(Invited) Measuring the Temporal Evolution of Surface Intermediates in Electrocatalysis

Ensemble measurements in electrocatalysis average over populations of single entities such as transient chemical intermediates and active sites. Ensemble-averaged empirical data provides general trends in reactivity but lost is a vast amount of information on how molecules interact and evolve on an electrocatalyst surface which could reveal over- or underperforming subpopulations within an ensemble. To validate and improve current theoretical predictions of reaction pathways, direct measurements of intermediates in electrocatalysis are required. Toward this goal, I will discuss our development of time-resolved surface-enhanced Raman scattering (SERS) microscopy as a tool to measure the evolution and dynamics of surface intermediates formed on metallic electrodes in CO 2 reduction. Combining diffraction-limited spatial resolution with µs temporal resolution, we observe the formation of surface-bound CO ca. 1 V below the ensemble onset potential. Further, our time-resolved spectroscopy reveals the timescales of surface intermediate accumulation on and evolution from electrode surfaces, providing insight into the residence times of intermediates. Time-resolved SERS microscopy reveals the action of surface intermediates previously hidden by spatially and temporally averaged ensemble measurements, providing new mechanistic insight to the CO 2 reduction reaction.