Zhaohui Wang

Lack of precise control over interfacial microenvironments limits the selectivity of Cu-based catalysts for the electrochemical CO2 reduction reaction (CO2RR). Here, we engineer an organic-metal interface by assembling a 1-octanethiol self-assembled monolayer (SAM) on Cu surfaces, enabling modulation of reaction pathways and inducing a pronounced selectivity shift from ethanol to methane. In situ infrared spectroscopy combined with hydrogen evolution kinetics reveals that the thiol-modified interface regulates the competitive kinetics of *CO and *H intermediates in a potential-dependent manner, which correlates with a structural transition of the SAM from a disordered to an ordered state as identified by sum frequency generation spectroscopy. DFT and AIMD simulations suggest that a disordered and mobile interface promotes high *CO coverage and C–C coupling toward ethanol production, whereas an ordered, water-stabilized SAM suppresses surface mobility, limits *CO coverage, and promotes hydrogenation pathways to methane. Overall, this work identifies SAM ordering-regulated interfacial mobility as a key descriptor linking interfacial structure, *CO coverage, and reaction selectivity, providing a general strategy for tuning CO2RR pathways via dynamic organic-metal interfaces.

Due to the complexity of electrochemical interface analysis and the lack of direct probing techniques, the reaction mechanism of the carbon dioxide reduction reaction (CO₂RR) on gold electrodes in aqueous solutions has remained controversial. In this study, sum frequency generation (SFG) spectroscopy was employed to investigate the specific roles of bicarbonate ions and metal cations at the gold electrode/electrolyte interface during the CO₂RR. It has revealed that bicarbonate ions (HCO₃^-) can be directly reduced to adsorbed CO intermediates (*CO_ad) on the electrode surface during the CO₂RR. The active sites occupied by these *CO_ad species differ from those occupied by adsorbed CO originating from the diffusion of dissolved CO gas (^dCO_ad). Furthermore, the cation layer formed by potassium ions at the electrode surface is found to hinder the approach of ^dCO_ad to the surface, while it does not impede the access of *CO_ad. These findings provide detailed and direct molecular-level spectroscopic evidence for the CO₂RR mechanism, which will facilitate the development of highly efficient electrocatalysts for carbon dioxide reduction.

Self‐assembled monolayers (SAMs) are extensively employed as hole‐selective interlayers in inverted perovskite solar cells (PSCs), yet their incomplete coverage and poor molecular ordering often induce interfacial defects and exacerbate non‐radiative recombination. To overcome these limitations, we developed a bulky methylthio‐functionalized carbazole‐based SAM, (2‐(3,6‐bis(bis(4‐(methylthio)phenyl)amino)‐9 H ‐carbazol‐9‐yl)ethyl)phosphonic acid (S‐2PACz), and implemented a sequential co‐assembly strategy utilizing cysteine (Cys). In this tailored architecture, Cys is pre‐anchored via carboxyl groups, followed by the competitive adsorption of S‐2PACz via phosphonic acid anchoring, yielding a mixed Cys‐S‐2PACz monolayer. The size complementarity and cooperative anchoring facilitated denser molecular packing and improved ordering, while synergistic methylthio and thiol functionalities jointly passivated interfacial defects. Consequently, this strategy enhanced perovskite crystallization, optimized energy‐level alignment, and facilitated efficient hole extraction. Ultimately, PSCs incorporating Cys‐S‐2PACz achieved higher power conversion efficiency, reduced recombination losses, and demonstrated superior thermal, operational, and outdoor stability compared with devices based on single‐component SAMs. This work establishes competitive co‐assembly as an effective interfacial engineering strategy, providing a scalable route to tailored SAM architectures for high‐performance and durable p–i–n PSCs.

