Transmission Mode 2D-IR Spectroelectrochemistry of In Situ Electrocatalytic Intermediates

Unraveling electrocatalytic mechanisms, as well as fundamental structural dynamics of intermediates, requires spectroscopy with high time and frequency resolution that can account for nonequilibrium in situ concentration changes inherent to electrochemistry. Two-dimensional infrared (2D-IR) spectroscopy is an ideal candidate, but several technical challenges have hindered development of this powerful tool for spectroelectrochemistry (SEC). We demonstrate a transmission-mode, optically transparent thin-layer electrochemical (OTTLE) cell adapted to 2D-IR-SEC to monitor the important Re(bpy)(CO)(3)Cl CO2-reduction electrocatalyst. 2D-IR-SEC reveals pronounced differences in both spectral diffusion time scales and spectral inhomogeneity in the singly reduced catalyst, [Re(bpy)(CO)(3)Cl](center dot-), relative to the starting Re(bpy)(CO)(3)Cl. Cross-peaks between well-resolved symmetric vibrations and congested low-frequency bands enable direct assignment of all distinct species during the electrochemical reaction. With this information, 2D-IR-SEC provides new mechanistic insights regarding unproductive, catalyst-degrading dimerization. 2D-IR-SEC opens new experimental windows into the electrocatalysis foundation of future energy conversion and greenhouse gas reduction.

Automated summary

2D-IR-SEC is a powerful tool for spectroelectrochemistry that can unravel electrocatalytic mechanisms and structural dynamics of intermediates. By directly assigning different species, it provides new mechanistic insights into catalyst degrading processes, opening new experimental windows for future energy conversion and greenhouse gas reduction.