Abstract: Electrochemical energy conversion and storage processes occurred in the electrolyzer and battery devices play a vital role in the development of sustainable energy technologies. The predominant mechanism of the devices involves the charge transfer and various redox reactions on the solid-liquid interfaces which affect the reactivity and performance. In order to reveal the reaction mechanism, in-situ vibrational spectroscopy techniques such as Raman and surface-enhanced infrared absorption spectroscopy are the powerful tools for examining reaction intermediates on the solid-liquid interfaces. In this talk, we report on our use of in-situ SEIRAS to investigate the electrochemical CO2 reduction mechanism over the Cu electrocatalysts and in situ Raman spectroscopy to study the effect of electrolyte on the sulfur reduction mechanism in lithium-sulfur battery. Various in situ techniques were used to provide the complementary information in the energy conversion and storage systems. The reaction mechanism will be discussed in detail.