In situ Raman and surface-enhanced Raman spectroscopy on working electrodes: spectroelectrochemical characterization of water oxidation electrocatalysts.

In situ Raman and surface-enhanced Raman scattering (SERS) are established vibrational spectroscopic techniques with a wide range of applications in the field of chemical, material and life sciences. Their particular characteristics make them especially useful when dealing with catalytic water oxidation at anodes. The in situ characterization of the fate of electrocatalysts (whether molecular or oxide materials) employed under reaction conditions is crucial to determine the chemical identity and the physical state of the actual catalytic species. Such studies also help in both, attaining mechanistic insights underlying the catalytic reaction and confirming/discarding the possibility of molecular to colloidal or heterogeneous phase conversions taking place prior or under turnover conditions. This perspective article highlights the use of in situ Raman and SERS as principal spectroscopic tools in the electrocatalysis field by means of recent contributions where they are employed to in operando characterize both molecular and oxide-based water oxidation electrocatalysts. These in situ spectroscopic measurements support in assessing both the progressive oxidation and the structural evolution of the employed catalytic species under electrochemical conditions. Therefore, this article provides an informative guideline for developing in situ spectroelectrochemical methods to study and characterize water oxidation catalysis at working anodes.