Unraveling electrocatalytic mechanisms and understanding the structural dynamics of transient intermediates demand spectroscopic techniques with high time and frequency resolution capable of capturing nonequilibrium concentration changes inherent in electrochemical systems. Two-dimensional infrared (2D-IR) spectroscopy emerges as a powerful tool, yet its application in spectroelectrochemistry (SEC) has been limited by technical challenges. This work presents the first implementation of transmission-mode 2D-IR spectroelectrochemistry using an optically transparent thin-layer electrochemical (OTTLE) cell, enabling in situ monitoring of key intermediates during the CO₂ reduction catalyzed by Re(bpy)(CO)₃Cl. The system operates under applied potential conditions that drive redox processes while preserving solution-phase accessibility for ultrafast vibrational probing.
The OTTLE cell design features a central aperture in the platinum working electrode, allowing beam transmission without obstruction from the electrode surface. This configuration supports bulk solution studies of post-redox species, where most catalytic steps occur. A commercially available setup was adapted to accommodate 2D-IR measurements, utilizing a tracer beam for real-time absorption monitoring during each rephasing and nonrephasing scan. By measuring transmission spectra before each 2D-IR acquisition and applying absorbance scaling based on calculated optical density, we successfully recover equilibrium spectral diffusion dynamics even under nonequilibrium reaction conditions—critical for practical applications where steady states are difficult to maintain.
We focus on the singly reduced species [Re(bpy)(CO)₃Cl]⁻ formed at −2.1 V vs. Fc/Fc⁺ in tetrahydrofuran with 0.1 M TBAPF₆ electrolyte. 2D-IR spectra reveal distinct differences in spectral diffusion time scales and inhomogeneity between the neutral catalyst and its radical anion. The reduced species exhibits slower spectral diffusion (5.5 ± 2.1 ps) compared to the starting material (4.0 ± 0.9 ps), indicating enhanced solvation complexity due to strong ion-dipole interactions and preferential electrolyte solvation around the charged intermediate. Additionally, a static heterogeneity offset of 0.3 is observed, suggesting long-lived local solvation structures or slow conformational dynamics beyond the measurement window.
Crucially, cross-peaks between well-resolved symmetric carbonyl stretches and congested low-frequency modes provide unambiguous assignment of vibrational couplings. These cross-peaks confirm the presence of a Re–Re dimer species in acetonitrile solvent, resolving prior controversy over whether such dimers form. In contrast to earlier assignments attributing the 1986 and 1948 cm⁻¹ bands to monomeric anions, our 2D-IR difference spectrum shows correlated cross-peaks between these frequencies, definitively linking them to the same dimeric species.MTDH Antibody supplier This observation provides direct experimental evidence for dimerization—a known deactivation pathway that limits catalyst turnover.ATP6V0A4 Antibody MedChemExpress
This study demonstrates that transmission-mode 2D-IR-SEC enables mechanistic insights into electrocatalytic processes previously inaccessible through conventional FTIR or linear SEC methods.PMID:35163325 It allows for precise identification of intermediates via vibrational coupling signatures, resolves spectral congestion issues, and extracts equilibrium dynamics from dynamic, nonequilibrium reactions. The technique opens new avenues for probing transient species in energy conversion technologies, particularly in CO₂ reduction, where understanding degradation pathways and optimizing efficiency are paramount. Future work will extend this approach to full catalytic cycles, exploring solvent and electrolyte effects on intermediate stability and reactivity.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com