Characterization of Electrocatalytic Water Splitting and CO2 Reduction Reactions Using In Situ/Operando Raman Spectroscopy

The electrocatalytic reduction of CO, and water splitting have received significant attention because recycling CO, into fuels and chemical feedstock is a crucial step to close the anthropogenic carbon circle, whereas splitting water produces H-2 gas, which is a valuable carbon-free energy carrier. The clear identification of the catalytic-active sites and elucidation of the reaction mechanisms in these systems remain a grand challenge. It requires simultaneous characterizations of the catalysts under actual reaction conditions. Raman spectroscopy is among the handful of techniques that are suitable for the in situ/operando investigations of heterogeneous catalytic systems. This Perspective will highlight primarily recent works on the application of Raman spectroscopy in unraveling the structural changes of catalysts, their possible active sites, and the intermediates formed during water electrolysis and CO, electroreduction. Results from complementary techniques such as X-ray absorption spectroscopy, among others, will also be presented in order to provide a more holistic discussion. The outlook for future work is discussed.