In-situ tracking of the transient processes of surface/interfacial chemical reactions is of great significance for understanding the essence of catalytic mechanisms but remains highly challenging. Herein, shell-isolated nanoparticle-enhanced femtosecond stimulated Raman spectroscopy (SHINE-FSRS) with high sensitivity and temporal resolution has been developed to explore the ultrafast molecular dynamics of surface reactions. The FSRS signals have been greatly enhanced through the fabrication of plasmonic nanocavities, achieving a maximum enhancement factor of ~10⁶ through optimal matching of the plasmonic band of the nanocavity with the wavelength of the Raman pump laser, using malachite green (MG) as the probe molecule. Using SHINE-FSRS, the ultrafast structural evolution during the photo-induced reaction of malachite green molecules adsorbed on Au or Ag surfaces has been successfully in-situ monitored at the femtosecond timescale. Direct spectroscopic evidence reveals that malachite green undergoes intramolecular twisting with 100 fs, and the strong localized plasmonic field can accelerate the twisting process. This work showcases the capability of SHINE-FSRS to effectively probe the molecular structural evolution of surface species during reactions with high temporal resolution, underscoring its potential for in-situ investigations of surface and interfacial catalytic processes.

A compact and enclosed optically transparent spectroelectrochemical flow cell was designed specifically for in situ sum frequency generation (SFG) measurements at the charged solid/liquid interface. This thin‐layer analysis cell allows the measurement of films on reflective metallic surfaces through a micrometer layer of solution. The cyclic voltammetry and SFG spectrum from an Au working electrode were used to demonstrate the electrochemical and spectroscopic capabilities of the cell. The potential dependent structural changes of the Au electrode and surface molecules were tested to prove the feasibility of the cell for in situ spectroscopy of the electrode processes. The development of this compact spectroelectrochemical flow cell would facilitate future operando studies employing SFG measurements at solid/liquid interfaces.

Understanding the electric double layer (EDL) of the metal electrode–electrolyte interface is essential to electrochemistry and relevant disciplines. In this study, potential-dependent electrode Sum Frequency Generation (SFG) intensities of polycrystalline gold electrodes in HClO4 and H2SO4 electrolytes were thoroughly analyzed. The potential of zero charges (PZC) of the electrodes was −0.06 and 0.38 V in HClO4 and H2SO4, respectively, determined from differential capacity curves. Without specific adsorption, the total SFG intensity was dominated by the contribution from the Au surface and increased similar to that of the visible (VIS) wavelength scanning, which pushed the SFG process closer to the double resonant condition in HClO4. However, the EDL contributed about 30% SFG signal with specific adsorption in H2SO4. Below PZC, the total SFG intensity was dominated by the Au surface contribution and increased with potential at a similar slope in these two electrolytes. Around PZC, as the EDL structure became less ordered and the electric field changed direction, there would be no EDL SFG contribution. Above PZC, the total SFG intensity increased much more rapidly with potential in H2SO4 than in HClO4, which suggested that the EDL SFG contribution kept increasing with more specific adsorbed surface ions from H2SO4.

Infrared free electron laser is a unique broadband tuning IR light source and useful tool to trace the reaction and vibrational energy transfer dynamics. It is essential for the infrared free electron laser debug and optimization to accurately characterize the wavelength and micropulse profile of the infrared free electron laser output. By synchronizing the infrared free electron laser and tabletop femtosecond laser with high precision, infrared free electron laser-sum frequency generation setup, a sum frequency generation spectroscopy setup using infrared free electron laser pulses, is developed. Through sum frequency generation cross-correlation, the infrared free electron laser output wavelength and micropulse duration are measured from the delaytime-dependent infrared free electron laser-sum frequency generation spectra of a ZnS window. The infrared free electron laser-sum frequency generation measured infrared free electron laser wavelength is linearly correlated with the theoretically calculation with the fixed electron beam energy and variable undulator magnetic gaps. And the measured micropulse duration is 2.0 ps@5.25 µm and 2.9 ps@8.35 µm. These results demonstrate the excellent ability of sum frequency generation in the diagnostic and characterization of infrared free electron laser output profile, and the quality of the infrared free electron laser pulse structure.

Vibrational spectroscopy is significant for identifying chemical specification. Here, the spectral band frequencies corresponding to the same molecular vibration in sum frequency generation (SFG) and difference frequency generation (DFG) spectra present delay-dependent deviation. Through numerical analysis of time resolved SFG and DFG spectra with a frequency marker in the incident IR pulse, the frequency ambiguity was not caused by any structure and dynamic variation on the surface, but from the dispersion in the incident visible pulse. Our results provide a helpful method to correct the vibrational frequency deviation and improve the assignment accuracy for SFG and DFG spectroscopies.