Understanding the structure-activity relationship of catalysts and the reaction pathway is crucial for designing efficient, selective, and stable electrocatalytic systems. In situ vibrational spectroscopy provides a unique tool for decoding molecular-level factors involved in electrocatalytic reactions. Typically, spectra are recorded when the system reaches steady states under set potentials, known as steady-state measurements, providing static pictures of electrode properties at specific potentials. However, transient information that is crucial for understanding the dynamic of electrocatalytic reactions remains elusive. Thus, time-resolved in situ vibrational spectroscopies are developed. This mini review summarizes time-resolved in situ infrared and Raman techniques and discusses their application in electrocatalytic research. With different time resolutions, these time-resolved techniques can capture unique dynamic processes of electrocatalytic reactions, short-lived intermediates, and the surface structure revolution that would be missed in steady-state measurements alone. Therefore, they are essential for understanding complex reaction mechanisms and can help unravel important molecular-level information hidden in steady states. Additionally, improving spectral time resolution, exploring low/ultralow frequency detection, and developing operando time-resolved devices are proposed as areas for advancing time-resolved techniques and their further applications in electrocatalytic research.

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The Electrochemical Ethanol Oxidation Reaction (EOR) plays a pivotal role in next‐generation energy conversion devices. A clear understanding of the EOR reaction mechanism is critical for rational catalyst design, a task complicated by the numerous reaction intermediates and pathways involved. To this end, in situ Raman spectroscopy has proven invaluable in identifying many such intermediates at the electrode/electrolyte interface under varying applied potentials. Therefore, this technique allows for inference of the reaction mechanism based on the detected Raman signals of intermediates and observed structural changes, positioning in situ Raman spectroscopy as one of the most suitable methods for studying the EOR reaction mechanism. In this short review, with an eye towards future applications, we concentrate on the essential fundamentals of EOR and highlight recent advancements in understanding the EOR mechanism by in situ Raman spectroscopy.

Fluorescence interference is a pervasive challenge in Raman spectroscopy, often limiting its broader application. Time-gated Raman spectroscopy offers a more universal solution by temporally separating Raman signals from fluorescence; however, it faces significant challenges when dealing with samples that exhibit short fluorescence lifetimes. Achieving high time resolution to effectively distinguish these signals typically requires advanced detectors that are not only costly but also difficult to source commercially, often resulting in substantial residual fluorescence that diminishes overall signal quality. In this work, we identified that the dominant noise in time-gated Raman spectroscopy is wavelength-to-wavelength fluctuation noise, which cannot be reduced by simply extending the collection time. Through our analysis, we discovered that this noise is linearly proportional to the fluorescence background and remains consistent across different time windows when collected using the time-correlated single-photon counting (TCSPC) technology. Recognizing this consistent pattern, we developed a novel, to the best of our knowledge, method to effectively remove this noise by leveraging the time-resolved fluorescence spectrum. For example, in the case of sesame oil excited with a 532 nm laser, it is typically difficult to obtain a recognizable Raman spectrum when the gate width exceeds 300 ps. However, using our method, we were able to achieve a decent signal even with a gate width of 4 ns. By correcting the Raman spectrum using the captured pure fluorescence spectrum, we achieve up to a 23-fold improvement in the signal-to-noise ratio (SNR). This innovation significantly reduces the dependence on high-cost, high-time-resolution detectors, potentially expanding the adoption and applicability of time-gated Raman spectroscopy across various fields.