Spatiotemporal Mapping of Local Heterogeneities during Electrochemical Carbon Dioxide Reduction

The activity andselectivity of a copper electrocatalyst duringthe electrochemical CO2 reduction reaction (eCO(2)RR) are largely dominated by the interplay between local reactionenvironment, the catalyst surface, and the adsorbed intermediates. In situ characterization studies have revealed many aspectsof this intimate relationship between surface reactivity and adsorbedspecies, but these investigations are often limited by the spatialand temporal resolution of the analytical technique of choice. Here,Raman spectroscopy with both space and time resolution was used toreveal the distribution of adsorbed species and potential reactionintermediates on a copper electrode during eCO(2)RR. Principalcomponent analysis (PCA) of the in situ Raman spectrarevealed that a working electrocatalyst exhibits spatial heterogeneitiesin adsorbed species, and that the electrode surface can be dividedinto CO-dominant (mainly located at dendrite structures) and C-Cdominant regions (mainly located at the roughened electrode surface).Our spectral evaluation further showed that in the CO-dominant regions,linear CO was observed (as characterized by a band at & SIM;2090cm(-1)), accompanied by the more classical Cu-CObending and stretching vibrations located at & SIM;280 and & SIM;360cm(-1), respectively. In contrast, in the C-Cdirecting region, these three Raman bands are suppressed, while atthe same time a band at & SIM;495 cm(-1) and a broadCu-CO band at & SIM;2050 cm(-1) dominatethe Raman spectra. Furthermore, PCA revealed that anodization createsmore C-C dominant regions, and labeling experiments confirmedthat the 495 cm(-1) band originates from the presenceof a Cu-C intermediate. These results indicate that a copperelectrode at work is very dynamic, thereby clearly displaying spatiotemporalheterogeneities, and that in situ micro-spectroscopictechniques are crucial for understanding the eCO(2)RR mechanismof working electrocatalyst materials.