of design strategies and to drive the knowledge-based development of next-generation biomass valorization/HER electrocatalysts. Combination of (photo-)electrochemical and cutting-edge in situ characterization techniques under operation can offer valuable insights at atomic-level to this end, leading to emergence of a wide range of in situ microscopic and spectroscopic methods, such as surface interrogation-scanning electrochemical microscopy (SI-SECM) [115][116][117] , transmission electron microscopy (TEM) 118 , Fourier transform infrared spectroscopy (FTIR), 59,119,120 vibrational sum-frequency generation (vSFG), [121][122][123] Raman spectroscopy, [124][125][126][127] X-ray absorption spectroscopy (XAS), [128][129][130] X-ray diffraction (XRD), 131,132 and Xray photoelectron spectroscopy (XPS). 133,134 In addition to these landmarks, facilitating the use of machine-learning methods for theoretical calculation is versatile approach for in-depth kinetic modeling of the focused catalyst interfaces, which can be used to predict the reaction mechanism by calculating the energy levels of the electrons in the catalytic material and the interactions between the electrons and the ions in the electrolyte.…”

Nano-Plasticity of an Electrified Ionic Liquid/Electrode Interface: Uncovering Hard–Soft Structuring via Controlled Metal Fill Factor

“…The electrochemical interface, where the realms of electricity and chemistry converge, plays a crucial role in shaping progress in energy storage and conversion. As global efforts intensify toward sustainable and efficient energy solutions, understanding the intricacies of the electrochemical interface becomes a paramount pursuit. − Notably, the structure of the ionic liquid (IL) interface has garnered extensive attention in the literature due to its promising and unique properties in various electrochemical applications. − Beginning with the theoretical models proposed by Kornyshev and co-workers, it has been acknowledged that ILs, akin to molten salts, deviate from the capacitance behavior of dilute electrolytes. − Numerous experimental electrochemical studies on different ILs and electrode materials have affirmed this observation. − These studies reveal a distinctive layering of IL ions near a polarized surface, leading to a highly organized distribution of ions across the electrode/electrolyte interface. The alignment of IL ions into discrete, well-ordered layers gradually transitions to a bulk-like structure away from the surface.…”